Annotation of OpenXM_contrib2/asir2000/gc5.3/README, Revision 1.1
1.1 ! noro 1: Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
! 2: Copyright (c) 1991-1996 by Xerox Corporation. All rights reserved.
! 3: Copyright (c) 1996-1999 by Silicon Graphics. All rights reserved.
! 4: Copyright (c) 1999 by Hewlett-Packard Company. All rights reserved.
! 5:
! 6: THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
! 7: OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
! 8:
! 9: Permission is hereby granted to use or copy this program
! 10: for any purpose, provided the above notices are retained on all copies.
! 11: Permission to modify the code and to distribute modified code is granted,
! 12: provided the above notices are retained, and a notice that the code was
! 13: modified is included with the above copyright notice.
! 14:
! 15: This is version 5.3 of a conservative garbage collector for C and C++.
! 16:
! 17: You might find a more recent version of this at
! 18:
! 19: http://www.hpl.hp.com/personal/Hans_Boehm/gc
! 20:
! 21: HISTORY -
! 22:
! 23: Early versions of this collector were developed as a part of research
! 24: projects supported in part by the National Science Foundation
! 25: and the Defense Advance Research Projects Agency.
! 26: Much of the code was rewritten by Hans-J. Boehm (boehm@acm.org) at Xerox PARC,
! 27: SGI, and HP Labs.
! 28:
! 29: Some other contributors:
! 30:
! 31: More recent contributors are mentioned in the modification history at the
! 32: end of this file. My apologies for any omissions.
! 33:
! 34: The SPARC specific code was contributed by Mark Weiser
! 35: (weiser@parc.xerox.com). The Encore Multimax modifications were supplied by
! 36: Kevin Kenny (kenny@m.cs.uiuc.edu). The adaptation to the RT is largely due
! 37: to Vernon Lee (scorpion@rice.edu), on machines made available by IBM.
! 38: Much of the HP specific code and a number of good suggestions for improving the
! 39: generic code are due to Walter Underwood (wunder@hp-ses.sde.hp.com).
! 40: Robert Brazile (brazile@diamond.bbn.com) originally supplied the ULTRIX code.
! 41: Al Dosser (dosser@src.dec.com) and Regis Cridlig (Regis.Cridlig@cl.cam.ac.uk)
! 42: subsequently provided updates and information on variation between ULTRIX
! 43: systems. Parag Patel (parag@netcom.com) supplied the A/UX code.
! 44: Jesper Peterson(jep@mtiame.mtia.oz.au), Michel Schinz, and
! 45: Martin Tauchmann (martintauchmann@bigfoot.com) supplied the Amiga port.
! 46: Thomas Funke (thf@zelator.in-berlin.de(?)) and
! 47: Brian D.Carlstrom (bdc@clark.lcs.mit.edu) supplied the NeXT ports.
! 48: Douglas Steel (doug@wg.icl.co.uk) provided ICL DRS6000 code.
! 49: Bill Janssen (janssen@parc.xerox.com) supplied the SunOS dynamic loader
! 50: specific code. Manuel Serrano (serrano@cornas.inria.fr) supplied linux and
! 51: Sony News specific code. Al Dosser provided Alpha/OSF/1 code. He and
! 52: Dave Detlefs(detlefs@src.dec.com) also provided several generic bug fixes.
! 53: Alistair G. Crooks(agc@uts.amdahl.com) supplied the NetBSD and 386BSD ports.
! 54: Jeffrey Hsu (hsu@soda.berkeley.edu) provided the FreeBSD port.
! 55: Brent Benson (brent@jade.ssd.csd.harris.com) ported the collector to
! 56: a Motorola 88K processor running CX/UX (Harris NightHawk).
! 57: Ari Huttunen (Ari.Huttunen@hut.fi) generalized the OS/2 port to
! 58: nonIBM development environments (a nontrivial task).
! 59: Patrick Beard (beard@cs.ucdavis.edu) provided the initial MacOS port.
! 60: David Chase, then at Olivetti Research, suggested several improvements.
! 61: Scott Schwartz (schwartz@groucho.cse.psu.edu) supplied some of the
! 62: code to save and print call stacks for leak detection on a SPARC.
! 63: Jesse Hull and John Ellis supplied the C++ interface code.
! 64: Zhong Shao performed much of the experimentation that led to the
! 65: current typed allocation facility. (His dynamic type inference code hasn't
! 66: made it into the released version of the collector, yet.)
! 67: (Blame for misinstallation of these modifications goes to the first author,
! 68: however.)
! 69:
! 70: OVERVIEW
! 71:
! 72: This is intended to be a general purpose, garbage collecting storage
! 73: allocator. The algorithms used are described in:
! 74:
! 75: Boehm, H., and M. Weiser, "Garbage Collection in an Uncooperative Environment",
! 76: Software Practice & Experience, September 1988, pp. 807-820.
! 77:
! 78: Boehm, H., A. Demers, and S. Shenker, "Mostly Parallel Garbage Collection",
! 79: Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design
! 80: and Implementation, SIGPLAN Notices 26, 6 (June 1991), pp. 157-164.
! 81:
! 82: Boehm, H., "Space Efficient Conservative Garbage Collection", Proceedings
! 83: of the ACM SIGPLAN '91 Conference on Programming Language Design and
! 84: Implementation, SIGPLAN Notices 28, 6 (June 1993), pp. 197-206.
! 85:
! 86: Possible interactions between the collector and optimizing compilers are
! 87: discussed in
! 88:
! 89: Boehm, H., and D. Chase, "A Proposal for GC-safe C Compilation",
! 90: The Journal of C Language Translation 4, 2 (December 1992).
! 91:
! 92: and
! 93:
! 94: Boehm H., "Simple GC-safe Compilation", Proceedings
! 95: of the ACM SIGPLAN '96 Conference on Programming Language Design and
! 96: Implementation.
! 97:
! 98: (Both are also available from
! 99: http://reality.sgi.com/boehm/papers/, among other places.)
! 100:
! 101: Unlike the collector described in the second reference, this collector
! 102: operates either with the mutator stopped during the entire collection
! 103: (default) or incrementally during allocations. (The latter is supported
! 104: on only a few machines.) It does not rely on threads, but is intended
! 105: to be thread-safe.
! 106:
! 107: Some of the ideas underlying the collector have previously been explored
! 108: by others. (Doug McIlroy wrote a vaguely similar collector that is part of
! 109: version 8 UNIX (tm).) However none of this work appears to have been widely
! 110: disseminated.
! 111:
! 112: Rudimentary tools for use of the collector as a leak detector are included, as
! 113: is a fairly sophisticated string package "cord" that makes use of the collector.
! 114: (See cord/README.)
! 115:
! 116:
! 117: GENERAL DESCRIPTION
! 118:
! 119: This is a garbage collecting storage allocator that is intended to be
! 120: used as a plug-in replacement for C's malloc.
! 121:
! 122: Since the collector does not require pointers to be tagged, it does not
! 123: attempt to ensure that all inaccessible storage is reclaimed. However,
! 124: in our experience, it is typically more successful at reclaiming unused
! 125: memory than most C programs using explicit deallocation. Unlike manually
! 126: introduced leaks, the amount of unreclaimed memory typically stays
! 127: bounded.
! 128:
! 129: In the following, an "object" is defined to be a region of memory allocated
! 130: by the routines described below.
! 131:
! 132: Any objects not intended to be collected must be pointed to either
! 133: from other such accessible objects, or from the registers,
! 134: stack, data, or statically allocated bss segments. Pointers from
! 135: the stack or registers may point to anywhere inside an object.
! 136: The same is true for heap pointers if the collector is compiled with
! 137: ALL_INTERIOR_POINTERS defined, as is now the default.
! 138:
! 139: Compiling without ALL_INTERIOR_POINTERS may reduce accidental retention
! 140: of garbage objects, by requiring pointers from the heap to to the beginning
! 141: of an object. But this no longer appears to be a significant
! 142: issue for most programs.
! 143:
! 144: There are a number of routines which modify the pointer recognition
! 145: algorithm. GC_register_displacement allows certain interior pointers
! 146: to be recognized even if ALL_INTERIOR_POINTERS is nor defined.
! 147: GC_malloc_ignore_off_page allows some pointers into the middle of large objects
! 148: to be disregarded, greatly reducing the probablility of accidental
! 149: retention of large objects. For most purposes it seems best to compile
! 150: with ALL_INTERIOR_POINTERS and to use GC_malloc_ignore_off_page if
! 151: you get collector warnings from allocations of very large objects.
! 152: See README.debugging for details.
! 153:
! 154: Note that pointers inside memory allocated by the standard "malloc" are not
! 155: seen by the garbage collector. Thus objects pointed to only from such a
! 156: region may be prematurely deallocated. It is thus suggested that the
! 157: standard "malloc" be used only for memory regions, such as I/O buffers, that
! 158: are guaranteed not to contain pointers to garbage collectable memory.
! 159: Pointers in C language automatic, static, or register variables,
! 160: are correctly recognized. (Note that GC_malloc_uncollectable has semantics
! 161: similar to standard malloc, but allocates objects that are traced by the
! 162: collector.)
! 163:
! 164: The collector does not always know how to find pointers in data
! 165: areas that are associated with dynamic libraries. This is easy to
! 166: remedy IF you know how to find those data areas on your operating
! 167: system (see GC_add_roots). Code for doing this under SunOS, IRIX 5.X and 6.X,
! 168: HP/UX, Alpha OSF/1, Linux, and win32 is included and used by default. (See
! 169: README.win32 for win32 details.) On other systems pointers from dynamic
! 170: library data areas may not be considered by the collector.
! 171:
! 172: Note that the garbage collector does not need to be informed of shared
! 173: read-only data. However if the shared library mechanism can introduce
! 174: discontiguous data areas that may contain pointers, then the collector does
! 175: need to be informed.
! 176:
! 177: Signal processing for most signals may be deferred during collection,
! 178: and during uninterruptible parts of the allocation process. Unlike
! 179: standard ANSI C mallocs, it can be safe to invoke malloc
! 180: from a signal handler while another malloc is in progress, provided
! 181: the original malloc is not restarted. (Empirically, many UNIX
! 182: applications already assume this.) To obtain this level of signal
! 183: safety, remove the definition of -DNO_SIGNALS in Makefile. This incurs
! 184: a minor performance penalty, and hence is no longer the default.
! 185:
! 186: The allocator/collector can also be configured for thread-safe operation.
! 187: (Full signal safety can also be achieved, but only at the cost of two system
! 188: calls per malloc, which is usually unacceptable.)
! 189:
! 190: INSTALLATION AND PORTABILITY
! 191:
! 192: As distributed, the macro SILENT is defined in Makefile.
! 193: In the event of problems, this can be removed to obtain a moderate
! 194: amount of descriptive output for each collection.
! 195: (The given statistics exhibit a few peculiarities.
! 196: Things don't appear to add up for a variety of reasons, most notably
! 197: fragmentation losses. These are probably much more significant for the
! 198: contrived program "test.c" than for your application.)
! 199:
! 200: Note that typing "make test" will automatically build the collector
! 201: and then run setjmp_test and gctest. Setjmp_test will give you information
! 202: about configuring the collector, which is useful primarily if you have
! 203: a machine that's not already supported. Gctest is a somewhat superficial
! 204: test of collector functionality. Failure is indicated by a core dump or
! 205: a message to the effect that the collector is broken. Gctest takes about
! 206: 35 seconds to run on a SPARCstation 2. On a slower machine,
! 207: expect it to take a while. It may use up to 8 MB of memory. (The
! 208: multi-threaded version will use more.) "Make test" will also, as
! 209: its last step, attempt to build and test the "cord" string library.
! 210: This will fail without an ANSI C compiler.
! 211:
! 212: The Makefile will generate a library gc.a which you should link against.
! 213: Typing "make cords" will add the cord library to gc.a.
! 214: Note that this requires an ANSI C compiler.
