取消挂在epoll_wait上的线程(Cancelling thread that is stuck on epoll_wait)

 我正在用C ++和pthreads进行一些事件处理。 我有一个从我定义的事件队列读取的主线程和一个填充事件队列的工作线程。 队列当然是线程安全的。 
 
 工作线程有一个文件描述符列表，并创建一个epoll系统调用来获取这些文件描述符上的事件。 它使用epoll_wait等待fd上的事件。 
 
 现在的问题。 假设我想彻底终止我的应用程序，我该如何正确取消工作线程？ epoll_wait不是pthread（7）的取消点之一，所以它不能在pthread_cancel正确反应。 
 
 工作线程main（）看起来像这样 
 
while(m_WorkerRunning) {
    epoll_wait(m_EpollDescriptor, events, MAXEVENTS, -1);
    //handle events and insert to queue
}
 
 当线程启动时， m_WorkerRunning设置为true ，看起来我可以通过主线程的设置m_WorkerRunning将其设置为false 来中断线程。 问题是epoll_wait理论上可以永远等待。 
 
 我的其他解决方案是：不是等待永久（-1），我可以等待例如X时隙，然后正确处理无事件的情况，如果m_WorkerRunning == false则退出循环并干净地终止工作线程。 主线程然后将m_WorkerRunning设置为false，并休眠X.但是我不确定这种epoll_wait的性能，也不确定什么是正确的X？ 500ms的？ 1秒？ 10秒？ 
 
 我想听听一些有经验的建议！ 
 
 更多相关信息：我正在等待事件的fd是/dev/input中的设备，因此技术上我正在做某种输入子系统。 目标操作系统是ARM架构上的Linux（最新内核）。 
 
 谢谢！ 

I'm doing some event handling with C++ and pthreads. I have a main thread that reads from event queue I defined, and a worker thread that fills the event queue. The queue is of course thread safe.
 
The worker thread have a list of file descriptors and create an epoll system call to get events on those file descriptors. It uses epoll_wait to wait for events on the fd's.
 
Now the problem. Assuming I want to terminate my application cleanly, how can I cancel the worker thread properly? epoll_wait is not one of the cancellation points of pthread(7) so it cannot react properly on pthread_cancel.
 
The worker thread main() looks like this
 
while(m_WorkerRunning) {
    epoll_wait(m_EpollDescriptor, events, MAXEVENTS, -1);
    //handle events and insert to queue
}
 
The m_WorkerRunning is set to true when the thread starts and it looks like I can interrupt the thread by settings m_WorkerRunning to false from the main thread. The problem is that epoll_wait theoretically can wait forever.
 
Other solution I though about is: instead of waiting forever (-1) I can wait for example X time slots, then handle properly no-events case and if m_WorkerRunning == false then exit the loop and terminate the worker thread cleanly. The main thread then sets m_WorkerRunning to false, and sleeps X. However I'm not sure about the performance of such epoll_wait and also not sure what would be the correct X? 500ms? 1s? 10s?
 
I'd like to hear some experienced advises!
 
More relevant information: the fd's I'm waiting events on, are devices in /dev/input so technically I'm doing some sort of input subsystem. The targeted OS is Linux (latest kernel) on ARM architecture.
 
Thanks!

原文：https://stackoverflow.com/questions/18614168