wait option of
thread_create_in_pool/4 and the backlog option described
below. Options are passed to thread_create/3, except for
infinite. Otherwise it must be a non-negative integer.
Using backlog(0) will never delay thread creation for this
pool.
The pooling mechanism does not interact with the detached
state of a thread. Threads can be created both detached and
normal and must be joined using thread_join/2 if they are not
detached.