线程互斥锁

与进程类似，线程的操作也存在互斥和共享的问题。

同步机制有互斥锁和信号量。

本实验用到互斥锁功能，系统调用有:pthread_mutex_init, pthread_mutex_lock, pthread_mutex_trylock, pthread_mutex_unlock, pthread_mutex_destroy.

源代码来自华清远见：

#include

#include

#include

 

#define THREAD_NUMBER   3

#define REPEAT_NUMBER   3

#define DELAY_TIME_LEVELS   10.0

pthread_mutex_t mutex;

 

void *thrd_func(void *arg)

{

    int thrd_num = (int)arg;

    int delay_time = 0;

    int count = 0;

    int res;

 

    res = pthread_mutex_lock(&mutex);//上锁

    if(res)

    {

        printf("Thread % lock failed\n", thrd_num);

        pthread_exit(NULL);

    }

 

    printf("Thread %d is starting\n", thrd_num);

    for(count = 0; count < REPEAT_NUMBER; count++)

    {

        delay_time = (int) (rand() *DELAY_TIME_LEVELS/(RAND_MAX) + 1);

        sleep(delay_time);

        printf("\tThread %d: job %d delay = %d\n", thrd_num, count, delay_time);

    }

    printf("Thread %d finished\n", thrd_num);

    pthread_exit(NULL);

}

 

int main()

{

    pthread_t thread[THREAD_NUMBER];

    int no = 0, res;

    void *thrd_ret;

 

    srand(time(NULL));

    pthread_mutex_init(&mutex, NULL);//互斥锁初始化

 

    for(no = 0; no < THREAD_NUMBER; no++)

    {

        res = pthread_create(&thread[no], NULL, thrd_func, (void*)no);//创建线程

        if(res != 0)

        {

            printf("Create thread %d failed\n", no);

            exit(res);

        }

    }

    printf("Create threads success\nWaiting for threads to finish..\n");

    for(no = 0; no < THREAD_NUMBER; no++)

    {

        res = pthread_join(thread[no], &thrd_ret);//挂起线程

        if(!res)

        {

            printf("Thread %d joined\n", no);

        }

        else

        {

            printf("Thread %d join failed\n", no);

        }

        pthread_mutex_unlock(&mutex);//解锁

    }

    pthread_mutex_destroy(&mutex);

    return 0;

}

编译运行，结果如下：

观察运行结果与上次试验比较，发现3个线程的运行顺序与创建顺序相同。而上次没有加锁的线程运行是独立无序的。由此可见互斥锁实现了同步的功能。