Madness with the 'select' function, sigalrm, and stdout. (CYGWIN_NT-6.1-WOW64)

[Larry Hall (Cygwin)]

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>

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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