# Dining Philosophers Problem

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## Dining Philosophers Problem

(parallel)
(DPP) A problem introduced by Dijkstra concerning resource allocation between processes. The DPP is a model and universal method for testing and comparing theories on resource allocation. Dijkstra hoped to use it to help create a layered operating system, by creating a machine which could be consider to be an entirely deterministic automaton.

The problem consists of a finite set of processes which share a finite set of resources, each of which can be used by only one process at a time, thus leading to potential deadlock.

The DPP visualises this as a number of philosophers sitting round a dining table with a fork between each adjacent pair. Each philosopher may arbitrarily decide to use either the fork to his left or the one to his right but each fork may only be used by one philosopher at a time.

Several potential solutions have been considered.

Semaphores - a simple, but unfair solution where each resources is a binary semaphore and additional semaphores are used to avoid deadlock and/or starvation.

Critical Regions - each processor is protected from interference while it exclusively uses a resource.

Monitors - the process waits until all required resources are available then grabs all of them for use.

The best solution allows the maximum parallelism for any number of processes (philosophers), by using an array to track the process' current state (i.e. hungry, eating, thinking). This solution maintains an array of semaphores, so hungry philosophers trying to acquire resources can block if the needed forks are busy.
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In particular, we illustrate MP-synthesis by applying it to the K-process mutual exclusion problem, the K-process dining philosophers problem, and the K-process drinking philosophers problem [Chandy and Misra 1984; Chandy and Misra 1988] for arbitrarily large finite K.
One thousand dining philosophers arranged in a ring:
These examples generalize the mutual exclusion example: in dining philosophers, only neighboring (I-related) philosophers are mutually excluded from simultaneous access to their critical sections, and in readers-writers, only reader/writer and writer/writer pairs are mutually excluded.
1] in the solution for the original dining philosophers problem (five philosophers in a circle), which is shown in Figure 6.
King, sponsor University of Pennsylvania ACM (Philadelphia, PA) The Dining Philosophers Rachel White, chairman Insup Lee, sponsor
With its seventy lines of (incomplete) code, six procedures, and four illustrative figures, Ringwood's Parlog86 program for solving the dining philosophers problem is indeed an easy mark.
Sure the picture of Linda versus concurrent logic languages looks different after rehabilitating the dining philosophers.
Compare the following occam code with the CLinda example for the Dining Philosophers Problem.
Turning to the dining philosophers example with which Shapiro begins-if we were members of the CLP community, we would find this demonstration deeply alarming.
This complexity is illustrated by an explanation of the dining philosophers problem.
Though the problem of the dining philosophers [10] appears to have greater entertainment value than practical importance, it has had huge theoretical influence.
A PARLOG86 SOLUTION TO THE DINING PHILOSOPHERS PROBLEM

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