對(duì)于socket編程一直有一種誤解：socket的阻塞連接下應(yīng)該調(diào)用send/recv來(lái)發(fā)送和接收數(shù)據(jù)，而無(wú)阻塞連接下應(yīng)該用WSASend/WSARecv函數(shù)來(lái)發(fā)送和接收數(shù)據(jù)。其實(shí)socket工作模式與調(diào)用哪個(gè)收發(fā)函數(shù)沒(méi)有任何關(guān)系，自己寫(xiě)段簡(jiǎn)單的代碼測(cè)試下就知道了。無(wú)阻塞模式下，send/recv都是立即返回的。并不會(huì)等待發(fā)送或接收完成才返回。測(cè)試還發(fā)現(xiàn)選擇模式下無(wú)阻塞連接，調(diào)用connect函數(shù)會(huì)立即返回，隨后調(diào)用select，在連接建立時(shí)會(huì)設(shè)置fdWrite。
SOCKET s = ::socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (s == INVALID_SOCKET)
{
return -1;
}
// Set the connection to non-blocking mode
unsigned long ulMode = 1;
if (::ioctlsocket(s, FIONBIO, &ulMode) != 0)
{
s = INVALID_SOCKET;
return -1;
}
char szHost[128] = "www.myhost.com";
int nPort = 8000;
char szBuffer[1024] = "test socket function.\n"
addrinfo aiHints;
addrinfo *aiList = NULL;
memset(&aiHints, 0, sizeof(aiHints));
aiHints.ai_family = AF_INET;
aiHints.ai_socktype = SOCK_STREAM;
aiHints.ai_protocol = IPPROTO_TCP;
if (0 != ::getaddrinfo(szHost, NULL, &aiHints, &aiList))
{
//m_nLastError = WSAGetLastError();
::WSASetLastError(WSAEINVAL);
return -1;
}
fd_set fdRead, fdWrite;
FD_ZERO(&fdRead);
FD_ZERO(&fdWrite);
FD_SET(s, &fdRead);
FD_SET(s, &fdWrite);
struct timeval tv;
tv.tv_sec = 3;
tv.tv_usec = 0;
SOCKADDR_IN hostAddr;
hostAddr = *((SOCKADDR_IN*)aiList->ai_addr);
hostAddr.sin_port = ::htons(nPort);
int retCode = ::connect(s, (SOCKADDR*) &hostAddr, sizeof(hostAddr));
if (retCode == SOCKET_ERROR)
{
int errCode = WSAGetLastError();
if (errCode != WSAEWOULDBLOCK)
{
::closesocket(s);
s = INVALID_SOCKET;
return -1;
}
}
retCode = ::select(0, &fdRead, &fdWrite, NULL, &tv);
if (retCode > 0)
{
if (FD_ISSET(s, &fdRead))
{
printf("error!\n");
}
if (FD_ISSET(s, &fdWrite))
{
//connection has succeeded.
printf("connect success!\n");
FD_SET(s, &fdWrite);
FD_ZERO(&fdRead);
retCode = ::select(0, &fdRead, &fdWrite, NULL, &tv);
if (retCode > 0)
{
if (FD_ISSET(s, &fdRead))
{
printf("error!\n");
}
if (FD_ISSET(s, &fdWrite))
{
retCode = send(s, szBuffer, strlen(szBuffer), 0);
if (retCode > 0)
{
retCode = recv(s, buf, 1023, 0);
if (retCode == SOCKET_ERROR)
{
retCode = WSAGetLastError();
}
else if (retCode > 0)
{
printf("recv %d bytes.\n", retCode);
}
}
}
}
}
}
return 0;很多問(wèn)題要想深入理解最好的方法就是寫(xiě)一段短的測(cè)試程序驗(yàn)證一下，既不要想當(dāng)然也不要道聽(tīng)途說(shuō)。