Question about Cygwin's select()

Corinna Vinschen
Fri Oct 21 09:45:00 GMT 2011

On Oct 20 08:13, Ken Brown wrote:
> On 10/19/2011 4:15 PM, Ken Brown wrote:
> >I don't have a testcase yet, but I have a clearer idea of what's
> >happening. It actually has nothing to do with the gdb subprocess, but
> >rather is a problem that can occur whenever emacs is running its main
> >command loop. emacs polls for keyboard input while also using select to
> >check for output from subprocesses. It's in this setting that select
> >often fails with EINTR, even when there are no subprocesses running. I
> >wonder if the keyboard polling is doing something that interrupts the
> >select call.
> I think this guess is correct.  If I start up emacs and do nothing,
> strace shows many sequences like the following:
>  - emacs calls select
>  - a timer sends SIGALRM
>  - select returns -1 with error EINTR
> The EINTR isn't actually visible in the strace output, but I do see
> "select_stuff::wait: signal received".  A glance at
> indicates that this is the debug output produced by select when it
> is about to return -1 with EINTR.
> These sequences always occur in connection with start_thread_socket.
> I've appended a typical excerpt from the strace output below.
> Please let me know if you need to see more strace output.  I didn't
> want to spam the list by sending too much.
> You still might need more information, but I can at least refine my
> original question:  Is it reasonable that select should give up and
> return -1 because a timer has sent SIGALRM?

If SIGALRM isn't blocked, then, yes.  What is setting up the timer?


Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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