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version 1.1, 1999/11/27 10:58:32 version 1.1.1.2, 2000/04/14 11:08:01
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 Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers  Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
 Copyright (c) 1991-1996 by Xerox Corporation.  All rights reserved.  Copyright (c) 1991-1996 by Xerox Corporation.  All rights reserved.
 Copyright (c) 1996-1998 by Silicon Graphics.  All rights reserved.  Copyright (c) 1996-1999 by Silicon Graphics.  All rights reserved.
   Copyright (c) 1999 by Hewlett-Packard Company. All rights reserved.
   
 THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED  THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.  OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
Line 11  Permission to modify the code and to distribute modifi
Line 12  Permission to modify the code and to distribute modifi
 provided the above notices are retained, and a notice that the code was  provided the above notices are retained, and a notice that the code was
 modified is included with the above copyright notice.  modified is included with the above copyright notice.
   
 This is version 4.14 of a conservative garbage collector for C and C++.  This is version 5.0alpha4 of a conservative garbage collector for C and C++.
   
 You might find a more recent version of this at  You might find a more recent version of this at
   
 http://reality.sgi.com/boehm/gc.html  http://www.hpl.hp.com/personal/Hans_Boehm/gc
   
 HISTORY -  HISTORY -
   
   Early versions of this collector were developed as a part of research    Early versions of this collector were developed as a part of research
 projects supported in part by the National Science Foundation  projects supported in part by the National Science Foundation
 and the Defense Advance Research Projects Agency.  and the Defense Advance Research Projects Agency.
 Much of the code was rewritten by Hans-J. Boehm at Xerox PARC  Much of the code was rewritten by Hans-J. Boehm (boehm@acm.org) at Xerox PARC
 and is now maintained by him at SGI (boehm@sgi.com).  and at SGI.
   
 Some other contributors:  Some other contributors:
   
Line 40  Robert Brazile (brazile@diamond.bbn.com) originally su
Line 41  Robert Brazile (brazile@diamond.bbn.com) originally su
 Al Dosser (dosser@src.dec.com) and Regis Cridlig (Regis.Cridlig@cl.cam.ac.uk)  Al Dosser (dosser@src.dec.com) and Regis Cridlig (Regis.Cridlig@cl.cam.ac.uk)
 subsequently provided updates and information on variation between ULTRIX  subsequently provided updates and information on variation between ULTRIX
 systems.  Parag Patel (parag@netcom.com) supplied the A/UX code.  systems.  Parag Patel (parag@netcom.com) supplied the A/UX code.
 Jesper Peterson(jep@mtiame.mtia.oz.au) and  Jesper Peterson(jep@mtiame.mtia.oz.au), Michel Schinz, and
 Michel Schinz supplied the Amiga port.  Martin Tauchmann (martintauchmann@bigfoot.com) supplied the Amiga port.
 Thomas Funke (thf@zelator.in-berlin.de(?)) and  Thomas Funke (thf@zelator.in-berlin.de(?)) and
 Brian D.Carlstrom (bdc@clark.lcs.mit.edu) supplied the NeXT ports.  Brian D.Carlstrom (bdc@clark.lcs.mit.edu) supplied the NeXT ports.
 Douglas Steel (doug@wg.icl.co.uk) provided ICL DRS6000 code.  Douglas Steel (doug@wg.icl.co.uk) provided ICL DRS6000 code.
Line 612  reclaimed.  Exclusive-or'ing forward and backward link
Line 613  reclaimed.  Exclusive-or'ing forward and backward link
 doesn't cut it.  doesn't cut it.
   Some C optimizers may lose the last undisguised pointer to a memory    Some C optimizers may lose the last undisguised pointer to a memory
 object as a consequence of clever optimizations.  This has almost  object as a consequence of clever optimizations.  This has almost
 never been observed in practice.  Send mail to boehm@sgi.com  never been observed in practice.  Send mail to boehm@acm.org
 for suggestions on how to fix your compiler.  for suggestions on how to fix your compiler.
   This is not a real-time collector.  In the standard configuration,    This is not a real-time collector.  In the standard configuration,
 percentage of time required for collection should be constant across  percentage of time required for collection should be constant across
Line 621  heap sizes.  But collection pauses will increase for l
Line 622  heap sizes.  But collection pauses will increase for l
 per MB of accessible memory that needs to be scanned.  Your mileage  per MB of accessible memory that needs to be scanned.  Your mileage
 may vary.)  The incremental/generational collection facility helps,  may vary.)  The incremental/generational collection facility helps,
 but is portable only if "stubborn" allocation is used.  but is portable only if "stubborn" allocation is used.
   Please address bug reports to boehm@sgi.com.  If you are    Please address bug reports to boehm@acm.org.  If you are
 contemplating a major addition, you might also send mail to ask whether  contemplating a major addition, you might also send mail to ask whether
 it's already been done (or whether we tried and discarded it).  it's already been done (or whether we tried and discarded it).
   
Line 1451  Since 4.14alpha1
Line 1452  Since 4.14alpha1
   
 Since 4.14alpha2  Since 4.14alpha2
  - changed STACKBOTTOM for DJGPP (Thanks to Salvador Eduardo Tropea).   - changed STACKBOTTOM for DJGPP (Thanks to Salvador Eduardo Tropea).
   
