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Re: Question about Cygwin's select()

On 10/19/2011 10:49 AM, Corinna Vinschen wrote:
On Oct 19 09:28, Ken Brown wrote:
I'm trying to debug an emacs problem, and I'm running into something
I don't understand involving Cygwin's select.  I'll try to make an
STC if necessary, but I thought I'd start with a verbal description
in case there's an easy answer.  Here's the situation:

emacs creates a subprocess running gdb and sends a bunch of commands
to gdb without immediately reading the resulting output.  emacs then
goes into a loop in which it waits for keyboard input and
periodically calls select to check for output from subprocesses.
The first call to select has a 30 second timeout and *always* fails
with EINTR.  As a result, emacs doesn't read the output from gdb
right away and doesn't properly initialize the gdb buffer.
Subsequent calls to select sometimes succeed and sometimes fail.
When I'm running emacs under gdb and stepping through it, the buffer
eventually gets initialized.  When I'm running emacs outside of gdb,
the buffer doesn't get initialized until I press Return.

I have a simple workaround for this, but I'd like to be sure there
isn't some underlying bug that I'm masking with the workaround.  So
my question is this: Is there some reason that I should expect that
first call to select to consistently fail with EINTR, or might this
indicate a bug?

I realize that it might not be possible to answer the question based
on the information I've provided, but I thought it was worth a try.

Some details are missing like the objects used to communicate with GDB. Does Emacs use a pseudo tty or a pipe? Is that with Cygwin from CVS or with 1.7.9? And what's your workaround? The EINTR sounds weird. A testcase would be most helpful.

Sorry for the missing details. Emacs uses a pseudo tty. I'm currently using the latest Cygwin snapshot, but I'm pretty sure I saw the same behavior with 1.7.9. I'll recheck that. My workaround is to force emacs to check for process output earlier in the initialization phase. For reasons I don't understand, the select call used at that point always succeeds.

I think you've answered my basic question by saying that the EINTR sounds weird. I'll try to make a testcase.


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