From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Helight.Xu" <helight.xu@gmail.com>
Subject: Re: select() timeout question
Date: Thu, 26 Nov 2009 08:57:57 +0800
Message-ID: <4B0DD295.1070506@gmail.com>
References: <34e1241d0911250029g5e56e1cdxe7abfce03eb15836@mail.gmail.com>
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To: Randi Botse <nightdecoder@gmail.com>
Cc: linux-c-programming@vger.kernel.org

Randi Botse wrote:
> Hi All,
>
> Im now learning the Linux's select() system call,
>
> #include <sys/select.h>
>
> int select(int fd, fd_set *rset, fd_set *wset, fd_set *excepfs, struct
> timeval *timeout);
>
> I want to receive notification when the given file descriptor is ready
> to read, i use TCP socket connection to demonstrate this, one for the
> sender and other for the receiver, with normal condition, when the
> sender send data via write(), the select() returns and tell the
> receiver there are data to read.
>
> My question is: what happen when the receiver's select() is reaching
> it's timeout while the sender send data? should the notification and
> it's data lost (discarded)?
>   
NO! if timeout ,the data will stay in kernel, and select will notice you 
when the select called again,

In fact , we always put select in while loop and set the timeout!
> Based on my above experiment, select() never fail to notify although
> it's in timeout state, and i awalys can read the data, i'm curious
> with this, but i'm not sure if this always right.
>
> Thanks before.
>
>                                             Randi,
> --
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>   


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---------------------------------
Zhenwen Xu - Open and Free
Home Page:	http://zhwen.org