The Dining Philosophers Problem (see Fig. 4)

Figure 4: Lunch time in the Philosophy Department.

• Five philosophers are seated around a circular table
• A philosopher needs two forks to eat
• The life of a philosopher consists of alternate periods of eating and thinking
• Write a program for each philosopher that does what it is supposed to do and never gets stuck
• one attempt is to use a binary semaphore (think)
  • before starting to acquire forks, a philosopher would do a down on mutex
  • after replacing the forks, he would up on mutex
  • bug: only one philosopher can be eating at any instant
• the solution presented in Fig. 5 uses an array, state, to keep track of whether a philosopher is eating, thinking, or hungry (trying to acquire forks)
• A philosopher may move only into eating state if neither neighbor is eating

  Figure 5: A solution to the dining philosophers problem.

  
• The solution is deadlock-free and allows the maximum parallelism for any number of philosophers