! 215:
! 216: It is suggested that if you need to replace a piece of the collector
! 217: (e.g. GC_mark_rts.c) you simply list your version ahead of gc.a on the
! 218: work.)
! 219: ld command line, rather than replacing the one in gc.a. (This will
! 220: generate numerous warnings under some versions of AIX, but it still
! 221: works.)
! 222:
! 223: All include files that need to be used by clients will be put in the
! 224: include subdirectory. (Normally this is just gc.h. "Make cords" adds
! 225: "cord.h" and "ec.h".)
! 226:
! 227: The collector currently is designed to run essentially unmodified on
! 228: machines that use a flat 32-bit or 64-bit address space.
! 229: That includes the vast majority of Workstations and X86 (X >= 3) PCs.
! 230: (The list here was deleted because it was getting too long and constantly
! 231: out of date.)
! 232: It does NOT run under plain 16-bit DOS or Windows 3.X. There are however
! 233: various packages (e.g. win32s, djgpp) that allow flat 32-bit address
! 234: applications to run under those systemsif the have at least an 80386 processor,
! 235: and several of those are compatible with the collector.
! 236:
! 237: In a few cases (Amiga, OS/2, Win32, MacOS) a separate makefile
! 238: or equivalent is supplied. Many of these have separate README.system
! 239: files.
! 240:
! 241: Dynamic libraries are completely supported only under SunOS
! 242: (and even that support is not functional on the last Sun 3 release),
! 243: IRIX 5&6, HP-PA, Win32 (not Win32S) and OSF/1 on DEC AXP machines.
! 244: On other machines we recommend that you do one of the following:
! 245:
! 246: 1) Add dynamic library support (and send us the code).
! 247: 2) Use static versions of the libraries.
! 248: 3) Arrange for dynamic libraries to use the standard malloc.
! 249: This is still dangerous if the library stores a pointer to a
! 250: garbage collected object. But nearly all standard interfaces
! 251: prohibit this, because they deal correctly with pointers
! 252: to stack allocated objects. (Strtok is an exception. Don't
! 253: use it.)
! 254:
! 255: In all cases we assume that pointer alignment is consistent with that
! 256: enforced by the standard C compilers. If you use a nonstandard compiler
! 257: you may have to adjust the alignment parameters defined in gc_priv.h.
! 258:
! 259: A port to a machine that is not byte addressed, or does not use 32 bit
! 260: or 64 bit addresses will require a major effort. A port to plain MSDOS
! 261: or win16 is hard.
! 262:
! 263: For machines not already mentioned, or for nonstandard compilers, the
! 264: following are likely to require change:
! 265:
! 266: 1. The parameters in gcconfig.h.
! 267: The parameters that will usually require adjustment are
! 268: STACKBOTTOM, ALIGNMENT and DATASTART. Setjmp_test
! 269: prints its guesses of the first two.
! 270: DATASTART should be an expression for computing the
! 271: address of the beginning of the data segment. This can often be
! 272: &etext. But some memory management units require that there be
! 273: some unmapped space between the text and the data segment. Thus
! 274: it may be more complicated. On UNIX systems, this is rarely
! 275: documented. But the adb "$m" command may be helpful. (Note
! 276: that DATASTART will usually be a function of &etext. Thus a
! 277: single experiment is usually insufficient.)
! 278: STACKBOTTOM is used to initialize GC_stackbottom, which
! 279: should be a sufficient approximation to the coldest stack address.
! 280: On some machines, it is difficult to obtain such a value that is
! 281: valid across a variety of MMUs, OS releases, etc. A number of
! 282: alternatives exist for using the collector in spite of this. See the
! 283: discussion in gcconfig.h immediately preceding the various
! 284: definitions of STACKBOTTOM.
! 285:
! 286: 2. mach_dep.c.
! 287: The most important routine here is one to mark from registers.
! 288: The distributed file includes a generic hack (based on setjmp) that
! 289: happens to work on many machines, and may work on yours. Try
! 290: compiling and running setjmp_t.c to see whether it has a chance of
! 291: working. (This is not correct C, so don't blame your compiler if it
! 292: doesn't work. Based on limited experience, register window machines
! 293: are likely to cause trouble. If your version of setjmp claims that
! 294: all accessible variables, including registers, have the value they
! 295: had at the time of the longjmp, it also will not work. Vanilla 4.2 BSD
! 296: on Vaxen makes such a claim. SunOS does not.)
! 297: If your compiler does not allow in-line assembly code, or if you prefer
! 298: not to use such a facility, mach_dep.c may be replaced by a .s file
! 299: (as we did for the MIPS machine and the PC/RT).
! 300: At this point enough architectures are supported by mach_dep.c
! 301: that you will rarely need to do more than adjust for assembler
! 302: syntax.
! 303:
! 304: 3. os_dep.c (and gc_priv.h).
! 305: Several kinds of operating system dependent routines reside here.
! 306: Many are optional. Several are invoked only through corresponding
! 307: macros in gc_priv.h, which may also be redefined as appropriate.
! 308: The routine GC_register_data_segments is crucial. It registers static
! 309: data areas that must be traversed by the collector. (User calls to
! 310: GC_add_roots may sometimes be used for similar effect.)
! 311: Routines to obtain memory from the OS also reside here.
! 312: Alternatively this can be done entirely by the macro GET_MEM
! 313: defined in gc_priv.h. Routines to disable and reenable signals
! 314: also reside here if they are need by the macros DISABLE_SIGNALS
! 315: and ENABLE_SIGNALS defined in gc_priv.h.
! 316: In a multithreaded environment, the macros LOCK and UNLOCK
! 317: in gc_priv.h will need to be suitably redefined.
! 318: The incremental collector requires page dirty information, which
! 319: is acquired through routines defined in os_dep.c. Unless directed
! 320: otherwise by gcconfig.h, these are implemented as stubs that simply
! 321: treat all pages as dirty. (This of course makes the incremental
! 322: collector much less useful.)
! 323:
! 324: 4. dyn_load.c
! 325: This provides a routine that allows the collector to scan data
! 326: segments associated with dynamic libraries. Often it is not
! 327: necessary to provide this routine unless user-written dynamic
! 328: libraries are used.
! 329:
! 330: For a different version of UN*X or different machines using the
! 331: Motorola 68000, Vax, SPARC, 80386, NS 32000, PC/RT, or MIPS architecture,
! 332: it should frequently suffice to change definitions in gcconfig.h.
! 333:
! 334:
! 335: THE C INTERFACE TO THE ALLOCATOR
! 336:
! 337: The following routines are intended to be directly called by the user.
! 338: Note that usually only GC_malloc is necessary. GC_clear_roots and GC_add_roots
! 339: calls may be required if the collector has to trace from nonstandard places
! 340: (e.g. from dynamic library data areas on a machine on which the
! 341: collector doesn't already understand them.) On some machines, it may
! 342: be desirable to set GC_stacktop to a good approximation of the stack base.
! 343: (This enhances code portability on HP PA machines, since there is no
! 344: good way for the collector to compute this value.) Client code may include
! 345: "gc.h", which defines all of the following, plus many others.
! 346:
! 347: 1) GC_malloc(nbytes)
! 348: - allocate an object of size nbytes. Unlike malloc, the object is
! 349: cleared before being returned to the user. Gc_malloc will
! 350: invoke the garbage collector when it determines this to be appropriate.
! 351: GC_malloc may return 0 if it is unable to acquire sufficient
! 352: space from the operating system. This is the most probable
! 353: consequence of running out of space. Other possible consequences
! 354: are that a function call will fail due to lack of stack space,
! 355: or that the collector will fail in other ways because it cannot
! 356: maintain its internal data structures, or that a crucial system
! 357: process will fail and take down the machine. Most of these
! 358: possibilities are independent of the malloc implementation.
! 359:
! 360: 2) GC_malloc_atomic(nbytes)
! 361: - allocate an object of size nbytes that is guaranteed not to contain any
! 362: pointers. The returned object is not guaranteed to be cleared.
! 363: (Can always be replaced by GC_malloc, but results in faster collection
! 364: times. The collector will probably run faster if large character
! 365: arrays, etc. are allocated with GC_malloc_atomic than if they are
! 366: statically allocated.)
! 367:
! 368: 3) GC_realloc(object, new_size)
! 369: - change the size of object to be new_size. Returns a pointer to the
! 370: new object, which may, or may not, be the same as the pointer to
! 371: the old object. The new object is taken to be atomic iff the old one
! 372: was. If the new object is composite and larger than the original object,
! 373: then the newly added bytes are cleared (we hope). This is very likely
! 374: to allocate a new object, unless MERGE_SIZES is defined in gc_priv.h.
! 375: Even then, it is likely to recycle the old object only if the object
! 376: is grown in small additive increments (which, we claim, is generally bad
! 377: coding practice.)
! 378:
! 379: 4) GC_free(object)
! 380: - explicitly deallocate an object returned by GC_malloc or
! 381: GC_malloc_atomic. Not necessary, but can be used to minimize
! 382: collections if performance is critical. Probably a performance
! 383: loss for very small objects (<= 8 bytes).
! 384:
! 385: 5) GC_expand_hp(bytes)
! 386: - Explicitly increase the heap size. (This is normally done automatically
! 387: if a garbage collection failed to GC_reclaim enough memory. Explicit
! 388: calls to GC_expand_hp may prevent unnecessarily frequent collections at
! 389: program startup.)
! 390:
! 391: 6) GC_malloc_ignore_off_page(bytes)
! 392: - identical to GC_malloc, but the client promises to keep a pointer to
! 393: the somewhere within the first 256 bytes of the object while it is
! 394: live. (This pointer should nortmally be declared volatile to prevent
! 395: interference from compiler optimizations.) This is the recommended
! 396: way to allocate anything that is likely to be larger than 100Kbytes
! 397: or so. (GC_malloc may result in failure to reclaim such objects.)
! 398:
! 399: 7) GC_set_warn_proc(proc)
! 400: - Can be used to redirect warnings from the collector. Such warnings
! 401: should be rare, and should not be ignored during code development.
! 402:
! 403: 8) GC_enable_incremental()
! 404: - Enables generational and incremental collection. Useful for large
! 405: heaps on machines that provide access to page dirty information.
! 406: Some dirty bit implementations may interfere with debugging
! 407: (by catching address faults) and place restrictions on heap arguments
! 408: to system calls (since write faults inside a system call may not be
! 409: handled well).
! 410:
! 411: 9) Several routines to allow for registration of finalization code.
! 412: User supplied finalization code may be invoked when an object becomes
! 413: unreachable. To call (*f)(obj, x) when obj becomes inaccessible, use
! 414: GC_register_finalizer(obj, f, x, 0, 0);
! 415: For more sophisticated uses, and for finalization ordering issues,
! 416: see gc.h.
! 417:
! 418: The global variable GC_free_space_divisor may be adjusted up from its
! 419: default value of 4 to use less space and more collection time, or down for
! 420: the opposite effect. Setting it to 1 or 0 will effectively disable collections
! 421: and cause all allocations to simply grow the heap.
! 422:
! 423: The variable GC_non_gc_bytes, which is normally 0, may be changed to reflect
! 424: the amount of memory allocated by the above routines that should not be
! 425: considered as a candidate for collection. Careless use may, of course, result
! 426: in excessive memory consumption.
! 427:
! 428: Some additional tuning is possible through the parameters defined
! 429: near the top of gc_priv.h.
! 430:
! 431: If only GC_malloc is intended to be used, it might be appropriate to define:
! 432:
! 433: #define malloc(n) GC_malloc(n)
! 434: #define calloc(m,n) GC_malloc((m)*(n))
! 435:
! 436: For small pieces of VERY allocation intensive code, gc_inl.h
! 437: includes some allocation macros that may be used in place of GC_malloc
! 438: and friends.
! 439:
! 440: All externally visible names in the garbage collector start with "GC_".
! 441: To avoid name conflicts, client code should avoid this prefix, except when
! 442: accessing garbage collector routines or variables.
