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import logging | |
from logging import handlers | |
import os | |
import random | |
import threading | |
import time | |
script_dir = os.path.dirname(os.path.realpath(__file__)) | |
log_filename = os.path.join(script_dir, "test.log") | |
handler = handlers.TimedRotatingFileHandler( | |
filename=log_filename, when="midnight", utc=True | |
) | |
logging.basicConfig( | |
level=logging.INFO, | |
format="%(levelname)-8s [%(asctime)s] %(threadName)-16s: %(message)s", | |
#handlers=[handler], | |
) | |
logger = logging.getLogger(__name__) | |
global_number = 1 | |
def worker(condition): | |
while True: | |
with condition: | |
logger.debug("acquired condition lock") | |
#while global_number != 10: | |
if global_number != 10: # <--- incorrect! | |
logger.info("the number is not 10, will wait for condition") | |
condition.wait() | |
#condition.wait_for(lambda: global_number == 10) # <--- alternative | |
logger.info(f"I see the number {global_number}") | |
logger.debug("releasing condition lock") | |
time.sleep(1) | |
def number_changer(condition): | |
global global_number | |
while True: | |
with condition: | |
logger.debug("acquired condition lock") | |
new_number = random.randint(1, 10) | |
logger.info(f"Changing number from {global_number:>2} to {new_number:>2}") | |
global_number = new_number | |
if new_number == 10: | |
logger.info("New number == 10, notifying others") | |
condition.notify_all() | |
logger.debug("releasing condition lock") | |
time.sleep(1) | |
def main(): | |
logger.info("main() started") | |
number_eq_10 = threading.Condition() | |
worker_thread = threading.Thread( | |
name="Thread-Worker", | |
target=worker, | |
args=(number_eq_10,), | |
daemon=True, | |
) | |
changer_threads = [ | |
threading.Thread( | |
name=f"Thread-Changer-{i}", | |
target=number_changer, | |
args=(number_eq_10,), | |
daemon=True, | |
) | |
for i in range(5) | |
] | |
worker_thread.start() | |
for t in changer_threads: | |
t.start() | |
while True: | |
try: | |
time.sleep(60) | |
except KeyboardInterrupt: | |
logger.info("Main thread exiting") | |
break | |
_ | |
if __name__ == "__main__": | |
main() |
Excellent code+explanation. Took me a while but I get it now. Thank you!
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@anguillanneuf The expected behavior is that the worker thread always prints out "I see the number 10" (the desired condition), and never "I see <N != 10 >". In other words, it should only proceed when the condition
number == 10
is fulfilled.In the
bidi.py
case, this would translate toBackgroundConsumer
always resuming whenself._paused == False
, and never resuming whenself._paused == True
is set by another thread.FWIW, if the number is set to 10, another thread might still quickly change it to something else, i.e. before the worker sees it. That will cause the worker to keep waiting (if using
while
), which is fine. We want the worker to only proceed when the conditionnumber == 10
definitely holds.