[Gc] GC_INIT? Threads?

The Devils Jester thedevilsjester at gmail.com
Mon Aug 19 23:08:37 PDT 2013


I apologize, I do not mean "crash" in the literal sense.  I appreciate the
help finding a solution to my problem.

The commands supplied, causes the program to lock up and consume all of the
CPU.

The code I have is as follows.  I am unsure about the stack_base or how it
is used.

In my primary thread:
    GC_INIT();
    GC_allow_register_threads();
    ClassFromMyLib * myclass = new ClassFromMyLib();

In my new thread:
    struct GC_stack_base *my_sb;
    GC_get_stack_base(my_sb);
    GC_register_my_thread(my_sb);
           myclass->myfunction();
    GC_unregister_my_thread();

Without the special GC_ functions, everything works fine until GC tries to
reclaim memory, with them it locks up.

Am I doing something wrong?




On Tue, Aug 20, 2013 at 12:00 AM, Bruce Hoult <bruce at hoult.org> wrote:

> 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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>
>
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