用setsockopt()来控制recv()与send()的超时

最新推荐文章于 2025-12-19 22:31:41 发布

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#socket #struct #structure #function #linux #header

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本文详细介绍了在Linux环境下如何正确地为socket设置发送和接收超时，避免因网络状况导致的数据收发失败。文中强调了使用struct timeval来定义超时时间的重要性，并解释了recv()函数的行为变化。

在send(),recv()过程中有时由于网络状况等原因，收发不能预期进行,而设置收发超时控制：

在Linux下需要注意的是时间的控制结构是struct timeval而并不是某一整型数，以下是来自于网上一篇文章中的摘录，它是这样写的：
int nNetTimeout=1000;//1秒，
//设置发送超时
setsockopt(socket，SOL_SOCKET,SO_SNDTIMEO，(char *)&nNetTimeout,sizeof(int));
//设置接收超时
setsockopt(socket，SOL_SOCKET,SO_RCVTIMEO，(char *)&nNetTimeout,sizeof(int));

这样做在Linux环境下是不会产生效果的，须如下定义：struct timeval timeout = {3,0};
//设置发送超时
setsockopt(socket，SOL_SOCKET,SO_SNDTIMEO，(char *)&timeout,sizeof(struct timeval));

//设置接收超时
setsockopt(socket，SOL_SOCKET,SO_RCVTIMEO，(char *)&timeout,sizeof(struct timeval));

有两点注意就是：

1）recv ()的第四个参数需为MSG_WAITALL，在阻塞模式下不等到指定数目的数据不会返回，除非超时时间到。还要注意的是只要设置了接收超时，在没有MSG_WAITALL时也是有效的。说到底超时就是不让你的程序老在那儿等，到一定时间进行一次返回而已。

2）即使等待超时时间值未到，但对方已经关闭了socket，则此时recv()会立即返回，并收到多少数据返回多少数据。

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http://blog.youkuaiyun.com/newger/article/details/2459113

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SO_RCVTIMEO and SO_SNDTIMEO

Specify the receiving or sending timeouts until reporting an error. The argument is a struct timeval. If an input or output function blocks for thisperiod of time, and data has been sent or received, the return value of that function will be the amount of data transferred; if no data has been transferredand the timeout has been reached then -1 is returned with errno set to EAGAIN or EWOULDBLOCK just as if the socket was specified to benonblocking. If the timeout is set to zero (the default) then the operation will never timeout. Timeouts only have effect for system calls that perform socketI/O (e.g., read(2), recvmsg(2), send(2), sendmsg(2)); timeouts have no effect for select(2), poll(2), epoll_wait(2), etc.

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The timeval structure is used to specify a time interval. It is associated with the Berkeley Software Distribution (BSD) Time.h header file.

Syntax

Copy

typedef struct timeval {
  long tv_sec;
  long tv_usec;
} timeval;

Members

tv_sec

Time interval, in seconds.

tv_usec

Time interval, in microseconds. This value is used in combination with the tv_sec member to represent time interval values that are not a multiple of seconds.

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http://msdn.microsoft.com/en-us/library/windows/desktop/ms740560%28v=vs.85%29.aspx