Re: Emacs Hangs on Filesystem Operations on Stale NFS

[Alexander Shukaev <emacs@alexander.shukaev.name>]

On 2018-06-11 13:59, Noam Postavsky wrote:
> On 11 June 2018 at 06:27, Alexander Shukaev
> <emacs@alexander.shukaev.name> wrote:
> 
>> Well, enough rant.  I think I have a proposal how to fix the issue, 
>> even
>> given the blocking nature of Emacs.  How about introducing a variable
>> `file-access-timeout' defaulting to `nil', which would reflect a
>> configurable timeout for all access operations (such as 
>> `file-readable-p')?
>> This would be achieved via `SIGALARM' in the C code, which would 
>> protect
>> every such operation.  For example,
> 
> Does it work? According to some messages on the previous thread you
> referenced [1], NFS hangs happen in the kernel so a signal would not
> help.
> 
> [1]: 
> https://lists.gnu.org/archive/html/help-gnu-emacs/2015-11/msg00266.html

Go ahead and try:

import os
import signal
import subprocess

class Alarm(Exception):
   pass

def alarm_handler(signum, frame):
   raise Alarm

path = '/mnt/<nfs>'

signal.signal(signal.SIGALRM, alarm_handler)
signal.alarm(3)
try:
   proc = subprocess.call('stat ' + path,
                shell=True,
                stderr=subprocess.PIPE,
                stdout=subprocess.PIPE)
   stdoutdata, stderrdata = proc.communicate()
   signal.alarm(0)
except Alarm:
   print "Timed out after 3 seconds..."