1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2002-2018, University of Amsterdam
    7                              CWI, Amsterdam
    8    All rights reserved.
    9
   10    Redistribution and use in source and binary forms, with or without
   11    modification, are permitted provided that the following conditions
   12    are met:
   13
   14    1. Redistributions of source code must retain the above copyright
   15       notice, this list of conditions and the following disclaimer.
   16
   17    2. Redistributions in binary form must reproduce the above copyright
   18       notice, this list of conditions and the following disclaimer in
   19       the documentation and/or other materials provided with the
   20       distribution.
   21
   22    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   24    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   25    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   26    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   27    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   28    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   29    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   30    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   31    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   32    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   33    POSSIBILITY OF SUCH DAMAGE.
   34*/
   35
   36:- module(stream_pool,
   37          [ add_stream_to_pool/2,       % +Stream, :Goal
   38            delete_stream_from_pool/1,  % +Stream
   39            close_stream_pool/0,
   40            dispatch_stream_pool/1,     % +TimeOut
   41            stream_pool_main_loop/0
   42          ]).   43:- use_module(library(debug),[debug/3]).   44
   45:- meta_predicate
   46    add_stream_to_pool(+, 0).   47
   48:- volatile
   49    pool/2.                         % sockets don't survive a saved-state
   50:- dynamic
   51    pool/2.                         % Stream, Action

 add_stream_to_pool(+Stream:Goal)

Call Goal whenever there is input on Stream.

   67add_stream_to_pool(Stream, Action) :-
   68    strip_module(Action, Module, Plain),
   69    register_stream(Stream, Module:Plain).
   70
   71register_stream(Stream, Goal) :-
   72    assert(pool(Stream, Goal)).

 delete_stream_from_pool(+Stream)

Retract stream from the pool

   78delete_stream_from_pool(Stream) :-
   79    retractall(pool(Stream, _)).

 close_stream_pool

Close all streams in the pool. This causes stream_pool_main_loop/0 to terminate.

   86close_stream_pool :-
   87    forall(retract(pool(Stream, _)),
   88           close(Stream, [force(true)])).

 dispatch_stream_pool(+TimeOut)

Wait for input on one or more streams and handle that. Wait for at most TimeOut seconds (0 means infinite).

   95dispatch_stream_pool(Timeout) :-
   96    findall(S, pool(S, _), Pool),
   97    debug(tcp, 'Select ~p ...', [Pool]),
   98    catch(wait_for_input(Pool, Ready, Timeout), E, true),
   99    debug(tcp, '    --> ~p (E=~p)', [Ready, E]),
  100    (   var(E)
  101    ->  actions(Ready)
  102    ;   E = error(existence_error(stream, Stream), _)
  103    ->  delete_stream_from_pool(Stream)
  104    ).
  105
  106actions([]).
  107actions([H|T]) :-
  108    action(H),
  109    actions(T).
  110
  111action(Stream) :-
  112    pool(Stream, Action),
  113    (   catch(Action, E, true)
  114    ->  (   var(E)
  115        ->  true
  116        ;   print_message(error, E)
  117        )
  118    ;   print_message(warning,
  119                      goal_failed(Action, stream_pool))
  120    ).

 stream_pool_main_loop

Keep handling input from the streams in the pool until they have all died away.

  127stream_pool_main_loop :-
  128    pool(_, _),
  129    !,
  130    (   current_prolog_flag(windows, true)
  131    ->  dispatch_stream_pool(1)     % so we can break out easily
  132    ;   dispatch_stream_pool(0)
  133    ),
  134    stream_pool_main_loop.
  135stream_pool_main_loop