! 443:
! 444: There are provisions for allocation with explicit type information.
! 445: This is rarely necessary. Details can be found in gc_typed.h.
! 446:
! 447: THE C++ INTERFACE TO THE ALLOCATOR:
! 448:
! 449: The Ellis-Hull C++ interface to the collector is included in
! 450: the collector distribution. If you intend to use this, type
! 451: "make c++" after the initial build of the collector is complete.
! 452: See gc_cpp.h for the definition of the interface. This interface
! 453: tries to approximate the Ellis-Detlefs C++ garbage collection
! 454: proposal without compiler changes.
! 455:
! 456: Cautions:
! 457: 1. Arrays allocated without new placement syntax are
! 458: allocated as uncollectable objects. They are traced by the
! 459: collector, but will not be reclaimed.
! 460:
! 461: 2. Failure to use "make c++" in combination with (1) will
! 462: result in arrays allocated using the default new operator.
! 463: This is likely to result in disaster without linker warnings.
! 464:
! 465: 3. If your compiler supports an overloaded new[] operator,
! 466: then gc_cpp.cc and gc_cpp.h should be suitably modified.
! 467:
! 468: 4. Many current C++ compilers have deficiencies that
! 469: break some of the functionality. See the comments in gc_cpp.h
! 470: for suggested workarounds.
! 471:
! 472: USE AS LEAK DETECTOR:
! 473:
! 474: The collector may be used to track down leaks in C programs that are
! 475: intended to run with malloc/free (e.g. code with extreme real-time or
! 476: portability constraints). To do so define FIND_LEAK in Makefile
! 477: This will cause the collector to invoke the report_leak
! 478: routine defined near the top of reclaim.c whenever an inaccessible
! 479: object is found that has not been explicitly freed. Such objects will
! 480: also be automatically reclaimed.
! 481: Productive use of this facility normally involves redefining report_leak
! 482: to do something more intelligent. This typically requires annotating
! 483: objects with additional information (e.g. creation time stack trace) that
! 484: identifies their origin. Such code is typically not very portable, and is
! 485: not included here, except on SPARC machines.
! 486: If all objects are allocated with GC_DEBUG_MALLOC (see next section),
! 487: then the default version of report_leak will report the source file
! 488: and line number at which the leaked object was allocated. This may
! 489: sometimes be sufficient. (On SPARC/SUNOS4 machines, it will also report
! 490: a cryptic stack trace. This can often be turned into a sympolic stack
! 491: trace by invoking program "foo" with "callprocs foo". Callprocs is
! 492: a short shell script that invokes adb to expand program counter values
! 493: to symbolic addresses. It was largely supplied by Scott Schwartz.)
! 494: Note that the debugging facilities described in the next section can
! 495: sometimes be slightly LESS effective in leak finding mode, since in
! 496: leak finding mode, GC_debug_free actually results in reuse of the object.
! 497: (Otherwise the object is simply marked invalid.) Also note that the test
! 498: program is not designed to run meaningfully in FIND_LEAK mode.
! 499: Use "make gc.a" to build the collector.
! 500:
! 501: DEBUGGING FACILITIES:
! 502:
! 503: The routines GC_debug_malloc, GC_debug_malloc_atomic, GC_debug_realloc,
! 504: and GC_debug_free provide an alternate interface to the collector, which
! 505: provides some help with memory overwrite errors, and the like.
! 506: Objects allocated in this way are annotated with additional
! 507: information. Some of this information is checked during garbage
! 508: collections, and detected inconsistencies are reported to stderr.
! 509:
! 510: Simple cases of writing past the end of an allocated object should
! 511: be caught if the object is explicitly deallocated, or if the
! 512: collector is invoked while the object is live. The first deallocation
! 513: of an object will clear the debugging info associated with an
! 514: object, so accidentally repeated calls to GC_debug_free will report the
! 515: deallocation of an object without debugging information. Out of
! 516: memory errors will be reported to stderr, in addition to returning
! 517: NIL.
! 518:
! 519: GC_debug_malloc checking during garbage collection is enabled
! 520: with the first call to GC_debug_malloc. This will result in some
! 521: slowdown during collections. If frequent heap checks are desired,
! 522: this can be achieved by explicitly invoking GC_gcollect, e.g. from
! 523: the debugger.
! 524:
! 525: GC_debug_malloc allocated objects should not be passed to GC_realloc
! 526: or GC_free, and conversely. It is however acceptable to allocate only
! 527: some objects with GC_debug_malloc, and to use GC_malloc for other objects,
! 528: provided the two pools are kept distinct. In this case, there is a very
! 529: low probablility that GC_malloc allocated objects may be misidentified as
! 530: having been overwritten. This should happen with probability at most
! 531: one in 2**32. This probability is zero if GC_debug_malloc is never called.
! 532:
! 533: GC_debug_malloc, GC_malloc_atomic, and GC_debug_realloc take two
! 534: additional trailing arguments, a string and an integer. These are not
! 535: interpreted by the allocator. They are stored in the object (the string is
! 536: not copied). If an error involving the object is detected, they are printed.
! 537:
! 538: The macros GC_MALLOC, GC_MALLOC_ATOMIC, GC_REALLOC, GC_FREE, and
! 539: GC_REGISTER_FINALIZER are also provided. These require the same arguments
! 540: as the corresponding (nondebugging) routines. If gc.h is included
! 541: with GC_DEBUG defined, they call the debugging versions of these
! 542: functions, passing the current file name and line number as the two
! 543: extra arguments, where appropriate. If gc.h is included without GC_DEBUG
! 544: defined, then all these macros will instead be defined to their nondebugging
! 545: equivalents. (GC_REGISTER_FINALIZER is necessary, since pointers to
! 546: objects with debugging information are really pointers to a displacement
! 547: of 16 bytes form the object beginning, and some translation is necessary
! 548: when finalization routines are invoked. For details, about what's stored
! 549: in the header, see the definition of the type oh in debug_malloc.c)
! 550:
! 551: INCREMENTAL/GENERATIONAL COLLECTION:
! 552:
! 553: The collector normally interrupts client code for the duration of
! 554: a garbage collection mark phase. This may be unacceptable if interactive
! 555: response is needed for programs with large heaps. The collector
! 556: can also run in a "generational" mode, in which it usually attempts to
! 557: collect only objects allocated since the last garbage collection.
! 558: Furthermore, in this mode, garbage collections run mostly incrementally,
! 559: with a small amount of work performed in response to each of a large number of
! 560: GC_malloc requests.
! 561:
! 562: This mode is enabled by a call to GC_enable_incremental().
! 563:
! 564: Incremental and generational collection is effective in reducing
! 565: pause times only if the collector has some way to tell which objects
! 566: or pages have been recently modified. The collector uses two sources
! 567: of information:
! 568:
! 569: 1. Information provided by the VM system. This may be provided in
! 570: one of several forms. Under Solaris 2.X (and potentially under other
! 571: similar systems) information on dirty pages can be read from the
! 572: /proc file system. Under other systems (currently SunOS4.X) it is
! 573: possible to write-protect the heap, and catch the resulting faults.
! 574: On these systems we require that system calls writing to the heap
! 575: (other than read) be handled specially by client code.
! 576: See os_dep.c for details.
! 577:
! 578: 2. Information supplied by the programmer. We define "stubborn"
! 579: objects to be objects that are rarely changed. Such an object
! 580: can be allocated (and enabled for writing) with GC_malloc_stubborn.
! 581: Once it has been initialized, the collector should be informed with
! 582: a call to GC_end_stubborn_change. Subsequent writes that store
! 583: pointers into the object must be preceded by a call to
! 584: GC_change_stubborn.
! 585:
! 586: This mechanism performs best for objects that are written only for
! 587: initialization, and such that only one stubborn object is writable
! 588: at once. It is typically not worth using for short-lived
! 589: objects. Stubborn objects are treated less efficiently than pointerfree
! 590: (atomic) objects.
! 591:
! 592: A rough rule of thumb is that, in the absence of VM information, garbage
! 593: collection pauses are proportional to the amount of pointerful storage
! 594: plus the amount of modified "stubborn" storage that is reachable during
! 595: the collection.
! 596:
! 597: Initial allocation of stubborn objects takes longer than allocation
! 598: of other objects, since other data structures need to be maintained.
! 599:
! 600: We recommend against random use of stubborn objects in client
! 601: code, since bugs caused by inappropriate writes to stubborn objects
! 602: are likely to be very infrequently observed and hard to trace.
! 603: However, their use may be appropriate in a few carefully written
! 604: library routines that do not make the objects themselves available
! 605: for writing by client code.
! 606:
! 607:
! 608: BUGS:
! 609:
! 610: Any memory that does not have a recognizable pointer to it will be
! 611: reclaimed. Exclusive-or'ing forward and backward links in a list
! 612: doesn't cut it.
! 613: Some C optimizers may lose the last undisguised pointer to a memory
! 614: object as a consequence of clever optimizations. This has almost
! 615: never been observed in practice. Send mail to boehm@acm.org
! 616: for suggestions on how to fix your compiler.
! 617: This is not a real-time collector. In the standard configuration,
! 618: percentage of time required for collection should be constant across
! 619: heap sizes. But collection pauses will increase for larger heaps.
! 620: (On SPARCstation 2s collection times will be on the order of 300 msecs
! 621: per MB of accessible memory that needs to be scanned. Your mileage
! 622: may vary.) The incremental/generational collection facility helps,
! 623: but is portable only if "stubborn" allocation is used.
! 624: Please address bug reports to boehm@acm.org. If you are
! 625: contemplating a major addition, you might also send mail to ask whether
! 626: it's already been done (or whether we tried and discarded it).
! 627:
! 628: RECENT VERSIONS:
! 629:
! 630: Version 1.3 and immediately preceding versions contained spurious
! 631: assembly language assignments to TMP_SP. Only the assignment in the PC/RT
! 632: code is necessary. On other machines, with certain compiler options,
! 633: the assignments can lead to an unsaved register being overwritten.
! 634: Known to cause problems under SunOS 3.5 WITHOUT the -O option. (With
! 635: -O the compiler recognizes it as dead code. It probably shouldn't,
! 636: but that's another story.)
! 637:
! 638: Version 1.4 and earlier versions used compile time determined values
! 639: for the stack base. This no longer works on Sun 3s, since Sun 3/80s use
! 640: a different stack base. We now use a straightforward heuristic on all
! 641: machines on which it is known to work (incl. Sun 3s) and compile-time
! 642: determined values for the rest. There should really be library calls
! 643: to determine such values.
! 644:
! 645: Version 1.5 and earlier did not ensure 8 byte alignment for objects
! 646: allocated on a sparc based machine.
! 647:
! 648: Version 1.8 added ULTRIX support in gc_private.h.
! 649:
! 650: Version 1.9 fixed a major bug in gc_realloc.
! 651:
! 652: Version 2.0 introduced a consistent naming convention for collector
! 653: routines and added support for registering dynamic library data segments
! 654: in the standard mark_roots.c. Most of the data structures were revamped.
! 655: The treatment of interior pointers was completely changed. Finalization
! 656: was added. Support for locking was added. Object kinds were added.
! 657: We added a black listing facility to avoid allocating at addresses known
! 658: to occur as integers somewhere in the address space. Much of this
! 659: was accomplished by adapting ideas and code from the PCR collector.
! 660: The test program was changed and expanded.
! 661:
! 662: Version 2.1 was the first stable version since 1.9, and added support
! 663: for PPCR.
! 664:
! 665: Version 2.2 added debugging allocation, and fixed various bugs. Among them:
! 666: - GC_realloc could fail to extend the size of the object for certain large object sizes.
! 667: - A blatant subscript range error in GC_printf, which unfortunately
! 668: wasn't exercised on machines with sufficient stack alignment constraints.
! 669: - GC_register_displacement did the wrong thing if it was called after
! 670: any allocation had taken place.
! 671: - The leak finding code would eventually break after 2048 byte
! 672: byte objects leaked.
! 673: - interface.c didn't compile.
