Title here
Summary here
Closing Channels in Python
In this example, we'll use a `jobs` queue to communicate work to be done from the main thread to a worker thread. When we have no more jobs for the worker, we'll signal the end of jobs using a sentinel value.
```python
import queue
import threading
import time
def main():
jobs = queue.Queue(maxsize=5)
done = threading.Event()
# Here's the worker thread. It repeatedly receives from
# `jobs`. We use a sentinel value (None) to indicate that
# no more jobs will be sent. When the sentinel is received,
# we set the `done` event to notify that all jobs have been processed.
def worker():
while True:
job = jobs.get()
if job is None:
print("received all jobs")
done.set()
return
print(f"received job {job}")
jobs.task_done()
# Start the worker thread
threading.Thread(target=worker, daemon=True).start()
# This sends 3 jobs to the worker over the `jobs` queue,
# then sends the sentinel value.
for j in range(1, 4):
jobs.put(j)
print(f"sent job {j}")
jobs.put(None)
print("sent all jobs")
# We wait for the worker using the `done` event.
done.wait()
# Trying to get from an empty queue will raise queue.Empty
# exception. We can use this to check if the queue is empty.
try:
job = jobs.get_nowait()
print("received more jobs:", job is not None)
except queue.Empty:
print("received more jobs: False")
if __name__ == "__main__":
main()When you run this program, you should see output similar to this:
$ python closing_channels.py
sent job 1
received job 1
sent job 2
received job 2
sent job 3
received job 3
sent all jobs
received all jobs
received more jobs: FalseIn this Python version, we’ve used a queue.Queue to represent the channel, and a threading.Event for synchronization. The None value acts as a sentinel to indicate the end of jobs, similar to closing a channel in the original example.
The worker function runs in a separate thread and processes jobs until it receives the sentinel value. The main thread sends jobs and waits for the worker to complete using the done event.
Finally, we attempt to get another job from the queue to check if it’s empty, which is analogous to reading from a closed channel in the original example.
This approach demonstrates how to implement a similar pattern of job processing and signaling completion in Python, even though Python doesn’t have built-in concepts directly equivalent to Go’s channels and goroutines.