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Asked: 2026-06-13T08:44:49+00:00

Im using a thread pool to execute tasks , that are mostly cpu based

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Im using a thread pool to execute tasks , that are mostly cpu based with a bit of I/O,
of size one larger than the number of cpus.

Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors() + 1)

Assuming case of simple program that submits all its tasks to this executor and does little else I assume having a thread pool any larger would slow things because the OS would have to timeslice it cpus more often chance to give each thread in the threadpool a chance to run.

Is that correct, and if so is this a real problem or mostly theoretical, i.e if I increased threadpool size to 1000 would I notice a massive difference.

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1 Answer

  1. Editorial Team

    If you have CPU bound tasks, as you increase the number of threads you get increasing overhead and slower performances. Note: having more threads than waiting tasks is just a waste of resources, but may not slow down the tasks so much.

    I would use a multiple (e.g. 1 or 2) of the number of cpus rather than adding just one as having one too many threads can have a surprising amount of overhead.

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