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

/* use -lpthread or -pthread on the gcc line */
#include <pthread.h>

/* global mutex variable */
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

#define CHILDREN 8

void * whattodo( void * arg );

int main()
{
  pthread_t tid[ CHILDREN ];   /* keep track of the thread IDs */
  int i, rc;
  int * t;
  
  for ( i = 0 ; i < CHILDREN ; i++ )
  {
    t = (int *)malloc( sizeof( int ) );
#if 0
    *t = 2 + i * 2;  /* 2, 4, 6, 8, 10 */
#endif
    *t = 20 - (2 + i * 2);

    printf( "MAIN: Next thread will nap for %d seconds.\n", *t );

    rc = pthread_create( &tid[i], NULL, whattodo, t );

    if ( rc != 0 )
    {
      perror( "MAIN: Could not create child thread" );
    }
  }

  /* wait for threads to terminate */
  for ( i = 0 ; i < CHILDREN ; i++ )
  {
    pthread_join( tid[i], NULL );
    printf( "MAIN: Joined a child thread.\n" );
  }

  printf( "MAIN: All threads successfully joined.\n" );

  return 0;
}

void critical_section( int t )
{
  printf( "THREAD %u: Entering critical section\n", (unsigned int)pthread_self() );
  sleep( t );
  printf( "THREAD %u: Leaving critical section\n", (unsigned int)pthread_self() );
}

void * whattodo( void * arg )
{
  int t = *(int *)arg;
  printf( "THREAD %u: I'm gonna nap for %d seconds.\n", (unsigned int)pthread_self(), t );

  pthread_mutex_lock( &mutex );    /* get the lock */
  critical_section( t );
  pthread_mutex_unlock( &mutex );   /* release the lock */

  printf( "THREAD %u: I'm awake now.\n", (unsigned int)pthread_self() );
  return NULL;    /* pthread_exit() */
}