Memory leakage in windows pthread. `pthread_join` does not deallocate memory

Question

The simple test:

void testMemoryLeak_PthreadCreateJoin(void)
{
   auto taskFunction = [](void*args) -> void*
   {
      return nullptr;
   };
   pthread_t pth;
   int err = pthread_create(&pth, /*attr*/nullptr, taskFunction, /*args*/nullptr);
   pthread_join(pth, nullptr);
}

void main(void)
{
   _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);
   testMemoryLeak_PthreadCreateJoin();
   testMemoryLeak_PthreadCreateJoin();
   testMemoryLeak_PthreadCreateJoin();
   testMemoryLeak_PthreadCreateJoin();
}

Here said:

A thread is an allocated resource and you did not free it before exiting. You should call pthread_join; this would also eliminate the need for your hackish and incorrect sleep loop.

It's possible that even once you fix this, valgrind will still see a "leak", since some implementations of POSIX threads (I'm guessing you're using glibc/NPTL) cache and reuse thread resources rather than freeing them fully. I'm not sure if valgrind works around this or not.

But I already use pthread_join. I use VS2015 and its heap analyzer. Could the problem be in pthread my particular implementation? I use PAL by Dongsheng Song

Causes memory leakage:

Detected memory leaks!
Dumping objects ->
{104} normal block at 0x007742C0, 24 bytes long.
 Data: <     X          > D8 00 00 00 E0 58 20 00 00 00 00 00 00 00 00 00 
{101} normal block at 0x00774398, 24 bytes long.
 Data: <     X          > D8 00 00 00 E0 58 20 00 00 00 00 00 00 00 00 00 
{98} normal block at 0x00774038, 24 bytes long.
 Data: <     X          > D8 00 00 00 E0 58 20 00 00 00 00 00 00 00 00 00 
{95} normal block at 0x00774860, 24 bytes long.
 Data: <     X          > D8 00 00 00 E0 58 20 00 00 00 00 00 00 00 00 00 
Object dump complete.

24 bytes for every pthread. pthread_join() had to free memory but it didn't. So i suppose implementation is buggy. Please confirm or confute this.

score 1 · Answer 1 · answered Dec 09 '16 at 10:40

1

If you want to track down the allocation point see _CrtSetAllocHook - you can set your own allocation hook and examine the stack for the blocks you know that will be leaked. However for this to bring any benefits you would need a debug version of the POSIX implementation to correctly see the stack. Then you can try and actually patch it so that the memory is freed.

answered Dec 09 '16 at 10:40

Rudolfs Bundulis

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I think `CrtSetDbgFlag` is good enough for analyze. I don't wont to debug `pthreads`. It is enough to know it is buggy or I admit mistake somewhere. – kyb Dec 09 '16 at 10:56
@kyb well if you want to sort out your mistakes then `CrtSetAllocHook` will show if the faulty memory blocks are allocated from your stack or from the pthreads library. – Rudolfs Bundulis Dec 09 '16 at 11:06

Memory leakage in windows pthread. `pthread_join` does not deallocate memory

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