可重入函数 read()
我通过 select() 找到了一个服务器，我想从一些客户端接收该服务器。
但我发现服务器会被gdb阻塞在read()中。
所以我想到通过添加一个SIGALRM来解决它，但是 当发生超时时，它仍然被阻塞在read()中。
发生这种情况是因为系统调用会自动重新启动，read() 当 SIGALRM 信号处理程序返回时，不会被中断。
这个解释正确吗？
I have found a server by select(), which I want to receive from some clients.
But I find that the server will get blocked in read() by gdb.
So I thought of solving it by adding a SIGALRM, but
when a timeout occurs, it's still blocked in read().
This happens because, system calls are automatically restarted, the read()
is not interrupted when the SIGALRM signal handler returns.
Is this interpretation correct?
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此问题的通常解决方案是使用
SOCK_NONBLOCK到socket(2)或O_NONBLOCK到fcntl(2)的F_SETFL命令。一旦套接字被标记为非阻塞，当您尝试从中读取数据时，它就永远不会阻塞，并且您无需尝试跨越阻塞与非阻塞之间的界限。您确定select(2)设置了文件描述符吗？select(2)联机帮助页确实描述了您看到所看到内容的原因之一，但似乎不太可能：如果您确实只是想阻止自动重新启动，请查看
sigaction(2)中的SA_RESTART以阻止可重新启动的系统调用重新启动。The usual solution to this problem is to use
SOCK_NONBLOCKtosocket(2)orO_NONBLOCKtofcntl(2)'sF_SETFLcommand. Once the socket is marked non-blocking, it'll never block when you try to read from it, and you won't need to try to straddle the divide between blocking or non-blocking. Are you sureselect(2)set the filedescriptor? Theselect(2)manpage does describe one reason why you see what you're seeing, but it doesn't seem likely:If you really just want to prevent the automatic restart, look into
SA_RESTARTinsigaction(2)to prevent restartable system calls from restarting.