Dining Philosophers (Diners) Problem

1
Dining Philosophers (Diners)Problem

• definition
• Chandy and Misra solution
• extension to drinking philosophers

2
Definition

• extension to mutual exclusion
• arbitrary topology
• each philosopher (process) proceedsthrough the
  following cycle
• thinking (out of the CS) may remain indefinitely
• hungry (requesting the CS)
• eating (executing the CS) has tofinish within
  finite time
• solution properties
• safety no two neighborseat at the same time
• liveness each hungry philosopher eventually
  eats
• can a DMX solution be used to solve the diners
  problem? If yes, would this solution be
  efficient?

3
Chandy-Misra84 (Hygenic) SolutionSetup

• each pair of diners share a fork
• fork is clean before eating, fork is dirty during
  and after
• diner cleans the fork only before giving it to
  neighbor
• edge between diners u and v is oriented from u to
  v (u has higher priority) if
• u holds clean fork
• v holds dirty fork,
• fork is in transition from v to u
• initially, thus oriented graph is acyclic, all
  forks are dirty

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Chandy-Misra84 (Hygenic) SolutionDetails

• if diner does not have fork it sends request to
  the neighbor
• processgives up dirty forksand holdsclean
• dinercan onlywait for higherpriority neighbor

• notice after eating, diner is a source (all his
  forks are dirty)
• graph remains acyclic throughout operation
• acyclic graph has a sink (lowest priority diner),
  that diner is guaranteed to eat

5
Extension to Drinking Philosophers

• definition
• arbitrary topology
• each pair of drinking philosophers share a bottle
• philosopher alternates between being tranquil,
  thirsty and drinking
• philosopher may be tranquil indefinitely but
  drinks only for finite amount of time
• philosopher may request to drink from an
  arbitrary subset of adjacent bottles
• properties
• two neighbors cannot drink from the same bottle
  at the same time
• each thirsty philosopher eventually drinks
• relation to the other problems
• can a solution to diners be used to solve the
  drinking philosophers problem? Can a DMX
  solution? If yes, are they going to be efficient?