兩種socket I/O模式
*阻塞模式： 執行I/O操作完成前會一直進行等待，不會将控制權交給程式。套接字預設為阻塞模式。可以通過多線程技術進行處理。
*非阻塞模式：執行I/O操作時，Winsock函數會傳回并交出控制權。這種模式使用起來比較複雜，因為函數在沒有運作完成就進行傳回，會不斷地傳回 WSAEWOULDBLOCK錯誤，但功能強大。為了解決這個問題，提出了進行I/O操作的一些非阻塞I/O模型，
下面将介紹最常見的三種：
◆select模型：
通過調用select函數可以确定一個或多個套接字的狀态，判斷套接字上是否有資料，或者能否向一個套接字寫入資料。
int select(
int nfds,
fd_set FAR *readfds,
fd_set FAR *writefds,
fd_set FAR *exceptfds,
const struct timeval FAR *timeout
);
nfds
[in] Ignored. The nfds parameter is included only for compatibility with Berkeley sockets.
readfds
[in, out] Optional pointer to a set of sockets to be checked for readability.
writefds
[in, out] Optional pointer to a set of sockets to be checked for writability
exceptfds
[in, out] Optional pointer to a set of sockets to be checked for errors.
timeout
[in] Maximum time for select to wait, provided in the form of a TIMEVAL structure. Set the timeout parameter to NULL for blocking operation.
readfds:
If listen has been called and a connection is pending, accept will succeed.
Data is available for reading (includes OOB data if SO_OOBINLINE is enabled).
Connection has been closed/reset/terminated.
writefds:
If processing a connect call (nonblocking), connection has succeeded.
Data can be sent.
exceptfds:
If processing a connect call (nonblocking), connection attempt failed.
OOB data is available for reading (only if SO_OOBINLINE is disabled).
The select function returns the total number of socket handles that are ready and contained in the fd_set structures,
zero if the time limit expired, or SOCKET_ERROR if an error occurred.
The fd_set structure is used by various Windows Sockets functions and service providers, such as the select function,
to place sockets into a "set" for various purposes, such as testing a given socket for readability using the readfds parameter of the select function.
typedef struct fd_set {
u_int fd_count; // how many are SET?
SOCKET fd_array[FD_SETSIZE]; // an array of SOCKETs
} fd_set;
Members:
fd_count
Number of sockets in the set.
fd_array
Array of sockets that are in the set.
操作下面一些宏檢查 fd_set 中的内容：
FD_CLR(s, *set)
Removes the descriptor s from set.
FD_ISSET(s, *set)
Nonzero if s is a member of the set. Otherwise, zero.
FD_SET(s, *set)
Adds descriptor s to set.
FD_ZERO(*set)
Initializes the set to the NULL set.
readfds、writefds、exceptfds三個變量至少有一個不為空，同時這個不為空的套接字組種至少有一個socket，道理很簡單，否則要select幹什麼呢。
舉例：
測試一個套接字是否可讀：
fd_set fdread;
FD_ZERO(&fdread);
FD_SET(s,&fdread)； //加入套接字
if(select(0,&fdread,NULL,NULL,NULL)>0
{
//成功
if(FD_ISSET(s,&fread) //是否存在fread中，詳細定義請看winsock2.h
{
//是可讀的
}
}
◆控制I/O模型套接字的函數：主要用于擷取與套接字相關的操作參數,如将套接字設定為 非阻塞模式。
The ioctlsocket function controls the I/O mode of a socket.
intioctlsocket(
SOCKET s,
long cmd,
u_long FAR *argp
);
s為I/O操作的套接字。
cmd為對套接字的操作指令。
argp為指令所帶參數的指針。
The ioctlsocket function can be used on any socket in any state. It is used to set or retrieve operating parameters associated with the socket
,independent of the protocol and communications subsystem. Here are the supported commands to use in the cmd parameter and their semantics:
FIONBIO
Use with a nonzero argp parameter to enable the nonblocking mode of socket s.
