[Gc] GC_INIT? Threads?

Bruce Hoult bruce at hoult.org
Mon Aug 19 22:00:59 PDT 2013


Once again, it's not crashing, it's a controlled exit because it detected
something wrong.

Try using these (from gc.h)

call GC_allow_register_threads() from your main program, after GC_INIT()
call GC_register_my_thread() at the start of the main function for each
thread you create. (and GC_unregister_my_thread() at the end)

You may also find  GC_call_with_stack_base() useful.

  /* Explicitly enable GC_register_my_thread() invocation.              */
  /* Done implicitly if a GC thread-creation function is called (or     */
  /* implicit thread registration is activated).  Otherwise, it must    */
  /* be called from the main (or any previously registered) thread      */
  /* between the collector initialization and the first explicit        */
  /* registering of a thread (it should be called as late as possible). */
  GC_API void GC_CALL GC_allow_register_threads(void);

  /* Register the current thread, with the indicated stack base, as     */
  /* a new thread whose stack(s) should be traced by the GC.  If it     */
  /* is not implicitly called by the GC, this must be called before a   */
  /* thread can allocate garbage collected memory, or assign pointers   */
  /* to the garbage collected heap.  Once registered, a thread will be  */
  /* stopped during garbage collections.                                */
  /* This call must be previously enabled (see above).                  */
  /* This should never be called from the main thread, where it is      */
  /* always done implicitly.  This is normally done implicitly if GC_   */
  /* functions are called to create the thread, e.g. by including gc.h  */
  /* (which redefines some system functions) before calling the system  */
  /* thread creation function.  Nonetheless, thread cleanup routines    */
  /* (eg., pthread key destructor) typically require manual thread      */
  /* registering (and unregistering) if pointers to GC-allocated        */
  /* objects are manipulated inside.                                    */
  /* It is also always done implicitly on some platforms if             */
  /* GC_use_threads_discovery() is called at start-up.  Except for the  */
  /* latter case, the explicit call is normally required for threads    */
  /* created by third-party libraries.                                  */
  /* A manually registered thread requires manual unregistering.        */
  GC_API int GC_CALL GC_register_my_thread(const struct GC_stack_base *);

  /* Unregister the current thread.  Only an explicitly registered      */
  /* thread (i.e. for which GC_register_my_thread() returns GC_SUCCESS) */
  /* is allowed (and required) to call this function.  (As a special    */
  /* exception, it is also allowed to once unregister the main thread.) */
  /* The thread may no longer allocate garbage collected memory or      */
  /* manipulate pointers to the garbage collected heap after making     */
  /* this call.  Specifically, if it wants to return or otherwise       */
  /* communicate a pointer to the garbage-collected heap to another     */
  /* thread, it must do this before calling GC_unregister_my_thread,    */
  /* most probably by saving it in a global data structure.  Must not   */
  /* be called inside a GC callback function (except for                */
  /* GC_call_with_stack_base() one).                                    */
  GC_API int GC_CALL GC_unregister_my_thread(void);



On Tue, Aug 20, 2013 at 4:48 PM, The Devils Jester <
thedevilsjester at gmail.com> wrote:

> The only output I get, aside from the stack trace is:
> Collecting from unknown thread
> Abort trap: 6
>
> My application is organized as follows:
>
> MAIN APP (does not use GC)
>    GC_INIT()
>    NEW THREAD
>          CALL LIBRARY FUNCTION (library uses GC)
>
> This crashes, while
>
> MAIN APP (does not use GC)
>    GC_INIT()
>    CALL LIBRARY FUNCTION (library uses GC)
>
> Works perfectly fine.
>
> What am I doing wrong?  Do I have to initialize the GC in some special
> fashion?
>
>
> On Mon, Aug 19, 2013 at 11:35 PM, Bruce Hoult <bruce at hoult.org> wrote:
>
>> That's not a crash, it's a deliberate abort because some sanity-checking
>> code found that your world was insane. There are several things that can go
>> wrong inside GC_push_all_stacks, so it would be helpful to have the
>> message that GC_abort() printed.
>>
>> However, you should always call GC_INIT() from your main program, and as
>> early as possible.
>>
>> On some versions and platforms GC_INIT() installs code that registers
>> threads in a GC data structure because it's not possible to ask the OS for
>> all your threads. If you call GC_INIT() from a new thread on those
>> platforms then that thread will remain unregistered, which is one of the
>> things that will make GC_push_all_stacks abort later.
>>
>>
>>
>> On Tue, Aug 20, 2013 at 4:10 PM, The Devils Jester <
>> thedevilsjester at gmail.com> wrote:
>>
>>> I have a library that makes heavy use of of the GC, and it works quite
>>> well when everything (the app, and the library) is in one thread.  I call
>>> GC_INIT in the app, and all is well.
>>>
>>> If, however, the app creates a new thread that calls the library
>>> function, then it crashes when the GC does its magic (below I have pasted
>>> some relevant output).
>>>
>>> Is there some trick to using GC on a separate thread?  Do I call GC_INIT
>>> from the main thread, or the one that calls the library functions?
>>>
>>>
>>> 0   libsystem_kernel.dylib         0x00007fff8ad14212 __pthread_kill +
>>> 10
>>> 1   libsystem_c.dylib             0x00007fff90d01b54 pthread_kill + 90
>>> 2   libsystem_c.dylib             0x00007fff90d45dce abort + 143
>>> 3   libgc.1.dylib                 0x000000010357676e GC_abort + 97
>>> 4   libgc.1.dylib                 0x000000010357b413 GC_push_all_stacks
>>> + 285
>>> 5   libgc.1.dylib                 0x000000010357396e GC_mark_some + 377
>>> 6   libgc.1.dylib                 0x000000010356d73e GC_stopped_mark +
>>> 148
>>> 7   libgc.1.dylib                 0x000000010356d645
>>> GC_try_to_collect_inner + 245
>>> 8   libgc.1.dylib                 0x000000010356e302
>>> GC_collect_or_expand + 147
>>> 9   libgc.1.dylib                 0x000000010356e51a GC_allocobj + 228
>>> 10  libgc.1.dylib                 0x0000000103572515
>>> GC_generic_malloc_inner + 249
>>> 11  libgc.1.dylib                 0x00000001035725dd GC_generic_malloc
>>> + 79
>>> 12  libgc.1.dylib                 0x00000001035728c0 GC_core_malloc +
>>> 196
>>>
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>>
>>
>
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