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1992-09-01
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184 lines
----------------------------------------------------------------------
--
-- The Dining Philosophers' Problem
--
-- written by
--
-- Edmond Schonberg
-- and
-- Gerry Fisher
--
-- Ada Project
-- Courant Institute
-- New York University
-- 251 Mercer Street
-- New York, New York 10012
--
-----------------------------------------------------------------------
with TEXT_IO; use TEXT_IO;
procedure DINING_PHILOSOPHERS is
type PHILOSOPHER is (Descartes, Hegel, Turing, Plato, Sartre);
meals: constant array(PHILOSOPHER) of INTEGER := (3,2,2,2,3);
Message1: constant array(PHILOSOPHER) of STRING(1 .. 30) :=
("I eat: therefore I am ",
"Hegel synthesizes ",
"Turing shifts ",
"Plato eats the ideal spaghetti",
"Sartre gorges "
);
Message2: constant array(PHILOSOPHER) of STRING(1 .. 30) :=
("Descartes cogitates ",
"Hegel's pure spirit at work ",
"Turing machinates ",
"Plato watches the shadows ",
"Sartre eats nothing "
);
Message3: constant array(PHILOSOPHER) of STRING(1 .. 30) :=
("Descartes concludes ",
"The owl of Minerva is stuffed ",
"Turing halts ",
"Plato retreats ",
"Sartre is nauseated "
);
task type DINING is
entry WHO_AM_I(p: PHILOSOPHER);
end DINING;
task TABLE_MANAGER is
entry EAT(PHILOSOPHER);
entry REST(p: PHILOSOPHER);
entry FAST_RELIEF(p: PHILOSOPHER);
end TABLE_MANAGER;
task body DINING is separate;
task body TABLE_MANAGER is separate;
begin
declare
PHILS: array(PHILOSOPHER) of DINING;
begin
for philo in PHILOSOPHER
loop
PHILS(philo).WHO_AM_I(philo);
end loop;
end;
put_line("Closing time ...");
end DINING_PHILOSOPHERS;
-----------------------------------------------------------------------
separate(DINING_PHILOSOPHERS)
task body DINING is
philo: PHILOSOPHER;
begin
accept WHO_AM_I(p: PHILOSOPHER) do
philo := p;
end WHO_AM_I;
for n in 1 .. meals(philo)
loop
TABLE_MANAGER.EAT(philo);
delay 1.0;
TABLE_MANAGER.REST(philo);
delay 0.5;
end loop;
TABLE_MANAGER.FAST_RELIEF(philo);
end DINING;
------------------------------------------------------------------------
separate(DINING_PHILOSOPHERS)
task body TABLE_MANAGER is
type AVAIL is
record
LEFT, RIGHT: BOOLEAN;
end record;
FORKS: array(PHILOSOPHER) of AVAIL :=
(PHILOSOPHER'FIRST..PHILOSOPHER'LAST => (TRUE, TRUE));
type ACTION is (seize,release);
numphil: constant INTEGER := 5;
TWO: constant AVAIL := (TRUE,TRUE);
procedure fork_action(p: PHILOSOPHER; a: ACTION) is separate;
begin
loop
select
when FORKS(Descartes) = TWO =>
accept EAT(Descartes);
fork_action(Descartes, seize);
put_line(Message1(Descartes));
or when FORKS(Hegel) = TWO =>
accept EAT(Hegel);
fork_action(Hegel, seize);
put_line(Message1(Hegel));
or when FORKS(Turing) = TWO =>
accept EAT(Turing);
fork_action(Turing, seize);
put_line(Message1(Turing));
or when FORKS(Plato) = TWO =>
accept EAT(Plato);
fork_action(Plato, seize);
put_line(Message1(Plato));
or when FORKS(Sartre) = TWO =>
accept EAT(Sartre);
fork_action(Sartre, seize);
put_line(Message1(Sartre));
or
accept REST(p: PHILOSOPHER) do
fork_action(p, release);
put_line(Message2(p));
end REST;
or
accept FAST_RELIEF(p: PHILOSOPHER) do
put_line(Message3(p));
end FAST_RELIEF;
or
terminate;
end select ;
end loop ;
end TABLE_MANAGER ;
----------------------------------------------------------------------
separate(DINING_PHILOSOPHERS.TABLE_MANAGER)
procedure fork_action(p: PHILOSOPHER; a: ACTION) is
pp: PHILOSOPHER;
v: array(ACTION) of BOOLEAN := (FALSE, TRUE);
begin
pp := PHILOSOPHER'VAL((PHILOSOPHER'POS(p) + 1) mod numphil);
FORKS(pp).LEFT := v(a);
pp := PHILOSOPHER'VAL((PHILOSOPHER'POS(p) + 4) mod numphil);
FORKS(pp).RIGHT := v(a);
end fork_action;