threads won't run concurrently

I can't seem to make my threads run concurrently.

I've posted a simple test program which should print out "Hello World" (along with some debugging messages.)

However, for some reason the main code doesn't advance beyond the 'pthread_create' call until the spawned thread finishes.

As a result, when the thread blocks on the 'pthread_mutex_lock' call (since main() has already locked the mutex), the whole program hangs.

I compile with:
gcc -g thread_test.c -pthread

I'm running a RedHat 7.3
kernel-2.4.18-3
glibc -2.2.5-34

****************************************************
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>

pthread_t test_thread;
pthread_mutex_t test_mutex;
sem_t test_sem;


void *test_thread_function()
{
puts("Thread spawned");
pthread_mutex_lock(&test_mutex);
puts("World");
}

int main()
{
pthread_t test_thread;

pthread_mutex_init(&test_mutex,NULL);
pthread_mutex_lock(&test_mutex);

puts("Ready to spawn thread");
pthread_create(&test_thread, NULL,
test_thread_function(), NULL);

puts("Hello");
pthread_mutex_unlock(&test_mutex);
}
********************************************

Thanks in advance for any help - this is ruining my day...

You are accidentially calling the thread's main function

You have:
pthread_create(&test_thread, NULL, test_thread_function(), NULL);

You need:
pthread_create(&test_thread, NULL, test_thread_function, NULL);

You need to pass in the pointer to the function. What you do instead is calling the function and then passing in the return value. Which would usually segfault if it wouldn't deadlock before

Bonus tip: you should use stderr, not stdout to print debug messages in timing-critical situations, because stdout will buffer.

However, be advised that any use of streams will change the timing and locking behavior of the program dramatically - because the I/O will lock the streams and hence synchronise the threads where an i/o free run wouldn't. So you program may work with debug prints but screw up without them.

That did the trick - infinite thanks: I was really tearing my hair out here.

(Thanks for the Bonus tip too - I guess that makes infinity + 1)

--S