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網絡編程（55）—— Windows下使用WSASocket基于Completion Routine進行IO重疊

來源：程序員人生發布時間：2017-03-07 08:23:49 閱讀次數：2697次

1、引言

上1文中我們介紹了使用基于事件進行IO堆疊的方法，本文主要介紹另外1種，基于回調函數void CALLBACK CompletionRoutine(DWORD dwError,DWORDszRecvBytes,LPWSAOVERLAPPED lpOverlapped,DWORD flags)進行IO堆疊。首先，我們先介紹1種線程的狀態——alertable wait狀態。

甚么是alertable wait狀態？

alertable wait狀態是線程等待接收操作系統消息的狀態，我們之前接觸過的WSAWaitForMultipleEvents函數就能夠觸發線程這類狀態。我們先來回顧下WSAWaitForMultipleEvents的函數原型：

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

它的第5個參數fAlertable就是設置alertablewait狀態的開關，當它設置為True時就會激活線程的alertable wait狀態。我們定義的回調函數CompletionRoutine，只有在線程進入alertablewait狀態后才會被操作系統調用。

2、定義CompletionRoutine回調函數

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1文中，采取基于事件的IO堆疊時，將WSARecv最后1個參數設置成了NULL。而實際上他就是我們定義的回調函數CompletionRoutine的函數指針。而CompletionRoutine函數的后3個參數分別來自WSARecv的第4~6個參數。當線程進入alertable wait狀態后，操作系統就會履行CompletionRoutine函數。

3、利用實例

上述是使用CompletionRoutine的理論部份，下面我們通過實例對CompletionRoutine進行學習。使用CompletionRoutine進行數據接收的例子：

// 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???建?§支?ì持?IO復??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函數的定義，在函數中操作系統將實際接收的字節szRecvBytes等信息傳遞給我們，在函數里對收到的buf進行打印

第17~19行，分別聲明了用于接收數據的buf，實際接收的字節數recvBytes，和用于WSARecv調用的wsaBuf，由于在回調函數CompletionRoutine中也會用到這些變量，所以它們被聲明成了全局變量。

第55~59行，初始化進行IO堆疊的相干變量，包括wsaBuf、hEvent和overLapped。

第61行，調用WSARecv進行數據的接收，并將定義好的CompletionRoutine函數傳給其最后1個參數。

下面是使用WSASend函數的1個例子，由于上上面的例子原理上相同，這里就不在贅述。

// 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???建?§支?ì持?IO復??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);
}

Github位置：
https://github.com/HymanLiuTS/NetDevelopment
克隆本項目：
git clone git@github.com:HymanLiuTS/NetDevelopment.git
獲得本文源代碼：
git checkout NL55