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如果几百个连接的话,用完成端口有点牛刀小试了,建议使用重叠IO模式。重叠IO模式能够管理的socket连接极限大概一万左右吧,这样的话,如果将来有需求,就比较容易扩展。
重叠I/O模型
Winsock2的发布使得Socket I/O有了和文件I/O统一的接口。我们可以通过使用Win32文件操纵函数ReadFile和WriteFile来进行Socket I/O。伴随而来的,用于普通文件I/O的重叠I/O模型和完成端口模型对Socket I/O也适用了。这些模型的优点是可以达到更佳的系统性能,但是实现较为复杂,里面涉及较多的C语言技巧。例如我们在完成端口模型中会经常用到所谓的“尾随数据”。
1.用事件通知方式实现的重叠I/O模型
#include <winsock2.h>
#include <stdio.h>
#define PORT 5150
#define MSGSIZE 1024
#pragma comment(lib, "ws2_32.lib")
typedef struct
{
WSAOVERLAPPED overlap;
WSABUF Buffer;
char szMessage[MSGSIZE];
DWORD NumberOfBytesRecvd;
DWORD Flags;
}PER_IO_OPERATION_#, *LPPER_IO_OPERATION_#;
int g_iTotalConn = 0;
SOCKET g_CliSocketArr[MAXIMUM_WAIT_OBJECTS];
WSAEVENT g_CliEventArr[MAXIMUM_WAIT_OBJECTS];
LPPER_IO_OPERATION_# g_pPerIO#Arr[MAXIMUM_WAIT_OBJECTS];
DWORD WINAPI WorkerThread(LPVOID);
void Cleanup(int);
int main()
{
WSA# wsa#;
SOCKET sListen, sClient;
SOCKADDR_IN local, client;
DWORD dwThreadId;
int iaddrSize = sizeof(SOCKADDR_IN);
// Initialize Windows Socket library
WSAStartup(0x0202, &wsa#);
// Create listening socket
sListen = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
// Bind
local.sin_addr.S_un.S_addr = htonl(INADDR_ANY);
local.sin_family = AF_INET;
local.sin_port = htons(PORT);
bind(sListen, (struct sockaddr *)&local, sizeof(SOCKADDR_IN));
// Listen
listen(sListen, 3);
// Create worker thread
CreateThread(NULL, 0, WorkerThread, NULL, 0, &dwThreadId);
while (TRUE)
{
// Accept a connection
sClient = accept(sListen, (struct sockaddr *)&client, &iaddrSize);
printf("Accepted client:%s:%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
g_CliSocketArr[g_iTotalConn] = sClient;
// Allocate a PER_IO_OPERATION_# structure
g_pPerIO#Arr[g_iTotalConn] = (LPPER_IO_OPERATION_#)HeapAlloc(
GetProcessHeap(),
HEAP_ZERO_MEMORY,
sizeof(PER_IO_OPERATION_#));
g_pPerIO#Arr[g_iTotalConn]->Buffer.len = MSGSIZE;
g_pPerIO#Arr[g_iTotalConn]->Buffer.buf = g_pPerIO#Arr[g_iTotalConn]->szMessage;
g_CliEventArr[g_iTotalConn] = g_pPerIO#Arr[g_iTotalConn]->overlap.hEvent = WSACreateEvent();
// Launch an asynchronous operation
WSARecv(
g_CliSocketArr[g_iTotalConn],
&g_pPerIO#Arr[g_iTotalConn]->Buffer,
1,
&g_pPerIO#Arr[g_iTotalConn]->NumberOfBytesRecvd,
&g_pPerIO#Arr[g_iTotalConn]->Flags,
&g_pPerIO#Arr[g_iTotalConn]->overlap,
NULL);
g_iTotalConn++;
}
closesocket(sListen);
WSACleanup();
return 0;
}
DWORD WINAPI WorkerThread(LPVOID lpParam)
{
int ret, index;
DWORD cbTransferred;
while (TRUE)
