truly fork, sort of

2019-08-18 10:53:25 -07:00
parent 11fdc81409
commit 2057d9ee74
4 changed files with 43 additions and 3 deletions
@@ -0,0 +1,41 @@
+:- multifile(func/3).
+
+func(fork, [F, G|S], [X, Y|S]) :-
+    fork(F, S, X, ChildPID),
+    thun(G, S, [Y|_]),
+    wait(ChildPID, Status).  % FIXME check status!!!
+
+fork(Expr, Stack, Result, ChildPID) :-
+    mkpipe(In, Out),
+    fork_prolog(ChildPID),
+    bar(ChildPID, In, Out, Expr, Stack, Result).
+
+bar(0, In, Out, Expr, Stack, Result) :-
+    close(In),
+    thun(Expr, Stack, [Result|_]),
+    w(Out, Result),
+    close(Out),
+    halt.
+
+bar(P, In, Out, Expr, Stack, Result) :-
+    integer(P), P =\= 0,
+    close(Out),
+    select([In], R, [], _, 1500),
+    (R=[In] ->
+        read(In, Result)
+    ;
+        Result=timeout
+    ),
+    close(In).
+
+mkpipe(In, Out) :-
+    create_pipe(In, Out),
+    set_stream_buffering(Out, none),
+    set_stream_buffering(In, none).
+
+w(Out, Term) :-          % To get a term written out and recognized,
+    write(Out, Term),    % you write it to the stream
+    put_code(Out, 0'.),  % add a period at the end
+    nl(Out),             % and a newline even if you set buffering
+    flush_output(Out).   % to none, then flush for good measure.
+