! 674: - The heap size remained much too small for large stacks.
! 675: - The stack clearing code behaved badly for large stacks, and perhaps
! 676: on HP/PA machines.
! 677:
! 678: Version 2.3 added ALL_INTERIOR_POINTERS and fixed the following bugs:
! 679: - Missing declaration of etext in the A/UX version.
! 680: - Some PCR root-finding problems.
! 681: - Blacklisting was not 100% effective, because the plausible future
! 682: heap bounds were being miscalculated.
! 683: - GC_realloc didn't handle out-of-memory correctly.
! 684: - GC_base could return a nonzero value for addresses inside free blocks.
! 685: - test.c wasn't really thread safe, and could erroneously report failure
! 686: in a multithreaded environment. (The locking primitives need to be
! 687: replaced for other threads packages.)
! 688: - GC_CONS was thoroughly broken.
! 689: - On a SPARC with dynamic linking, signals stayed diabled while the
! 690: client code was running.
! 691: (Thanks to Manuel Serrano at INRIA for reporting the last two.)
! 692:
! 693: Version 2.4 added GC_free_space_divisor as a tuning knob, added
! 694: support for OS/2 and linux, and fixed the following bugs:
! 695: - On machines with unaligned pointers (e.g. Sun 3), every 128th word could
! 696: fail to be considered for marking.
! 697: - Dynamic_load.c erroneously added 4 bytes to the length of the data and
! 698: bss sections of the dynamic library. This could result in a bad memory
! 699: reference if the actual length was a multiple of a page. (Observed on
! 700: Sun 3. Can probably also happen on a Sun 4.)
! 701: (Thanks to Robert Brazile for pointing out that the Sun 3 version
! 702: was broken. Dynamic library handling is still broken on Sun 3s
! 703: under 4.1.1U1, but apparently not 4.1.1. If you have such a machine,
! 704: use -Bstatic.)
! 705:
! 706: Version 2.5 fixed the following bugs:
! 707: - Removed an explicit call to exit(1)
! 708: - Fixed calls to GC_printf and GC_err_printf, so the correct number of
! 709: arguments are always supplied. The OS/2 C compiler gets confused if
! 710: the number of actuals and the number of formals differ. (ANSI C
! 711: doesn't require this to work. The ANSI sanctioned way of doing things
! 712: causes too many compatibility problems.)
! 713:
! 714: Version 3.0 added generational/incremental collection and stubborn
! 715: objects.
! 716:
! 717: Version 3.1 added the following features:
! 718: - A workaround for a SunOS 4.X SPARC C compiler
! 719: misfeature that caused problems when the collector was turned into
! 720: a dynamic library.
! 721: - A fix for a bug in GC_base that could result in a memory fault.
! 722: - A fix for a performance bug (and several other misfeatures) pointed
! 723: out by Dave Detlefs and Al Dosser.
! 724: - Use of dirty bit information for static data under Solaris 2.X.
! 725: - DEC Alpha/OSF1 support (thanks to Al Dosser).
! 726: - Incremental collection on more platforms.
! 727: - A more refined heap expansion policy. Less space usage by default.
! 728: - Various minor enhancements to reduce space usage, and to reduce
! 729: the amount of memory scanned by the collector.
! 730: - Uncollectable allocation without per object overhead.
! 731: - More conscientious handling of out-of-memory conditions.
! 732: - Fixed a bug in debugging stubborn allocation.
! 733: - Fixed a bug that resulted in occasional erroneous reporting of smashed
! 734: objects with debugging allocation.
! 735: - Fixed bogus leak reports of size 4096 blocks with FIND_LEAK.
! 736:
! 737: Version 3.2 fixed a serious and not entirely repeatable bug in
! 738: the incremental collector. It appeared only when dirty bit info
! 739: on the roots was available, which is normally only under Solaris.
! 740: It also added GC_general_register_disappearing_link, and some
! 741: testing code. Interface.c disappeared.
! 742:
! 743: Version 3.3 fixes several bugs and adds new ports:
! 744: - PCR-specific bugs.
! 745: - Missing locking in GC_free, redundant FASTUNLOCK
! 746: in GC_malloc_stubborn, and 2 bugs in
! 747: GC_unregister_disappearing_link.
! 748: All of the above were pointed out by Neil Sharman
! 749: (neil@cs.mu.oz.au).
! 750: - Common symbols allocated by the SunOS4.X dynamic loader
! 751: were not included in the root set.
! 752: - Bug in GC_finalize (reported by Brian Beuning and Al Dosser)
! 753: - Merged Amiga port from Jesper Peterson (untested)
! 754: - Merged NeXT port from Thomas Funke (significantly
! 755: modified and untested)
! 756:
! 757: Version 3.4:
! 758: - Fixed a performance bug in GC_realloc.
! 759: - Updated the amiga port.
! 760: - Added NetBSD and 386BSD ports.
! 761: - Added cord library.
! 762: - Added trivial performance enhancement for
! 763: ALL_INTERIOR_POINTERS. (Don't scan last word.)
! 764:
! 765: Version 3.5
! 766: - Minor collections now mark from roots only once, if that
! 767: doesn't cause an excessive pause.
! 768: - The stack clearing heuristic was refined to prevent anomalies
! 769: with very heavily recursive programs and sparse stacks.
! 770: - Fixed a bug that prevented mark stack growth in some cases.
! 771: GC_objects_are_marked should be set to TRUE after a call
! 772: to GC_push_roots and as part of GC_push_marked, since
! 773: both can now set mark bits. I think this is only a performance
! 774: bug, but I wouldn't bet on it. It's certainly very hard to argue
! 775: that the old version was correct.
! 776: - Fixed an incremental collection bug that prevented it from
! 777: working at all when HBLKSIZE != getpagesize()
! 778: - Changed dynamic_loading.c to include gc_priv.h before testing
! 779: DYNAMIC_LOADING. SunOS dynamic library scanning
! 780: must have been broken in 3.4.
! 781: - Object size rounding now adapts to program behavior.
! 782: - Added a workaround (provided by Manuel Serrano and
! 783: colleagues) to a long-standing SunOS 4.X (and 3.X?) ld bug
! 784: that I had incorrectly assumed to have been squished.
! 785: The collector was broken if the text segment size was within
! 786: 32 bytes of a multiple of 8K bytes, and if the beginning of
! 787: the data segment contained interesting roots. The workaround
! 788: assumes a demand-loadable executable. The original may have
! 789: have "worked" in some other cases.
! 790: - Added dynamic library support under IRIX5.
! 791: - Added support for EMX under OS/2 (thanks to Ari Huttunen).
! 792:
! 793: Version 3.6:
! 794: - fixed a bug in the mark stack growth code that was introduced
! 795: in 3.4.
! 796: - fixed Makefile to work around DEC AXP compiler tail recursion
! 797: bug.
! 798:
! 799: Version 3.7:
! 800: - Added a workaround for an HP/UX compiler bug.
! 801: - Fixed another stack clearing performance bug. Reworked
! 802: that code once more.
! 803:
! 804: Version 4.0:
! 805: - Added support for Solaris threads (which was possible
! 806: only by reimplementing some fraction of Solaris threads,
! 807: since Sun doesn't currently make the thread debugging
! 808: interface available).
! 809: - Added non-threads win32 and win32S support.
! 810: - (Grudgingly, with suitable muttering of obscenities) renamed
! 811: files so that the collector distribution could live on a FAT
! 812: file system. Files that are guaranteed to be useless on
! 813: a PC still have long names. Gc_inline.h and gc_private.h
! 814: still exist, but now just include gc_inl.h and gc_priv.h.
! 815: - Fixed a really obscure bug in finalization that could cause
! 816: undetected mark stack overflows. (I would be surprised if
! 817: any real code ever tickled this one.)
! 818: - Changed finalization code to dynamically resize the hash
! 819: tables it maintains. (This probably does not matter for well-
! 820: -written code. It no doubt does for C++ code that overuses
! 821: destructors.)
! 822: - Added typed allocation primitives. Rewrote the marker to
! 823: accommodate them with more reasonable efficiency. This
! 824: change should also speed up marking for GC_malloc allocated
! 825: objects a little. See gc_typed.h for new primitives.
! 826: - Improved debugging facilities slightly. Allocation time
! 827: stack traces are now kept by default on SPARC/SUNOS4.
! 828: (Thanks to Scott Schwartz.)
! 829: - Added better support for small heap applications.
! 830: - Significantly extended cord package. Fixed a bug in the
! 831: implementation of lazily read files. Printf and friends now
! 832: have cord variants. Cord traversals are a bit faster.
! 833: - Made ALL_INTERIOR_POINTERS recognition the default.
! 834: - Fixed de so that it can run in constant space, independent
! 835: of file size. Added simple string searching to cords and de.
! 836: - Added the Hull-Ellis C++ interface.
! 837: - Added dynamic library support for OSF/1.
! 838: (Thanks to Al Dosser and Tim Bingham at DEC.)
! 839: - Changed argument to GC_expand_hp to be expressed
! 840: in units of bytes instead of heap blocks. (Necessary
! 841: since the heap block size now varies depending on
! 842: configuration. The old version was never very clean.)
! 843: - Added GC_get_heap_size(). The previous "equivalent"
! 844: was broken.
! 845: - Restructured the Makefile a bit.
! 846:
! 847: Since version 4.0:
! 848: - Changed finalization implementation to guarantee that
! 849: finalization procedures are called outside of the allocation
! 850: lock, making direct use of the interface a little less dangerous.
! 851: MAY BREAK EXISTING CLIENTS that assume finalizers
! 852: are protected by a lock. Since there seem to be few multithreaded
! 853: clients that use finalization, this is hopefully not much of
! 854: a problem.
! 855: - Fixed a gross bug in CORD_prev.
! 856: - Fixed a bug in blacklst.c that could result in unbounded
! 857: heap growth during startup on machines that do not clear
! 858: memory obtained from the OS (e.g. win32S).
! 859: - Ported de editor to win32/win32S. (This is now the only
! 860: version with a mouse-sensitive UI.)
! 861: - Added GC_malloc_ignore_off_page to allocate large arrays
! 862: in the presence of ALL_INTERIOR_POINTERS.
! 863: - Changed GC_call_with_alloc_lock to not disable signals in
! 864: the single-threaded case.
! 865: - Reduced retry count in GC_collect_or_expand for garbage
! 866: collecting when out of memory.
! 867: - Made uncollectable allocations bypass black-listing, as they
! 868: should.
! 869: - Fixed a bug in typed_test in test.c that could cause (legitimate)
! 870: GC crashes.
! 871: - Fixed some potential synchronization problems in finalize.c
! 872: - Fixed a real locking problem in typd_mlc.c.
! 873: - Worked around an AIX 3.2 compiler feature that results in
! 874: out of bounds memory references.
! 875: - Partially worked around an IRIX5.2 beta problem (which may
! 876: or may not persist to the final release).
! 877: - Fixed a bug in the heap integrity checking code that could
! 878: result in explicitly deallocated objects being identified as
! 879: smashed. Fixed a bug in the dbg_mlc stack saving code
! 880: that caused old argument pointers to be considered live.
! 881: - Fixed a bug in CORD_ncmp (and hence CORD_str).
! 882: - Repaired the OS2 port, which had suffered from bit rot
! 883: in 4.0. Worked around what appears to be CSet/2 V1.0
! 884: optimizer bug.
! 885: - Fixed a Makefile bug for target "c++".
! 886:
! 887: Since version 4.1:
! 888: - Multiple bug fixes/workarounds in the Solaris threads version.
! 889: (It occasionally failed to locate some register contents for
! 890: marking. It also turns out that thr_suspend and friends are
! 891: unreliable in Solaris 2.3. Dirty bit reads appear
! 892: to be unreliable under some weird
! 893: circumstances. My stack marking code
! 894: contained a serious performance bug. The new code is
! 895: extremely defensive, and has not failed in several cpu
! 896: hours of testing. But no guarantees ...)
