http_spawn/2

Documentation
- Reference manual
- Packages
  - SWI-Prolog HTTP support
    - The HTTP server libraries
      - Running the server
        
        Multi-threaded Prolog
        
        http_server/2
        
        http_server_property/2
        
        http_workers/2
        
        http_add_worker/2
        
        http_stop_server/2
        
        http_current_worker/2
        
        http_spawn/2

Availability::- use_module(library(http/thread_httpd)).

http_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)]).