/******************************************************************************
* FILE: hellox.c
* DESCRIPTION:
*   A pThreads program to demonstrate use of mutex objects to protect access
*   to a file.  
* AUTHOR: Dr. Spiegel
* LAST REVISED: 03/10/07
******************************************************************************/
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

// These declarations must be global; parameter of thread fn is predetermined
pthread_mutex_t    mutex;

void *PrintHello(void *threadid)
{ 
   printf("\n%d: Writing to file\n", threadid);
   // Open a file to write stuff to.
   FILE *TheFile;
   TheFile=fopen("thread.txt","a");
   pthread_mutex_lock(&mutex);
   fprintf(TheFile,"Thread %d writes to file\n", threadid);
   pthread_mutex_unlock(&mutex);
   fclose(TheFile);
   pthread_exit(NULL);
}

int main(int argc, char *argv[])
{  // Check for single command line argument
   if (argc<2) {
     printf("Form: hellox <# threads>\n");
     exit(1);
   }
   int rc=0;
   printf("Create the mutex using default mutex attributes \n");
   rc = pthread_mutex_init(&mutex,NULL);
   if (rc!=0) {
     perror("Mutex not initialized");
     exit(-1);
   }
   int numThreads=atoi(argv[1]);
   pthread_t *threads=malloc(sizeof(pthread_t)*numThreads);
   int t;
   for(t=0;t<numThreads;t++){
     printf("Creating thread %d\n", t);
     rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
     if (rc){
       printf("ERROR; return code from pthread_create() is %d\n", rc);
       exit(-1);
     }
   }
   pthread_mutex_destroy(&mutex);
   pthread_exit(NULL);
}