/*
 * $RCSfile: index.html,v $
 *
 * Simple POSIX threads example
 * uses a mutex so two threads can change
 * a global variable without creating a 
 * race condition
 *
 * rcampos@dcmonster.com
 * $Id: index.html,v 1.6 2005/05/18 00:02:55 rcampos Exp rcampos $
 *
 */

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

void threadFunc(int);

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
int globalvar = 0;
static char rcsid[] = "$Id: index.html,v 1.6 2005/05/18 00:02:55 rcampos Exp rcampos $";

int main(int argc, char *argv[])
{
        pthread_t t1, t2;
        int argt1, argt2;
        int rc[2]; 

        if (argc < 3)
        {
                fprintf(stderr, "Usage:\n\t%s <arg1>g  <arg2>\n\tWhere arg1 and arg2 are integer\n", argv[0]);
                exit(1);
        }

        argt1 = atoi(argv[1]);
        argt2 = atoi(argv[2]);

        /* int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
                           void *(*start_routine)(void *), void *arg); */

        /* Create first thread, rc will hold the return code for pthread_create */
        rc[0] = pthread_create(&t1, NULL, (void *)threadFunc, (void *) argt1);
        rc[1] = pthread_create(&t2, NULL, (void *)threadFunc, (void *) argt2);


        /* pthread_create should return 0, otherwise something is wrong */
        if (rc[0] != 0 || rc[1] != 0)
        {
                perror("main: error creating threads");
                exit(1);
        }
        



        /* Wait for the first thread to finish */
        rc[0] = pthread_join(t1, NULL);
        rc[1] = pthread_join(t2, NULL);
        if (rc[0] != 0 || rc[1] != 0)
        {
                perror("main: error joining threads");
                exit(1);
        }
        else
        {
                printf("main: threads returned successfully\n");
        }



        printf("main: argt1 = %d, argt2 = %d\n", argt1, argt2);
        printf("main: globalvar is %d\n", globalvar);

        return 0;
}

void threadFunc(int arg)
{
        pthread_t myId;

        myId = pthread_self();

        printf("threadFunc: my ID is %d\n", myId);
        printf("threadFunc: my arg is %d\n", arg);

        pthread_mutex_lock(&mutex);
        globalvar += arg;
        pthread_mutex_unlock(&mutex);
        printf("threadFunc: globalvar is %d\n", globalvar);

}


O resultado na prática, após a compilação, é o seguinte:

rcampos ~ $ gcc -o simple_mutex_var simple_mutex_var.c 
rcampos ~ $ ./simple_mutex_var 30 -10
threadFunc: my ID is 41944064
threadFunc: my arg is 30
threadFunc: globalvar is 30
threadFunc: my ID is 41945088
threadFunc: my arg is -10
threadFunc: globalvar is 20
main: threads returned successfully
main: argt1 = 30, argt2 = -10
main: globalvar is 20