thread1

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
void thread(void)
{
    printf("This is a pthread.\n");
}

int main(void)
{
    pthread_t id;
    int i,ret;
    ret=pthread_create(&id,NULL,(void *) thread,NULL);
    if(ret!=0){
    printf ("Create pthread error!\n");
    exit (1);
                 }
    printf("This is the main process.\n");
    return (0);
}

thread2

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

int sharedi = 0;
void increse_num(void);

int main(){
    int ret;
    pthread_t thrd1, thrd2, thrd3;

    ret = pthread_create(&thrd1, NULL, (void *)increse_num, NULL);
    ret = pthread_create(&thrd2, NULL, (void *)increse_num, NULL);
    ret = pthread_create(&thrd3, NULL, (void *)increse_num, NULL);

    pthread_join(thrd1, NULL);
    pthread_join(thrd2, NULL);
    pthread_join(thrd3, NULL);

    printf("sharedi = %d\n", sharedi);

    return 0;

}

void increse_num(void) {
    long i,tmp;
    for(i=1; i<=1000000; i++) {
        tmp = sharedi;
        tmp = tmp + 1;
        sharedi = tmp;
    }
}