class Concurrent::FixedThreadPool

@!macro fixed_thread_pool

A thread pool that reuses a fixed number of threads operating off an unbounded queue.
At any point, at most `num_threads` will be active processing tasks. When all threads are busy new
tasks `#post` to the thread pool are enqueued until a thread becomes available.
Should a thread crash for any reason the thread will immediately be removed
from the pool and replaced.

The API and behavior of this class are based on Java's `FixedThreadPool`

@!macro thread_pool_options