WSAAsyncSelect模式的一个疑惑

WSAAsyncSelect模式的一个疑惑:
在书Network Programming for Microsoft Windows, Second Edition中,有这么一段话:
One final detail worth noting is how applications should process FD_WRITE event notifications. FD_WRITE notifications are sent under only three conditions:
......
When a send, WSASend, sendto, or WSASendTo operation fails with WSAEWOULDBLOCK and buffer space becomes available

Therefore, an application should assume that sends are always possible on a socket starting from the first FD_WRITE message and lasting until a send, WSASend, sendto, or WSASendTo returns the socket error WSAEWOULDBLOCK. After such failure, another FD_WRITE message notifies the application that sends are once again possible.

这段话令我很疑惑.send()返回WSAEWOULDBLOCK 之后,系统就产生一个FD_WRITE消息,而返回此值正是发送缓冲区已满之时.这意味着当传送一个较大块的数据时,send直到发送缓冲区满,系统就产生FD_WRTIE,此时应用程序收到FD_WRITE,又试图发送数据,结果是因缓冲区满又返回此值.这样当发送一个较大块的数据时,系统会产生大量无用的FD_WRITE,应用程序又会试图反复执行send操作,这样一来,我怀疑比最落后的轮询方式还要差.
如果我的理解无错,那么WSAAsyncSelect应该是一个非常糟糕的模型?
我正想写一个高性能的代理服务器,原本考虑使用这一IO模型的.

8 个解决方案

#1

FD_WRTIE不是出错后立即产生，是可以再发送数据时才产生的，所以不会产生大量无用的FD_WRTIE。
另外，发送数据不用响应FD_WRTIE，可以直接发送，只要判断发送是否成功即可。

#2

引用 1 楼 cnzdgs 的回复:

发送数据不用响应FD_WRTIE，可以直接发送，只要判断发送是否成功即可。

我堵到这里好几天了，原来是这样.....
cnzdgs 果然好样滴~

#3

顶.................

#4

LRESULT CALLBACK WindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
int main()
{
char szClassName[] = "MainWClass";
WNDCLASSEX wndclass;
// 用描述主窗口的参数填充WNDCLASSEX结构
wndclass.cbSize = sizeof(wndclass);
wndclass.style = CS_HREDRAW|CS_VREDRAW;
wndclass.lpfnWndProc = WindowProc;
wndclass.cbClsExtra = 0;
wndclass.cbWndExtra = 0;
wndclass.hInstance = NULL;
wndclass.hIcon = ::LoadIcon(NULL, IDI_APPLICATION);
wndclass.hCursor = ::LoadCursor(NULL, IDC_ARROW);
wndclass.hbrBackground = (HBRUSH)::GetStockObject(WHITE_BRUSH);
wndclass.lpszMenuName = NULL;
wndclass.lpszClassName = szClassName ;
wndclass.hIconSm = NULL;
::RegisterClassEx(&wndclass);
// 创建主窗口
HWND hWnd = ::CreateWindowEx(
0,
szClassName,
"",
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT,
CW_USEDEFAULT,
CW_USEDEFAULT,
CW_USEDEFAULT,
NULL,
NULL,
NULL,
NULL);
if(hWnd == NULL)
{
::MessageBox(NULL, "创建窗口出错！", "error", MB_OK);
return -1;
}

USHORT nPort = 4567; // 此服务器监听的端口号

// 创建监听套节字
SOCKET sListen = ::socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
sockaddr_in sin;
sin.sin_family = AF_INET;
sin.sin_port = htons(nPort);
sin.sin_addr.S_un.S_addr = INADDR_ANY;
// 绑定套节字到本地机器
if(::bind(sListen, (sockaddr*)&sin, sizeof(sin)) == SOCKET_ERROR)
{
printf(" Failed bind() \n");
return -1;
}

// 将套接字设为窗口通知消息类型。
::WSAAsyncSelect(sListen, hWnd, WM_SOCKET, FD_ACCEPT|FD_CLOSE);

// 进入监听模式
::listen(sListen, 5);

// 从消息队列中取出消息
MSG msg;
while(::GetMessage(&msg, NULL, 0, 0))
{
// 转化键盘消息
::TranslateMessage(&msg);
// 将消息发送到相应的窗口函数
::DispatchMessage(&msg);
}
// 当GetMessage返回0时程序结束
return msg.wParam;
}

LRESULT CALLBACK WindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch (uMsg)
{
case WM_SOCKET:
{
// 取得有事件发生的套节字句柄
SOCKET s = wParam;
// 查看是否出错
if(WSAGETSELECTERROR(lParam))
{
::closesocket(s);
return 0;
}
// 处理发生的事件
switch(WSAGETSELECTEVENT(lParam))
{
case FD_ACCEPT: // 监听中的套接字检测到有连接进入
{
SOCKET client = ::accept(s, NULL, NULL);
::WSAAsyncSelect(client, hWnd, WM_SOCKET, FD_READ|FD_WRITE|FD_CLOSE);
}
break;
case FD_WRITE:
{
}
break;
case FD_READ:
{
char szText[1024] = { 0 };
if(::recv(s, szText, 1024, 0) == -1)
::closesocket(s);
else
printf("接收数据：%s", szText);
}
break;
case FD_CLOSE:
{
::closesocket(s);
}
break;
}
}
return 0;
case WM_DESTROY:
::PostQuitMessage(0) ;
return 0 ;
}

