阅读()的socket编程不堵 [英] read() is not blocking in socket programming
问题描述
我有数据发送到客户端,每5秒的服务器。我想在客户端上阅读()阻塞,直到服务器发送一些数据,然后打印。我知道,阅读()默认情况下阻止。我的问题是我的客户不阻塞的read()。这是很奇怪的,这似乎并没有成为一个正常的问题。
我的code打印在一个无限循环没有回来。我是一个Linux机器上,C编程。我的code片断如下。请指点。
而(1)
{
N =读取(的sockfd,recvline,MAXLINE);
如果(N 0)
{
recvline [η] = 0;
如果(的fputs(recvline,标准输出)== EOF)
输出(的fputs错误);
}
否则,如果(N == 0)
的printf(没什么回来了);
否则如果(正℃,)
的printf(读取错误);
}
返回;
有可能有几个原因,几个例外是可以在不同的地方:
-
检查插座在其中创建:
=的sockfd插座(AF_INET,SOCK_STREAM,0);
如果(的sockfd == - 1){
PERROR(创建插座);
}
块引用> -
您还可使阻塞模式明确之前使用它:
//设置套接字I / O模式:在这种情况下FIONBIO
//启用或禁用阻塞模式为
//基于的iMode的数值插座。
//如果iMode平台= 0,阻止已启用;
//如果iMode平台!= 0,非阻塞模式已启用。
的ioctl(的sockfd,FIONBIO,&安培; iMode平台);
块引用>您也可以使用
的setsockopt
一>如下:timeval结构吨;
t.tv_sec = 0;
tv_usec = 0;
setsockopt的(
的sockfd // socket描述符
SOL_SOCKET,//要操纵在套接字API级别选项
SO_RCVTIMEO,//指定接收或发送超时
常量无效*(& T公司),//选项值
的sizeof(T)
); -
检查读函数调用(错误的原因)
N =读取(的sockfd,recvline,MAXLINE);
如果(正℃,){
PERROR(读错误:);
}
块引用> -
此外检查服务器code :
-
愿你的服务器发送一些空白(非打印,空,进入)章程(S)。而你不知道这一点。打扰你的服务器code了。
-
或者您的服务器终止之前客户端可以读。
块引用> -
-
还有一个有趣的事情,试着去了解:
当你调用ñ
的write()
在服务器上的没有必要,应该为N阅读()
在呼叫另一边。
块引用>
I have a server that sends data to a client every 5 seconds. I want the client to block on read() until the server sends some data and then print it. I know read () is blocking by default. My problem is that my client is not blocking on read(). This is very odd and this does not seem to be a normal issue.
My code prints "Nothing came back" in an infinite loop. I am on a linux machine, programming in c. My code snippet is below. Please advice.
while(1)
{
n = read(sockfd, recvline, MAXLINE);
if ( n > 0)
{
recvline[n] = 0;
if (fputs(recvline, stdout) == EOF)
printf("fputs error");
}
else if(n == 0)
printf("Nothing came back");
else if (n < 0)
printf("read error");
}
return;
There may be several cause and several exceptions are possible at different place:
check socket where you create:
sockfd=socket(AF_INET,SOCK_STREAM,0); if (sockfd==-1) { perror("Create socket"); }
You and also enable blocking mode explicitly before use it:
// Set the socket I/O mode: In this case FIONBIO // enables or disables the blocking mode for the // socket based on the numerical value of iMode. // If iMode = 0, blocking is enabled; // If iMode != 0, non-blocking mode is enabled. ioctl(sockfd, FIONBIO, &iMode);
or you can use
setsockopt
as below:struct timeval t; t.tv_sec = 0; tv_usec = 0; setsockopt( sockfd, // Socket descriptor SOL_SOCKET, // To manipulate options at the sockets API level SO_RCVTIMEO,// Specify the receiving or sending timeouts const void *(&t), // option values sizeof(t) );
Check Read function call (Reason of bug)
n = read(sockfd, recvline, MAXLINE); if(n < 0){ perror("Read Error:"); }
Also check server code!:
May your server send some blank(non-printable, null, enter) charter(s). And your are unaware of this. Bug you server code too.
Or your server terminated before your client can read.
One more interesting thing, Try to understand:
When you call N
write()
at server its not necessary there should be Nread()
call at other side.
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