{
ret = WSAWaitForMultipleEvents(g_iTotalConn, g_CliEventArr, FALSE, 1000, FALSE);
if (ret == WSA_WAIT_FAILED || ret == WSA_WAIT_TIMEOUT)
{
continue;
}
index = ret - WSA_WAIT_EVENT_0;
WSAResetEvent(g_CliEventArr[index]);
WSAGetOverlappedResult(
g_CliSocketArr[index],
&g_pPerIO#Arr[index]->overlap,
&cbTransferred,
TRUE,
&g_pPerIO#Arr[g_iTotalConn]->Flags);
if (cbTransferred == 0)
{
// The connection was closed by client
Cleanup(index);
}
else
{
// g_pPerIO#Arr[index]->szMessage contains the received #
g_pPerIO#Arr[index]->szMessage[cbTransferred] = '\0';
send(g_CliSocketArr[index], g_pPerIO#Arr[index]->szMessage,\
cbTransferred, 0);
// Launch another asynchronous operation
WSARecv(
g_CliSocketArr[index],
&g_pPerIO#Arr[index]->Buffer,
1,
&g_pPerIO#Arr[index]->NumberOfBytesRecvd,
&g_pPerIO#Arr[index]->Flags,
&g_pPerIO#Arr[index]->overlap,
NULL);
}
}
return 0;
}
void Cleanup(int index)
{
closesocket(g_CliSocketArr[index]);
WSACloseEvent(g_CliEventArr[index]);
HeapFree(GetProcessHeap(), 0, g_pPerIO#Arr[index]);
if (index < g_iTotalConn - 1)
{
g_CliSocketArr[index] = g_CliSocketArr[g_iTotalConn - 1];
g_CliEventArr[index] = g_CliEventArr[g_iTotalConn - 1];
g_pPerIO#Arr[index] = g_pPerIO#Arr[g_iTotalConn - 1];
}
g_pPerIO#Arr[--g_iTotalConn] = NULL;
}
这个模型与上述其他模型不同的是它使用Winsock2提供的异步I/O函数WSARecv。在调用WSARecv时,指定一个 WSAOVERLAPPED结构,这个调用不是阻塞的,也就是说,它会立刻返回。一旦有数据到达的时候,被指定的WSAOVERLAPPED结构中的 hEvent被Signaled。由于下面这个语句
g_CliEventArr[g_iTotalConn] = g_pPerIO#Arr[g_iTotalConn]->overlap.hEvent;
使 得与该套接字相关联的WSAEVENT对象也被Signaled,所以WSAWaitForMultipleEvents的调用操作成功返回。我们现在应 该做的就是用与调用WSARecv相同的WSAOVERLAPPED结构为参数调用WSAGetOverlappedResult,从而得到本次I/O传 送的字节数等相关信息。在取得接收的数据后,把数据原封不动的发送到客户端,然后重新激活一个WSARecv异步操作。
2.用完成例程方式实现的重叠I/O模型
#include <WINSOCK2.H>
#include <stdio.h>
#define PORT 5150
#define MSGSIZE 1024
#pragma comment(lib, "ws2_32.lib")
typedef struct
{
WSAOVERLAPPED overlap;
WSABUF Buffer;
char szMessage[MSGSIZE];
DWORD NumberOfBytesRecvd;
DWORD Flags;
SOCKET sClient;
}PER_IO_OPERATION_#, *LPPER_IO_OPERATION_#;
DWORD WINAPI WorkerThread(LPVOID);
void CALLBACK CompletionROUTINE(DWORD, DWORD, LPWSAOVERLAPPED, DWORD);
SOCKET g_sNewClientConnection;
BOOL g_bNewConnectionArrived = FALSE;
int main()
{
WSA# wsa#;
SOCKET sListen;
SOCKADDR_IN local, client;
DWORD dwThreadId;
int iaddrSize = sizeof(SOCKADDR_IN);
// Initialize Windows Socket library
WSAStartup(0x0202, &wsa#);
// Create listening socket
sListen = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
