Thread pool

A sample thread pool (green boxes) with waiting tasks (blue) and completed tasks (yellow)

In computer programming, a thread pool is a software design pattern for achieving concurrency of execution in a computer program. Often also called a replicated workers or worker-crew model, a thread pool maintains multiple threads waiting for tasks to be allocated for concurrent execution by the supervising program. By maintaining a pool of threads, the model increases performance and avoids latency in execution due to frequent creation and destruction of threads for short-lived tasks. Another good property - the ability to limit system load, when we use fewer threads than available. The number of available threads is tuned to the computing resources available to the program, such as a parallel task queue after completion of execution.

The cost of having a larger thread pool is increased resource usage. The algorithm used to determine when to create or destroy threads affects the overall performance:

• Creating too many threads wastes resources and costs time creating the unused threads.
• Destroying too many threads requires more time later when creating them again.
• Creating threads too slowly might result in poor client performance (long wait times).
• Destroying threads too slowly may starve other processes of resources.

In bash implemented by --max-procs / -P in xargs, for example:

With unbuffered channels:

• "Query by Slice, Parallel Execute, and Join: A Thread Pool Pattern in Java" by Binildas C. A.
• "Thread pools and work queues" by Brian Goetz
• "A Method of Worker Thread Pooling" by Pradeep Kumar Sahu
• "Work Queue" by Uri Twig: C++ code demonstration of pooled threads executing a work queue.
• "Windows Thread Pooling and Execution Chaining"
• "Smart Thread Pool" by Ami Bar
• "Programming the Thread Pool in the .NET Framework" by David Carmona
• "Creating a Notifying Blocking Thread Pool in Java" by Amir Kirsh
• "Practical Threaded Programming with Python: Thread Pools and Queues" by Noah Gift
• "Optimizing Thread-Pool Strategies for Real-Time CORBA" by Irfan Pyarali, Marina Spivak, Douglas C. Schmidt and Ron Cytron
• "Deferred cancellation. A behavioral pattern" by Philipp Bachmann
• "A C++17 Thread Pool for High-Performance Scientific Computing" by Barak Shoshany

Gang of Four
patterns

Creational	Abstract factory Builder Factory method Prototype Singleton
Structural	Adapter Bridge Composite Decorator Facade Flyweight Proxy
Behavioral	Chain of responsibility Command Interpreter Iterator Mediator Memento Observer State Strategy Template method Visitor

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