blocks|key|2855489|text|当被信号中断时，epoll_wait返回-1和errno+==+EINTR。在这种情况下，您需要从signal_fd执行read。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2855490|将信号的信号处理程序设置为SIG_IGN，否则信号可能会终止应用程序。|2855491|请参阅man+signal+7|2855492|2855493|以下接口在被信号处理程序中断后永远不会重新启动，无论是否使用SA_RESTART；当被信号处理程序中断时，它们总是失败并显示错误EINTR：|blockquote|2855494|2855495|2855496|2855497|文件描述符多路复用接口:+epoll_wait(2)、epoll_pwait(2)、poll(2)、ppoll(2)、select(2)和pselect(2)。|unordered-list-item|2855498|2855499|entityMap|0|LINK|mutability|MUTABLE|url|http://man7.org/linux/man-pages/man7/signal.7.html^0|8|A|K|2|N|E|1D|9|1O|4|0|D|7|0|3|C|0|0|0|U|A|1S|5|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1G|8|@]|D|@$9|1H|A|1I|1|1J]]|E|$]]|$1|J|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]|$1|K|3|L|5|M|7|1L|8|@$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]]|D|@]|E|$]]|$1|N|3|-4|5|6|7|1Q|8|@]|D|@]|E|$]]|$1|O|3|-4|5|6|7|1R|8|@]|D|@]|E|$]]|$1|P|3|-4|5|6|7|1S|8|@]|D|@]|E|$]]|$1|Q|3|R|5|S|7|1T|8|@]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1U|8|@]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1V|8|@]|D|@]|E|$]]]|V|$W|$5|X|Y|Z|E|$10|11]]]]

<code>epoll_wait</code> returns <code>-1</code> and <code>errno == EINTR</code> when it is interrupted by a signal. In this case you need to <code>read</code> from <code>signal_fd</code>.

Set the signal handler for your signals to <code>SIG_IGN</code>, otherwise signals may terminate your application.

See <a href="http://man7.org/linux/man-pages/man7/signal.7.html" rel="nofollow noreferrer">man signal 7</a>:

<blockquote>
 The following interfaces are never restarted after being interrupted by
 a signal handler, regardless of the use of <code>SA_RESTART</code>; they always fail
 with the error <code>EINTR</code> when interrupted by a signal handler:
 
 <ul>
 <li>File descriptor multiplexing interfaces: epoll_wait(2),
 epoll_pwait(2), poll(2), ppoll(2), select(2), and pselect(2).</li>
 </ul>
</blockquote>

blocks|key|2855531|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2855532|，但在现实中，服务器只是停止而不处理信号。我做错了什么，解决问题的正确方法是什么？如果我没有正确理解信号，在什么地方应该使用signalfd？|blockquote|2855533|2855534|2855535|信号处理程序是针对每个进程的。您将信号处理程序保留为默认值，即终止进程。|2855536|所以你需要添加像这样的东西，|2855537|struct+sigaction+action;
std::memset(&action,+0,+sizeof(struct+sigaction));
action.sa_handler+=+your_handler;
sigaction(signum,+&action,+NULL);|code-block|syntax|javascript|2855538|对于您希望应用程序接收中断的每个signum。还要处理sigaction的返回值。我的经验是，如果你使用SIG_IGN作为处理程序，你仍然会从“外部”中断像epoll_pwait这样的系统调用，但当你试图通过使用pthread_kill将信号直接发送到线程来从程序本身唤醒线程时，它不会起作用。|offset|length|style|CODE|2855539|接下来，您需要屏蔽来自每个线程的所有信号，以便默认情况下没有线程会收到它(否则会唤醒一个随机线程来处理该信号)。要做到这一点，最简单的方法是在创建线程之前在main中完成。|2855540|例如,|2855541|sigset_t+all_signals;
sigemptyset(&all_signals);
sigaddset(&all_signals,+signum);+//+Repeat+for+each+signum+that+you+use.
sigprocmask(SIG_BLOCK,+&all_signals,+NULL);|2855542|然后，当您希望每个线程接收信号时，取消阻塞该线程的信号。|2855543|如果您使用signalfd，那么您不希望取消阻止它们-系统调用本身取消阻止信号，只传递适当掩码(为signalfd设置位)(它使用传递的掩码取消阻止)。另请参阅signalfd的手册页)。|2855544|epoll_pwait的工作方式有所不同；与pselect一样，您可以解锁您感兴趣的信号。您可以为该信号设置一个设置标志的处理程序(见上)。然后在调用epoll_pwait之前阻塞信号，然后测试标志并处理它，然后调用epoll_pwait而不首先解除阻塞信号。在epoll_wait返回之后，您可以再次取消阻塞该信号，以便可以再次调用您的处理程序。|2855545|entityMap^0|0|0|0|0|0|0|0|2Y|C|0|0|0|0|0|5|8|1D|8|0|0|B|M|7|23|B|30|B|0^^$0|@$1|2|3|-4|4|5|6|18|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|19|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|1A|7|@]|8|@]|9|$]]|$1|E|3|-4|4|5|6|1B|7|@]|8|@]|9|$]]|$1|F|3|G|4|5|6|1C|7|@]|8|@]|9|$]]|$1|H|3|I|4|5|6|1D|7|@]|8|@]|9|$]]|$1|J|3|K|4|L|6|1E|7|@]|8|@]|9|$M|N]]|$1|O|3|P|4|5|6|1F|7|@$Q|1G|R|1H|S|T]]|8|@]|9|$]]|$1|U|3|V|4|5|6|1I|7|@]|8|@]|9|$]]|$1|W|3|X|4|5|6|1J|7|@]|8|@]|9|$]]|$1|Y|3|Z|4|L|6|1K|7|@]|8|@]|9|$M|N]]|$1|10|3|11|4|5|6|1L|7|@]|8|@]|9|$]]|$1|12|3|13|4|5|6|1M|7|@$Q|1N|R|1O|S|T]|$Q|1P|R|1Q|S|T]]|8|@]|9|$]]|$1|14|3|15|4|5|6|1R|7|@$Q|1S|R|1T|S|T]|$Q|1U|R|1V|S|T]|$Q|1W|R|1X|S|T]|$Q|1Y|R|1Z|S|T]]|8|@]|9|$]]|$1|16|3|-4|4|5|6|20|7|@]|8|@]|9|$]]]|17|$]]

