Re: select() not interrupted by signals

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

On Sat, Jan 12, 2013 at 06:41:27PM +0100, Thomas Wolff wrote:
>Am 11.01.2013 16:38, schrieb Christopher Faylor:
>> On Fri, Jan 11, 2013 at 09:41:37AM +0100, Thomas Wolff wrote:
>>> I had previously reported "select() hanging after terminal killed"
>>> (http://cygwin.com/ml/cygwin/2011-05/msg00418.html).
>>> It turns out that select() does not get interrupted by a SIGWINCH signal
>>> either (with likely the same cause).
>>> This raises problems with interactive programs that want to react to
>>> window size changes (like text editors).
>>>
>>> See attached updated test case; run the program, while select() is
>>> waiting (before 5 second timeout each), change window size and see no
>>> interrupt.
>> "No interrupt"?  I see a "HUP" but select() keeps going.  That was the
>> way I designed it but apparently that differs from the way Linux works.
>> select() is not restartable like read() or write().
>>
>> That behavior should be fixed in the next snapshot.  If you are seeing
>> something different than this then that is not fixed.
>After Corinna wrote:
>> You could test using the binary...
>Yes, fixed with latest snapshot, thanks a lot. At least as far as I am 
>concerned, i.e.
>Not sure what exactly you mean with "select is not restartable" -

http://pubs.opengroup.org/onlinepubs/9699919799/functions/sigaction.html

Look for "restart".

>actually, that made me test again more deeply, and it seems you 
>interrupt select() now on every signal;
>as I understood it should only get interrupted on a signal related to a 
>file descriptor for which the bit in the exceptfds vector is set...
>I'll recheck that on Unix next week.

I have standard test cases for select() which do not use the "exceptfds"
field.  They are interrupted by a signal on both Linux and Cygwin.  I
don't see anything in the Single Unix Specification or Linux man page
which would indicate that signals are in any way related to exceptfds.

Also:

http://stackoverflow.com/questions/1342712/nix-select-and-exceptfds-errorfds-semantics

cgf

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple