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Date:	Tue, 17 Jan 2012 17:28:09 -0500
From:	"Larry Hall (Cygwin)" <reply-to-list-only-lh AT cygwin DOT com>
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To:	cygwin AT cygwin DOT com
Subject:	Re: Madness with the 'select' function, sigalrm, and stdout. (CYGWIN_NT-6.1-WOW64)
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On 1/17/2012 5:25 PM, Larry Hall (Cygwin) wrote:
> On 1/17/2012 5:16 PM, Robert F wrote:
>> This could be a cygwin bug, but I'm not 100% sure. It may even be a weird
>> interaction with the windows console.
>>
>> I have a single threaded app that loops, polls network activity with a
>> 'select'
>> function and interrupts the flow of the loop when a SIGALRM signal is ran,
>> the
>> handler of which sets a variable that the loop responds to.
>>
>> While this app more-or-less ran fine in its native linux environment, when
>> trying to run it at home in cygwin a problem occurs. Basically, between about
>> 2-100 seconds of starting the process (on average), the alarm signal never
>> runs
>> as scheduled and never runs again, except for one more time when I hit CTRL+C
>> (which I know by inserting debugging output into the signal handler).
>>
>> The funny thing is the app happily continues looping and calling the 'select'
>> function, it just never gets interrupted by an alarm signal. The select
>> function
>> handles cases of EINTR where it was interrupted by an alarm, btw (sockets are
>> nonblocking and timeout is 1 second).
>>
>> Now here's the REALLY weird bit. IF I insert a printf (with newline
>> terminated
>> string) after the select function, _the problem never occurs_. If there's no
>> newline, the printed strings are buffered without being shown, until either a
>> newline arrives or I hit CTRL-C.
>>
>> Doesn't work if I put it before the select function, only after.
>>
>> I haven't included any io streams into the fd_sets passed to the select
>> function, in case you were wondering. They are zeroed and then only receive
>> network connections.
>>
>> This has me stumped.
>
> I'd suggest trying a snapshot - <http://cygwin.com/problems.html>
                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                                    http://cygwin.com/snapshots/

> If that doesn't help, a full problem report might help someone on the list
> spot an issue.
>
>> Problem reports: http://cygwin.com/problems.html
>


-- 
Larry

_____________________________________________________________________

A: Yes.
 > Q: Are you sure?
 >> A: Because it reverses the logical flow of conversation.
 >>> Q: Why is top posting annoying in email?

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