Скачать или смотреть How to Terminate a Thread Subprocess Call and Exit in Python?

Learn the best practices to `terminate subprocesses and threads` in Python, ensuring smooth execution and proper cleanup.
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This video is based on the question https://stackoverflow.com/q/67150716/ asked by the user 'user3243499' ( https://stackoverflow.com/u/3243499/ ) and on the answer https://stackoverflow.com/a/67197263/ provided by the user 'Booboo' ( https://stackoverflow.com/u/2823719/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

If you're working with Python’s threading module alongside subprocess management, you may encounter a common challenge: how to effectively terminate a thread that runs a subprocess. This issue often arises when a subprocess must run continuously, collecting logs or executing commands until a certain condition is met externally. In this post, we’ll explore the best way to handle thread termination and subprocess cleanup in Python, ensuring that your program behaves as intended without getting stuck.

The Problem

Let's consider a scenario where you have a thread that runs a subprocess to execute a continuous command, like so:

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

The above implementation often leads to a hang because myclass.proc.kill() is called without proper synchronization or signaling—especially if the subprocess is waiting for input or output.

The Solution

The solution to this problem lies in implementing a thread-safe mechanism using threading.Event. This approach will allow the thread to listen for a kill signal while ensuring the subprocess can be terminated gracefully. Let’s break down the steps:

Step 1: Use threading.Event

The threading.Event object can act as a signal between the main thread and the worker thread. If the event is set, the thread will proceed to kill the subprocess.

Step 2: Modify Your Thread Class

With this in mind, here's how you can rewrite your thread class:

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

Breakdown of the Code

Subprocess Management: The subprocess runs an infinite loop with a command (here replaced with echo hello) until it is explicitly killed.

Event Handling: By calling self.evt.wait(), the thread will pause until the event is set, thus allowing for a flexible and responsive design.

Killing the Subprocess: When evt.set() is called from the main thread after a specified wait time (in this case, 5 seconds), the event triggers and the subprocess is terminated seamlessly.

Output Management: Finally, the standard output from the subprocess is captured and printed, allowing you to see what was generated during its execution.

Conclusion

Managing threads and subprocesses can be tricky, especially when it comes to cleanup and termination. However, by utilizing threading.Event, we can create a clean and efficient way to signal when to stop a running subprocess in a thread without encountering deadlocks. This pattern ensures your application remains responsive and handles background tasks as expected.

Now you have the tools to control your threading and subprocesses effectively without running into hang-ups. Implement these strategies in your Python applications to ensure they operate smoothly.