Question about pthreads

Hi guys I have a question about thread programming. Based on the material on the web, I created a simple program that would create a bunch of threads in a loop like this: #define N_THREADS 5 void* thread_function(void*); pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER; int counter = 0; int main() { int i; int j; int i_ptr=&i; pthread_t threads[N_THREADS]; for(i=0; i < N_THREADS; i++) {pthread_create( &threads[i], NULL, thread_function, (void*) i_ptr); //sleep (1);} for(j=0; j < N_THREADS; j++) pthread_join( threads[j], NULL); return (0); } void* thread_function(void* data) { pthread_mutex_lock( &mutex1 ); int thread_data=*(int*)data; counter++; printf("I am thread number %d Counter value is %d\n",thread_data, counter); pthread_mutex_unlock( &mutex1 ); pthread_exit("NULL"); } When I execute the code above, I should normally get: I am thread number 0 Counter value is 1 I am thread number 1 Counter value is 2 I am thread number 2 Counter value is 3 I am thread number 3 Counter value is 4 I am thread number 4 Counter value is 5 But instead i get: I am thread number 1 Counter value is 1 I am thread number 5 Counter value is 2 I am thread number 5 Counter value is 3 I am thread number 5 Counter value is 4 I am thread number 5 Counter value is 5 or I am thread number 1 Counter value is 1 I am thread number 5 Counter value is 3 I am thread number 2 Counter value is 2 I am thread number 5 Counter value is 4 I am thread number 5 Counter value is 5 or even(!): I am thread number 5 Counter value is 1 I am thread number 5 Counter value is 2 I am thread number 5 Counter value is 3 I am thread number 5 Counter value is 4 I am thread number 5 Counter value is 5 Counter values seem to be fine, but why is the thread numbers not working properly? When i debug it with gdb, it works fine. When I add the sleep in the first loop, i also get correct output. What could be the reason for this weird behavior?:shock:

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