// 将我们不处理的消息交给系统做默认处理
return ::DefWindowProc(hWnd, uMsg, wParam, lParam);
}

#5

#6

LRESULT CALLBACK WindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

int main()

{

	char szClassName[] = "MainWClass";	

	WNDCLASSEX wndclass;

	// 用描述主窗口的参数填充WNDCLASSEX结构

	wndclass.cbSize = sizeof(wndclass);	

	wndclass.style = CS_HREDRAW|CS_VREDRAW;	

	wndclass.lpfnWndProc = WindowProc;	

	wndclass.cbClsExtra = 0;		

	wndclass.cbWndExtra = 0;		

	wndclass.hInstance = NULL;		

	wndclass.hIcon = ::LoadIcon(NULL, IDI_APPLICATION);	

	wndclass.hCursor = ::LoadCursor(NULL, IDC_ARROW);		

	wndclass.hbrBackground = (HBRUSH)::GetStockObject(WHITE_BRUSH);	

	wndclass.lpszMenuName = NULL;		

	wndclass.lpszClassName = szClassName ;

	wndclass.hIconSm = NULL;	

	::RegisterClassEx(&wndclass); 

	// 创建主窗口

	HWND hWnd = ::CreateWindowEx( 

		0,						

		szClassName,			

		"",	

		WS_OVERLAPPEDWINDOW,	

		CW_USEDEFAULT,	

		CW_USEDEFAULT,		

		CW_USEDEFAULT,	

		CW_USEDEFAULT,			

		NULL,				

		NULL,		

		NULL,	

		NULL);		

	if(hWnd == NULL)

	{

		::MessageBox(NULL, "创建窗口出错！", "error", MB_OK);

		return -1;

	}


	USHORT nPort = 4567;	// 此服务器监听的端口号


	// 创建监听套节字

	SOCKET sListen = ::socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);	

	sockaddr_in sin;

	sin.sin_family = AF_INET;

	sin.sin_port = htons(nPort);

	sin.sin_addr.S_un.S_addr = INADDR_ANY;

	// 绑定套节字到本地机器

	if(::bind(sListen, (sockaddr*)&sin, sizeof(sin)) == SOCKET_ERROR)

	{

		printf(" Failed bind() \n");

		return -1;

	}


	// 将套接字设为窗口通知消息类型。

	::WSAAsyncSelect(sListen, hWnd, WM_SOCKET, FD_ACCEPT|FD_CLOSE);


	// 进入监听模式

	::listen(sListen, 5);


	// 从消息队列中取出消息

	MSG msg;	

	while(::GetMessage(&msg, NULL, 0, 0))

	{

		// 转化键盘消息

		::TranslateMessage(&msg);

		// 将消息发送到相应的窗口函数

		::DispatchMessage(&msg);

	}

	// 当GetMessage返回0时程序结束

	return msg.wParam;

}



LRESULT CALLBACK WindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)

{

	switch (uMsg)

	{	

	case WM_SOCKET:

		{

			// 取得有事件发生的套节字句柄

			SOCKET s = wParam;

			// 查看是否出错

			if(WSAGETSELECTERROR(lParam))

			{

				::closesocket(s);

				return 0;

			}

			// 处理发生的事件

			switch(WSAGETSELECTEVENT(lParam))

			{

			case FD_ACCEPT:		// 监听中的套接字检测到有连接进入

				{

					SOCKET client = ::accept(s, NULL, NULL);

					::WSAAsyncSelect(client, hWnd, WM_SOCKET, FD_READ|FD_WRITE|FD_CLOSE);

				}

				break;

			case FD_WRITE:

				{

				}

				break;

			case FD_READ:

				{

					char szText[1024] = { 0 };

					if(::recv(s, szText, 1024, 0) == -1)

						::closesocket(s);

					else

						printf("接收数据：%s", szText);

				}

				break;

			case FD_CLOSE:

				{ 

					::closesocket(s);

				}

				break;

			}

		}

		return 0;

	case WM_DESTROY:

		::PostQuitMessage(0) ;

		return 0 ;

	}


	// 将我们不处理的消息交给系统做默认处理

	return ::DefWindowProc(hWnd, uMsg, wParam, lParam);

}

#7

引用楼主 pclion 的帖子:

WSAAsyncSelect模式的一个疑惑:
在书Network Programming for Microsoft Windows, Second Edition中,有这么一段话:
One final detail worth noting is how applications should process FD_WRITE event notifications. FD_WRITE notifications are sent under only three conditions:
......
When a send, WSASend, sendto, or WSASendTo operation fails with WSAEWOULDBLOCK and buffer space becomes available

T…

CN正解

#8

学习

#1

#2