网络编程（55）—— Windows下使用WSASocket基于Completion Routine进行IO重叠

一、引言

        上一文中我们介绍了使用基于事件进行IO重叠的方法，本文主要介绍另外一种，基于回调函数void CALLBACK CompletionRoutine(DWORD dwError,DWORDszRecvBytes,LPWSAOVERLAPPED lpOverlapped,DWORD flags)进行IO重叠。首先，我们先介绍一种线程的状态——alertable wait状态。
        什么是alertable wait状态？
alertable wait状态是线程等待接收操作系统消息的状态，我们之前接触过的WSAWaitForMultipleEvents函数就可以触发线程这种状态。我们先来回顾下WSAWaitForMultipleEvents的函数原型：
DWORDWSAWaitForMultipleEvents(
__in DWORD cEvents,
__in const WSAEVENT *lphEvents,
__in BOOL fWaitAll,
__in DWORD dwTimeout,
__in BOOL fAlertable
);
        它的第5个参数fAlertable就是设置alertablewait状态的开关，当它设置为True时就会激活线程的alertable wait状态。我们定义的回调函数CompletionRoutine，只有在线程进入alertablewait状态后才会被操作系统调用。

二、定义CompletionRoutine回调函数

        我们先来回顾下

WSARecv

的原型（WSASend类似）：

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，采用基于事件的IO重叠时，将

WSARecv

最后一个参数设置成了NULL。而实际上他就是我们定义的回调函数

CompletionRoutine的函数指针。而CompletionRoutine函数的后三个参数分别来自

WSARecv

的第4~6个参数。当线程进入

alertable wait状态后，操作系统就会执行CompletionRoutine函数。

 

三、应用实例

        上述是使用CompletionRoutine的理论部分，下面我们通过实例对CompletionRoutine进行学习。使用CompletionRoutine进行数据接收的例子：

// WSASocketCompletionRoutineServ.cpp : 定¡§义°?控?制?台¬¡§应®|用®?程¨¬序¨°的Ì?入¨?口¨²点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);

//创ä¡ä建¡§支¡ì持?IO复¡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，是对CompletionRoutine函数的定义，在函数中操作系统将实际接收的字节szRecvBytes等信息传递给我们，在函数里对收到的buf进行打印
第17~19行，分别声明了用于接收数据的buf，实际接收的字节数recvBytes，和用于WSARecv调用的wsaBuf，由于在回调函数CompletionRoutine中也会用到这些变量，所以它们被声明成了全局变量。
第55~59行，初始化进行IO重叠的相关变量，包括wsaBuf、hEvent和overLapped。
第61行，调用WSARecv进行数据的接收，并将定义好的CompletionRoutine函数传给其最后一个参数。
       下面是使用WSASend函数的一个例子，由于上上面的例子原理上相同，这里就不在赘述。
// WSASocketCompletionRoutineClnt.cpp : 定¡§义°?控?制?台¬¡§应®|用®?程¨¬序¨°的Ì?入¨?口¨²点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);

//创ä¡ä建¡§支¡ì持?IO复¡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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