tpool is a simple thread pool library built on top of POSIX threads.
When a task is submitted to the thread pool, the library will spawn a thread
to run the task and/or queue the task for later execution.  The number of
threads in the thread pool is dynamic but the user specifies a fixed maximum
size at startup time.

When initialized with tpool_init(), the thread pool will have 0 threads
running.  When a task is added to the pool with tpool_submit(), the pool will
spawn a thread for that task.  For subsequent tasks, if the pool has not
reached its maximum size, it will spawn a new thread; otherwise, it will
queue the task and an existing thread will take the task when it finishes a
previous task.

When a task is submitted with tpool_submit(), a pointer to a FUTURE may be
provided.  Its value will not be available until the task finishes.  The value
may be obtained via future_get(), which may block until the value is available.
After the value has been obtained, the future should be destroyed with
future_destroy().

The thread pool may be shut down with tpool_shutdown(), in which case it will
refuse any new tasks.  All running and queued tasks will run to completion.
When they have run to completion, resources used by the thread pool can be
freed with tpool_destroy().

tpool is currently maintained by:
Patrick MacArthur <[email protected]>