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