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Learn how to effectively manage child and parent processes in Python by ensuring the parent closes when the child exits using the multiprocessing module.
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How to Close Parent Process When Child Process Exits in Python Multiprocessing

When working with Python's multiprocessing module, it’s common to have multiple processes running independently. However, there might be scenarios where you want the parent process to close automatically when the child process exits. In this guide, we will explore how to achieve this in a straightforward manner.

Understanding the Problem

Let's say we have a parent process that starts multiple child processes. For instance, we might start a Flask server in one child process while a GUI interface runs in another. When the user closes the GUI window, we want the Python application to also terminate the running Flask server.

Below is a simplified version of what our initial code might look like:

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Here, p1 runs a Flask server, and p2 runs a web view. If the user closes the GUI represented by p2, we want the Flask server (p1) to also shut down.

Solution Steps

To ensure that the parent process effectively closes when any child process exits, we'll take the following steps:

Step 1: Joining the Child Process

Use the join() method on the child process. This causes the parent process to wait until the child process has finished executing. Here’s how you can do it:

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Step 2: Terminating the Other Process

After the child process has ended, you can terminate other running processes. In this case, we will terminate p1, our Flask server, using the terminate() method:

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Step 3: Putting It All Together

Here’s the complete code demonstrating how to apply these changes in practice:

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Additional Note

In some cases, if a process does not close promptly upon termination, you might need to use kill():

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Conclusion

By implementing the above steps, you ensure that your parent process will exit properly when one of its child processes closes. This approach is especially useful in applications like web servers and GUIs where resource management is crucial.

With the correct usage of join() and terminate(), you can achieve efficient process control in your Python multiprocessing programs. Happy coding!