jaltmayerpizzorno / signal_queue

queue.SimpleQueue lookalike for use within Python signal handlers.

signal_queue

Python C++ extension that replicates (most of the) functionality from queue.SimpleQueue (available in Python 3.7+) and is safe to use within a Python signal handler.

Why it exists

I was looking for a way implement a producer-consumer queue for handling Python signals, and didn't realize queue.SimpleQueue was already reentrant.

If you attempt to use queue.Queue from within a (Python) signal handler, a deadlock is likely to result: it uses a threading.Lock and a signal may be delivered a second time after that lock has been acquired, causing it to attempt to acquire it again.

Starting a thread (to handle that signal) from a signal handler has the same issue, as starting it involves acquiring a lock or two.

signal_queue.SimpleQueue makes use of the fact that Python signal handlers are only called from within the interpreter (i.e., can't interrupt native code).

How to Use

Pretty much like you'd use Python's queue.SimpleQueue:

import threading, signal
from signal_queue import SimpleQueue

q = SimpleQueue()

def handle_signal(signum, stack):
    q.put(stack)

def handler_thread():
    while True:
        item = q.get()
        ...

...
signal.signal(signal.SIGUSR1, handle_signal)
threading.Thread(target=handler_thread, daemon=True).start()
...