[Gc] GC_INIT? Threads?
Bruce Hoult
bruce at hoult.org
Tue Aug 20 06:42:07 PDT 2013
Oh!
I just looked at your code.
In my new thread:
struct GC_stack_base *my_sb;
GC_get_stack_base(my_sb);
You need to allocate a GC_stack_base structure, not a pointer to one! You
just made an uninitialized pointer, which means that when GC_get_stack_base()
tries to fill in the structure it could be writing to any random place in
memory.
It should be:
struct GC_stack_base my_sb;
GC_get_stack_base(&my_sb);
On Tue, Aug 20, 2013 at 6:08 PM, The Devils Jester <
thedevilsjester at gmail.com> wrote:
> 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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