Re: "xm save" trouble -- deadlock?

[Gerd Knorr <kraxel@suse.de>]

>>   master-xen root /vm/ttylinux# strace -p6568
>>   Process 6568 attached - interrupt to quit
>>   select(4, [3], [], [], {0, 960000})     = 0 (Timeout)
>>   futex(0x80e53b8, FUTEX_WAKE, 1)         = 0
>>   accept(3, 0x408193f8, [110])            = -1 EAGAIN (Resource 
>> temporarily unavailable)
>>
>> There is no point in calling accept(3) unless select() flags file handle 
>> #3 as readable.
> 
> This mindboggling piece of loveliness is in xen/web/connection.py.  If you can
> unpick it, a patch would be more than welcome!

Can someone explain the comment on the start of the file?

<quote>
    """We make sockets non-blocking so that operations like accept()
    don't block. We also select on a timeout. Otherwise we have no way
    of getting the threads to shutdown.
    """
</quote>

What exactly is the thread shutdown problem here?  Why the timeout is 
needed in the first place?

cheers,

   Gerd