3.14.2 Multi-threaded Prolog
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Availability::- use_module(library(http/thread_httpd)).
Sourcehttp_spawn(:Goal, +Spec)
Continue handling this request in a new thread running Goal. After http_spawn/2, the worker returns to the pool to process new requests. In its simplest form, Spec is the name of a thread pool as defined by thread_pool_create/3. Alternatively it is an option list, whose options are passed to thread_create_in_pool/4 if Spec contains pool(Pool) or to thread_create/3 of the pool option is not present. If the dispatch module is used (see section 3.2), spawning is normally specified as an option to the http_handler/3 registration.

We recomment the use of thread pools. They allow registration of a set of threads using common characteristics, specify how many can be active and what to do if all threads are active. A typical application may define a small pool of threads with large stacks for computation intensive tasks, and a large pool of threads with small stacks to serve media. The declaration could be the one below, allowing for max 3 concurrent solvers and a maximum backlog of 5 and 30 tasks creating image thumbnails. 

:- use_module(library(thread_pool)).

:- thread_pool_create(compute, 3,
                      [ local(20000), global(100000), trail(50000),
                        backlog(5)
                      ]).
:- thread_pool_create(media, 30,
                      [ local(100), global(100), trail(100),
                        backlog(100)
                      ]).

:- http_handler('/solve',     solve,     [spawn(compute)]).
:- http_handler('/thumbnail', thumbnail, [spawn(media)]).