多线程 一个mutex互斥量实例（unix环境高级编程）

/*
 * mutex.c
 *
 *  Created on: 2011-11-23
 *      Author: lc
 */

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

struct foo {
	int count;
	pthread_mutex_t mutex;
};
struct foo * fp;
struct foo * init_foo() {
	struct foo * fp;

	if ((fp = (struct foo *) malloc(sizeof(struct foo))) != NULL) {
		fp->count = 1;
		//初始化mutex失败
		if (pthread_mutex_init(&fp->mutex, NULL) != 0) {
			pthread_mutex_destroy(&fp->mutex);
			free(fp);
			return NULL;
		}
	}

	return fp;
}

/*
 * add reference to foo
 */
void attach_foo(struct foo * fp) {
	pthread_mutex_lock(&fp->mutex);
	fp->count++;
	fprintf(stderr, "%d thread has attached foo in thread %d\n", fp->count,(unsigned int)pthread_self());
	sleep(1);
	pthread_mutex_unlock(&fp->mutex);
}

/*
 * release reference to foo
 * 如果count的值最后是0，说明已经没有线程引用该对象，先删除mutex互斥量，然后free掉fp的内存
 */
void detach_foo(struct foo * fp) {
	int count;
	pthread_mutex_lock(&fp->mutex);
	count == --(fp->count);
	pthread_mutex_unlock(&fp->mutex);

	if (count == 0) {

		pthread_mutex_destroy(&fp->mutex);
		free(fp);
	}
}

void * func1(void * arg) {
	attach_foo(fp);
}
void * func2(void * arg) {
	attach_foo(fp);
}

void * func3(void *arg) {
	attach_foo(fp);
}

int main(int argc, char **argv) {
	int ret;
	pthread_t tid1, tid2, tid3;

	fp = init_foo();
	fprintf(stderr, "%d thread has attached foo\n", fp->count);

	ret = pthread_create(&tid1, NULL, func1, NULL);
	if (ret != 0) {
		fprintf(stderr, "%s\n", strerror(errno));
	}
	ret = pthread_create(&tid2, NULL, func2, NULL);
	if (ret != 0) {
		fprintf(stderr, "%s\n", strerror(errno));

	}

	ret = pthread_create(&tid3, NULL, func3, NULL);
	if (ret != 0) {
		fprintf(stderr, "%s\n", strerror(errno));

	}
	sleep(4);
	fprintf(stderr, "%d thread has attached foo\n", fp->count);
	return 0;
}

输出：

snape@snape-virtual-machine:~/桌面$ gcc -o mutex mutex.c -lpthread
snape@snape-virtual-machine:~/桌面$ ./mutex 
1 thread has attached foo
2 thread has attached foo in thread -1215399056
3 thread has attached foo in thread -1223791760
4 thread has attached foo in thread -1232184464
4 thread has attached foo