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我正在使用 Winsock API 在 C++ 中创建服务器。我想知道是否只有在某些连接实际到来时才调用accept（）函数，所以我不必在accept（）上阻塞我的线程。换句话说，我想让我的线程等待并仅在客户端尝试连接时调用 accept() 函数。那可能吗？

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1 回答 1

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当您使用 Winsock 时，您可以使用 Microsoft 特定的扩展功能AcceptEx。这允许您将接受作为“重叠 I/O”执行，这在概念上意味着接受在后台运行，您可以偶尔进入并检查它是否发生，方法是检查OverlappedResult，或执行等待在重叠句柄上。AcceptEx还可以选择执行第一次接收。

在不编写所有代码并对其进行彻底测试的情况下，类似以下的内容应该可以工作：

// The following:
//   Has no error checking
//   Assumes sListen is a bound listening socket
//   Some other assumptions I've not listed :)

// Allocate space to store the two sockaddr's that AcceptEx will give you
// 
char lpOutputBuffer[sizeof((sockaddr_in)+16) * 2];

SOCKET sAccept = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
WSAOVERLAPPED olOverlap;

ZeroMemory(&olOverlap, sizeof(WSAOVERLAPPED));
olOverlap.hEvent = WSACreateEvent();

DWORD dwBytes;

BOOL bAcceptRet =
    AcceptEx(sListen, // the listen socket
             sAccept, // the socket to use for the accepted connection
             lpOutputBuffer, // where to store the received information
             0, // don't do a receive, just store the local and remote addresses
             sizeof((sockaddr_in)+16), // size of the local address area
             sizeof((sockaddr_in)+16), // size of the remote address area
             &dwBytes, // set to received bytes if we complete synchronously
             &olOverlap); // our overlapped structure

if (bAcceptRet) {
    // the function completed synchronously.
    // lpOutputBuffer should contain the address information.
    // sAccept should be a connected socket
} else {
    // the function didn't complete synchronously, so is the accept Pending?
    if (ERROR_IO_PENDING == WSAGetLastError()) {
        // in this case, our Accept hasn't happened yet...
        // later in our code we can do the following to check if an accept has occurred:
        // note that the FALSE tells WSAGetOverlappedResult not to wait for the I/O to complete
        // it should return immediately
        ...
        DWORD dwFlags;
        if (WSAGetOverlappedResult(sListen, &olOverlap, &dwBytes, FALSE, &dwFlags)) {
            // the accept has succeeded, so do whatever we need to do with sAccept.
        }
        ...
    }
}

当然，这是一个非常快速的、被破解的可能无法工作、不可编译的代码，但它应该让您了解如何执行与您想要的类似的事情，以及在哪里查看。

hEvent顺便说一句，设置结构的参数在技术上不是必需的WSAOVERLAPPED，但这样做可以让您真正等待请求完成：

if (WAIT_OBJECT_0 == WaitForSingleObject(olOverlap.hEvent, INFINITE)) {
    // The accept occurred, so do something with it
}

我现在将等待有人指出我的代码中巨大的明显错误......

于 2013-06-12T11:28:12.797 回答