The Dining Philosophers . . .
The Dining Philosophers problem is a classic multi-process
synchronization problem. The problem consists of five philosophers
sitting at a table who do nothing but think and eat. Between each
philosopher, there is a single stick. In order to eat, a philosopher
must have both sticks. A problem can arise if each philosopher grabs
the stick on the right, then waits for the stick on the left. In this
case a deadlock has occurred, and all philosophers will starve. Also,
the philosophers should be fair. Each philosopher should be able to
eat as much as the rest.
. . . click on the blue bullets to change program parameters.
The first four control the sound track(the last one makes them shut
up). The three slide bars control the speed, thinking time, and
The algorithm . . .
Initially, all philosophers are thinking. As they think, their eyes
randomly(direction probability determined by the slider) move around.
If a philosopher's eyes do a complete counter-clock wise circle, it
will become hungry and its eyebrows will bow in. The philosopher will
then wait for one stick, then the other. To prevent deadlocks, one of
the sticks is marked. If a philosopher picks up the marked stick, it
must put it back down and try the other stick. When this happens, the
philosopher will raise its right eyebrow. Once the philosopher has
both sticks, it will begin eating. After each bite, there is a chance
(controlled by the slider) that the philosopher will start thinking
again. The philosopher will then swap the sticks in its hands and
return them. This is done so that the marked stick will not remain in
the same place.
The secrets of the implementation . . .
Each philosopher is its own thread. There is an additonal thread that
is used to control the repainting. Each stick is represented by an
instance of a class. When a philosopher wishes to pick up or drop a
stick, it will make a call to the appropriate stick. To ensure that
two philosophers do not simultaneously grab the same stick, a
synchronized method is used. The images were ray-traced
using povray2.3. The new state of each philosopher is re-painted on top of
the old one.
The source of it all . . .
This example was taken from the book: Hooked on Java by Arthur van Hoff, Sami Shaio and Orca Starbuck. (See also the Java homepage!)