线程同步机制

互斥锁通信机制

int pthread_mutex_init (pthread_mutex_t *__mutex, __const pthread_mutexattr_t *__mutexattr) ：初始化互斥锁，成功返回0

　　参数1：要初始化的互斥锁

　　参数2：定义要初始化的互斥锁属性，NULL表默认

宏 PTHREAD_MUTEX_INITIALIZER 初始化静态分配互斥锁   ？？这个语法是什么原理？？？

#define PTHREAD_MUTEX_INITIALIZER {{0,}}

初始化代码如下：

pthread_mutex_t mp = PTHREAD_MUTEX_INITIALIZER;

int pthread_mutex_destroy (pthread_mutex_t * __mutex) ：销毁互斥锁，成功返回0

int pthread_mutex_lock (pthread_mutex_t *__mutex) ：以阻塞方式申请互斥锁

int pthread_mutex_trylock (pthread_mutex_t *__mutex) ：以非阻塞方式申请互斥锁

int pthread_mutex_unlock (pthread_mutex_t *__mutex) ：释放互斥锁

例子：实现读写线程，读时不写，写时不读（我说不清楚下面的代码好不好，因为代码里面循环测试锁，跟我想象的不同，而且是写一句，读一句的。我觉得应该是可以任意写，读按顺序读）

#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<pthread.h>
#include<semaphore.h>
#include<string.h>
void *thread_function (void *arg);
//全局互斥锁对象
pthread_mutex_t work_mutex;
#define WORK_SIZE 1024
//全局共享数据区
char work_area[WORK_SIZE];
int time_to_exit = 0;
int main(int argc, char *argv[])
{
    int res;
    pthread_t a_thread;
    void *thread_result;
    //初始化互斥锁
    res = pthread_mutex_init(&work_mutex, NULL);
    if(res != 0)
    {
        printf("Mutex initialization failed");
        exit(EXIT_FAILURE);
    }
    //创建新线程
    res = pthread_create(&a_thread, NULL, thread_function, NULL);
    if(res != 0)
    {
        printf("Thread creation failed");
        exit(EXIT_FAILURE);
    }
    //接收输入前，给互斥锁上锁
    pthread_mutex_lock(&work_mutex);
    printf("Input some text. Enter ‘end‘ to finish\n");
    while(!time_to_exit)
    {
        fgets(work_area, WORK_SIZE, stdin);
        //解锁
        pthread_mutex_unlock(&work_mutex);
        while(1)
        {
            //上锁
            pthread_mutex_lock(&work_mutex);
            if(work_area[0] != ‘\0‘)  //检测数据是否读出
            {
                pthread_mutex_unlock(&work_mutex); //如果没有输出，解锁
                sleep(1);
            }
            else
            {
                break;
            }
        }
    }
    pthread_mutex_unlock(&work_mutex);  //解锁
    printf("\nWaiting for thread to finish...\n");
    res = pthread_join(a_thread, &thread_result);
    if(res != 0)
    {
        printf("Thread join failed");
        exit(EXIT_FAILURE);
    }
    printf("Thread joined\n");
    pthread_mutex_destroy(&work_mutex);
    exit(EXIT_SUCCESS);
}

void *thread_function(void *arg)
{
    sleep(1);
    //上锁，抢占资源
    pthread_mutex_lock(&work_mutex);
    while(strncmp("end", work_area, 3) != 0)
    {
        printf("You input %d characters\n", strlen(work_area));
        printf("the characters is %s", work_area);
        work_area[0] = ‘\0‘;
        pthread_mutex_unlock(&work_mutex);
        sleep(1);
        pthread_mutex_lock(&work_mutex);
        while(work_area[0] == ‘\0‘)
        {
            pthread_mutex_unlock(&work_mutex);
            sleep(1);
            pthread_mutex_lock(&work_mutex);
        }
    }
    time_to_exit = 1;
    work_area[0] = ‘\0‘;
    pthread_mutex_unlock(&work_mutex);
    pthread_exit(0);
}