Mail Archives: cygwin/2022/09/23/11:38:25

Ken Brown <kbrown AT cornell DOT edu> · Fri, 23 Sep 2022 11:36:56 -0400

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On 9/20/2022 1:20 PM, Enrico Forestieri wrote:
> On Tue, Sep 20, 2022 at 06:18:54PM -0700, Ken Brown wrote:
>>
>> On 9/20/2022 2:54 AM, Enrico Forestieri wrote:
>>>
>>>   I compared the behavior of read() and select() on 3 different platforms.
>>>   My conclusion is that, actually, read() behaves the same on all of them,
>>>   whereas cygwin differs in the way select() works.
>>
>> Then I'm even more confused than I was before. Are you saying that
>> there are situations in which read() reports EOF but select() does not
>> report read ready? Could you post the code you used for testing?
> 
> I simply introduced a timeout for select() such that it returns on any
> platform. On cygwin, when using "O_RDONLY | O_NONBLOCK" for the input
> pipe, select() always returns 1, while on all other platforms it returns 0
> unless a client actually opens it for writing.
> 
> As the "if (FD_ISSET(infd, &readfds))" block would not be entered on the
> other platforms, I replaced it with "if (TRUE)" so that the read() is
> always executed. In this conditions, the output is the same on all
> platforms, meaning that the issue is the select() and not the read() call.
> 
> This is the attached fifocomm-test.c file.

I've just sent a patch to the cygwin-patches list that makes Cygwin behave the 
same as Linux.  Thanks for reporting this problem.

Ken

P.S. I'm attaching a simplified test case that I used for testing the patch.
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Date:	Fri, 23 Sep 2022 11:36:56 -0400
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Subject:	Re: FIFO issues
To:	cygwin AT cygwin DOT com
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From:	Ken Brown <kbrown AT cornell DOT edu>
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