#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
void *thread_a(void *in)
{
printf("I am thread_a/n");
pthread_exit((void *)0);
}
void *thread_b(void *in)
{
printf("I am thread_b/n");
pthread_exit((void *)0);
}
void *thread_c(void *in)
{
printf("I am thread_c/n");
pthread_exit((void *)0);
}
int main()
{
pthread_t a,b,c; /* thread id a, b, c*/
int val; /* used for function return result */
/* create thread a, b, c */
pthread_create(&a, NULL, thread_a, (void *)0);
pthread_create(&b, NULL, thread_b, (void *)0);
pthread_create(&c, NULL, thread_c, (void *)0);
/* main thread waits for termination of a,b,c */
pthread_join(a, (void **)0);
pthread_join(b, (void **)0);
pthread_join(c, (void **)0);
printf("Main thread is over/n");
return 0;
}
在Linux下进行编译: gcc -o My_Thread My_Thread.c ./MyThread 得到的输出: I am thread_a I am thread_b I am thread_c Main thread is over 现在我们希望线程C的最先打印，然后线程B打印，最后线程A打印。即三个线程之间的打印有一定的先后关系。看下面程序：#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
sem_t sem1;
sem_t sem2;
void *thread_a(void *in)
{
sem_wait(&sem1); /* wait for sem1 */
printf("I am thread_a/n");
pthread_exit((void *)0);
}
void *thread_b(void *in)
{
sem_wait(&sem2); /* wait for sem2 */
printf("I am thread_b/n");
sem_post(&sem1); /* increase sem1 by 1, make thread_a run*/
pthread_exit((void *)0);
}
void *thread_c(void *in)
{
printf("I am thread_c/n");
sem_post(&sem2); /* increase sem2 by 1, make thread_b run*/
pthread_exit((void *)0);
}
int main()
{
pthread_t a,b,c; /* thread id a, b, c*/
int val; /* used for function return result */
/* init sem1 sem2 to 0 , any thread waits for it will be blocked*/
sem_init(&sem1, 0, 0);
sem_init(&sem2, 0, 0);
/* create thread a, b, c */
pthread_create(&a, NULL, thread_a, (void *)0);
pthread_create(&b, NULL, thread_b, (void *)0);
pthread_create(&c, NULL, thread_c, (void *)0);
/* main thread waits for termination of a,b,c */
pthread_join(a, (void **)0);
pthread_join(b, (void **)0);
pthread_join(c, (void **)0);
/* destroy sem1 sem2 */
sem_destroy(&sem1);
sem_destroy(&sem2);
printf("Main thread is over/n");
return 0;
}
gcc -o My_thread1 My_thread1.c -lpthread ./My_thread1 I am thread_c I am thread_b I am thread_a Main thread is over 可以见到，线程的执行顺序已经改变。