! 897: - Added MacOS support (thanks to Patrick Beard.)
! 898: - Fixed several syntactic bugs in gc_c++.h and friends. (These
! 899: didn't bother g++, but did bother most other compilers.)
! 900: Fixed gc_c++.h finalization interface. (It didn't.)
! 901: - 64 bit alignment for allocated objects was not guaranteed in a
! 902: few cases in which it should have been.
! 903: - Added GC_malloc_atomic_ignore_off_page.
! 904: - Added GC_collect_a_little.
! 905: - Added some prototypes to gc.h.
! 906: - Some other minor bug fixes (notably in Makefile).
! 907: - Fixed OS/2 / EMX port (thanks to Ari Huttunen).
! 908: - Fixed AmigaDOS port. (thanks to Michel Schinz).
! 909: - Fixed the DATASTART definition under Solaris. There
! 910: was a 1 in 16K chance of the collector missing the first
! 911: 64K of static data (and thus crashing).
! 912: - Fixed some blatant anachronisms in the README file.
! 913: - Fixed PCR-Makefile for upcoming PPCR release.
! 914:
! 915: Since version 4.2:
! 916: - Fixed SPARC alignment problem with GC_DEBUG.
! 917: - Fixed Solaris threads /proc workaround. The real
! 918: problem was an interaction with mprotect.
! 919: - Incorporated fix from Patrick Beard for gc_c++.h (now gc_cpp.h).
! 920: - Slightly improved allocator space utilization by
! 921: fixing the GC_size_map mechanism.
! 922: - Integrated some Sony News and MIPS RISCos 4.51
! 923: patches. (Thanks to Nobuyuki Hikichi of
! 924: Software Research Associates, Inc. Japan)
! 925: - Fixed HP_PA alignment problem. (Thanks to
! 926: xjam@cork.cs.berkeley.edu.)
! 927: - Added GC_same_obj and friends. Changed GC_base
! 928: to return 0 for pointers past the end of large objects.
! 929: Improved GC_base performance with ALL_INTERIOR_POINTERS
! 930: on machines with a slow integer mod operation.
! 931: Added GC_PTR_ADD, GC_PTR_STORE, etc. to prepare
! 932: for preprocessor.
! 933: - changed the default on most UNIX machines to be that
! 934: signals are not disabled during critical GC operations.
! 935: This is still ANSI-conforming, though somewhat dangerous
! 936: in the presence of signal handlers. But the performance
! 937: cost of the alternative is sometimes problematic.
! 938: Can be changed back with a minor Makefile edit.
! 939: - renamed IS_STRING in gc.h, to CORD_IS_STRING, thus
! 940: following my own naming convention. Added the function
! 941: CORD_to_const_char_star.
! 942: - Fixed a gross bug in GC_finalize. Symptom: occasional
! 943: address faults in that function. (Thanks to Anselm
! 944: Baird-Smith (Anselm.BairdSmith@inria.fr)
! 945: - Added port to ICL DRS6000 running DRS/NX. Restructured
! 946: things a bit to factor out common code, and remove obsolete
! 947: code. Collector should now run under SUNOS5 with either
! 948: mprotect or /proc dirty bits. (Thanks to Douglas Steel
! 949: (doug@wg.icl.co.uk)).
! 950: - More bug fixes and workarounds for Solaris 2.X. (These were
! 951: mostly related to putting the collector in a dynamic library,
! 952: which didn't really work before. Also SOLARIS_THREADS
! 953: didn't interact well with dl_open.) Thanks to btlewis@eng.sun.com.
! 954: - Fixed a serious performance bug on the DEC Alpha. The text
! 955: segment was getting registered as part of the root set.
! 956: (Amazingly, the result was still fast enough that the bug
! 957: was not conspicuous.) The fix works on OSF/1, version 1.3.
! 958: Hopefully it also works on other versions of OSF/1 ...
! 959: - Fixed a bug in GC_clear_roots.
! 960: - Fixed a bug in GC_generic_malloc_words_small that broke
! 961: gc_inl.h. (Reported by Antoine de Maricourt. I broke it
! 962: in trying to tweak the Mac port.)
! 963: - Fixed some problems with cord/de under Linux.
! 964: - Fixed some cord problems, notably with CORD_riter4.
! 965: - Added DG/UX port.
! 966: Thanks to Ben A. Mesander (ben@piglet.cr.usgs.gov)
! 967: - Added finalization registration routines with weaker ordering
! 968: constraints. (This is necessary for C++ finalization with
! 969: multiple inheritance, since the compiler often adds self-cycles.)
! 970: - Filled the holes in the SCO port. (Thanks to Michael Arnoldus
! 971: <chime@proinf.dk>.)
! 972: - John Ellis' additions to the C++ support: From John:
! 973:
! 974: * I completely rewrote the documentation in the interface gc_c++.h
! 975: (later renamed gc_cpp.h). I've tried to make it both clearer and more
! 976: precise.
! 977:
! 978: * The definition of accessibility now ignores pointers from an
! 979: finalizable object (an object with a clean-up function) to itself.
! 980: This allows objects with virtual base classes to be finalizable by the
! 981: collector. Compilers typically implement virtual base classes using
! 982: pointers from an object to itself, which under the old definition of
! 983: accessibility prevented objects with virtual base classes from ever
! 984: being collected or finalized.
! 985:
! 986: * gc_cleanup now includes gc as a virtual base. This was enabled by
! 987: the change in the definition of accessibility.
! 988:
! 989: * I added support for operator new[]. Since most (all?) compilers
! 990: don't yet support operator new[], it is conditionalized on
! 991: -DOPERATOR_NEW_ARRAY. The code is untested, but its trivial and looks
! 992: correct.
! 993:
! 994: * The test program test_gc_c++ (later renamed test_cpp.cc)
! 995: tries to test for the C++-specific functionality not tested by the
! 996: other programs.
! 997: - Added <unistd.h> include to misc.c. (Needed for ppcr.)
! 998: - Added PowerMac port. (Thanks to Patrick Beard again.)
! 999: - Fixed "srcdir"-related Makefile problems. Changed things so
! 1000: that all externally visible include files always appear in the
! 1001: include subdirectory of the source. Made gc.h directly
! 1002: includable from C++ code. (These were at Per
! 1003: Bothner's suggestion.)
! 1004: - Changed Intel code to also mark from ebp (Kevin Warne's
! 1005: suggestion).
! 1006: - Renamed C++ related files so they could live in a FAT
! 1007: file system. (Charles Fiterman's suggestion.)
! 1008: - Changed Windows NT Makefile to include C++ support in
! 1009: gc.lib. Added C++ test as Makefile target.
! 1010:
! 1011: Since version 4.3:
! 1012: - ASM_CLEAR_CODE was erroneously defined for HP
! 1013: PA machines, resulting in a compile error.
! 1014: - Fixed OS/2 Makefile to create a library. (Thanks to
! 1015: Mark Boulter (mboulter@vnet.ibm.com)).
! 1016: - Gc_cleanup objects didn't work if they were created on
! 1017: the stack. Fixed.
! 1018: - One copy of Gc_cpp.h in the distribution was out of
! 1019: synch, and failed to document some known compiler
! 1020: problems with explicit destructor invocation. Partially
! 1021: fixed. There are probably other compilers on which
! 1022: gc_cleanup is miscompiled.
! 1023: - Fixed Makefile to pass C compiler flags to C++ compiler.
! 1024: - Added Mac fixes.
! 1025: - Fixed os_dep.c to work around what appears to be
! 1026: a new and different VirtualQuery bug under newer
! 1027: versions of win32S.
! 1028: - GC_non_gc_bytes was not correctly maintained by
! 1029: GC_free. Fixed. Thanks to James Clark (jjc@jclark.com).
! 1030: - Added GC_set_max_heap_size.
! 1031: - Changed allocation code to ignore blacklisting if it is preventing
! 1032: use of a very large block of memory. This has the advantage
! 1033: that naive code allocating very large objects is much more
! 1034: likely to work. The downside is you might no
! 1035: longer find out that such code should really use
! 1036: GC_malloc_ignore_off_page.
! 1037: - Changed GC_printf under win32 to close and reopen the file
! 1038: between calls. FAT file systems otherwise make the log file
! 1039: useless for debugging.
! 1040: - Added GC_try_to_collect and GC_get_bytes_since_gc. These
! 1041: allow starting an abortable collection during idle times.
! 1042: This facility does not require special OS support. (Thanks to
! 1043: Michael Spertus of Geodesic Systems for suggesting this. It was
! 1044: actually an easy addition. Kumar Srikantan previously added a similar
! 1045: facility to a now ancient version of the collector. At the time
! 1046: this was much harder, and the result was less convincing.)
! 1047: - Added some support for the Borland development environment. (Thanks
! 1048: to John Ellis and Michael Spertus.)
! 1049: - Removed a misfeature from checksums.c that caused unexpected
! 1050: heap growth. (Thanks to Scott Schwartz.)
! 1051: - Changed finalize.c to call WARN if it encounters a finalization cycle.
! 1052: WARN is defined in gc_priv.h to write a message, usually to stdout.
! 1053: In many environments, this may be inappropriate.
! 1054: - Renamed NO_PARAMS in gc.h to GC_NO_PARAMS, thus adhering to my own
! 1055: naming convention.
! 1056: - Added GC_set_warn_proc to intercept warnings.
! 1057: - Fixed Amiga port. (Thanks to Michel Schinz (schinz@alphanet.ch).)
! 1058: - Fixed a bug in mark.c that could result in an access to unmapped
! 1059: memory from GC_mark_from_mark_stack on machines with unaligned
! 1060: pointers.
! 1061: - Fixed a win32 specific performance bug that could result in scanning of
! 1062: objects allocated with the system malloc.
! 1063: - Added REDIRECT_MALLOC.
! 1064:
! 1065: Since version 4.4:
! 1066: - Fixed many minor and one major README bugs. (Thanks to Franklin Chen
! 1067: (chen@adi.com) for pointing out many of them.)
! 1068: - Fixed ALPHA/OSF/1 dynamic library support. (Thanks to Jonathan Bachrach
! 1069: (jonathan@harlequin.com)).
! 1070: - Added incremental GC support (MPROTECT_VDB) for Linux (with some
! 1071: help from Bruno Haible).
! 1072: - Altered SPARC recognition tests in gc.h and config.h (mostly as
! 1073: suggested by Fergus Henderson).
! 1074: - Added basic incremental GC support for win32, as implemented by
! 1075: Windows NT and Windows 95. GC_enable_incremental is a noop
! 1076: under win32s, which doesn't implement enough of the VM interface.
! 1077: - Added -DLARGE_CONFIG.
! 1078: - Fixed GC_..._ignore_off_page to also function without
! 1079: -DALL_INTERIOR_POINTERS.
! 1080: - (Hopefully) fixed RS/6000 port. (Only the test was broken.)
! 1081: - Fixed a performance bug in the nonincremental collector running
! 1082: on machines supporting incremental collection with MPROTECT_VDB
! 1083: (e.g. SunOS 4, DEC AXP). This turned into a correctness bug under
! 1084: win32s with win32 incremental collection. (Not all memory protection
! 1085: was disabled.)
! 1086: - Fixed some ppcr related bit rot.
! 1087: - Caused dynamic libraries to be unregistered before reregistering.
! 1088: The old way turned out to be a performance bug on some machines.
! 1089: - GC_root_size was not properly maintained under MSWIN32.
! 1090: - Added -DNO_DEBUGGING and GC_dump.
! 1091: - Fixed a couple of bugs arising with SOLARIS_THREADS +
! 1092: REDIRECT_MALLOC.
! 1093: - Added NetBSD/M68K port. (Thanks to Peter Seebach
! 1094: <seebs@taniemarie.solon.com>.)
! 1095: - Fixed a serious realloc bug. For certain object sizes, the collector
! 1096: wouldn't scan the expanded part of the object. (Thanks to Clay Spence
! 1097: (cds@peanut.sarnoff.com) for noticing the problem, and helping me to
! 1098: track it down.)
