Thread_poolA thread pool is a set of OCaml threads used to do work, where each piece of work is simply a thunk. One creates a thread pool, and then uses add_work to submit work to it. Work is done first-come-first-served by available threads in the pool. Any of the available threads in the pool could be used to do work submitted to the pool (except helper threads, see below).
Thread_safe_pipeA thread-safe pipe is a thread-safe interface to the write end of a normal Async.Pipe. All operations except for create must be called from threads outside Async, while create can be called from inside or outside Async.