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Joining Threads: Threads created using linda_eval/(1-2) are not allowed to linger. They are joined (blocking the parent, if necessary) under three conditions: backtracking on failure into an linda_eval/(1-2), receipt of an uncaught exception, and cut of choice-points. Goals are evaluated using forall/2. They are expected to provide nondeterministic behavior. That is they may succeed zero or more times on backtracking. They must however, eventually fail or succeed deterministically. Otherwise, the thread will hang, which will eventually hang the parent thread. Cutting choice points in the parent's body has the effect of joining all children created by the parent. This provides a barrier that guarantees that all child instances of Goal have run to completion before the parent proceeds. Detached threads behave as above, except that they operate independently and cannot be joined. They will continue to run while the host process continues to run.
Here is an example of a parallel quicksort:
qksort(, ). qksort([X | List], Sorted) :- partition(@>(X), List, Less, More), linda_eval(qksort(More, SortedMore)), qksort(Less, SortedLess), !, in_noblock(qksort(More, SortedMore)), append(SortedLess, [X | SortedMore], Sorted).