! 1099:
! 1100: Since version 4.5:
! 1101: - Added Linux ELF support. (Thanks to Arrigo Triulzi <arrigo@ic.ac.uk>.)
! 1102: - GC_base crashed if it was called before any other GC_ routines.
! 1103: This could happen if a gc_cleanup object was allocated outside the heap
! 1104: before any heap allocation.
! 1105: - The heap expansion heuristic was not stable if all objects had finalization
! 1106: enabled. Fixed finalize.c to count memory in finalization queue and
! 1107: avoid explicit deallocation. Changed alloc.c to also consider this count.
! 1108: (This is still not recommended. It's expensive if nothing else.) Thanks
! 1109: to John Ellis for pointing this out.
! 1110: - GC_malloc_uncollectable(0) was broken. Thanks to Phong Vo for pointing
! 1111: this out.
! 1112: - The collector didn't compile under Linux 1.3.X. (Thanks to Fred Gilham for
! 1113: pointing this out.) The current workaround is ugly, but expected to be
! 1114: temporary.
! 1115: - Fixed a formatting problem for SPARC stack traces.
! 1116: - Fixed some '=='s in os_dep.c that should have been assignments.
! 1117: Fortunately these were in code that should never be executed anyway.
! 1118: (Thanks to Fergus Henderson.)
! 1119: - Fixed the heap block allocator to only drop blacklisted blocks in small
! 1120: chunks. Made BL_LIMIT self adjusting. (Both of these were in response
! 1121: to heap growth observed by Paul Graham.)
! 1122: - Fixed the Metrowerks/68K Mac code to also mark from a6. (Thanks
! 1123: to Patrick Beard.)
! 1124: - Significantly updated README.debugging.
! 1125: - Fixed some problems with longjmps out of signal handlers, especially under
! 1126: Solaris. Added a workaround for the fact that siglongjmp doesn't appear to
! 1127: do the right thing with -lthread under Solaris.
! 1128: - Added MSDOS/djgpp port. (Thanks to Mitch Harris (maharri@uiuc.edu).)
! 1129: - Added "make reserved_namespace" and "make user_namespace". The
! 1130: first renames ALL "GC_xxx" identifiers as "_GC_xxx". The second is the
! 1131: inverse transformation. Note that doing this is guaranteed to break all
! 1132: clients written for the other names.
! 1133: - descriptor field for kind NORMAL in GC_obj_kinds with ADD_BYTE_AT_END
! 1134: defined should be -ALIGNMENT not WORDS_TO_BYTES(-1). This is
! 1135: a serious bug on machines with pointer alignment of less than a word.
! 1136: - GC_ignore_self_finalize_mark_proc didn't handle pointers to very near the
! 1137: end of the object correctly. Caused failures of the C++ test on a DEC Alpha
! 1138: with g++.
! 1139: - gc_inl.h still had problems. Partially fixed. Added warnings at the
! 1140: beginning to hopefully specify the remaining dangers.
! 1141: - Added DATAEND definition to config.h.
! 1142: - Fixed some of the .h file organization. Fixed "make floppy".
! 1143:
! 1144: Since version 4.6:
! 1145: - Fixed some compilation problems with -DCHECKSUMS (thanks to Ian Searle)
! 1146: - Updated some Mac specific files to synchronize with Patrick Beard.
! 1147: - Fixed a serious bug for machines with non-word-aligned pointers.
! 1148: (Thanks to Patrick Beard for pointing out the problem. The collector
! 1149: should fail almost any conceivable test immediately on such machines.)
! 1150:
! 1151: Since version 4.7:
! 1152: - Changed a "comment" in a MacOS specific part of mach-dep.c that caused
! 1153: gcc to fail on other platforms.
! 1154:
! 1155: Since version 4.8
! 1156: - More README.debugging fixes.
! 1157: - Objects ready for finalization, but not finalized in the same GC
! 1158: cycle, could be prematurely collected. This occasionally happened
! 1159: in test_cpp.
! 1160: - Too little memory was obtained from the system for very large
! 1161: objects. That could cause a heap explosion if these objects were
! 1162: not contiguous (e.g. under PCR), and too much of them was blacklisted.
! 1163: - Due to an improper initialization, the collector was too hesitant to
! 1164: allocate blacklisted objects immediately after system startup.
! 1165: - Moved GC_arrays from the data into the bss segment by not explicitly
! 1166: initializing it to zero. This significantly
! 1167: reduces the size of executables, and probably avoids some disk accesses
! 1168: on program startup. It's conceivable that it might break a port that I
! 1169: didn't test.
! 1170: - Fixed EMX_MAKEFILE to reflect the gc_c++.h to gc_cpp.h renaming which
! 1171: occurred a while ago.
! 1172:
! 1173: Since 4.9:
! 1174: - Fixed a typo around a call to GC_collect_or_expand in alloc.c. It broke
! 1175: handling of out of memory. (Thanks to Patrick Beard for noticing.)
! 1176:
! 1177: Since 4.10:
! 1178: - Rationalized (hopefully) GC_try_to_collect in an incremental collection
! 1179: environment. It appeared to not handle a call while a collection was in
! 1180: progress, and was otherwise too conservative.
! 1181: - Merged GC_reclaim_or_delete_all into GC_reclaim_all to get rid of some
! 1182: code.
! 1183: - Added Patrick Beard's Mac fixes, with substantial completely untested
! 1184: modifications.
! 1185: - Fixed the MPROTECT_VDB code to deal with large pages and imprecise
! 1186: fault addresses (as on an UltraSPARC running Solaris 2.5). Note that this
! 1187: was not a problem in the default configuration, which uses PROC_VDB.
! 1188: - The DEC Alpha assembly code needed to restore $gp between calls.
! 1189: Thanks to Fergus Henderson for tracking this down and supplying a
! 1190: patch.
! 1191: - The write command for "de" was completely broken for large files.
! 1192: I used the easiest portable fix, which involved changing the semantics
! 1193: so that f.new is written instead of overwriting f. That's safer anyway.
! 1194: - Added README.solaris2 with a discussion of the possible problems of
! 1195: mixing the collector's sbrk allocation with malloc/realloc.
! 1196: - Changed the data segment starting address for SGI machines. The
! 1197: old code failed under IRIX6.
! 1198: - Required double word alignment for MIPS.
! 1199: - Various minor fixes to remove warnings.
! 1200: - Attempted to fix some Solaris threads problems reported by Zhiying Chen.
! 1201: In particular, the collector could try to fork a thread with the
! 1202: world stopped as part of GC_thr_init. It also failed to deal with
! 1203: the case in which the original thread terminated before the whole
! 1204: process did.
! 1205: - Added -DNO_EXECUTE_PERMISSION. This has a major performance impact
! 1206: on the incremental collector under Irix, and perhaps under other
! 1207: operating systems.
! 1208: - Added some code to support allocating the heap with mmap. This may
! 1209: be preferable under some circumstances.
! 1210: - Integrated dynamic library support for HP.
! 1211: (Thanks to Knut Tvedten <knuttv@ifi.uio.no>.)
! 1212: - Integrated James Clark's win32 threads support, and made a number
! 1213: of changes to it, many of which were suggested by Pontus Rydin.
! 1214: This is still not 100% solid.
! 1215: - Integrated Alistair Crooks' support for UTS4 running on an Amdahl
! 1216: 370-class machine.
! 1217: - Fixed a serious bug in explicitly typed allocation. Objects requiring
! 1218: large descriptors where handled in a way that usually resulted in
! 1219: a segmentation fault in the marker. (Thanks to Jeremy Fitzhardinge
! 1220: for helping to track this down.)
! 1221: - Added partial support for GNU win32 development. (Thanks to Fergus
! 1222: Henderson.)
! 1223: - Added optional support for Java-style finalization semantics. (Thanks
! 1224: to Patrick Bridges.) This is recommended only for Java implementations.
! 1225: - GC_malloc_uncollectable faulted instead of returning 0 when out of
! 1226: memory. (Thanks to dan@math.uiuc.edu for noticing.)
! 1227: - Calls to GC_base before the collector was initialized failed on a
! 1228: DEC Alpha. (Thanks to Matthew Flatt.)
! 1229: - Added base pointer checking to GC_REGISTER_FINALIZER in debugging
! 1230: mode, at the suggestion of Jeremy Fitzhardinge.
! 1231: - GC_debug_realloc failed for uncollectable objects. (Thanks to
! 1232: Jeremy Fitzhardinge.)
! 1233: - Explicitly typed allocation could crash if it ran out of memory.
! 1234: (Thanks to Jeremy Fitzhardinge.)
! 1235: - Added minimal support for a DEC Alpha running Linux.
! 1236: - Fixed a problem with allocation of objects whose size overflowed
! 1237: ptrdiff_t. (This now fails unconditionally, as it should.)
! 1238: - Added the beginning of Irix pthread support.
! 1239: - Integrated Xiaokun Zhu's fixes for djgpp 2.01.
! 1240: - Added SGI-style STL allocator support (gc_alloc.h).
! 1241: - Fixed a serious bug in README.solaris2. Multithreaded programs must include
! 1242: gc.h with SOLARIS_THREADS defined.
! 1243: - Changed GC_free so it actually deallocates uncollectable objects.
! 1244: (Thanks to Peter Chubb for pointing out the problem.)
! 1245: - Added Linux ELF support for dynamic libararies. (Thanks again to
! 1246: Patrick Bridges.)
! 1247: - Changed the Borland cc configuration so that the assembler is not
! 1248: required.
! 1249: - Fixed a bug in the C++ test that caused it to fail in 64-bit
! 1250: environments.
! 1251:
! 1252: Since 4.11:
! 1253: - Fixed ElfW definition in dyn_load.c. (Thanks to Fergus Henderson.)
! 1254: This prevented the dynamic library support from compiling on some
! 1255: older ELF Linux systems.
! 1256: - Fixed UTS4 port (which I apparently mangled during the integration)
! 1257: (Thanks to again to Alistair Crooks.)
! 1258: - "Make C++" failed on Suns with SC4.0, due to a problem with "bool".
! 1259: Fixed in gc_priv.h.
! 1260: - Added more pieces for GNU win32. (Thanks to Timothy N. Newsham.)
! 1261: The current state of things should suffice for at least some
! 1262: applications.
! 1263: - Changed the out of memory retry count handling as suggested by
! 1264: Kenjiro Taura. (This matters only if GC_max_retries > 0, which
! 1265: is no longer the default.)
! 1266: - If a /proc read failed repeatedly, GC_written_pages was not updated
! 1267: correctly. (Thanks to Peter Chubb for diagnosing this.)
! 1268: - Under unlikely circumstances, the allocator could infinite loop in
! 1269: an out of memory situation. (Thanks again to Kenjiro Taura for
! 1270: identifying the problem and supplying a fix.)
! 1271: - Fixed a syntactic error in the DJGPP code. (Thanks to Fergus
! 1272: Henderson for finding this by inspection.) Also fixed a test program
! 1273: problem with DJGPP (Thanks to Peter Monks.)
! 1274: - Atomic uncollectable objects were not treated correctly by the
! 1275: incremental collector. This resulted in weird log statistics and
! 1276: occasional performance problems. (Thanks to Peter Chubb for pointing
! 1277: this out.)
! 1278: - Fixed some problems resulting from compilers that dont define
! 1279: __STDC__. In this case void * and char * were used inconsistently
! 1280: in some cases. (Void * should not have been used at all. If
! 1281: you have an ANSI superset compiler that does not define __STDC__,
! 1282: please compile with -D__STDC__=0. Thanks to Manuel Serrano and others
! 1283: for pointing out the problem.)
! 1284: - Fixed a compilation problem on Irix with -n32 and -DIRIX_THREADS.
! 1285: Also fixed some other IRIX_THREADS problems which may or may not have
! 1286: had observable symptoms.
! 1287: - Fixed an HP PA compilation problem in dyn_load.c. (Thanks to
! 1288: Philippe Queinnec.)
