Multiprocessing: True Parallelism in Python

Learning Objectives: After this lesson, you'll understand how to bypass the GIL with multiprocessing, use process pools efficiently, manage shared state safely, and implement inter-process communication patterns.

Why Multiprocessing?

Multiprocessing creates separate Python processes, each with its own GIL, enabling true parallelism.

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Multiprocessing vs Threading

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Basic Process Creation

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Process Pools

Process pools manage a fixed number of worker processes for efficient task distribution.

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Using Pool

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Pool Methods

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Shared State and Communication

Processes don't share memory by default. Here's how to share data.

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Shared Memory Values

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Manager for Complex Shared Objects

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Queues for Communication

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Pipes for Two-Way Communication

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Practical Patterns

Map-Reduce Pattern

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Parallel Pipeline

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Worker Pool with Callbacks

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Best Practices

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Key Takeaways

ConceptDescription
ProcessSeparate Python interpreter, own GIL
PoolReusable worker processes
ProcessPoolExecutorModern, clean pool interface
Value/ArrayShared memory primitives
ManagerShared complex objects (dict, list)
QueueThread/process-safe communication
PipeTwo-way process communication

Multiprocessing vs Alternatives

ScenarioBest Choice
CPU-heavy calculationMultiprocessing
Network I/OThreading or asyncio
File I/OThreading
Many small tasksPool with chunksize
Large shared dataSharedMemory (Python 3.8+)
NumPy operationsNumPy (already parallel)

Next Steps

In the next lesson, we'll explore Async/Await Fundamentals—understand event loops, write coroutines, use asyncio for concurrent I/O, and build async patterns for production code.


Ready for non-blocking Python? Async/await awaits!