multiprocessing.
Understanding the Concept
multiprocessing.Process starts a separate process to run a picklable top-level function. Guard worker-launching code with if __name__ == "__main__" for portability.
Process.join waits for termination; avoid long blocks without a shutdown strategy.
How to reason about concurrent execution
Workers may start and finish in a different order on every run. Focus on ownership of data, how work and errors move between workers, and what happens when one worker stops early. Locks protect invariants, queues exchange messages, and explicit shutdown logic prevents blocked or orphaned workers.
Concurrency adds overhead and failure modes. Begin with a working sequential solution, choose bounded worker counts and explicit timeouts, then measure whether overlap or parallel execution improves the target workload.
Worked Example
Read the code from the first line to the last. Identify which values are inputs, which operation is being demonstrated and what should happen before running it.
from multiprocessing import Process
def worker():
print("Child process finished")
if __name__ == "__main__":
process = Process(target=worker)
process.start()
process.join(timeout=3)
print("Exit code:", process.exitcode)Walkthrough: What Each Part Does
- The imports make multiprocessing available. These are standard-library building blocks unless the example explicitly names an external tool.
- The definition worker creates reusable behavior. Its body runs when called, awaited or instantiated; defining it alone does not run the body of an ordinary function.
- The coordination call waits for a result or a completion condition. Predict what would happen if the worker failed or never became ready.
- The last lines coordinate completion and inspect results. Actual worker scheduling may differ between executions.
This demonstration focuses on one practical behavior. Before changing several lines, vary one input or one configuration choice and check whether the result changes for the reason you expected.
The example uses terminal, platform, external tool or process behavior that was not exercised automatically. Run it only in a suitable environment after reviewing the shown permissions and paths.
Important Behavior and Edge Cases
Creating processes at import time under spawn, which can recursively launch new workers.
Process.join waits for termination; avoid long blocks without a shutdown strategy.
Practice Exercise
Save and run this script, then change worker to raise an exception and inspect exitcode.
Write down the result you expect before running your changed code. Check at least one normal case and one boundary or failure case. If your example starts workers or opens resources, verify how they are cleaned up.
Further reading: official documentation and API reference.
Common Beginner Mistakes
- Creating processes at import time under spawn, which can recursively launch new workers.
- Forgetting to handle worker errors and shutdown, even when the normal completion path appears correct.
Key Takeaways
- multiprocessing.
- Process.join waits for termination; avoid long blocks without a shutdown strategy.
- Practice: Save and run this script, then change worker to raise an exception and inspect exitcode.