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Annotation of OpenXM_contrib/gc/README.linux, Revision 1.1.1.1

1.1       maekawa     1: See README.alpha for Linux on DEC AXP info.
                      2:
                      3: This file applies mostly to Linux/Intel IA32.  Ports to Linux on an M68K
                      4: and PowerPC are also integrated.  They should behave similarly, except that
                      5: the PowerPC port lacks incremental GC support, and it is unknown to what
                      6: extent the Linux threads code is functional.
                      7:
                      8: Incremental GC is supported on Intel IA32 and M68K.
                      9:
                     10: Dynamic libraries are supported on an ELF system.  A static executable
                     11: should be linked with the gcc option "-Wl,-defsym,_DYNAMIC=0".
                     12:
                     13: The collector appears to work with Linux threads.  We have seen
                     14: intermittent hangs in sem_wait.  So far we have been unable to reproduce
                     15: these unless the process was being debugged or traced.  Thus it's
                     16: possible that the only real issue is that the debugger loses
                     17: signals on rare occasions.
                     18:
                     19: The garbage collector uses SIGPWR and SIGXCPU if it is used with
                     20: Linux threads.  These should not be touched by the client program.
                     21:
                     22: To use threads, you need to abide by the following requirements:
                     23:
                     24: 1) You need to use LinuxThreads (which are included in libc6).
                     25:
                     26:    The collector relies on some implementation details of the LinuxThreads
                     27:    package.  It is unlikely that this code will work on other
                     28:    pthread implementations (in particular it will *not* work with
                     29:    MIT pthreads).
                     30:
                     31: 2) You must compile the collector with -DLINUX_THREADS and -D_REENTRANT
                     32:    specified in the Makefile.
                     33:
                     34: 3) Every file that makes thread calls should define LINUX_THREADS and
                     35:    _REENTRANT and then include gc.h.  Gc.h redefines some of the
                     36:    pthread primitives as macros which also provide the collector with
                     37:    information it requires.
                     38:
                     39: 4) Currently dlopen() is probably not safe.  The collector must traverse
                     40:    the list of libraries maintained by the runtime loader.  That can
                     41:    probably be an inconsistent state when a thread calling the loader is
                     42:    is stopped for GC.  (It's possible that this is fixable in the
                     43:    same way it is handled for SOLARIS_THREADS, with GC_dlopen.)
                     44:
                     45: 5) The combination of LINUX_THREADS, REDIRECT_MALLOC, and incremental
                     46:    collection fails in seemingly random places.  This hasn't been tracked
                     47:    down yet, but is perhaps not completely astonishing.  The thread package
                     48:    uses malloc, and thus can presumably get SIGSEGVs while inside the
                     49:    package.  There is no real guarantee that signals are handled properly
                     50:    at that point.