Examines the thread message queue and if necessary blocks execution
until a term that unifies to Term arrives in the queue. After
a term from the queue has been unified to Term, the term is
deleted from the queue.
Please note that non-unifying messages remain in the queue. After the
following has been executed, thread 1 has the term b(gnu)
in its queue and continues execution using A = gnat.
<thread 1>
thread_get_message(a(A)),
<thread 2>
thread_send_message(Thread_1, b(gnu)),
thread_send_message(Thread_1, a(gnat)),
Term may contain attributed variables (see section
8), in which case only terms for which the constraints successfully
execute are returned. Handle constraints applies for all predicates that
extract terms from message queues. For example, we can get the even
numbers from a queue using this code:
get_matching_messages(Queue, Pattern, [H|T]) :-
copy_term(Pattern, H),
thread_get_message(Queue, H, [timeout(0)]),
!,
get_matching_messages(Queue, Pattern, T).
get_matching_messages(_, _, []).
even_numbers(Q, List) :-
freeze(Even, Even mod 2 =:= 0),
get_matching_messages(Q, Even, List).
See also thread_peek_message/1.
