source: CIVL/examples/pthread/CDAC/pthread-demo-datarace.c

/***********************************************************************************
                         C-DAC Tech Workshop : hyPACK-2013
                             October 15-18,2013 
  Example     : pthread-demo-datarace.c
  
  Objective   : Write Pthread code to illustrate Data Race Condition
            and its solution using MUTEX.
 
  Input       : Nothing.
 
  Output      : Value of Global variable with and without using Mutex.
                                                                                                                         
  Created     :MAY-2013
   
  E-mail      : hpcfte@cdac.in        
                                  
****************************************************************************/
 
#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>


int myglobal;                                        // declaration of global variable
pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;  // initialization of MUTEX variable
 
 
void *thread_function_datarace(void *arg)       // Function which operates on myglobal without using mutex
{
    int i,j;                                       
    for ( i=0; i<20; i++ )
    {
            j=myglobal;
            j=j+1;                                        
            printf("\nIn thread_function_datarace..\t");    // Incrementing j and assign myglobal value of j
//          fflush(stdout);                              
        sleep(1);
            myglobal=j;
    }
    return NULL;
}
 
void *thread_function_mutex(void *arg)   // Function which operates on myglobal using mutex
{
    int i,j;
    for ( i=0; i<20; i++ )
    {
            pthread_mutex_lock(&mymutex);
        j=myglobal;
            j=j+1;
            printf("\nIn thread_function_mutex..\t");
  //        fflush(stdout);
        sleep(0.1);
            myglobal=j;
        pthread_mutex_unlock(&mymutex);
    }
    return NULL;
}
 
int main(void)
{
 
    pthread_t mythread;
    int i;
 
    if ( pthread_create( &mythread, NULL, thread_function_datarace, NULL) )   // calling thread_function_datarace
    {
        printf("error creating thread.");
            abort();
    }
 
    printf("\n\t\t---------------------------------------------------------------------------");
        printf("\n\t\t Centre for Development of Advanced Computing (C-DAC)");
        printf("\n\t\t Email : hpcfte@cdac.in");
        printf("\n\t\t---------------------------------------------------------------------------");
        printf("\n\t\t Objective : Pthread code to illustrate data race condition and its solution \n ");
        printf("\n\t\t..........................................................................\n");
 
 
 
    for ( i=0; i<20; i++)
    {
            myglobal=myglobal+1;
            printf("\nIn main..\t");
    //      fflush(stdout);
            sleep(1);
    }
 
    if ( pthread_join ( mythread, NULL ) )
    {
            printf("error joining thread.");
            abort();
    }
 
    printf("\nValue of myglobal in thread_function_datarace is :  %d\n",myglobal);
     
    printf("\n ----------------------------------------------------------------------------------------------------\n");   
 
    myglobal = 0;
 
    if ( pthread_create( &mythread, NULL, thread_function_mutex, NULL) ) // calling thread_function_mutex
        {
                printf("error creating thread.");
                abort();
        }
 
        for ( i=0; i<20; i++)
        {
                pthread_mutex_lock(&mymutex);
            myglobal=myglobal+1;
            pthread_mutex_unlock(&mymutex);
            printf("\nIn main..\t");
    //      fflush(stdout);
            sleep(1);
        }
 
        if ( pthread_join ( mythread, NULL ) )
        {
                printf("error joining thread.");
                abort();
        }
     
    printf("\n");
        printf("\nValue of myglobal in thread_function_mutex is :  %d\n",myglobal);
 
 
    exit(0);
 
}