linux程序设计——用信号量进行同步（第十二章）

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12.5.2    用互斥量进行同步

#include <pthread.c>
int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *mutexattr);
int pthread_mutex_lock(pthread_mutex_t *mutex);
int pthread_mutex_unlock(pthread_mutex_t *mutex);
int pthread_mutex_destroy(pthread_mutex_t *mutex);

/*************************************************************************
 > File Name:    thread4.c
 > Description:  thread4.c通过互斥量来保证任一时刻只有一个线程访问字符数组work_area(对它进行读(统计)/写)
 > Author:       Liubingbing
 > Created Time: 2015年07月05日 星期日 20时47分06秒
 > Other:        thread4.c省略了对互斥量加锁和解锁调用的返回值应该进行的一些错误检查
 ************************************************************************/

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <semaphore.h>

void *thread_function(void *arg);
pthread_mutex_t work_mutex; /* protects both work_acea and time_to_exit */

#define WORK_SIZE 1024
char work_area[WORK_SIZE];
int time_to_exit = 0;

int main(){
	int res;
	pthread_t a_thread;
	void *thread_result;

	/* pthread_mutex_init初始化互斥量work_mutex */
	res = pthread_mutex_init(&work_mutex, NULL);
	if (res != 0) {
		perror("Mutex initialization failed");
		exit(EXIT_FAILURE);
	}

	/* pthread_create创建新线程 
	 * a_thread中保存新线程的标识符, thread_function为新线程启动调用的函数 */
	res = pthread_create(&a_thread, NULL, thread_function, NULL);
	if (res != 0) {
		perror("Thread creation failed");
		exit(EXIT_FAILURE);
	}

	/* pthread_mutex_lock对互斥量work_mutex加锁,如果它已经被锁住,则这个调用将被阻塞直到它被释放为止 */
	pthread_mutex_lock(&work_mutex);
	printf("Input some text. Enter 'end' to finish\n");
	while (!time_to_exit) {
		fgets(work_area, WORK_SIZE, stdin);
		/* pthread_mutex_unlock对互斥量work_mutext解锁 */
		pthread_mutex_unlock(&work_mutex);
		while (1) {
			/* pthread_mutex_lock对互斥量work_mutex加锁 */
			pthread_mutex_lock(&work_mutex);
			/* 如果work_area第一个字符不为null,则对互斥量work_mutex解锁,然后等待新线程执行 */
			if (work_area[0] != '\0') {
				pthread_mutex_unlock(&work_mutex);
				sleep(1);
			} else {
				break;
			}
		}
	}
	pthread_mutex_unlock(&work_mutex);
	printf("\nWaiting for thread to finish...\n");
	res = pthread_join(a_thread, &thread_result);
	if (res != 0) {
		perror("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);
	/* 首先试图对互斥量work_mutex加锁,如果它已经被锁住,这个调用将被阻塞直到它释放为止. */
	pthread_mutex_lock(&work_mutex);
	while (strncmp("end", work_area, 3) != 0) {
		printf("You input %d characters\n", strlen(work_area) - 1);
		/* 通过将第一个字符设置为null的方法来通知读取输入的线程, 新线程完成了字符统计 */
		work_area[0] = '\0';
		/* 对互斥量work_mutex解锁, 并等待主线程继续运行*/
		pthread_mutex_unlock(&work_mutex);
		sleep(1);
		/* 对互斥量work_mutex加锁, 如果加锁成功就检查是否主线程又有字符送来要处理 */
		pthread_mutex_lock(&work_mutex);
		while (work_area[0] == '\0') {
			/* 如果没有字符要处理,就解锁互斥量,继续等待 */
			pthread_mutex_unlock(&work_mutex);
			sleep(1);
			pthread_mutex_lock(&work_mutex);
		}
	}
	/* 如果work_area="end",则设置time_to_exit = 1, 之后退出 */
	time_to_exit = 1;
	work_area[0] = '\0';
	pthread_mutex_unlock(&work_mutex);
	pthread_exit(0);
}

linux程序设计——用信号量进行同步（第十二章）

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原文地址：http://blog.csdn.net/yiranant/article/details/46772403