eventfd的用法

最新推荐文章于 2024-05-07 15:56:26 发布

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最新推荐文章于 2024-05-07 15:56:26 发布

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本文链接：https://blog.youkuaiyun.com/liangdsing/article/details/56014910

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eventfd不同于以前使用的fd，其write和read方法不一样。

举例子说明：

ThreadNotifyFD = eventfd(0, 0);

static void thread_notify(evutil_socket_t fd, short event, void *arg) 
{
	uint64_t  msg = 0;
	uint64_t r;

	sleep(4);
	
	r = read(fd, (void*) &msg, sizeof(msg));
	
	log_debug("msg = %llu, rc = %d\n",msg, r);

	return;
}

void *my_test(void *arg)
{
	int rc, i;

	uint64_t msg = 0;;

	for (i=0;i< 5;i++) {
		msg = i + 6;
		rc = write(ThreadNotifyFD, (void*) &msg, sizeof(msg));//file_thread_notify
		log_debug("write msg rc = %d, msg = %llu\n", rc, msg);
	}
}

void thread_init()
{
	pthread_t thread_id;
	int s;

	s = pthread_create(&thread_id, NULL, (void *)my_test, (void *)NULL);	
}

int main()
{
	...

	event_add(event_new(gevent.base, ThreadNotifyFD, EV_READ|EV_PERSIST, thread_notify, NULL), NULL) ;
	thread_init();

	...
}

若不加上红色的sleep代码，则结果是：

Mon Feb 20 16:44:46 2017: pid: 20620, msg = 6, rc = 8
Mon Feb 20 16:44:46 2017: pid: 20620, write msg rc = 8, msg = 6
Mon Feb 20 16:44:46 2017: pid: 20620, msg = 7, rc = 8
Mon Feb 20 16:44:46 2017: pid: 20620, write msg rc = 8, msg = 7
Mon Feb 20 16:44:46 2017: pid: 20620, msg = 8, rc = 8
Mon Feb 20 16:44:46 2017: pid: 20620, write msg rc = 8, msg = 8
Mon Feb 20 16:44:46 2017: pid: 20620, msg = 9, rc = 8
Mon Feb 20 16:44:46 2017: pid: 20620, write msg rc = 8, msg = 9
Mon Feb 20 16:44:46 2017: pid: 20620, msg = 10, rc = 8
Mon Feb 20 16:44:46 2017: pid: 20620, write msg rc = 8, msg = 10

若加上红色的sleep代码，则结果是：

Mon Feb 20 16:44:02 2017: pid: 20016, binloader loop running...
Mon Feb 20 16:44:02 2017: pid: 20016, write msg rc = 8, msg = 6
Mon Feb 20 16:44:02 2017: pid: 20016, write msg rc = 8, msg = 7
Mon Feb 20 16:44:02 2017: pid: 20016, write msg rc = 8, msg = 8
Mon Feb 20 16:44:02 2017: pid: 20016, write msg rc = 8, msg = 9
Mon Feb 20 16:44:02 2017: pid: 20016, write msg rc = 8, msg = 10
Mon Feb 20 16:44:06 2017: pid: 20016, msg = 40, rc = 8

eventfd是一个事件通知fd，所有的write会在一次read后被清空，且它们的值会累加在一起。