Thread Pool in linux actualy means Process Pool, which use process to simulate the thead.It may be called Process Pool.

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A example (can't run oh)

In Thread Pool, there are 10 processes, each one is a linux process.

When you call the method(I assume that)

ThreadPool::CreateThread(int id_...);

This method pick up one process which are availible curently in your thread pool.
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for each call, The thread pool is response for checking if there is threadss(process) availible in your thread pool, if 10 processes are using now, This method will wait, Thread pool will allocate and deallocate all resource for your request automactilly..The algorithm is not that simple, but anyway you can do it in the simple way.