Скачать или смотреть Resolving the infinite loop Issue with queue.get() in Python Multiprocessing

Learn why using `queue.get()` can lead to an `infinite loop` when working with Python's multiprocessing and how to effectively resolve this common issue.
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This video is based on the question https://stackoverflow.com/q/74174873/ asked by the user 'Rivered' ( https://stackoverflow.com/u/9536233/ ) and on the answer https://stackoverflow.com/a/74174922/ provided by the user 'Omer Dagry' ( https://stackoverflow.com/u/15010874/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the infinite loop Issue with queue.get() in Python Multiprocessing

When working with Python's multiprocessing module, many developers encounter a confusing situation where their program gets stuck in an infinite loop while calling queue.get() multiple times. This issue becomes particularly apparent when trying to retrieve results from multiple threads working with different queues. In this guide, we will explore the underlying problem and provide practical solutions to ensure your code runs smoothly.

Understanding the Problem

In the code snippet shared, you are attempting to run two functions concurrently using threads and a multiprocessing queue. The goal is to retrieve outputs from each function via separate queues without getting stuck on a subsequent call to queue.get().

The Code Snippet

Here is the simplified version of your initial implementation:

[[See Video to Reveal this Text or Code Snippet]]

Why Does q1.get() Cause an Infinite Loop?

Single Call to get(): The first call to print(q1.get()) retrieves the data successfully from q1. However, on the second call to print(q1.get()), there's no more data available in q1, leading to the program blocking indefinitely, waiting for new data to arrive.

Multiple Queues Confusion: You have two separate queues (q1 and q2). Since you loop only through q1, your program doesn't have the chance to retrieve data from q2. Therefore, if you're only calling q1.get(), it won't work correctly on subsequent calls.

Solutions to Resolve Infinite Loop

1. Retrieve from Both Queues Correctly

To successfully retrieve from both queues and avoid blocking, modify your retrieval logic like this:

[[See Video to Reveal this Text or Code Snippet]]

By ensuring you call both q1.get() and q2.get(), you will consume the expected data and avoid getting stuck waiting for data that won’t arrive.

2. Using a Single Queue

Alternatively, you can streamline your queues by using just one:

[[See Video to Reveal this Text or Code Snippet]]

By doing this, both results will be placed in the same queue, allowing you to call get() twice without running into an infinite loop issue.

Conclusion

Managing multiple threads and queues in Python can be tricky, especially when attempting to retrieve outputs from them. Remember to handle each queue correctly or consider consolidating your queues to prevent the infinite loop issue.

By following the solutions outlined in this post, you can streamline your code and enhance your understanding of concurrency in Python’s implementation of multiprocessing. Happy coding!