! 1289: - SEGV fault handlers sometimes did not get reset correctly. (Thanks
! 1290: to David Pickens.)
! 1291: - Added a fix for SOLARIS_THREADS on Intel. (Thanks again to David
! 1292: Pickens.) This probably needs more work to become functional.
! 1293: - Fixed struct sigcontext_struct in os_dep.c for compilation under
! 1294: Linux 2.1.X. (Thanks to Fergus Henderson.)
! 1295: - Changed the DJGPP STACKBOTTOM and DATASTART values to those suggested
! 1296: by Kristian Kristensen. These may still not be right, but it is
! 1297: it is likely to work more often than what was there before. They may
! 1298: even be exactly right.
! 1299: - Added a #include <string.h> to test_cpp.cc. This appears to help
! 1300: with HP/UX and gcc. (Thanks to assar@sics.se.)
! 1301: - Version 4.11 failed to run in incremental mode on recent 64-bit Irix
! 1302: kernels. This was a problem related to page unaligned heap segments.
! 1303: Changed the code to page align heap sections on all platforms.
! 1304: (I had mistakenly identified this as a kernel problem earlier.
! 1305: It was not.)
! 1306: - Version 4.11 did not make allocated storage executable, except on
! 1307: one or two platforms, due to a bug in a #if test. (Thanks to Dave
! 1308: Grove for pointing this out.)
! 1309: - Added sparc_sunos4_mach_dep.s to support Sun's compilers under SunOS4.
! 1310: - Added GC_exclude_static_roots.
! 1311: - Fixed the object size mapping algorithm. This shouldn't matter,
! 1312: but the old code was ugly.
! 1313: - Heap checking code could die if one of the allocated objects was
! 1314: larger than its base address. (Unsigned underflow problem. Thanks
! 1315: to Clay Spence for isolating the problem.)
! 1316: - Added RS6000 (AIX) dynamic library support and fixed STACK_BOTTOM.
! 1317: (Thanks to Fred Stearns.)
! 1318: - Added Fergus Henderson's patches for improved robustness with large
! 1319: heaps and lots of blacklisting.
! 1320: - Added Peter Chubb's changes to support Solaris Pthreads, to support
! 1321: MMAP allocation in Solaris, to allow Solaris to find dynamic libraries
! 1322: through /proc, to add malloc_typed_ignore_off_page, and a few other
! 1323: minor features and bug fixes.
! 1324: - The Solaris 2 port should not use sbrk. I received confirmation from
! 1325: Sun that the use of sbrk and malloc in the same program is not
! 1326: supported. The collector now defines USE_MMAP by default on Solaris.
! 1327: - Replaced the djgpp makefile with Gary Leavens' version.
! 1328: - Fixed MSWIN32 detection test.
! 1329: - Added Fergus Henderson's patches to allow putting the collector into
! 1330: a DLL under GNU win32.
! 1331: - Added Ivan V. Demakov's port to Watcom C on X86.
! 1332: - Added Ian Piumarta's Linux/PowerPC port.
! 1333: - On Brian Burton's suggestion added PointerFreeGC to the placement
! 1334: options in gc_cpp.h. This is of course unsafe, and may be controversial.
! 1335: On the other hand, it seems to be needed often enough that it's worth
! 1336: adding as a standard facility.
! 1337:
! 1338: Since 4.12:
! 1339: - Fixed a crucial bug in the Watcom port. There was a redundant decl
! 1340: of GC_push_one in gc_priv.h.
! 1341: - Added FINALIZE_ON_DEMAND.
! 1342: - Fixed some pre-ANSI cc problems in test.c.
! 1343: - Removed getpagesize() use for Solaris. It seems to be missing in one
! 1344: or two versions.
! 1345: - Fixed bool handling for SPARCCompiler version 4.2.
! 1346: - Fixed some files in include that had gotten unlinked from the main
! 1347: copy.
! 1348: - Some RS/6000 fixes (missing casts). Thanks to Toralf Foerster.
! 1349: - Fixed several problems in GC_debug_realloc, affecting mostly the
! 1350: FIND_LEAK case.
! 1351: - GC_exclude_static_roots contained a buggy unsigned comparison to
! 1352: terminate a loop. (Thanks to Wilson Ho.)
! 1353: - CORD_str failed if the substring occurred at the last possible position.
! 1354: (Only affects cord users.)
! 1355: - Fixed Linux code to deal with RedHat 5.0 and integrated Peter Bigot's
! 1356: os_dep.c code for dealing with various Linux versions.
! 1357: - Added workaround for Irix pthreads sigaction bug and possible signal
! 1358: misdirection problems.
! 1359: Since alpha1:
! 1360: - Changed RS6000 STACKBOTTOM.
! 1361: - Integrated Patrick Beard's Mac changes.
! 1362: - Alpha1 didn't compile on Irix m.n, m < 6.
! 1363: - Replaced Makefile.dj with a new one from Gary Leavens.
! 1364: - Added Andrew Stitcher's changes to support SCO OpenServer.
! 1365: - Added PRINT_BLACK_LIST, to allow debugging of high densities of false
! 1366: pointers.
! 1367: - Added code to debug allocator to keep track of return address
! 1368: in GC_malloc caller, thus giving a bit more context.
! 1369: - Changed default behavior of large block allocator to more
! 1370: aggressively avoid fragmentation. This is likely to slow down the
! 1371: collector when it succeeds at reducing space cost.
! 1372: - Integrated Fergus Henderson's CYGWIN32 changes. They are untested,
! 1373: but needed for newer versions.
! 1374: - USE_MMAP had some serious bugs. This caused the collector to fail
! 1375: consistently on Solaris with -DSMALL_CONFIG.
! 1376: - Added Linux threads support, thanks largely to Fergus Henderson.
! 1377: Since alpha2:
! 1378: - Fixed more Linux threads problems.
! 1379: - Changed default GC_free_space_divisor to 3 with new large block allocation.
! 1380: (Thanks to Matthew Flatt for some measurements that suggest the old
! 1381: value sometimes favors space too much over time.)
! 1382: - More CYGWIN32 fixes.
! 1383: - Integrated Tyson-Dowd's Linux-M68K port.
! 1384: - Minor HP PA and DEC UNIX fixes from Fergus Henderson.
! 1385: - Integrated Christoffe Raffali's Linux-SPARC changes.
! 1386: - Allowed for one more GC fixup iteration after a full GC in incremental
! 1387: mode. Some quick measurements suggested that this significantly
! 1388: reduces pause times even with smaller GC_RATE values.
! 1389: - Moved some more GC data structures into GC_arrays. This decreases
! 1390: pause times and GC overhead, but makes debugging slightly less convenient.
! 1391: - Fixed namespace pollution problem ("excl_table").
! 1392: - Made GC_incremental a constant for -DSMALL_CONFIG, hopefully shrinking
! 1393: that slightly.
! 1394: - Added some win32 threads fixes.
! 1395: - Integrated Ivan Demakov and David Stes' Watcom fixes.
! 1396: - Various other minor fixes contributed by many people.
! 1397: - Renamed config.h to gcconfig.h, since config.h tends to be used for
! 1398: many other things.
! 1399: - Integrated Matthew Flatt's support for 68K MacOS "far globals".
! 1400: - Fixed up some of the dynamic library Makefile targets for consistency
! 1401: across platforms.
! 1402: - Fixed a USE_MMAP typo that caused out-of-memory handling to fail
! 1403: on Solaris.
! 1404: - Added code to test.c to test thread creation a bit more.
! 1405: - Integrated GC_win32_free_heap, as suggested by Ivan Demakov.
! 1406: - Fixed Solaris 2.7 stack base finding problem. (This may actually
! 1407: have been done in an earlier alpha release.)
! 1408: Since alpha3:
! 1409: - Fixed MSWIN32 recognition test, which interfered with cygwin.
! 1410: - Removed unnecessary gc_watcom.asm from distribution. Removed
! 1411: some obsolete README.win32 text.
! 1412: - Added Alpha Linux incremental GC support. (Thanks to Philipp Tomsich
! 1413: for code for retrieving the fault address in a signal handler.)
! 1414: Changed Linux signal handler context argument to be a pointer.
! 1415: - Took care of some new warnings generated by the 7.3 SGI compiler.
! 1416: - Integrated Phillip Musumeci's FreeBSD/ELF fixes.
! 1417: - -DIRIX_THREADS was broken with the -o32 ABI (typo in gc_priv.h>
! 1418:
! 1419: Since 4.13:
! 1420: - Fixed GC_print_source_ptr to not use a prototype.
! 1421: - generalized CYGWIN test.
! 1422: - gc::new did the wrong thing with PointerFreeGC placement.
! 1423: (Thanks to Rauli Ruohonen.)
! 1424: - In the ALL_INTERIOR_POINTERS (default) case, some callee-save register
! 1425: values could fail to be scanned if the register was saved and
! 1426: reused in a GC frame. This showed up in verbose mode with gctest
! 1427: compiled with an unreleased SGI compiler. I vaguely recall an old
! 1428: bug report that may have been related. The bug was probably quite old.
! 1429: (The problem was that the stack scanning could be deferred until
! 1430: after the relevant frame was overwritten, and the new save location
! 1431: might be outside the scanned area. Fixed by more eager stack scanning.)
! 1432: - PRINT_BLACK_LIST had some problems. A few source addresses were garbage.
! 1433: - Replaced Makefile.dj and added -I flags to cord make targets.
! 1434: (Thanks to Gary Leavens.)
! 1435: - GC_try_to_collect was broken with the nonincremental collector.
! 1436: - gc_cleanup destructors could pass the wrong address to
! 1437: GC_register_finalizer_ignore_self in the presence of multiple
! 1438: inheritance. (Thanks to Darrell Schiebel.)
! 1439: - Changed PowerPC Linux stack finding code.
! 1440:
! 1441: Since 4.14alpha1
! 1442: - -DSMALL_CONFIG did not work reliably with large (> 4K) pages.
! 1443: Recycling the mark stack during expansion could result in a size
! 1444: zero heap segment, which confused things. (This was probably also an
! 1445: issue with the normal config and huge pages.)
! 1446: - Did more work to make sure that callee-save registers were scanned
! 1447: completely, even with the setjmp-based code. Added USE_GENERIC_PUSH_REGS
! 1448: macro to facilitate testing on machines I have access to.
! 1449: - Added code to explicitly push register contents for win32 threads.
! 1450: This seems to be necessary. (Thanks to Pierre de Rop.)
! 1451:
! 1452: Since 4.14alpha2
! 1453: - changed STACKBOTTOM for DJGPP (Thanks to Salvador Eduardo Tropea).
! 1454:
! 1455: Since 4.14
! 1456: - Reworked large block allocator. Now uses multiple doubly linked free
! 1457: lists to approximate best fit.
! 1458: - Changed heap expansion heuristic. Entirely free blocks are no longer
! 1459: counted towards the heap size. This seems to have a major impact on
! 1460: heap size stability; the old version could expand the heap way too
! 1461: much in the presence of large block fragmentation.
! 1462: - added -DGC_ASSERTIONS and some simple assertions inside the collector.
! 1463: This is mainlyt for collector debugging.
! 1464: - added -DUSE_MUNMAP to allow the heap to shrink. Suupported on only
! 1465: a few UNIX-like platforms for now.
! 1466: - added GC_dump_regions() for debugging of fragmentation issues.
! 1467: - Changed PowerPC pointer alignment under Linux to 4. (This needs
! 1468: checking by someone who has one. The suggestions came to me via a
! 1469: rather circuitous path.)
! 1470: - Changed the Linux/Alpha port to walk the data segment backwards until
! 1471: it encounters a SIGSEGV. The old way to find the start of the data
! 1472: segment broke with a recent release.
! 1473: - cordxtra.c needed to call GC_REGISTER_FINALIZER instead of
! 1474: GC_register_finalizer, so that it would continue to work with GC_DEBUG.
