Modern Python Standard Library Cookbook

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The futures executors are very similar to the worker pools provided by multiprocessing.pool, but they have some differences that might push you toward one direction or another.

The major difference is probably the way the workers are started. The pools start a fixed number of workers that are created and started all at the same time when the pool is created. So, creating the pool early moves the cost of spawning the workers at the beginning of the application. This means that the application can be quite slow to start because it might have to fork many processes according to the number of workers you requested or the number of cores your system has. Instead, the executor creates workers only when they are needed, and it's ...