GetQueuedCompletionStatus - 如何在没有任何套接字结构的情况下读取客户端消息

Question

我正在尝试在 Windows 中使用 C 来学习 IOCP。这个想法是拥有一个非阻塞服务器，其中包含处理客户端消息的线程。

我现在明白如何接受客户等了。

但我还是不明白如何从GetQueuedCompletionStatus()读取每个客户的消息并打印出来。

我在网上看到所有人都通过GetQueuedCompletionStatus()使用LPOVERLAPPED参数传递一个结构来引用它，但是没有任何结构怎么办？

谁能告诉我这是否可行，并举个小例子？

Answer 1

您必须跟踪传递给WSARecv() 等的缓冲区。您可以通过将OVERLAPPED 与每个缓冲区相关联来做到这一点。当GetQueuedCompletionStatus() 告诉您哪个OVERLAPPED 已完成时，您因此知道相关的缓冲区已准备好。

这通常通过定义struct 和OVERLAPPED 作为其第一个成员来处理，因此指向OVERLAPPED 的指针也等于指向struct 的指针。然后，您可以在 struct 中添加您想要的任何其他详细信息，例如缓冲区、套接字等，无论您的应用需要什么来处理数据。

例如：

enum IocpOp { opRead, opWrite };

typedef struct
{
    WSAOVERLAPPED ov;
    IocpOp opCode;
    SOCKET sckt;
    BYTE buffer[256];
    DWORD numBytesInBuffer;
} MYIOCPINFO, *PMYIOCPINFO;

void IoComplete(PMYIOCPINFO io, DWORD errorCode, DWORD numBytesTransferred)
{
    if (errorCode != ERROR_SUCCESS)
    {
        // handle failure as needed ...
        free(io);
        return;
    }

    switch (io->opCode)
    {
        case opRead:
            // use io->buffer up to numBytesTransferred as needed ...
            break;

        case opWrite:
            if (numBytesTransferred < io->numBytesInBuffer)
            {
                info->numBytesInBuffer -= numBytesTransferred;
                memmove(io->buffer, io->buffer + numBytesTransferred, io->numBytesInBuffer);

                WSABUF buf;
                buf.len = io->numBytesInBuffer;
                buf.buf = (CHAR*) io->buffer;

                if (WSASend(io->sckt, &buf, 1, NULL, 0, &(io->ov), NULL) == SOCKET_ERROR)
                {
                    if (WSAGetLastError() != WSA_IO_PENDING)
                    {
                        // handle failure as needed ...
                        free(io);
                    }
                }

                return;
            }

            break;
        }

        // reuse io for the next I/O operation on io->sckt
        // or free io now if done using it ...
        free(io);
    }
}

...

PMYIOCPINFO io = malloc(sizeof(MYIOCPINFO));
if (!io) ...
io->opCode = opRead;
io->sckt = sckt;

WSABUF buf;
buf.len = sizeof(io->buffer);
buf.buf = (CHAR*) io->buffer;

DWORD dwFlags = 0;
if (WSARecv(sckt, &buf, 1, NULL, &dwFlags, &(io->ov), NULL) == SOCKET_ERROR)
{
    if (WSAGetLastError() != WSA_IO_PENDING)
        IoComplete(io, WSAGetLastError(), 0);
}

...

PMYIOCPINFO io = malloc(sizeof(MYIOCPINFO));
if (!io) ...
io->opCode = opWrite;
io->sckt = sckt;

// fill io->buffer as needed ...
io->numBytesInBuffer = ...;

WSABUF buf;
buf.len = io->numBytesInBuffer;
buf.buf = (CHAR*) io->buffer;

if (WSASend(sckt, &buf, 1, NULL, 0, &(io->ov), NULL) == SOCKET_ERROR)
{
    if (WSAGetLastError() != WSA_IO_PENDING)
        IoComplete(io, WSAGetLastError(), 0);
}

...

DWORD dwBytesTransferred = 0;
ULONG_PTR ulCompletionKey = 0;
LPOVERLAPPED lpOverlapped = NULL;

if (GetQueuedCompletionStatus(hIOCP, &dwBytesTransferred, &ulCompletionKey, &lpOverlapped, INFINITE))
{
    if (ulCompletionKey == MySocketIOCPKey) // specified in CreateIOCompletionPort()...
    {
        IoComplete((PMYIOCPINFO)lpOverlapped, ERROR_SUCCESS, dwBytesTransferred);
    }
    else
    {
        ...
    }
}
else
{
    if (lpOverlapped)
    {
        // I/O operation belonging to ulCompletionKey failed...

        if (ulCompletionKey == MySocketIOCPKey) // specified in CreateIOCompletionPort()...
        {
            IoComplete((PMYIOCPINFO)lpOverlapped, GetLastError(), dwBytesTransferred);
        }
        else
        {
            ...
        }
    }
    else
    {
        // GetQueuedCompletionStatus() itself failed...
    }
}