rusty_pool

Simple self growing / shrinking ThreadPool implementation based on crossbeam's multi-producer multi-consumer channels.

This ThreadPool has two different pool sizes; a core pool size filled with threads that live for as long as the channel and a max pool size which describes the maximum amount of worker threads that may live at the same time. Those additional non-core threads have a specific keep_alive time described when creating the ThreadPool that defines how long such threads may be idle for without receiving any work before giving up and terminating their work loop.

This ThreadPool does not spawn any threads until a task is submitted to it. Then it will create a new thread for each task until the core pool size is full. After that a new thread will only be created upon an execute() call if the current pool is lower than the max pool size and there are no idle threads.

When creating a new worker this ThreadPool always re-checks whether the new worker is still required before spawning a thread and passing it the submitted task in case an idle thread has opened up in the meantime or another thread has already created the worker. If the re-check failed for a core worker the pool will try creating a new non-core worker before deciding no new worker is needed. Panicking workers are always cloned and replaced.

Locks are only used for the join functions to lock the Condvar, apart from that this ThreadPool implementation fully relies on crossbeam and atomic operations. This ThreadPool decides whether it is currently idle (and should fast-return join attempts) by comparing the total worker count to the idle worker count, which are two u32 values stored in one AtomicU64 making sure that if both are updated they may be updated in a single atomic operation.

The thread pool and its crossbeam channel can be destroyed by using the shutdown function, however that does not stop tasks that are already running but will terminate the thread the next time it will try to fetch work from the channel.