// Bind
local.sin_addr.S_un.S_addr = htonl(INADDR_ANY);
local.sin_family = AF_INET;
local.sin_port = htons(PORT);
bind(sListen, (struct sockaddr *)&local, sizeof(SOCKADDR_IN));
// Listen
listen(sListen, 3);
// Create worker thread
CreateThread(NULL, 0, WorkerThread, NULL, 0, &dwThreadId);
while (TRUE)
{
// Accept a connection
g_sNewClientConnection = accept(sListen, (struct sockaddr *)&client, &iaddrSize);
g_bNewConnectionArrived = TRUE;
printf("Accepted client:%s:%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
}
}
DWORD WINAPI WorkerThread(LPVOID lpParam)
{
LPPER_IO_OPERATION_# lpPerIO# = NULL;
while (TRUE)
{
if (g_bNewConnectionArrived)
{
// Launch an asynchronous operation for new arrived connection
lpPerIO# = (LPPER_IO_OPERATION_#)HeapAlloc(
GetProcessHeap(),
HEAP_ZERO_MEMORY,
sizeof(PER_IO_OPERATION_#));
lpPerIO#->Buffer.len = MSGSIZE;
lpPerIO#->Buffer.buf = lpPerIO#->szMessage;
lpPerIO#->sClient = g_sNewClientConnection;
WSARecv(lpPerIO#->sClient,
&lpPerIO#->Buffer,
1,
&lpPerIO#->NumberOfBytesRecvd,
&lpPerIO#->Flags,
&lpPerIO#->overlap,
CompletionROUTINE);
g_bNewConnectionArrived = FALSE;
}
SleepEx(1000, TRUE);
}
return 0;
}
void CALLBACK CompletionROUTINE(DWORD dwError,
DWORD cbTransferred,
LPWSAOVERLAPPED lpOverlapped,
DWORD dwFlags)
{
LPPER_IO_OPERATION_# lpPerIO# = (LPPER_IO_OPERATION_#)lpOverlapped;
if (dwError != 0 || cbTransferred == 0)
{
// Connection was closed by client
closesocket(lpPerIO#->sClient);
HeapFree(GetProcessHeap(), 0, lpPerIO#);
}
else
{
lpPerIO#->szMessage[cbTransferred] = '\0';
send(lpPerIO#->sClient, lpPerIO#->szMessage, cbTransferred, 0);
// Launch another asynchronous operation
memset(&lpPerIO#->overlap, 0, sizeof(WSAOVERLAPPED));
lpPerIO#->Buffer.len = MSGSIZE;
lpPerIO#->Buffer.buf = lpPerIO#->szMessage;
WSARecv(lpPerIO#->sClient,
&lpPerIO#->Buffer,
1,
&lpPerIO#->NumberOfBytesRecvd,
&lpPerIO#->Flags,
&lpPerIO#->overlap,
CompletionROUTINE);
}
}
用完成例程来实现重叠I/O比用事件通知简单得多。在这个模型中,主线程只用不停的接受连接即可;辅助线程判断有没有新的客户端连接被建立,如果 有,就为那个客户端套接字激活一个异步的WSARecv操作,然后调用SleepEx使线程处于一种可警告的等待状态,以使得I/O完成后 CompletionROUTINE可以被内核调用。如果辅助线程不调用SleepEx,则内核在完成一次I/O操作后,无法调用完成例程(因为完成例程 的运行应该和当初激活WSARecv异步操作的代码在同一个线程之内)。
完成例程内的实现代码比较简单,它取出接收到的数据,然后将数据原封不动 的发送给客户端,最后重新激活另一个WSARecv异步操作。注意,在这里用到了“尾随数据”。我们在调用WSARecv的时候,参数 lpOverlapped实际上指向一个比它大得多的结构PER_IO_OPERATION_#,这个结构除了WSAOVERLAPPED以外,还 被我们附加了缓冲区的结构信息,另外还包括客户端套接字等重要的信息。这样,在完成例程中通过参数lpOverlapped拿到的不仅仅是 WSAOVERLAPPED结构,还有后边尾随的包含客户端套接字和接收数据缓冲区等重要信息。这样的C语言技巧在我后面介绍完成端口的时候还会使用到。