How to Gracefully Handle Keyboard Interrupts in Python\'s Multiprocessing Pools?

Handling Keyboard Interrupts in Python's Multiprocessing Pools

When attempting to manage KeyboardInterrupt events within Python's multiprocessing Pools, users often encounter issues with the process hanging and requiring external termination. This article aims to address this problem and provide a workable solution.

To elaborate on the challenge introduced in the question, the provided code intends to gracefully terminate all processes within a Pool upon receiving a KeyboardInterrupt signal (by pressing ^C). However, as observed, the KeyboardInterrupt triggers a pause in the execution, preventing the intended termination procedure from taking effect.

This is attributed to a Python bug that hinders the delivery of KeyboardInterrupt signals to threading.Condition.wait() conditions. This issue arises due to wait() not returning unless a timeout is specified. Consequently, KeyboardInterrupts are not received during this process.

To overcome this challenge, the suggested solution involves introducing a time limit to the wait() condition:

<code class="python">results = pool.map_async(slowly_square, range(40)).get(9999999)</code>

By incorporating this timeout, the wait() condition is forced to respond to KeyboardInterrupt signals promptly, allowing for graceful termination of all processes within the Pool.

Therefore, this modification provides a robust approach to managing KeyboardInterrupts in Python's multiprocessing Pools, enabling users to effectively halt all processes in a controlled manner at any given time.

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