   Since 4.14
    - Reworked large block allocator.  Now uses multiple doubly linked free
      lists to approximate best fit.
    - Changed heap expansion heuristic.  Entirely free blocks are no longer
      counted towards the heap size.  This seems to have a major impact on
      heap size stability; the old version could expand the heap way too
      much in the presence of large block fragmentation.
    - added -DGC_ASSERTIONS and some simple assertions inside the collector.
      This is mainlyt for collector debugging.
    - added -DUSE_MUNMAP to allow the heap to shrink.  Suupported on only
      a few UNIX-like platforms for now.
    - added GC_dump_regions() for debugging of fragmentation issues.
    - Changed PowerPC pointer alignment under Linux to 4.  (This needs
      checking by someone who has one.  The suggestions came to me via a
      rather circuitous path.)
    - Changed the Linux/Alpha port to walk the data segment backwards until
      it encounters a SIGSEGV.  The old way to find the start of the data
      segment broke with a recent release.
    - cordxtra.c needed to call GC_REGISTER_FINALIZER instead of
      GC_register_finalizer, so that it would continue to work with GC_DEBUG.
    - allochblk sometimes cleared the wrong block for debugging purposes
      when it dropped blacklisted blocks.  This could result in spurious
      error reports with GC_DEBUG.
    - added MACOS X Server support.  (Thanks to Andrew Stone.)
    - Changed the Solaris threads code to ignore stack limits > 8 MB with
      a warning.  Empirically, it is not safe to access arbitrary pages
      in such large stacks.  And the dirty bit implementation does not
      guarantee that none of them will be accessed.
    - Integrated Martin Tauchmann's Amiga changes.
    - Integrated James Dominy's OpenBSD/SPARC port.
   
   Since 5.0alpha1
    - Fixed bugs introduced in alpha1 (OpenBSD & large block initialization).
    - Added -DKEEP_BACK_PTRS and backptr.h interface.  (The implementation
      idea came from Al Demers.)
   
   Since 5.0alpha2
    - Added some highly incomplete code to support a copied young generation.
      Comments on nursery.h are appreciated.
    - Changed -DFIND_LEAK, -DJAVA_FINALIZATION, and -DFINALIZE_ON_DEMAND,
      so the same effect could be obtained with a runtime switch.   This is
      a step towards standardizing on a single dynamic GC library.
    - Significantly changed the way leak detection is handled, as a consequence
      of the above.
   
   Since 5.0 alpha3
    - Added protection fault handling patch for Linux/M68K from Fergus
      Henderson and Roman Hodek.
    - Removed the tests for SGI_SOURCE in new_gc_alloc.h.  This was causing that
      interface to fail on nonSGI platforms.
    - Changed the Linux stack finding code to use /proc, after chnging it
      to use HEURISTIC1.  (Thanks to David Mossberger for pointing out the
      /proc hook.)
    - Added HP/UX incremental GC support and HP/UX 11 thread support.
    - Added basic Linux/IA64 support.
    - Integrated Anthony Green's PicoJava support.
    - Integrated Scott Ananian's StrongARM/NetBSD support.
    - Fixed some fairly serious performance bugs in the incremental
      collector.  These have probably been there essentially forever.
      (Mark bits were sometimes set before scanning dirty pages.
      The reclaim phase unnecessarily dirtied full small object pages.)
    - Changed the reclaim phase to ignore nearly full pages to avoid
      touching them.
    - Limited GC_black_list_spacing to roughly the heap growth increment.
    - Changed full collection triggering heuristic to decrease full GC
      frequency by default, but to explicitly trigger full GCs during
      heap growth.  This doesn't always improve things, but on average it's
      probably a win.
    - GC_debug_free(0, ...) failed.  Thanks to Fergus Henderson for the
      bug report and fix.
   
 To do:  To do:
  - Very large root set sizes (> 16 MB or so) could cause the collector   - Very large root set sizes (> 16 MB or so) could cause the collector
    to abort with an unexpected mark stack overflow.  (Thanks again to     to abort with an unexpected mark stack overflow.  (Thanks again to
Line 1465  To do:
Line 1537  To do:
    be possible to conditionally intercept mmap and use GC_exclude_static_roots.     be possible to conditionally intercept mmap and use GC_exclude_static_roots.
    The real fix is to walk rld data structures, which looks possible.     The real fix is to walk rld data structures, which looks possible.
  - Integrate MIT and DEC pthreads ports.   - Integrate MIT and DEC pthreads ports.
  - Deal with very uneven black-listing distributions.  If all the black listed   - Incremental collector should handle large objects better.  Currently,
    blocks reside in the newly allocated heap section, the heuristic for     it looks like the whole object is treated as dirty if any part of it
    temporarily ignoring black-listing fails, and the heap grows too much.     is.
    (This was observed in only one case, and could be worked around, but ...)  
  - I've started work on rewriting the large block allocator to use approximate  
    best fit.  There are rare cases in which the current allocator results in  
    excessive large block fragmentation, even with the 4.13 fixes.  This should  
    also reduce large block allocation time, whcih has become occasionally  
    noticable in 4.13.  
   
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  Added in v.1.1.1.2
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