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Subject: Re: select() hanging after terminal killed
References: <201004291053 DOT o3TAr15g018361 AT mail DOT bln1 DOT bf DOT nsn-intra DOT net> <4BD96D59 DOT 7080808 AT gmx DOT de> <4BD989A9 DOT 4080402 AT towo DOT net>
Date: Thu, 29 Apr 2010 17:59:27 +0200
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From: "Matthias Andree" <matthias DOT andree AT gmx DOT de>
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Thomas Wolff wrote on 2010-04-29:

> On 29.04.2010 13:28, Matthias Andree wrote:
>> Am 29.04.2010 12:53, schrieb Thomas Wolff:
>>
>> [on closed terminal]
>>
>>> On Linux, select() indicates an exception and EIO.
>>> On SunOS, select() indicates both an exception and input (weird),
>>>
>> Not weird, you appear to be misunderstanding select().
>> An IEEE Std 1003.1 compliant select():
>>
>>   - only states that a subsequent read() will *not block*
>>     this includes EOF and error, as they make read() return without  
>> blocking)
>>
>>   - makes *no statements about success*
>>
> Oh, right, so apparently Linux is wrong here (since it does not report  
> read availability...).

Arguably yes, probably an omission in your system. (Note that older POSIX  
versions didn't specify that errors means readability).

Please look if a relevant bug is filed, and if not, please do so.

>>> On Cygwin, the following is observed:
>>> * EOF is not signalled on read(); rather EIO is indicated right away.
>>>    (Maybe not too bad, an application can handle that as well.)
>>> * select() with timeout hangs.
>>>
>>> Especially the latter can hardly be handled by an application.
>>>
>> Pointers for workarounds: alarm(), signal().
>>
> So I could setup alarm() to get myself signal()ed while waiting in a  
> long sleep().
> But the granularity is in seconds only, so this is not a substitute for  
> most use cases typically handled by calling select().
> Thanks for the information anyway.

Rather than discussing the downsides, you might more efficiently just read  
the standard, or the system documentation, which would then point you to  
setitimer().

-- 
Matthias Andree

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