pthread_create() and memory leaks

Question

This question seems to be asked a lot. I had some legacy production code that was seemingly fine, until it started getting many more connections per day. Each connection kicked off a new thread. Eventually, it would exhaust memory and crash.

I'm going back over pthread (and C sockets) which I've not dealt with in years. The tutorial I had was informative, but I'm seeing the same thing when I use top. All the threads exit, but there's still some virtual memory taken up. Valgrind tells me there is a possible memory loss when calling pthread_create(). The very basic sample code is below.

The scariest part is that pthread_exit( NULL ) seems to leave about 100m in VIRT unaccounted for when all the threads exit. If I comment out this line, it's much more liveable, but there is still some there. On my system it start with about 14k, and ends with 47k.

If I up the thread count to 10,000, VIRT goes up to 70+ gigs, but finishes somewhere around 50k, assuming I comment out pthread_exit( NULL ). If I use pthread_exit( NULL ) it finishes with about 113m still in VIRT. Are these acceptable? Is top not telling me everything?

void* run_thread( void* id )
{
    int thread_id = *(int*)id;
    int count = 0;
    while ( count < 10 ) {
        sleep( 1 );
        printf( "Thread %d at count %d\n", thread_id, count++ );
    }

    pthread_exit( NULL );
    return 0;
}

int main( int argc, char* argv[] )
{
    sleep( 5 ); 
    int thread_count    = 0;
    while( thread_count < 10 ) {
        pthread_t my_thread;
        if ( pthread_create( &my_thread, NULL, run_thread, (void*)&thread_count ) < 0 )   {
            perror( "Error making thread...\n" );
            return 1;
        }

        pthread_detach( my_thread );
        thread_count++;
        sleep( 1 );
    }

    pthread_exit( 0 );  // added as per request
    return 0;
}

Answer 1

I know this is rather old question, but I hope others wil benefit. This is indeed a memory leak. The thread is created with default attributes. By default the thread is joinable. A joinable threads keeps its underlying bookkeeping until it is finished... and joined. If a thread is never joined, set de Detached attribute. All (thread) resources will be freed once the thread terminates. Here's an example:

pthread_attr_t attr;
pthread_t thread;
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, 1);
pthread_create(&thread, &attr, &threadfunction, NULL);
pthread_attr_destroy(&attr);