The argp parameter is zero if nonblocking is to be disabled.
When a socket is created, it operates in blocking mode by default (nonblocking mode is disabled).
To set the socket back to blocking mode, an application must first disable WSAAsyncSelect by calling WSAAsyncSelect with the lEvent parameter equal to zero,
or disable WSAEventSelect by calling WSAEventSelect with the lNetworkEvents parameter equal to zero.
FIONREAD
Use to determine the amount of data pending in the network's input buffer that can be read from socket s.
The argp parameter points to an unsigned long value in which ioctlsocket stores the result.
FIONREAD returns the amount of data that can be read in a single call to the recv function,
which may not be the same as the total amount of data queued on the socket.
If s is message oriented (for example, type SOCK_DGRAM), FIONREAD still returns the amount of pending data in the network buffer
, however, the amount that can actually be read in a single call to the recv function is limited to the data size written in the send or sendto function call.
SIOCATMARK
Use to determine whether or not all OOB data has been read. (See section Windows Sockets 1.1 Blocking Routines and EINPROGRESS for a discussion on out of band (OOB) data.)
This applies only to a stream oriented socket (for example, type SOCK_STREAM) that has been configured for in-line reception of any OOB data (SO_OOBINLINE). If no OOB data is waiting to be read, the operation returns TRUE. Otherwise, it returns FALSE, and the next recv or recvfrom performed on the socket will retrieve some or all of the data preceding the mark. The application should use the SIOCATMARK operation to determine whether any data remains. If there is any normal data preceding the urgent (out of band) data, it will be received in order. (A recv or recvfrom will never mix OOB and normal data in the same call.)
The argp parameter points to an unsigned long value in which ioctlsocket stores the Boolean result.
◆WSAAsynSelect模型：
WSAAsynSelect模型也是一個常用的異步I/O模型。
應用程式可以在一個套接字上接收以WINDOWS消息為基礎的網絡事件通知。該模型的實作方法是通過調用WSAAsyncSelect函數自動将套接字設定為非阻塞模式，并向WINDOWS注冊一個或多個網絡事件，并提供一個通知時使用的視窗句柄。
當注冊的事件發生時，對應的視窗将收到一個基于消息的通知。
int WSAAsyncSelect( SOCKET s, HWND hWnd, u_int wMsg, long lEvent);
作用：
自動将套接字設定為非阻塞模式，并向windows注冊一個或多個應用程式感興趣的網絡事件，并提供一個通知時使用的視窗句柄。
當這些事件發生時,應用程式相應的視窗函數将收到一個消息。
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)；
參數說明：
s為需要事件通知的套接字
hWnd為接收消息的視窗句柄
wMsg為要接收的消息
lEvent為掩碼，指定應用程式感興趣的網絡事件組合，主要如下：
#define FD_READ_BIT 0
#define FD_READ (1 << FD_READ_BIT)
