linux-kernel - Re: EINTR under Linux

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Message-ID: <487FF1A2.8000404@shaw.ca>
Date:	Thu, 17 Jul 2008 19:28:02 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	akineko <akineko@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: EINTR under Linux

akineko wrote:
> Hello,
> 
> I have a socket program that is running flawlessly under Solaris.
> When I re-compiled it under Linux (CentOS 5.1) and run it, I got the
> following error:
> 
> recv() failed: Interrupted system call
> 
> This only occurs very infrequently (probably one out of a million
> packets exchanged).
> 
> select() in my program is getting EINTR.
> 
> From the postings I found in the news group seem suggesting that it is
> due to GC.
> 
>> The GC sends signals to each thread which causes them all to enter a stop-the-world state.  When the GC
>> is finished,  all the threads are resumed.  When the threads are  resumed, any that were blocked in a
>> blocking system call (like poll()) will return with EINTR.  Normally you would just retry the system call.
> 
> So, I added to check if the errno == EINTR and now my program seems
> working fine.
> 
> //
> 
> My question I would like to ask in this group is:
> Does this mean any system call under Linux could return empty-hand
> with EINTR due to GC?
> I usually assume fatal if system call returns -1.
> It is quite painful to check all system-call return status.
> 
> My second question is:
> Does this can occur in other OS's? (free-BSD, Solaris, ...)
> Or, is this specific to Linux OS?

I'm not sure what the GC you're referring to is, but I assume it's using 
a signal handler for that stop signal. If the signal handler is not 
installed with the SA_RESTART flag, then if a system call is interrupted 
by that signal it will get EINTR instead of being restarted 
automatically. For some system calls, EINTR can still occur, for 
example, see:

http://www.opengroup.org/onlinepubs/007908775/xsh/select.html

This is not Linux specific, but the specs allow for some different 
behavior between UNIX variants.
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