A test script to demonstrate that Twisted was locking up after 30k file deletions

test.py

import sys

from twisted.internet import inotify, reactor, threads
from twisted.python import filepath

# Resources:
#  Introduction to Deferreds:
#    http://twisted.readthedocs.io/en/twisted-16.1.1/core/howto/defer-intro.html
#  Returning Deferreds from synchronous functions:
#    https://twistedmatrix.com/documents/current/core/howto/gendefer.html#returning-deferreds-from-synchronous-functions
#  addCallbacks Docs:
#    https://twistedmatrix.com/documents/16.1.1/api/twisted.internet.defer.Deferred.html#addCallbacks
#  filepath Docs:
#    http://twistedmatrix.com/documents/current/api/twisted.python.filepath.FilePath.html


def file_delete(filepath):
    """
    Some slow deletion that should be run in a separate thread.
    """
    filepath.remove()

def errback(failure):
    print("Failure", failure.getErrorMessage())


def new_file_handler(_, filepath, mask):
    """
    For historical reasons, an opaque handle is passed as first
    parameter. This object should never be used.

    @param filepath: FilePath on which the event happened.
    @param mask: inotify event as hexadecimal masks
    """

    if (mask & inotify.IN_Q_OVERFLOW):
        sys.exit(1)

    d = threads.deferToThread(file_delete, filepath)
    print("Scheduling callback for %s" % filepath.path)
    d.addErrback(errback)


notifier = inotify.INotify()
notifier.startReading()
notifier.watch(filepath.FilePath('/tmp/bar'), mask=inotify.IN_MODIFY, callbacks=[new_file_handler])

print("Starting watcher...")
reactor.run()

# To create 10k test files:
# $ dd if=/dev/zero of=../masterfile bs=1 count=1000000 && split -b 100 -a 10 /tmp/masterfile