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import atexit
import os
import sys
from ansible.plugins.callback import CallbackBase
from ansible.utils.display import Display
from threading import Thread
# This callback plugin reliably triggers the deadlock from https://github.com/ansible/ansible-runner/issues/1164 when
# run on a TTY/PTY. It starts a thread in the controller that spews unprintable characters to stdout as fast as
# possible, while causing forked children to write directly to the inherited stdout immediately post-fork. If a fork
# occurs while the spew thread holds stdout's internal BufferedIOWriter lock, the lock will be orphaned in the child,
# and attempts to write to stdout there will hang forever.
# Any mechanism that ensures non-main threads do not hold locks before forking should allow this test to pass.
# ref: https://docs.python.org/3/library/io.html#multi-threading
# ref: https://github.com/python/cpython/blob/0547a981ae413248b21a6bb0cb62dda7d236fe45/Modules/_io/bufferedio.c#L268
class CallbackModule(CallbackBase):
CALLBACK_VERSION = 2.0
CALLBACK_NAME = 'spewstdio'
def __init__(self):
super().__init__()
self.display = Display()
if os.environ.get('SPEWSTDIO_ENABLED', '0') != '1':
self.display.warning('spewstdio test plugin loaded but disabled; set SPEWSTDIO_ENABLED=1 to enable')
return
self.display = Display()
self._keep_spewing = True
# cause the child to write directly to stdout immediately post-fork
os.register_at_fork(after_in_child=lambda: print(f"hi from forked child pid {os.getpid()}"))
# in passing cases, stop spewing when the controller is exiting to prevent fatal errors on final flush
atexit.register(self.stop_spew)
self._spew_thread = Thread(target=self.spew, daemon=True)
self._spew_thread.start()
def stop_spew(self):
self._keep_spewing = False
def spew(self):
# dump a message so we know the callback thread has started
self.display.warning("spewstdio STARTING NONPRINTING SPEW ON BACKGROUND THREAD")
while self._keep_spewing:
# dump a non-printing control character directly to stdout to avoid junking up the screen while still
# doing lots of writes and flushes.
sys.stdout.write('\x1b[K')
sys.stdout.flush()
self.display.warning("spewstdio STOPPING SPEW")
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