smclacke/philosophers

Image: Ron Swanson - adit.io

Philosophers

I never thought philosophy would be so deadly

A solution to the classic Dining Philosophers problem using threads.

Program arguments:

• number of philosophers
• time to die - in milliseconds
• time to sleep - in milliseconds
• number of times each philosphers must eat - optional

Problem statement:

Five philosophers dine together at the same table. Each philosopher has his own plate at the table. There is a fork between each plate. The dish served is a kind of spaghetti which has to be eaten with two forks. Each philosopher can only alternately think and eat. Moreover, a philosopher can only eat his spaghetti when he has both a left and right fork. Thus two forks will only be available when his two nearest neighbors are thinking, not eating. After an individual philosopher finishes eating, he will put down both forks. The problem is how to design a regimen (a concurrent algorithm) such that any philosopher will not starve; i.e., each can forever continue to alternate between eating and thinking, assuming that no philosopher can know when others may want to eat or think (an issue of incomplete information).

Problems:

The problem was designed to illustrate the challenges of avoiding deadlock, a system state in which no progress is possible. To see that a proper solution to this problem is not obvious, consider a proposal in which each philosopher is instructed to behave as follows:

• think unless the left fork is available; when it is, pick it up;
• think unless the right fork is available; when it is, pick it up;
• when both forks are held, eat for a fixed amount of time;
• put the left fork down;
• put the right fork down;
• repeat from the beginning.

However, each philosopher will think for an undetermined amount of time and may end up holding a left fork thinking, staring at the right side of the plate, unable to eat because there is no right fork, until he starves.

source: https://en.wikipedia.org/wiki/Dining_philosophers_problem