如何干净地中断recv调用中的线程阻塞? [英] How to cleanly interrupt a thread blocking on a recv call?

问题描述

我有一个用C编写的多线程服务器，每个客户端线程看起来像这样:

I have a multithreaded server written in C, with each client thread looking something like this:

ssize_t n;
struct request request;

// Main loop: receive requests from the client and send responses.
while(running && (n = recv(sockfd, &request, sizeof(request), 0)) == sizeof(request)) {
    // Process request and send response.
}
if(n == -1)
    perror("Error receiving request from client");
else if(n != sizeof(act))
    fprintf(stderr, "Error receiving request from client: Incomplete data\n");

// Clean-up code.

在某个时候，客户端满足一定的条件，必须将其断开连接.如果客户端定期发送请求，则可以这样做，因为可以在响应中通知客户端断开连接；但是，有时客户端需要花费很长时间发送请求，因此客户端线程最终在recv调用中阻塞，并且直到下一个请求/响应，客户端才断开连接.

At some point, a client meets a certain criteria where it must be disconnected. If the client is regularly sending requests, this is fine because it can be informed of the disconnection in the responses; However sometimes the clients take a long time to send a request, so the client threads end up blocking in the recv call, and the client does not get disconnected until the next request/response.

当客户端线程在recv调用中阻塞时，是否存在一种将客户端与另一个线程断开连接的干净方法?我尝试了close(sockfd)，但这会导致发生错误Error receiving request from client: Bad file descriptor，这确实不正确.

Is there a clean way to disconnect the client from another thread while the client thread is blocking in the recv call? I tried close(sockfd) but that causes the error Error receiving request from client: Bad file descriptor to occur, which really isn't accurate.

或者，对我来说，还有更好的方法来处理错误吗?

Alternatively, is there a better way for me to be handling errors here?

推荐答案

因此，您至少具有以下可能性:

So you have at least these possibilities:

(1)pthread_kill将使用errno == EINTR将线程吹出recv，您可以自行清理并退出线程.有人认为这很讨厌.确实取决于.

(1) pthread_kill will blow the thread out of recv with errno == EINTR and you can clean up and exit the thread on your own. Some people think this is nasty. Depends, really.

(2)使您的客户端套接字不阻塞，并使用select在特定时间段内等待输入，然后检查是否已将线程之间使用的开关设置为指示它们应该关闭.

(2) Make your client socket(s) non-blocking and use select to wait on input for a specific period of time before checking if a switch used between the threads has been set to indicated they should shut down.

(3)与(2)组合，使每个线程与主线程共享一个管道.将其添加到select.如果它变得可读并包含关闭请求，则线程将自行关闭.

(3) In combo with (2) have each thread share a pipe with the master thread. Add it to the select. If it becomes readable and contains a shutdonw request, the thread shuts itself down.

(4)如果以上(或其变体)都不满足您的需求，请研究pthread_cancel机制.

(4) Look into the pthread_cancel mechanism if none of the above (or variations thereof) do not meet your needs.

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