LIMITED-THREAD-TASKMASTER is a simple HUNCHENTOOT:TASKMASTER subclass
that limits the number of worker threads.

Hunchentoot's default TASKMASTER creates a new thread each time a
request comes in, and destroys that thread as soon as it's finished
serving the request. LIMITED-THEAD-TASKMASTER allows you to set a
limit to the total number of threads created, and leaves them running
to serve requests faster. If a request comes in when all the worker
threads are busy, it will be queued until one of the workers can serve
it.

Exported symbols:

LIMITED-THREAD-TASKMASTER
Subclass of HUNCHENTOOT:TASKMASTER
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Use an instance of this class as the :TASKMASTER initarg for a
HUNCHENTOOT:ACCEPTOR to get limited threads.

LIMITED-THREAD-ACCEPTOR
Subclass of HUNCHENTOOT:ACCEPTOR
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Pass an instance of this class, or a subclass, to HUNCHENTOOT:START to
get limited threads. E.g.

  (hunchentoot:start
    (make-instance 'limited-thread-taskmaster:limited-thread-acceptor
                   :port 8080))

LIMITED-THREAD-SSL-ACCEPTOR
Subclass of HUNCHENTOOT:SSL-ACCEPTOR
-----
Same as LIMITED-THREAD-ACCEPTOR but based on HUNCHENTOOT:SSL-ACCEPTOR
instead of HUNCHENTOOT:ACCEPTOR.

LIMITED-THREAD-LIMIT ()
Function
-----
Return the maximum number of threads that will be created to serve
all the LIMITED-THREAD-TASKMASTER instances. All limited thread
acceptors share on process pool.

(SETF LIMITED-THREAD-LIMIT) (limit)
Function
-----
Set the maximum number of threads that will be created to serve all
LIMITED-THREAD-TASKMASTER instances. This affects current and future
instances.