#define FD_WRITE_BIT 1
#define FD_WRITE (1 << FD_WRITE_BIT)
#define FD_OOB_BIT 2
#define FD_OOB (1 << FD_OOB_BIT)
#define FD_ACCEPT_BIT 3
#define FD_ACCEPT (1 << FD_ACCEPT_BIT)
#define FD_CONNECT_BIT 4
#define FD_CONNECT (1 << FD_CONNECT_BIT)
#define FD_CLOSE_BIT 5
#define FD_CLOSE (1 << FD_CLOSE_BIT)
用法：
要接收讀寫通知：
int nResult= WSAAsyncSelect(s,hWnd,wMsg,FD_READ|FD_WRITE)；
if(nResult==SOCKET_ERROR)
{
//錯誤處理
}
取消通知：
int nResult= WSAAsyncSelect(s,hWnd,0，0)；
當應用程式視窗hWnd收到消息時，wMsg.wParam參數辨別了套接字，lParam的低字标明了網絡事件，高字則包含錯誤代碼。
int wmEvent = LOWORD(wParam);
int wmId = HIWORD(wParam);
◆WSAEventSelect模型
WSAEventSelect模型類似WSAAsynSelect模型，但最主要的差別是網絡事件發生時會被發送到一個事件對象句柄，而不是發送到一個視窗。
使用步驟如下：
1)、 建立事件對象來接收網絡事件：
#define WSAEVENT HANDLE
#define LPWSAEVENT LPHANDLE
WSAEVENT WSACreateEvent( void );
該函數的傳回值為一個事件對象句柄，它具有兩種工作狀态：已傳信(signaled)和未傳信(nonsignaled)以及兩種工作模式：人工重設(manual reset)和自動重設(auto reset)。預設未未傳信的工作狀态和人工重設模式。
2)、将事件對象與套接字關聯，同時注冊事件，使事件對象的工作狀态從未傳信轉變未已傳信。
int WSAEventSelect( SOCKET s,WSAEVENT hEventObject,long lNetworkEvents );
s為套接字
hEventObject為剛才建立的事件對象句柄
lNetworkEvents為掩碼，定義如上面所述
3)、I/O處理後，設定事件對象為未傳信
BOOL WSAResetEvent( WSAEVENT hEvent );
Hevent為事件對象
成功傳回TRUE，失敗傳回FALSE。
4)、等待網絡事件來觸發事件句柄的工作狀态：
DWORD WSAWaitForMultipleEvents( DWORD cEvents,
const WSAEVENT FAR * lphEvents, BOOL fWaitAll,
DWORD dwTimeout, BOOL fAlertable );
lpEvent為事件句柄數組的指針
cEvent為為事件句柄的數目，其最大值為WSA_MAXIMUM_WAIT_EVENTS
fWaitAll指定等待類型：TRUE：當lphEvent數組重所有事件對象同時有信号時傳回；
FALSE：任一事件有信号就傳回。
dwTimeout為等待逾時（毫秒）
fAlertable為指定函數傳回時是否執行完成例程
對事件數組中的事件進行引用時，應該用WSAWaitForMultipleEvents的傳回值，減去預聲明值WSA_WAIT_EVENT_0，得到具體的引用值。例如：
nIndex=WSAWaitForMultipleEvents(…);
MyEvent=EventArray[Index- WSA_WAIT_EVENT_0];
5)、判斷網絡事件類型：
int WSAEnumNetworkEvents( SOCKET s,
WSAEVENT hEventObject, LPWSANETWORKEVENTS lpNetworkEvents );
s為套接字
hEventObject為需要重設的事件對象
lpNetworkEvents為記錄網絡事件和錯誤代碼，其結構定義如下：
typedef struct _WSANETWORKEVENTS {
long lNetworkEvents;
int iErrorCode[FD_MAX_EVENTS];
} WSANETWORKEVENTS, FAR * LPWSANETWORKEVENTS;
6)、關閉事件對象句柄：
BOOL WSACloseEvent(WSAEVENT hEvent);
調用成功傳回TRUE，否則傳回FALSE
對比：
使用阻塞套接字，可能會對應用程式的性能造成影響，在阻塞套接字時，程式必須等待SOCKET處理完畢或者出錯後才傳回，這段時間CPU就無聊的等待；
而對于非阻塞可以在這段時間做一些資料準備工作，一旦SOCKET可以用就立即發送資料，并行性更好。
非阻塞在單socket的情況下操作起來比阻塞要複雜點，但是對于多個socket并且要求實時性比較高的場合下基本上阻塞就不能用。
譬如，socket A先進行了一個阻塞操作，那麼不逾時/不結束調用的話，代碼的控制權不會傳回，那麼B socket上面就算有資料需要被接受并且處理，由于已經阻塞在A上面了，此時沒有辦法去處理B上面的資料。而非阻塞的時候調用立即傳回，B就可以被處理。
非阻塞的伺服器程式：
#include <winsock2.h>
#include <stdio.h>
#define MYPORT 5550 // 定義預設通信端口
void main(void)
{
WSADATA wsaData;
SOCKET ListeningSocket; // 伺服器套接字
SOCKET NewConnection; // 客戶機套接字
