版权声明:guojawee https://blog.csdn.net/weixin_36750623/article/details/84447437
runInLoop()函数的有用之处
“EventLoop有一个非常有用的功能:在它的IO线程内执行某个用户任务回调,即EventLoop::runInLoop(const Functor& cb),其中Functor是boost::function<void()>。如果用户在当前IO线程调用这个函数,回调会同步进行;如果用户在其他线程调用runInLoop(),cb会被加入队列,IO线程会被唤醒来调用这个Functor。”
即我们可以在线程间方便地进行任务调配,而且可以在不用锁的情况下保证线程安全。
1、eventfd()唤醒线程
(1) eventfd()函数介绍:创建一个文件描述符efd,用于事件通知
(2) efd可以像普通的文件描述符一样,用epoll_wait进行监听:当epoll_wait检测到efd可读时,说明当前线程被其他线程通知notify
(2) efd的全部缓冲区大小只有定长8byte
先来看看eventfd函数的用法,直接上示例:
#include <stdio.h>
#include <unistd.h>
#include <sys/time.h>
#include <stdint.h>
#include <pthread.h>
#include <sys/eventfd.h>
#include <sys/epoll.h>
int efd = -1;
void *read_thread(void *dummy)
{
int ret = 0;
uint64_t count = 0;
int ep_fd = -1;
struct epoll_event events[10];
if (efd < 0)
{
printf("efd not inited.\n");
goto fail;
}
ep_fd = epoll_create(1024);
if (ep_fd < 0)
{
perror("epoll_create fail: ");
goto fail;
}
{
struct epoll_event read_event;
read_event.events = EPOLLHUP | EPOLLERR | EPOLLIN;
read_event.data.fd = efd;
//将efd添加到epoll中,监听读事件
ret = epoll_ctl(ep_fd, EPOLL_CTL_ADD, efd, &read_event);
if (ret < 0)
{
perror("epoll ctl failed:");
goto fail;
}
}
while (1)
{
//发生阻塞,直到efd可读事件到来
ret = epoll_wait(ep_fd, &events[0], 10, 5000);
if (ret > 0)
{
int i = 0;
for (; i < ret; i++)
{
if (events[i].events & EPOLLHUP)
{
printf("epoll eventfd has epoll hup.\n");
goto fail;
}
else if (events[i].events & EPOLLERR)
{
printf("epoll eventfd has epoll error.\n");
goto fail;
}
else if (events[i].events & EPOLLIN)
{
int event_fd = events[i].data.fd;
ret = read(event_fd, &count, sizeof(count));
if (ret < 0)
{
perror("read fail:");
goto fail;
}
else
{
struct timeval tv;
gettimeofday(&tv, NULL);
printf("success read from efd, read %d bytes(%llu) at %lds %ldus\n",
ret, count, tv.tv_sec, tv.tv_usec);
}
}
}
}
else if (ret == 0)
{
/* time out */
printf("epoll wait timed out.\n");
break;
}
else
{
perror("epoll wait error:");
goto fail;
}
}
fail:
if (ep_fd >= 0)
{
close(ep_fd);
ep_fd = -1;
}
return NULL;
}
int main(int argc, char *argv[])
{
pthread_t pid = 0;
uint64_t count = 0;
int ret = 0;
int i = 0;
efd = eventfd(0, 0); //创建fd用于事件通知
if (efd < 0)
{
perror("eventfd failed.");
goto fail;
}
ret = pthread_create(&pid, NULL, read_thread, NULL);
if (ret < 0)
{
perror("pthread create:");
goto fail;
}
for (i = 0; i < 5; i++)
{
count = 4;
ret = write(efd, &count, sizeof(count));
if (ret < 0)
{
perror("write event fd fail:");
goto fail;
}
else
{
struct timeval tv;
gettimeofday(&tv, NULL);
printf("success write to efd, write %d bytes(%llu) at %lds %ldus\n",
ret, count, tv.tv_sec, tv.tv_usec);
}
sleep(1);
}
fail:
if (0 != pid)
{
pthread_join(pid, NULL);
pid = 0;
}
if (efd >= 0)
{
close(efd);
efd = -1;
}
return ret;
}
输出结果如下所示:
success write to efd, write 8 bytes(4) at 1328805612s 21939us
success read from efd, read 8 bytes(4) at 1328805612s 21997us
success write to efd, write 8 bytes(4) at 1328805613s 22247us
success read from efd, read 8 bytes(4) at 1328805613s 22287us
success write to efd, write 8 bytes(4) at 1328805614s 22462us
success read from efd, read 8 bytes(4) at 1328805614s 22503us
success write to efd, write 8 bytes(4) at 1328805615s 22688us
success read from efd, read 8 bytes(4) at 1328805615s 22726us
success write to efd, write 8 bytes(4) at 1328805616s 22973us
success read from efd, read 8 bytes(4) at 1328805616s 23007us
epoll wait timed out
上述例子,首先使用eventfd创建描述符efd,并在线程里面使用epoll管理这个描述符efd,当在主线程中write时,线程中的epoll返回,描述符可读。
不难发现,通过eventfd创建的描述符efd,读/写大小为sizeof(uint_64)数据,就可以完成两个线程间的唤醒。比如上述例子,由于epoll_wait()的等待,pthread_create出来的线程阻塞,在主线程中,通过往eventfd中write数据,使描述符可读,epoll返回,这就达到了唤醒的目的。
2、 EventLoop::runInLoop()函数
这个函数的效果就是在loop中执行某个用户回调
void EventLoop::runInLoop(const Functor& cb)
{
if (isInLoopThread())//如果是在本线程中
{
cb();
}
else//
{
queueInLoop(cb);
}
}