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Annotation of OpenXM_contrib2/asir2000/gc5.3/README.linux, Revision 1.1

1.1     ! noro        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: 3a) 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: 3b) A new alternative to (3a) is to build the collector with
        !            40:    -DUSE_LD_WRAP, and to link the final program with
        !            41:
        !            42:    (for ld) --wrap read --wrap dlopen --wrap pthread_create \
        !            43:            --wrap pthread_join --wrap pthread_sigmask
        !            44:
        !            45:    (for gcc) -Wl,--wrap -Wl,read -Wl,--wrap -Wl,dlopen -Wl,--wrap \
        !            46:             -Wl,pthread_create -Wl,--wrap -Wl,pthread_join -Wl,--wrap \
        !            47:             -Wl,pthread_sigmask
        !            48:
        !            49:    In any case, _REENTRANT should be defined during compilation.
        !            50:
        !            51: 4) Dlopen() disables collection during its execution.  (It can't run
        !            52:    concurrently with the collector, since the collector looks at its
        !            53:    data structures.  It can't acquire the allocator lock, since arbitrary
        !            54:    user startup code may run as part of dlopen().)  Under unusual
        !            55:    conditions, this may cause unexpected heap growth.
        !            56:
        !            57: 5) The combination of LINUX_THREADS, REDIRECT_MALLOC, and incremental
        !            58:    collection fails in seemingly random places.  This hasn't been tracked
        !            59:    down yet, but is perhaps not completely astonishing.  The thread package
        !            60:    uses malloc, and thus can presumably get SIGSEGVs while inside the
        !            61:    package.  There is no real guarantee that signals are handled properly
        !            62:    at that point.
        !            63:
        !            64: 6) Thread local storage may not be viewed as part of the root set by the
        !            65:    collector.  This probably depends on the linuxthreads version.  For the
        !            66:    time being, any collectable memory referenced by thread local storage should
        !            67:    also be referenced from elsewhere, or be allocated as uncollectable.
        !            68:    (This is really a bug that should be fixed somehow.)