SOCKADDR_IN ServerAddr;
SOCKADDR_IN ClientAddr;
int Ret, ClientAddrLen;
char DataBuffer[1024]; // 接收資料的緩沖區
fd_set readfds; // 等待可讀性檢查的套接口結構體
unsigned long ul = 1;
struct timeval timeout; // 最多等待時間
printf("\n------------------非阻塞模式的套接字(伺服器)------------------\n\n");
// 初始化 Winsock 2.2 版本
if ((Ret = WSAStartup(MAKEWORD(2,2), &wsaData)) != 0)
{
printf("WSAStartup failed with error %d\n", Ret);
return;
}
// 建立一個新套接字來監聽客戶機的連接配接
if ((ListeningSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == INVALID_SOCKET)
{
printf("socket failed with error %d\n", WSAGetLastError());
WSACleanup();
return;
}
// 初始化一個 SOCKADDR_IN 結構
ServerAddr.sin_family = AF_INET; // 使用IP位址族
ServerAddr.sin_port = htons(MYPORT); // 通信端口(5550)
ServerAddr.sin_addr.s_addr = htonl(INADDR_ANY); // 使用自己的IP位址，實際預設為0
// 将這個位址資訊和套接字關聯起來
if (bind(ListeningSocket, (SOCKADDR *)&ServerAddr, sizeof(ServerAddr)) == SOCKET_ERROR)
{
printf("bind failed with error %d\n", WSAGetLastError());
closesocket(ListeningSocket);
WSACleanup();
return;
}
// 将套接字轉入監聽模式，監聽客戶機的連接配接，指定最大隊列長度為5
if (listen(ListeningSocket, 5) == SOCKET_ERROR)
{
printf("listen failed with error %d\n", WSAGetLastError());
closesocket(ListeningSocket);
WSACleanup();
return;
}
// 設定套接字為非阻塞模式
Ret = ioctlsocket(ListeningSocket, FIONBIO, (unsigned long *) &ul);
if (Ret == SOCKET_ERROR)
{
printf("ioctlsocket failed with error %d\n", WSAGetLastError());
}
else
{
printf("set nonblock mode successed, return value %d\n", Ret);
}
printf("waiting for connection on port %d....\n", MYPORT);
// 定義Select() 的最多等待時間
timeout.tv_sec = 0;
timeout.tv_usec = 500;
while (1)
{
FD_ZERO(&readfds); // 對結構體進行初始化
FD_SET(ListeningSocket, &readfds); // 把套接字加入集合
// 查詢套接口的可讀性
Ret = select(0, &readfds, NULL, NULL, &timeout);
if (Ret > 0)
{
if (FD_ISSET(ListeningSocket, &readfds))
{
ClientAddrLen = sizeof(ClientAddr);
// 當有連接配接請求到達時，接受一個新連接配接
if ((NewConnection = accept(ListeningSocket, (SOCKADDR *) &ClientAddr,
&ClientAddrLen)) == INVALID_SOCKET)
{
printf("accept failed with error %d\n", WSAGetLastError());
closesocket(ListeningSocket);
WSACleanup();
exit(1);
}
printf("got a connection from %s .\n", inet_ntoa(ClientAddr.sin_addr));
// 循環
while(1)
{
// FD_ZERO(&readfds);
FD_SET(NewConnection, &readfds);
// 第二次檢查套接口的可讀性,等待時間設為空，否則會出現逾時錯誤
Ret = select(0, &readfds, NULL, NULL, NULL);
if (FD_ISSET(NewConnection, &readfds))
{
// 接收資料
Ret = recv(NewConnection, DataBuffer, sizeof(DataBuffer)-1, 0);
if (Ret == SOCKET_ERROR || Ret == 0)
{
// 接收錯誤
printf("recv failed with error %d\n", WSAGetLastError());
closesocket(NewConnection);
