1。 互斥量
Linux提供了控制线程执行和访问代码临界区域的方法。其中最基本的两种办法是信号量和互斥量。
关于信号量，笔者在Linux信号量介绍中介绍
本文只介绍semaphore.h 相关的信号量的简单的操作。关于信号量在笔者其他博客里有详细介绍。
Linux还有其他共享内存的方法。
2. 与互斥量相关的函数
#include <pthread.h>
int pthread_mutex_init(pthread_mutex_t*mutex, pthread_mutexattr_t *mutexattr); //创建互斥量
int pthread_mutex_lock(pthread_mutex_t*mutex);//加锁
int pthread_mutex_unlock(pthread_mutex_t*mutex);//解锁
int pthread_mutex_destroy(pthread_mutex_t*mutex);//清理互斥量
3. 一个简单的程序例子
/***************************************
* @file mutex.c
* @brief 互斥锁
* @author Windeal
* @date 2013/08/06
***************************************/
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <pthread.h>
#define WORK_SIZE 1024
char work_area[WORK_SIZE];
pthread_mutex_t work_mutex;
int time_to_exit = 0;
void *thread_function(void *arg);
int main(int argc,char* argv[])
{
int ret;
pthread_t a_thread;
void *thread_result;
ret = pthread_mutex_init(&work_mutex, NULL);
if (ret != 0) {
perror("pthread_mutex_init failed ");
exit(EXIT_FAILURE);
}
printf("It time to create a thread! "); /////////////////////
ret = pthread_create(&a_thread, NULL, thread_function, NULL);
if (ret != 0) {
perror("Thread creation failed! ");
exit(EXIT_FAILURE);
}
pthread_mutex_lock(&work_mutex); //加锁
printf("Input some text. Enter "end" to finished ");
while (!time_to_exit) { //
fgets(work_area, WORK_SIZE, stdin);
pthread_mutex_unlock(&work_mutex); // 解锁
while (1) {
pthread_mutex_lock(&work_mutex); //加锁
if (work_area[0]!= ' '){ //如果有数据则到解锁，没有数据则继续输入
pthread_mutex_unlock(&work_mutex);// 解锁 因为workarea里有数据
//因此到另一个线程里比对
sleep(1);
}
else {
break;
}
}
}
pthread_mutex_unlock(&work_mutex); // 解锁
printf("Waiting for thread finish! "); /////////////////
ret = pthread_join(a_thread, &thread_result);
if (ret != 0) {
perror("Thread finished failed ");
exit(EXIT_FAILURE);
}
printf("Thread joined ");
pthread_mutex_destroy(&work_mutex);
exit(EXIT_SUCCESS);
}
void *thread_function(void * arg) {
sleep(1);
pthread_mutex_lock(&work_mutex);
while (strncmp("end", work_area,3) != 0) {
printf("You have enter %d charactor ", strlen(work_area)-1);
work_area[0] = ' '; //清零数据区
pthread_mutex_unlock(&work_mutex); //让主线程继续输入数据
sleep(1);
pthread_mutex_lock(&work_mutex); //尝试加锁，如果主线程已输入数据，则加锁成功
while (work_area[0]== ' ') { //如果输入为空，则继续等待输入.输入不为空时，跳出循环
pthread_mutex_unlock(&work_mutex);
sleep(1);
pthread_mutex_lock(&work_mutex);
}
}
time_to_exit = 1;
work_area[0] =' ';
pthread_mutex_unlock(&work_mutex);
pthread_exit(0);
}
结果如下所示：
