/*
	Bruce A. Maxwell
	Fall 2012 CS 333

	An example of a race condition if the code does not use mutex locks.
	
	gcc -o mutexsimple mutex-simple.c -lpthread
 */

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

void *fcounter(void *);
void *fbad(void *);
int counter = 0;

// data structure passed to the thread functions
typedef struct {
  pthread_mutex_t mutex;
  int id;
} threadInfo;

// main: expects "bad" or "good" on the command line
int main(int argc, char *argv[]) {
  int i;
  pthread_mutex_t mutex;
  pthread_t thread[4];
  threadInfo ti[4];
	int usebad;

	if( argc < 2 ) {
		printf("usage: %s <bad | good>\n", argv[0]);
		return(-1);
	}

	// which function to run
	usebad = !strcmp( "bad", argv[1] ) ? 1 : 0;
		

  // init mutex
  pthread_mutex_init( &(mutex), NULL );
  // spawn three threads
  for(i=0;i<4;i++) {
    ti[i].id = i;
    ti[i].mutex = mutex;
		if( usebad ) 
			pthread_create( &(thread[i]), NULL, fbad, &(ti[i]) );
		else
			pthread_create( &(thread[i]), NULL, fcounter, &(ti[i]) );
  }
  // wait until both are done (join)
  for(i=0;i<4;i++) {
    pthread_join( thread[i], NULL );
  }
  // destroy mutex
  pthread_mutex_destroy( &(mutex) );

  return(0);
}

// Increment a global counter variable
// This function uses mutex locks
void *fcounter( void *userdata ) {
  int i;
  threadInfo *ti = (threadInfo *)userdata;
  
  for(i=0;i<3;i++) {
    pthread_mutex_lock( &(ti->mutex) ); // P(s)
    counter++;
    printf("%d counter is %d\n", ti->id, counter );
    pthread_mutex_unlock( &(ti->mutex) ); // V(s)
    usleep( rand() % 10 );
  }
  return( NULL );
}

// Increment a global counter variable
// This function does not use mutex locks
void *fbad( void *userdata ) {
  int i;
  threadInfo *ti = (threadInfo *)userdata;
  
  for(i=0;i<3;i++) {
    counter++;
    usleep( rand() % 10 );
    printf("%d counter is %d\n", ti->id, counter );
  }
  return( NULL );
}