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问题:
Whenever I create a pthread, valgrind outputs a memory leak,
For example the below code:
#include #include #include void *timer1_function (void *eit){ (void) eit; printf("hello world\n"); pthread_exit(NULL); } int main(void){ pthread_t timer1; pthread_create( &timer1, NULL, timer1_function, NULL); ///////line13 int i=0; for(i=0;i
valgrind outputs
==1395== HEAP SUMMARY: ==1395== in use at exit: 136 bytes in 1 blocks ==1395== total heap usage: 6 allocs, 5 frees, 1,134 bytes allocated ==1395== ==1395== 136 bytes in 1 blocks are possibly lost in loss record 1 of 1 ==1395== at 0x402A629: calloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so) ==1395== by 0x4011304: allocate_dtv (dl-tls.c:297) ==1395== by 0x4011AAB: _dl_allocate_tls (dl-tls.c:461) ==1395== by 0x4052470: pthread_create@@GLIBC_2.1 (allocatestack.c:571) ==1395== by 0x8048566: main (test.c:13) ==1395== ==1395== LEAK SUMMARY: ==1395== definitely lost: 0 bytes in 0 blocks ==1395== indirectly lost: 0 bytes in 0 blocks ==1395== possibly lost: 136 bytes in 1 blocks ==1395== still reachable: 0 bytes in 0 blocks ==1395== suppressed: 0 bytes in 0 blocks
why pthread_create cause a problem although I was using the man page as reference, and how can I fix it?
回答1:
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.
回答2:
I think that valgrind analyzes the state of your program at the time it exits, which is likely before the thread finishes its execution: two microseconds may not be enough to write "Hello, world!\n" to console. Adding a call to pthread_join should fix this leak:
pthread_join(timer1, NULL);
回答3:
I've seen similar results when I fail to call pthread_join.
When I do call pthread_join, Valgrind will indicate no memory errors or leaks. I've had a clean result using pthread_kill to see if the thread still exists, then calling join to clean up and release resources.
int stop_worker(worker_t *self) { if (self) { // signal the thread to quit // (here using a variable and semaphore) self->thread_quit=TRUE; sem_post(&self->sem); // wait for it to stop // (could use counter, etc. to limit wait) int test=0; while (pthread_kill(self->thread,0) == 0) { MDEBUG(MD_XF_LOGGER,"waiting for thread to exit...\n",test); delay_msec(50); } // even though thread is finished, need to call join // otherwise, it will not release its memory (and valgrind indicates a leak) test=pthread_join(self->thread,NULL); return 0; } return -1; }
回答4:
memory leak is a result of the fact that if the thread is left running without cancellation , then the corresponding dynamically allocated memory is not freed. Use pthread_cancel() along with pthread_cleanup_push(CleanupHandler, NULL) and pthread_cleanup_pop(0) to do the thread cleanup after cancellation.
回答5:
The leak that shows up is related to the DTV (Dynamic Thread Vector) structure that is allocated in the child thread's local storage (tls).
Using pthread_join() in the main thread (i.e. the thread that spawned the child) will ensure to fix the leak. For use cases where pthread_join() call is not required, calling pthread_detach with child pthread_t ensures the memory is released.
From man for pthread_detach:
The pthread_detach() function marks the thread identified by thread as detached. When a detached thread terminates, its resources are automatically released back to the system without the need for another thread to join with the terminated thread.
