New submission from Manoj C <>:

I have been using asyncio to run subprocess calls in a separate thread. For 
this purpose I start an event loop in my main thread as per the recommendation 

Now when I use a normal subprocess call in the main thread, I start getting 
following file descriptor error after few iterations:

Exception ignored when trying to write to the signal wakeup fd:
BlockingIOError: [Errno 11] Resource temporarily unavailable

I have reproduced the problem in a small script and am seeing that the error 
goes away if I do not start the even loop in the main thread.

import asyncio
import subprocess
import time

def try_error():
    for i in range(1,500):
  ["ls", "-l"], check=True, stdout=subprocess.PIPE, 
        except subprocess.CalledProcessError as e:
            print(f"Exception raised {e.stderr}\nOutput {e.stdout}")

def definite_error():
    w = asyncio.get_child_watcher()
    l = asyncio.get_event_loop()

if __name__ == "__main__":

This is the smallest subset of the code which can reproduce the error. In the 
original code, I run a asyncio.create_subprocess_exec in a parallel thread. The 
normal subprocess call is part of third party code which call from the main 
thread and hence cannot modify it.

components: asyncio
messages: 351795
nosy: Manoj C, asvetlov, yselivanov
priority: normal
severity: normal
status: open
title: File descriptor error when subprocess call is used with event loop 
enabled in main thread
type: crash
versions: Python 3.6

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