Question about Cygwin's select()

Ken Brown
Wed Oct 19 13:29:00 GMT 2011

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 

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 

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.


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