! 1475: - allochblk sometimes cleared the wrong block for debugging purposes
! 1476: when it dropped blacklisted blocks. This could result in spurious
! 1477: error reports with GC_DEBUG.
! 1478: - added MACOS X Server support. (Thanks to Andrew Stone.)
! 1479: - Changed the Solaris threads code to ignore stack limits > 8 MB with
! 1480: a warning. Empirically, it is not safe to access arbitrary pages
! 1481: in such large stacks. And the dirty bit implementation does not
! 1482: guarantee that none of them will be accessed.
! 1483: - Integrated Martin Tauchmann's Amiga changes.
! 1484: - Integrated James Dominy's OpenBSD/SPARC port.
! 1485:
! 1486: Since 5.0alpha1
! 1487: - Fixed bugs introduced in alpha1 (OpenBSD & large block initialization).
! 1488: - Added -DKEEP_BACK_PTRS and backptr.h interface. (The implementation
! 1489: idea came from Al Demers.)
! 1490:
! 1491: Since 5.0alpha2
! 1492: - Added some highly incomplete code to support a copied young generation.
! 1493: Comments on nursery.h are appreciated.
! 1494: - Changed -DFIND_LEAK, -DJAVA_FINALIZATION, and -DFINALIZE_ON_DEMAND,
! 1495: so the same effect could be obtained with a runtime switch. This is
! 1496: a step towards standardizing on a single dynamic GC library.
! 1497: - Significantly changed the way leak detection is handled, as a consequence
! 1498: of the above.
! 1499:
! 1500: Since 5.0 alpha3
! 1501: - Added protection fault handling patch for Linux/M68K from Fergus
! 1502: Henderson and Roman Hodek.
! 1503: - Removed the tests for SGI_SOURCE in new_gc_alloc.h. This was causing that
! 1504: interface to fail on nonSGI platforms.
! 1505: - Changed the Linux stack finding code to use /proc, after changing it
! 1506: to use HEURISTIC1. (Thanks to David Mossberger for pointing out the
! 1507: /proc hook.)
! 1508: - Added HP/UX incremental GC support and HP/UX 11 thread support.
! 1509: Thread support is currently still flakey.
! 1510: - Added basic Linux/IA64 support.
! 1511: - Integrated Anthony Green's PicoJava support.
! 1512: - Integrated Scott Ananian's StrongARM/NetBSD support.
! 1513: - Fixed some fairly serious performance bugs in the incremental
! 1514: collector. These have probably been there essentially forever.
! 1515: (Mark bits were sometimes set before scanning dirty pages.
! 1516: The reclaim phase unnecessarily dirtied full small object pages.)
! 1517: - Changed the reclaim phase to ignore nearly full pages to avoid
! 1518: touching them.
! 1519: - Limited GC_black_list_spacing to roughly the heap growth increment.
! 1520: - Changed full collection triggering heuristic to decrease full GC
! 1521: frequency by default, but to explicitly trigger full GCs during
! 1522: heap growth. This doesn't always improve things, but on average it's
! 1523: probably a win.
! 1524: - GC_debug_free(0, ...) failed. Thanks to Fergus Henderson for the
! 1525: bug report and fix.
! 1526:
! 1527: Since 5.0 alpha4
! 1528: - GC_malloc_explicitly_typed and friends sometimes failed to
! 1529: initialize first word.
! 1530: - Added allocation routines and support in the marker for mark descriptors
! 1531: in a type structure referenced by the first word of an object. This was
! 1532: introduced to support gcj, but hopefully in a way that makes it
! 1533: generically useful.
! 1534: - Added GC_requested_heapsize, and inhibited collections in nonincremental
! 1535: mode if the actual used heap size is less than what was explicitly
! 1536: requested.
! 1537: - The Solaris pthreads version of GC_pthread_create didn't handle a NULL
! 1538: attribute pointer. Solaris thread support used the wrong default thread
! 1539: stack size. (Thanks to Melissa O'Neill for the patch.)
! 1540: - Changed PUSH_CONTENTS macro to no longer modify first parameter.
! 1541: This usually doesn't matter, but it was certainly an accident waiting
! 1542: to happen ...
! 1543: - Added GC_register_finalizer_no_order and friends to gc.h. They're
! 1544: needed by Java implementations.
! 1545: - Integrated a fix for a win32 deadlock resulting from clock() calling
! 1546: malloc. (Thanks to Chris Dodd.)
! 1547: - Integrated Hiroshi Kawashima's port to Linux/MIPS. This was designed
! 1548: for a handheld platform, and may or may not be sufficient for other
! 1549: machines.
! 1550: - Fixed a va_arg problem with the %c specifier in cordprnt.c. It appears
! 1551: that this was always broken, but recent versions of gcc are the first to
! 1552: report the (statically detectable) bug.
! 1553: - Added an attempt at a more general solution to dlopen races/deadlocks.
! 1554: GC_dlopen now temporarily disables collection. Still not ideal, but ...
! 1555: - Added -DUSE_I686_PREFETCH, -DUSE_3DNOW_PREFETCH, and support for IA64
! 1556: prefetch instructions. May improve performance measurably, but I'm not
! 1557: sure the code will run correctly on processors that don't support the
! 1558: instruction. Won't build except with very recent gcc.
! 1559: - Added caching for header lookups in the marker. This seems to result
! 1560: in a barely measurable performance gain. Added support for interleaved
! 1561: lookups of two pointers, but unconfigured that since the performance
! 1562: gain is currently near zero, and it adds to code size.
! 1563: - Changed Linux DATA_START definition to check both data_start and
! 1564: __data_start, since nothing else seems to be portable.
! 1565: - Added -DUSE_LD_WRAP to optionally take advantage of the GNU ld function
! 1566: wrapping mechanism. Probably currently useful only on Linux.
! 1567: - Moved some variables for the scratch allocator into GC_arrays, on
! 1568: Martin Hirzel's suggestion.
! 1569: - Fixed a win32 threads bug that caused the collector to not look for
! 1570: interior pointers from one of the thread stacks without
! 1571: ALL_INTERIOR_POINTERS. (Thanks to Jeff Sturm.)
! 1572: - Added Mingw32 support. (Thanks again to Jeff Sturm for the patch.)
! 1573: - Changed the alpha port to use the generic register scanning code instead
! 1574: of alpha_mach_dep.s. Alpha_mach_dep.s doesn't look for pointers in fp
! 1575: registers, but gcc sometimes spills pointers there. (Thanks to Manuel
! 1576: Serrano for helping me debug this by email.) Changed the IA64 code to
! 1577: do something similar for similar reasons.
! 1578:
! 1579: Since 5.0alpha6:
! 1580: - -DREDIRECT_MALLOC was broken in alpha6. Fixed.
! 1581: - Cleaned up gc_ccp.h slightly, thus also causing the HP C++ compiler to
! 1582: accept it.
! 1583: - Removed accidental reference to dbg_mlc.c, which caused dbg_mlc.o to be
! 1584: linked into every executable.
! 1585: - Added PREFETCH to bitmap marker. Changed it to use the header cache.
! 1586: - GC_push_marked sometimes pushed one object too many, resulting in a
! 1587: segmentation fault in GC_mark_from_mark_stack. This was probably an old
! 1588: bug. It finally showed up in gctest on win32.
! 1589: - Gc_priv.h erroneously #defined GC_incremental to be TRUE instead of FALSE
! 1590: when SMALL_CONFIG was defined. This was no doubt a major performance bug for
! 1591: the default win32 configuration.
! 1592: - Removed -DSMALL_CONFIG from NT_MAKEFILE. It seemed like an anchronism now
! 1593: that the average PC has 64MB or so.
! 1594: - Integrated Bryce McKinley's patches for linux threads and dynamic loading
! 1595: from the libgcj tree. Turned on dynamic loading support for Linux/PPC.
! 1596: - Changed the stack finding code to use environ on HP/UX. (Thanks
! 1597: to Gustavo Rodriguez-Rivera for the suggestion.) This should probably
! 1598: be done on other platforms, too. Since I can't test those, that'll
! 1599: wait until after 5.0.
! 1600:
! 1601: Since 5.0alpha7:
! 1602: - Fixed threadlibs.c for linux threads. -DUSE_LD_WRAP was broken and
! 1603: -ldl was omitted. Fixed Linux stack finding code to handle
! 1604: -DUSE_LD_WRAP correctly.
! 1605: - Added MSWIN32 exception handler around marker, so that the collector
! 1606: can recover from root segments that are unmapped during the collection.
! 1607: This caused occasional failures under Windows 98, and may also be
! 1608: an issue under Windows NT/2000.
! 1609:
! 1610: Since 5.0
! 1611: - Fixed a gc.h header bug which showed up under Irix. (Thanks to
! 1612: Dan Sullivan.)
! 1613: - Fixed a typo in GC_double_descr in typd_mlc.c not getting traced correctly.
! 1614: This probably could result in objects described by array descriptors not
! 1615: getting traced correctly. (Thanks to Ben Hutchings for pointing this out.)
! 1616: - The block nearly full tests in reclaim.c were not correct for 64 bit
! 1617: environments. This could result in unnecessary heap growth under unlikely
! 1618: conditions.
! 1619: - Removed use of CLEAR_DOUBLE from generic reclaim code, since odd sizes
! 1620: could occur.
! 1621:
! 1622: Since 5.1
! 1623: - dyn_load.c declared GC_scratch_last_end_ptr as an extern even if it
! 1624: was defined as a macro. This prevented the collector from building on
! 1625: Irix.
! 1626: - We quietly assumed that indirect mark descriptors were never 0.
! 1627: Our own typed allocation interface violated that. This could result
! 1628: in segmentation faults in the marker with typed allocation.
! 1629: - Fixed a _DUSE_MUNMAP bug in the heap block allocation code.
! 1630: (Thanks to Ben Hutchings for the patch.)
! 1631: - Taught the collector about VC++ handling array operator new.
! 1632: (Thanks again to Ben Hutchings for the patch.)
! 1633: - The two copies of gc_hdrs.h had diverged. Made one a link to the other
! 1634: again.
! 1635:
! 1636: Since 5.2
! 1637: - Fixed _end declaration for OSF1.
! 1638: - There were lots of spurious leak reports in leak detection mode, caused
! 1639: by the fact that some pages were not being swept, and hence unmarked
! 1640: objects weren't making it onto free lists. (This bug dated back to 5.0.)
! 1641: - Fixed a typo in the liblinuxgc.so Makefile rule.
! 1642: - Added the GetExitCodeThread to Win32 GC_stop_world to (mostly) work
! 1643: around a Windows 95 GetOpenFileName problem. (Thanks to Jacob Navia.)
! 1644:
! 1645: To do:
! 1646: - Integrate Linux/SPARC fixes.
! 1647: - Very large root set sizes (> 16 MB or so) could cause the collector
! 1648: to abort with an unexpected mark stack overflow. (Thanks again to
! 1649: Peter Chubb.) NOT YET FIXED. Workaround is to increase the initial
! 1650: size.
! 1651: - The SGI version of the collector marks from mmapped pages, even
! 1652: if they are not part of dynamic library static data areas. This
! 1653: causes performance problems with some SGI libraries that use mmap
! 1654: as a bitmap allocator. NOT YET FIXED. It may be possible to turn
! 1655: off DYNAMIC_LOADING in the collector as a workaround. It may also
! 1656: be possible to conditionally intercept mmap and use GC_exclude_static_roots.
! 1657: The real fix is to walk rld data structures, which looks possible.
! 1658: - Integrate MIT and DEC pthreads ports.
! 1659: - Incremental collector should handle large objects better. Currently,
! 1660: it looks like the whole object is treated as dirty if any part of it
! 1661: is.
! 1662: - Cord/cordprnt.c doesn't build on a few platforms (notably PowerPC), since
! 1663: we make some unwarranted assumptions about how varargs are handled. This
! 1664: currently makes the cord-aware versions of printf unusable on some platforms.
! 1665: Fixing this is unfortunately not trivial.
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