Socket I/O模型之完成端口(completion port)

http://tangfeng.iteye.com/blog/518148

“完成端口”模型是迄今为止最为复杂的一种I/O模型。然而，假若一个应用程序同时需要管理为数众多的套接字，那么采用这种模型，往往可以达到最佳的系统性能！但不幸的是，该模型只适用于Windows NT和Windows 2000操作系统。因其设计的复杂性，只有在你的应用程序需要同时管理数百乃至上千个套接字的时候，而且希望随着系统内安装的CPU数量的增多，应用程序的性能也可以线性提升，才应考虑采用“完成端口”模型。要记住的一个基本准则是，假如要为Windows NT或Windows 2000开发高性能的服务器应用，同时希望为大量套接字I/O请求提供服务（Web服务器便是这方面的典型例子），那么I/O完成端口模型便是最佳选择！ 

使用完成端口模型的服务器端代码： 

// write by larry
// 2009-8-20
// This is a server using completion port.
#include "stdafx.h"
#include <WINSOCK2.H>
#include <stdio.h>
#pragma comment(lib, "ws2_32.lib")
#define PORT  5150
#define MSGSIZE  1024
typedef enum
{
    RECV_POSTED
} OPERATION_TYPE;
typedef struct
{
    WSAOVERLAPPED  overlap;
    WSABUF         Buffer;
    char           szMessage[MSGSIZE];
    DWORD          NumberOfBytesRecvd;
    DWORD          Flags;
    OPERATION_TYPE OperationType;
} PER_IO_OPERATION_DATA, *LPPER_IO_OPERATION_DATA;
DWORD WINAPI WorkerThread(LPVOID CompletionPortID);

int main(int argc, char* argv[])
{
    WSADATA wsaData;
    SOCKET sListen, sClient;
    SOCKADDR_IN local, client;
    DWORD i, dwThreadId;
    int iAddrSize = sizeof(SOCKADDR_IN);
    HANDLE CompletionPort = INVALID_HANDLE_VALUE;
    SYSTEM_INFO sysinfo;
    LPPER_IO_OPERATION_DATA lpPerIOData = NULL;
    // Initialize windows socket library
    WSAStartup(0x0202, &wsaData);
    // Create completion port
    CompletionPort = CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 0);
    // Create worker thread
    GetSystemInfo(&sysinfo);
    for (i = 0; i < sysinfo.dwNumberOfProcessors; i++)
    {
        CreateThread(NULL, 0, WorkerThread, CompletionPort, 0, &dwThreadId);
    }
    // Create listening socket
    sListen = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    // Bind
    local.sin_family = AF_INET;
    local.sin_addr.S_un.S_addr = htonl(INADDR_ANY);
    local.sin_port = htons(PORT);
    bind(sListen, (sockaddr*)&local, sizeof(SOCKADDR_IN));
    // Listen
    listen(sListen, 3);
    while (TRUE)
    {
        // Accept a connection
        sClient = accept(sListen, (sockaddr*)&client, &iAddrSize);
        printf("Accepted client:%s:%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
        // Associate the newly arrived client socket with completion port
        CreateIoCompletionPort((HANDLE)sClient, CompletionPort, (DWORD)sClient, 0);
        // Launch an asynchronous operation for new arrived connection
        lpPerIOData = (LPPER_IO_OPERATION_DATA)HeapAlloc(
            GetProcessHeap(),
            HEAP_ZERO_MEMORY,
            sizeof(PER_IO_OPERATION_DATA));
        lpPerIOData->Buffer.len = MSGSIZE;
        lpPerIOData->Buffer.buf = lpPerIOData->szMessage;
        lpPerIOData->OperationType = RECV_POSTED;
        WSARecv(sClient,
            &lpPerIOData->Buffer,
            1,
            &lpPerIOData->NumberOfBytesRecvd,
            &lpPerIOData->Flags,
            &lpPerIOData->overlap,
            NULL);
    }
    PostQueuedCompletionStatus(CompletionPort, 0xFFFFFFFF, 0, NULL);
    CloseHandle(CompletionPort);
    closesocket(sListen);
    WSACleanup();
    return 0;
}
DWORD WINAPI WorkerThread(LPVOID CompletionPortID)
{
    HANDLE CompletionPort = (HANDLE)CompletionPortID;
    DWORD dwBytesTransferred;
    SOCKET sClient;
    LPPER_IO_OPERATION_DATA lpPerIOData = NULL;
    while (TRUE)
    {
        GetQueuedCompletionStatus(
            CompletionPort,
            &dwBytesTransferred,
            (DWORD*)&sClient,
            (LPOVERLAPPED*)&lpPerIOData,
            INFINITE);
        if (dwBytesTransferred == 0xFFFFFFFF)
        {
            return 0;
        }
        if (lpPerIOData->OperationType == RECV_POSTED)
        {
            if (dwBytesTransferred == 0)
            {
                // Connection was closed by client
                closesocket(sClient);
                HeapFree(GetProcessHeap(), 0, lpPerIOData);
            }
            else
            {
                lpPerIOData->szMessage[dwBytesTransferred] = '\0';
                send(sClient, lpPerIOData->szMessage, dwBytesTransferred, 0);

                // Launch another asynchronous operation for sClient
                memset(lpPerIOData, 0, sizeof(PER_IO_OPERATION_DATA));
                lpPerIOData->Buffer.len = MSGSIZE;
                lpPerIOData->Buffer.buf = lpPerIOData->szMessage;
                lpPerIOData->OperationType = RECV_POSTED;
                WSARecv(sClient,
                    &lpPerIOData->Buffer,
                    1,
                    &lpPerIOData->NumberOfBytesRecvd,
                    &lpPerIOData->Flags,
                    &lpPerIOData->overlap,
                    NULL);
            }
        }
    }
    return 0;
}

服务器端得主要流程： 
1.创建完成端口对象 
2.创建工作者线程（这里工作者线程的数量是按照CPU的个数来决定的，这样可以达到最佳性能） 
3.创建监听套接字，绑定，监听，然后程序进入循环 
4.在循环中，我做了以下几件事情： 
(1).接受一个客户端连接 
(2).将该客户端套接字与完成端口绑定到一起(还是调用CreateIoCompletionPort，但这次的作用不同)， 注意，按道理来讲，此时传递给CreateIoCompletionPort的第三个参数应该是一个完成键，一般来讲，程序都是传递一个单句柄数据结构的地址，该单句柄数据包含了和该客户端连接有关的信息，由于我们只关心套接字句柄，所以直接将套接字句柄作为完成键传递； 
(3).触发一个WSARecv异步调用，这次又用到了“尾随数据”，使接收数据所用的缓冲区紧跟在WSAOVERLAPPED对象之后，此外，还有操作类型等重要信息。 

在工作者线程的循环中，我们 
1.调用GetQueuedCompletionStatus取得本次I/O的相关信息（例如套接字句柄、传送的字节数、单I/O数据结构的地址等等） 
2.通过单I/O数据结构找到接收数据缓冲区，然后将数据原封不动的发送到客户端 
3.再次触发一个WSARecv异步操作