WSACleanup();
return ;
}
else
{
DataBuffer[Ret] = '\0';
printf("received %d byte: %s", (Ret-1), DataBuffer);
}
}
}
}
}
}
// 關閉套接字
closesocket(NewConnection);
// 釋放由 winsock 配置設定的資源
WSACleanup();
}
非阻塞的客戶機程式：
#include <winsock2.h>
#include <stdio.h>
#define MYPORT 5550 // 定義預設通信端口
#define LINELEN 128 // 定義一行資料的最大長度
void main(int argc, char **argv)
{
WSADATA wsaData;
SOCKET s;
SOCKADDR_IN ServerAddr;
int Ret, length;
char buf[LINELEN];
fd_set writefds; // 等待可寫性檢查的套接口結構體
unsigned long ul = 1;
struct timeval timeout; // 最多等待時間
// 對主函數的參數進行處理
switch(argc)
{
case 1:
argv[1] = "127.0.0.1"; // 定義一個預設的IP位址
break;
case 2:
argv[1]
argv[2]
break;
default:
printf("argument error!\n");
exit(1);
}
printf("\n------------------非阻塞模式的套接字(客戶機)------------------\n\n");
// 初始化 Winsock 2.2 版本
if ((Ret = WSAStartup(MAKEWORD(2,2), &wsaData)) != 0)
{
printf("WSAStartup failed with error %d\n", Ret);
return;
}
// 建立一個新套接字來建立客戶機連接配接
if ((s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == INVALID_SOCKET)
{
printf("socket failed with error %d\n", WSAGetLastError());
WSACleanup();
return;
}
// 設定套接字為非阻塞模式
Ret = ioctlsocket(s, FIONBIO, (unsigned long *) &ul);
if (Ret == SOCKET_ERROR)
{
printf("ioctlsocket failed with error %d\n", WSAGetLastError());
}
else
{
printf("set nonblock mode successed, return value %d\n", Ret);
}
// 初始化一個 SOCKADDR_IN 結構
ServerAddr.sin_family = AF_INET;
ServerAddr.sin_port = htons(MYPORT);
ServerAddr.sin_addr.s_addr = inet_addr(argv[1]); // 定義伺服器位址
// 用套接字 s 來建立一個到伺服器的連接配接
Ret = connect(s, (SOCKADDR *) &ServerAddr, sizeof(ServerAddr));
if (WSAGetLastError() != WSAEWOULDBLOCK)
{
printf("connect failed with error %d\n", WSAGetLastError());
closesocket(s);
WSACleanup();
return;
}
else
{
// 和伺服器的連接配接成功
printf("connect to %s on %d succeeded.\n", argv[1], MYPORT);
printf("please input send data....\n");
// 定義Select() 的最多等待時間
timeout.tv_sec = 0;
timeout.tv_usec = 500;
while (1)
{
FD_ZERO(&writefds);
FD_SET(s, &writefds);
// 查詢套接口的可寫性
Ret = select( 0, NULL, &writefds, NULL, &timeout);
if (Ret > 0)
{
if (FD_ISSET(s, &writefds))
{
// 循環：從輸入流中取資料
while (fgets(buf, sizeof(buf), stdin))
{
buf[LINELEN] = '\0'; // 在字元串最後加終止符
length = strlen(buf); // 實際發送位元組數
// 如果輸入是回車，則結束程式
if (buf[0] == '\n')
{
closesocket(s);
WSACleanup();
return;
}
// 發送資料
if ((Ret = send(s, buf, length, 0)) == SOCKET_ERROR)
{
printf("send failed with error %d\n", WSAGetLastError());
closesocket(s);
WSACleanup();
return;
}
}
}
}
}
}
// 關閉套接字
closesocket(s);
// 釋放由 winsock 配置設定的資源
WSACleanup();
}
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