Dining Philosophers (Diners)
Problem
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definition
Chandy and Misra solution
extension to drinking philosophers
Definition
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extension to mutual exclusion
arbitrary topology
each philosopher (process) proceeds
through the following cycle
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thinking (out of the CS) may
remain indefinitely
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hungry (requesting the CS)
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eating (executing the CS) has to
finish within finite time
solution properties
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safety – no two neighbors
eat at the same time
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liveness – each hungry philosopher eventually eats
can a DMX solution be used to solve the diners problem? If yes, would
this solution be efficient?
Chandy-Misra[84] (Hygenic) Solution
Setup
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each pair of diners share a fork
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fork is clean before eating, fork is dirty during and after
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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
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u holds clean fork
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v holds dirty fork,
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fork is in transition from v to u
initially, thus oriented graph is acyclic, all forks are dirty
Chandy-Misra[84] (Hygenic) Solution
Details
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if diner does not have fork – it sends request to the neighbor
process
gives up
dirty forks
and holds
clean
diner
can only
wait for higher
priority
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
Extension to Drinking Philosophers
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definition
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arbitrary topology
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each pair of drinking philosophers share a bottle
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philosopher alternates between being tranquil, thirsty and drinking
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philosopher may be tranquil indefinitely but drinks only for finite
amount of time
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philosopher may request to drink from an arbitrary subset of
adjacent bottles
properties
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two neighbors cannot drink from the same bottle at the same time
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each thirsty philosopher eventually drinks
relation to the other problems
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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?