thread1.c

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

#define NUM_THREADS 1

// The function executed by each thread
void *PrintHello(void *threadid)
{
  // Print greeting with thread ID info
  long tid;
  tid = (long)threadid;
  printf("Hello World! It's me, thread #%ld!\n", tid);
  sleep(30);
  pthread_exit(NULL);
}

int main (int argc, char *argv[])
{
  // Will create 5 threads, so will need a reference to each
  pthread_t threads[NUM_THREADS];

  int rc;
  long n;
  for(n = 0; n < NUM_THREADS; ++n){
    
    printf("In main: creating thread %ld\n", n);

    // Create a thread here, and get the thread to run the PrintHello
    // function. Note the way the parameters are passed
    rc = pthread_create(&threads[n], NULL, PrintHello, (void *)n);

    // A non-zero return code means something went wrong
    if (rc){
      printf("ERROR; return code from pthread_create() is %d\n", rc);
      exit(-1);
    }
  }

  // Useful to call this in the main to ensure that all threads are
  // kept alive. Otherwise threads that are still going will be
  // automatically terminated
  pthread_exit(NULL);
}

thread2.c

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
 
void *print_message( void *ptr );
 
main()
{
  pthread_t thread1, thread2;
  char *message1 = "Thread 1";
  char *message2 = "Thread 2";
  int  iret1, iret2;
  
  /* Create independent threads each of which will execute function */
  iret1 = pthread_create( &thread1, NULL, print_message, 
			  (void*) message1);
  iret2 = pthread_create( &thread2, NULL, print_message, 
			  (void*) message2);
  
  /* Wait till threads are complete before main continues. Unless we  */
  /* wait we run the risk of executing an exit which will terminate   */
  /* the process and all threads before the threads have completed.   */
  pthread_join( thread1, NULL);
  pthread_join( thread2, NULL);
  
  printf("Thread 1 returns: %d\n",iret1);
  printf("Thread 2 returns: %d\n",iret2);
  exit(0);
  
}

void *print_message( void *ptr )
{
  char *message;
  message = (char *) ptr;
  printf("%s \n", message);
}