Thread don't terminate their job - c

Question

I am writing a concurrent C program where I want to wait for all threads to finish in the main().
Based on this solution, I wrote the following code in main():
// Create threads
pthread_t cid[num_mappers];
int t_iter;
for (t_iter = 0; t_iter < num_mappers; t_iter++){
pthread_create(&(cid[t_iter]), NULL, &map_consumer, NULL);
}
// Wait for all threads to finish
for (t_iter = 0; t_iter < num_mappers; t_iter++){
printf("Joining %d\n", t_iter);
int result = pthread_join(cid[t_iter], NULL);
}
printf("Done mapping.\n");
The function passed into threads is defined as:
// Consumer function for mapping phase
void *map_consumer(void *arg){
while (1){
pthread_mutex_lock(&g_lock);
if (g_cur >= g_numfull){
// No works to do, just quit
return NULL;
}
// Get the file name
char *filename = g_job_queue[g_cur];
g_cur++;
pthread_mutex_unlock(&g_lock);
// Do the mapping
printf("%s\n", filename);
g_map(filename);
}
}
The threads are all successfully created and executed, but the join loop will never finish if num_mappers >= 2.

Answer 1

You return without unlocking the mutex:
pthread_mutex_lock(&g_lock);
if (g_cur >= g_numfull){
// No works to do, just quit
return NULL; <-- mutex is still locked here
}
// Get the file name
char *filename = g_job_queue[g_cur];
g_cur++;
pthread_mutex_unlock(&g_lock);
So only one thread ever returns and ends - the first one, but since it never unlocks the mutex, the other threads remain blocked.
You need something more like
pthread_mutex_lock(&g_lock);
if (g_cur >= g_numfull){
// No works to do, just quit
pthread_mutex_unlock(&g_lock);
return NULL;
}
// Get the file name
char *filename = g_job_queue[g_cur];
g_cur++;
pthread_mutex_unlock(&g_lock);