一、引言

        上一文中我們介紹了使用基於事件進行IO重疊的方法，本文主要介紹另外一種，基於回撥函式void CALLBACK CompletionRoutine(DWORD dwError,DWORDszRecvBytes,LPWSAOVERLAPPED lpOverlapped,DWORD flags)進行IO重疊。首先，我們先介紹一種執行緒的狀態——alertable wait狀態。

        什麼是alertable wait狀態？

alertable wait狀態是執行緒等待接收作業系統訊息的狀態，我們之前接觸過的WSAWaitForMultipleEvents函式就可以觸發執行緒這種狀態。我們先來回顧下WSAWaitForMultipleEvents的函式原型：

DWORDWSAWaitForMultipleEvents(
  __in DWORD cEvents,
  __in const WSAEVENT *lphEvents,
  __in BOOL fWaitAll,
  __in DWORD dwTimeout,
  __in BOOL fAlertable
);

        它的第5個引數fAlertable就是設定alertablewait狀態的開關，當它設定為True時就會啟用執行緒的alertable wait狀態。我們定義的回撥函式CompletionRoutine，只有在執行緒進入alertablewait狀態後才會被作業系統呼叫。

二、定義CompletionRoutine回撥函式

        我們先來回顧下WSARecv的原型（WSASend類似）：

int WSARecv(
  __in     SOCKET s,
  __inout  LPWSABUF lpBuffers,
  __in     DWORD dwBufferCount,
  __out    LPDWORD lpNumberOfBytesRecvd,
  __inout  LPDWORD lpFlags,
  __in     LPWSAOVERLAPPED lpOverlapped,
  __in     LPWSAOVERLAPPED_COMPLETION_ROUTINE lpCompletionRoutine
);
 

        在上一文中，採用基於事件的IO重疊時，將WSARecv最後一個引數設定成了NULL。而實際上他就是我們定義的回撥函式CompletionRoutine的函式指標。而CompletionRoutine函式的後三個引數分別來自WSARecv的第4~6個引數。當執行緒進入alertable wait狀態後，作業系統就會執行CompletionRoutine函式。

三、應用例項

        上述是使用CompletionRoutine的理論部分，下面我們通過例項對CompletionRoutine進行學習。使用CompletionRoutine進行資料接收的例子：

// WSASocketCompletionRoutineServ.cpp : 定¡§義°?控?制?臺¬¡§應®|用®?程¨¬序¨°的Ì?入¨?口¨²點Ì?。¡ê
//
 
#include "stdafx.h"
#include "stdio.h"
#include "stdlib.h"
#include <WinSock2.h>
#include <string.h>
 
#pragma comment(lib,"ws2_32.lib")
 
#define BUF_SIZE 30
 
void ErrorHandler(const char* message);
void CALLBACK CompletionRoutine(DWORD dwError,DWORDszRecvBytes,LPWSAOVERLAPPED lpOverlapped,DWORD flags);
 
char buf[BUF_SIZE];
DWORD recvBytes = 0;
WSABUF wsaBuf;
int _tmain(int argc, _TCHAR* argv[])
{
    SOCKETservSock,clntSock;
    SOCKADDR_INservAddr,clntAddr;
    int clntAddrSz;
   
    WSAOVERLAPPEDoverLapped;
    HANDLEhEvent;
   
    DWORDret,flags=0;
 
    WSADATAwsaData;
    WSAStartup(MAKEWORD(2,2),&wsaData);
 
 
 
    //創ä¡ä建¡§支¡ì持?IO復¡ä用®?的Ì?套¬¡Á接¨®字Á?
    servSock=WSASocket(AF_INET,SOCK_STREAM,0,NULL,0,WSA_FLAG_OVERLAPPED);
    if(servSock==INVALID_SOCKET)
        ErrorHandler("WSASocket Error");
 
    memset(&servAddr,0,sizeof(servAddr));
    servAddr.sin_family=AF_INET;
    servAddr.sin_addr.s_addr=htonl(INADDR_ANY);
    servAddr.sin_port=htons(atoi("8888"));
 
    if(bind(servSock,(SOCKADDR*)&servAddr,sizeof(servAddr))==SOCKET_ERROR)
        ErrorHandler("bind error");
 
    if(listen(servSock,5)==SOCKET_ERROR)
        ErrorHandler("listen error");
 
    clntAddrSz=sizeof(clntAddr);
    clntSock=accept(servSock,(SOCKADDR*)&clntAddr,&clntAddrSz);
 
    memset(&overLapped,0,sizeof(overLapped));
    wsaBuf.buf=buf;
    wsaBuf.len=BUF_SIZE;
    hEvent=WSACreateEvent();
    overLapped.hEvent=hEvent;
 
    if(WSARecv(clntSock,&wsaBuf,1,&recvBytes,&flags,&overLapped,CompletionRoutine)==SOCKET_ERROR)
    {
        if(WSAGetLastError()==WSA_IO_PENDING)
            puts("background recieve data");
    }
    ret=WSAWaitForMultipleEvents(1,&hEvent,false,WSA_INFINITE,true);
    if(ret==WAIT_IO_COMPLETION)
        puts("Overlapped I/O Compeleted");
    else
        ErrorHandler("WSARecv Error");
 