<blockquote>
 Though in reality the server just stops without handling the signal. What am I doing wrong, what is the correct way to solve my problem? And if I'm not understanding signals correctly, what is the place, where one should use signalfd?
</blockquote>

Signal handlers are per process. You left the signal handler at the default, which is to terminate the processes.

So you need to add something like this,

<pre><code>struct sigaction action;
std::memset(&amp;action, 0, sizeof(struct sigaction));
action.sa_handler = your_handler;
sigaction(signum, &amp;action, NULL);
</code></pre>

for each signum that you want your application to receive interrupts for. Also handle the return value of sigaction. My experience is that if you use SIG_IGN as handler than you still interrupt a system call like epoll_pwait from the "outside", but it won't work when you try to wake up the thread from the program itself by sending the signal directly to that thread using <code>pthread_kill</code>.

Next you need to mask all signals from every thread, so that by default no thread will receive it (otherwise a random thread is woken up to handle the signal). The easiest way to do that is by doing it in main before creating any thread.

For example,

<pre><code>sigset_t all_signals;
sigemptyset(&amp;all_signals);
sigaddset(&amp;all_signals, signum); // Repeat for each signum that you use.
sigprocmask(SIG_BLOCK, &amp;all_signals, NULL);
</code></pre>

And then unblock the signals per thread when you want that thread to receive the signal.

If you use <code>signalfd</code>, then you do not want to unblock them - that system call unblocks the signals itself, just pass the appropriate mask (set bits for <code>signalfd</code> (it uses the passed mask to unblock). See also the man page of signalfd).

<code>epoll_pwait</code> works differently; like <code>pselect</code> you unblock the signal that you are interested in. You set a handler for that signal (see above) that sets a flag. Then just before calling <code>epoll_pwait</code> you block the signal, then test the flag and handle it, and then call <code>epoll_pwait</code> without first unblocking the signal. After epoll_wait returns you can unblock the signal again so that your handler can be called again.

blocks|key|104107|text|在创建信号FD之前，必须阻止所有要用信号FD处理的信号。否则，这些信号仍然会中断被阻塞的系统调用，如您所观察到的epoll_wait()。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|104108|另请参阅signalfd(2)+man+page|104109|104110|通常情况下，应该使用sigprocmask(2)阻塞通过文件描述符接收的信号集，以防止信号根据其默认配置进行处理。|blockquote|104111|104112|104113|因此，您必须像这样更改您的示例：|104114|++++sigset_t+mask;
++++sigemptyset(&mask);
++++sigaddset(&mask,+SIGTERM);
++++sigaddset(&mask,+SIGINT);
++++int+r+=+sigprocmask(SIG_BLOCK,+&mask,+0);
++++if+(r+==+-1)+{
++++++++//+XXX+handle+errors
++++}
++++signal_fd+=+signalfd(-1,+&mask,+0);
++++if+(signal_fd+==+-1)+{
++++++++//+XXX+handle+errors
++++}

