Module Mode

Jan Burse, created Aug 15. 2016

* The programming interface allows mode changes from a secondary
* thread. The secondary thread acts as a controller of the primary
* thread. By changing the mode it controls the behav-iour of the
* primary thread. A typical example of a secondary thread is the
* user interface event thread. The primary threads are then the
* console window Prolog threads. The secondary thread can then
* for example start tracing a console window Prolog thread by
* changing into an appropriate mode.
* The normal flow allows that mode changes can happen at any
* time. Their effect is also not delimited to the call port of
* a predicate or to an interrupted blocking operation. This is
* not very problematic except when inside a trace handler. A mode
* change might cause an undesired invocation of the trace handler.
* The system predicate sys_ignore/1 allows calling a goal with
* the mode cloak mask temporarily set off.
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:- use_package(foreign(jekdev/reference/system)).
:- module(user, []).
* sys_ignore(A):
* The predicate succeeds whenever A succeeds. The goal A is invoked
* with the mode cloak temporarily set to off.
% sys_ignore(+Goal)
:- public sys_ignore/1.
:- meta_predicate sys_ignore(0).
:- special(sys_ignore/1, 'SpecialMode', 0).
:- set_predicate_property(sys_ignore/1, sys_notrace).
% The instrumentation hooks
:- public sys_in/0.
:- static sys_in/0.
:- set_predicate_property(sys_in/0, sys_noinstrument).
:- set_predicate_property(sys_in/0, sys_nowakeup).
:- set_predicate_property(sys_in/0, sys_nostack).
sys_port(fail), fail.
:- set_predicate_property(sys_in/0, sys_notrace).
:- public sys_out/0.
:- static sys_out/0.
:- set_predicate_property(sys_out/0, sys_noinstrument).
:- set_predicate_property(sys_out/0, sys_nowakeup).
:- set_predicate_property(sys_out/0, sys_nostack).
sys_port(redo), fail.
:- set_predicate_property(sys_out/0, sys_notrace).
:- public sys_at/0.
:- static sys_at/0.
:- set_predicate_property(sys_at/0, sys_noinstrument).
:- set_predicate_property(sys_at/0, sys_nowakeup).
:- set_predicate_property(sys_at/0, sys_nostack).
sys_port(chop), fail.
:- set_predicate_property(sys_at/0, sys_notrace).
:- private sys_port/1.
:- special(sys_port/1, 'SpecialMode', 1).