    WSACloseEvent(hEvent);
    closesocket(servSock);
    closesocket(clntSock);
    WSACleanup();
    return 0;
}
 
void CALLBACK CompletionRoutine(DWORD dwError,DWORDszRecvBytes,LPWSAOVERLAPPED lpOverlapped,DWORD flags)
{
    if(dwError!=0)
    {
        ErrorHandler("CompletionRoutine Error");
    }
    else
    {
        recvBytes=szRecvBytes;
        printf("Recieve Message:%s\n",buf);
    }
}
 
void ErrorHandler(const char* message)
{
    fputs(message,stderr);
    fputc('/n',stderr);
    exit(1);
}

第79~90行，是對CompletionRoutine函式的定義，在函式中作業系統將實際接收的位元組szRecvBytes等資訊傳遞給我們，在函式裡對收到的buf進行列印

第17~19行，分別聲明瞭用於接收資料的buf，實際接收的位元組數recvBytes，和用於WSARecv呼叫的wsaBuf，由於在回撥函式CompletionRoutine中也會用到這些變數，所以它們被宣告成了全域性變數。

第55~59行，初始化進行IO重疊的相關變數，包括wsaBuf、hEvent和overLapped。

第61行，呼叫WSARecv進行資料的接收，並將定義好的CompletionRoutine函式傳給其最後一個引數。

       下面是使用WSASend函式的一個例子，由於上上面的例子原理上相同，這裡就不在贅述。

// WSASocketCompletionRoutineClnt.cpp : 定¡§義°?控?制?臺¬¡§應®|用®?程¨¬序¨°的Ì?入¨?口¨²點Ì?。¡ê
//
 
#include "stdafx.h"
#include "stdio.h"
#include "stdlib.h"
#include <WinSock2.h>
#include <string.h>
 
#pragma comment(lib,"ws2_32.lib")
 
#define BUF_SIZE 30
 
void ErrorHandler(const char* message);
void CALLBACK CompletionRoutine(DWORD dwError,DWORDszRecvBytes,LPWSAOVERLAPPED lpOverlapped,DWORD flags);
 
char buf[BUF_SIZE]="Hello world";
DWORD recvBytes = 0;
int _tmain(int argc, _TCHAR* argv[])
{
    SOCKETservSock;
    SOCKADDR_INservAddr;
 
    WSAOVERLAPPEDoverLapped;
    HANDLEhEvent;
    WSABUFwsaBuf;
    DWORDret,flags=0;
 
    WSADATAwsaData;
    WSAStartup(MAKEWORD(2,2),&wsaData);
 
 
 
    //創ä¡ä建¡§支¡ì持?IO復¡ä用®?的Ì?套¬¡Á接¨®字Á?
    servSock=WSASocket(AF_INET,SOCK_STREAM,0,NULL,0,WSA_FLAG_OVERLAPPED);
    if(servSock==INVALID_SOCKET)
        ErrorHandler("WSASocket Error");
 
    memset(&servAddr,0,sizeof(servAddr));
    servAddr.sin_family=AF_INET;
    servAddr.sin_addr.s_addr=inet_addr("127.0.0.1");
    servAddr.sin_port=htons(atoi("8888"));
 
    connect(servSock,(SOCKADDR*)&servAddr,sizeof(servAddr));
 
    memset(&overLapped,0,sizeof(overLapped));
    wsaBuf.buf=buf;
    wsaBuf.len=BUF_SIZE;
    hEvent=WSACreateEvent();
    overLapped.hEvent=hEvent;
 
    if(WSASend(servSock,&wsaBuf,1,&recvBytes,flags,&overLapped,CompletionRoutine)==SOCKET_ERROR)
    {
        if(GetLastError()==WSA_IO_PENDING)
            puts("background data send");
    }
    ret=WSAWaitForMultipleEvents(1,&hEvent,false,WSA_INFINITE,true);
    if(ret==WAIT_IO_COMPLETION)
        puts("Overlapped I/O Compeleted");
    else
        ErrorHandler("WSASend Error");
 
    WSACloseEvent(hEvent);
    closesocket(servSock);
    WSACleanup();
    return 0;
}
 
void CALLBACK CompletionRoutine(DWORD dwError,DWORDszRecvBytes,LPWSAOVERLAPPED lpOverlapped,DWORD flags)
{
    if(dwError!=0)
    {
        ErrorHandler("CompletionRoutine Error");
    }
    else
    {
        recvBytes=szRecvBytes;
        printf("Send Message:%s\n",buf);
    }
}
 
void ErrorHandler(const char* message)
{
    fputs(message,stderr);
    fputc('/n',stderr);
    exit(1);
}
 

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