一、前言
初期学习socket的时候,为了方便理解,使用默认的阻塞模式比较多。而实际做项目时,我们必须考虑程序的并发性,非阻塞模式在其中担任着很重要的角色,是必会的点之一。本文不对阻塞IO和非阻塞IO的概念做说明,不了解的请自行了解。下文代码以linux平台为例。
二、设置非阻塞模式
设置非阻塞模式,通过fcntl方法设置,为了保存socket其他设置,一般选择先获取 status flags, 并在其基础上设置O_NONBLOCK属性, 代码如下:
fcntl失败返回值为-1, 同时errno会被设置成对应的错误码。(errno在此不做说明,不了解的自行了解。) 考虑失败的情况,个人注意到网上有些例子(包括ss-libev项目)在 F_GETFL 失败后,给了flags默认值,代码如下:
经过测试,默认情况下,flags得到的值为2,也就是O_RDWR 读写, 而 0 对应的相关宏为O_RDONLY只读,明显不合理。个人感觉,对于一个正常的socket来说,F_GETFL 出错的机会不大吧, 至少我是没遇到过。如果实在出错了,还是建议走错误流程而不是给个默认值。
三、 非阻塞server
server端通常在accept后,我们为客户端连接的fd设置为非阻塞。设置O_NONBLOCK后,recv和send发生了变化。默认阻塞模式下,recv在没有数据可以接收(对方未发数据,或者缓冲区的数据已读完对方没有继续发)情况下,recv会阻塞等待,直到下次有数据发送过来。而非阻塞模式下,recv在没有数据可以接收的时候, recv会直接返回-1, 同时errno会被设置为EAGAIN/EWOULDBLOCK 。同理,非阻塞send也会在对方缓冲区满的情况下直接返回-1并设置errno, 而不是阻塞等待。 非阻塞模式下server代码大致如下:
四、非阻塞client
client除了在send/recv, 还可以在connect前设置非阻塞模式,这样在connect时候可以直接返回。
client 非阻塞connect的时候,如果返回0表示连接成功,如果返回-1, 则需要判断errno 是否为EINPROGRESS,EINPROGRESS表示非阻塞连接不能立刻获取connect结果,后面可使用select/poll/epoll等对socket 可写性进行判断,如果socket已可写,使用 getsockopt(iSocket, SOL_SOCKET, SO_ERROR ,&err, &len)进行判断。。。好像挺麻烦是不是,但是我还是建议在大部分项目中connect前设置非阻塞(小工具之类的就无所谓了,项目中一定要保证效率)。如果使用阻塞模式,有可能的问题:
下面是个非阻塞connect的部分代码, 使用select, 至于poll/epoll请自行搜索代码,跟非阻塞逻辑无关:
void* CTCPClient::AUReceive(void *aInstance){
struct timeval tv_out
CTCPClient *pInstance = (CTCPClient *)aInstance
fd_set sockfd
pInstance->m_IsExit = false
char ReceiveDataInfo[1024]={0}
char Temp[4] = {0}
while(pInstance->m_IsExit == false)
{
if(pInstance->m_socket == SOCKETERROR)
{
FD_ZERO(&sockfd)
}
else
{
FD_ZERO(&sockfd)
FD_SET(pInstance->m_socket,&sockfd)
}
fd_set mySet = sockfd
memset(ReceiveDataInfo,0,1024)
int Max_ID = pInstance->m_socket
int position=0
tv_out.tv_sec = 0
tv_out.tv_usec = 1000
if(select(Max_ID+1,&mySet,NULL,NULL,&tv_out)>0) //主要这一句
{
long nBytesRead = 0
unsigned long nBytesToRecv = pInstance->mreceivebuflen -pInstance->hasrecvlen
pInstance->recvsignal.Wait()
if(pInstance->m_socket == SOCKETERROR)
{
FD_ZERO(&sockfd)
pInstance->recvsignal.Release()
continue
}
nBytesRead = recv(pInstance->m_socket,(char *)pInstance->mreceivebuf + pInstance->hasrecvlen, nBytesToRecv, 0)
pInstance->recvsignal.Release()
if(nBytesRead == -1 || nBytesRead == 0)
{
pInstance->m_CSocket.SocketClose(pInstance->m_socket)
FD_ZERO(&sockfd)
pInstance->m_socket = SOCKETERROR
continue
}
pInstance->hasrecvlen += nBytesRead
pInstance->m_CLog->ddprintf("CTCPClient","AUReceive",1,"recv a package!")
pInstance->m_CLog->ddprintf("CTCPClient","AUReceive",1,"recvlen is %ld",nBytesRead)
if((pInstance->FindCompletePackage(pInstance->receive,nBytesRead,pInstance->mreceivebuf))==false)
{
continue
}
//printf("validlen is %d\n",pInstance->validlen)
pInstance->hasrecvlen =0
if(pInstance->validlen < 8)
{
pInstance->m_CLog->ddprintf("CTCPClient","AUReceive",1,"receive data is error(len is error)!")
continue
}
for(int i =0 i< pInstance->validlen i++)
{
sprintf(Temp,"%2x-", pInstance->receive[i])
strcat(ReceiveDataInfo, Temp)
}
pInstance->m_CLog->ddprintf("CTCPClient","AUReceive",1,"recv data is:%s",ReceiveDataInfo)
unsigned int recvSN = Char2Int(pInstance->receive)
position+=4
unsigned int recvCMD = Char2Short(pInstance->receive + position)
position+=2
unsigned long buflen = Char2Short(pInstance->receive + position)
position+=2
if(pInstance->validlen - position != buflen)
{
pInstance->m_CLog->ddprintf("CTCPClient","AUReceive",1,"receive data is error(len error)!")
continue
}
stCommand newReceiveCommand
newReceiveCommand.CmdSN = recvSN
//newReceiveCommand.DataBuffer = ""
bool rest = pInstance->FindSentCommand(newReceiveCommand)
if(rest == false)
{
pInstance->m_CLog->ddprintf("CTCPClient","AUReceive",1,"receive data is error(SN can not find)!")
continue
}
if(newReceiveCommand.CmdCode != recvCMD)
{
pInstance->m_CLog->ddprintf("CTCPClient","AUReceive",1,"receive data is error(CMD is error)!")
continue
}
char *RecvData = new char[buflen]
memcpy(RecvData,pInstance->receive+position,buflen)
pInstance->UpdateSentCommand(recvSN,buflen,RecvData)
newReceiveCommand.WaitEvent->Release()
pInstance->m_CLog->ddprintf("CTCPClient","AUReceive",1,"send a signal of recv!")
delete[] RecvData
}
else
Csleep(100)
}
//pInstance->m_ThdRecv.ThreadExit()
return NULL
}
这个是recv设置非阻塞的方式,accept也是差不多
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