++++epoll_event+event;
++++event.data.fd+=+signal_fd;
++++event.events+=+EPOLLIN;
++++r+=+epoll_ctl(fd,+EPOLL_CTL_ADD,+signal_fd,+&event);
++++if+(r+==+-1)+{
++++++++//+XXX+handle+errors
++++}|code-block|syntax|javascript|104115|entityMap|0|LINK|mutability|MUTABLE|url|https://manpath.be/f33/2/signalfd#L22|1|https://manpath.be/f33/2/sigprocmask^0|1K|C|0|4|K|0|0|0|A|E|1|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@$9|15|A|16|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|17|8|@]|D|@$9|18|A|19|1|1A]]|E|$]]|$1|H|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]|$1|I|3|J|5|K|7|1C|8|@]|D|@$9|1D|A|1E|1|1F]]|E|$]]|$1|L|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]|$1|N|3|O|5|6|7|1I|8|@]|D|@]|E|$]]|$1|P|3|Q|5|R|7|1J|8|@]|D|@]|E|$S|T]]|$1|U|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]]|V|$W|$5|X|Y|Z|E|$10|11]]|12|$5|X|Y|Z|E|$10|13]]]]

You have to block all the signals you want to handle with your signal-FD before you create that signal-FD. Otherwise, those signals still interrupt blocked system calls such as <code>epoll_wait()</code> - as you observed.
See also the <a href="https://manpath.be/f33/2/signalfd#L22" rel="nofollow noreferrer">signalfd(2) man page</a>:
<blockquote>
Normally, the set of signals to be received via the file descriptor
should be blocked using <a href="https://manpath.be/f33/2/sigprocmask" rel="nofollow noreferrer">sigprocmask(2)</a>, to prevent the signals being
handled according to their default dispositions.
</blockquote>
Thus, you have to change your example like this:
<pre><code> sigset_t mask;
 sigemptyset(&amp;mask);
 sigaddset(&amp;mask, SIGTERM);
 sigaddset(&amp;mask, SIGINT);
 int r = sigprocmask(SIG_BLOCK, &amp;mask, 0);
 if (r == -1) {
 // XXX handle errors
 }
 signal_fd = signalfd(-1, &amp;mask, 0);
 if (signal_fd == -1) {
 // XXX handle errors
 }

 epoll_event event;
 event.data.fd = signal_fd;
 event.events = EPOLLIN;
 r = epoll_ctl(fd, EPOLL_CTL_ADD, signal_fd, &amp;event);
 if (r == -1) {
 // XXX handle errors
 }
</code></pre>

I'm writing my own <code>echo server</code> using sockets and syscalls. I am using <code>epoll</code> to work with many different clients at the same time and all the operations done with clients are nonblocking. When the server is on and doing nothing, it is in <code>epoll_wait</code>. Now I want to add the possibility to shut the server down using signals. For example, I start the server in <code>bash terminal</code>, then I press <code>ctrl-c</code> and the server somehow handles <code>SIGINT</code>. My plan is to use <code>signalfd</code>. I create new <code>signalfd</code> and add it to <code>epoll</code> instance with the following code:

<pre><code> sigset_t mask;
 sigemptyset(&amp;mask);
 sigaddset(&amp;mask, SIGTERM);
 sigaddset(&amp;mask, SIGINT);
 signal_fd = signalfd(-1, &amp;mask, 0);

 epoll_event event;
 event.data.fd = signal_fd;
 event.events = EPOLLIN;
 epoll_ctl(fd, EPOLL_CTL_ADD, signal_fd, &amp;event);
</code></pre>

Then I expect, that when <code>epoll</code> is waiting and I press <code>ctrl-c</code>, event on <code>epoll</code> happens, it wakes up and then I handle the signal with the following code:

<pre><code> if (events[i].data.fd == signal_fd)
 {
 //do something
 exit(0);
 }
</code></pre>

Though in reality the server just stops without handling the signal. What am I doing wrong, what is the correct way to solve my problem? And if I'm not understanding signals correctly, what is the place, where the one should use <code>signalfd</code>?

Handle signals with epoll_wait and signalfd

服务器

我正在使用套接字和系统调用编写自己的echo server。我正在使用epoll同时处理许多不同的客户端，并且使用客户端完成的所有操作都是非阻塞的。当服务器启动且不执行任何操作时，它处于epoll_wait中。现在我想添加使用信号关闭服务器的可能性。例如，我在bash terminal中启动服务器，然后按ctrl-c，...

问使用epoll_wait和signalfd处理信号
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