Cigarette Smokers Problem - Solution

Solution

If we remove the second of Patil's constraints, the cigarette smokers problem becomes solvable using binary semaphores, or mutexes. Let us define an array of binary semaphores A, one for each smoker; and a binary semaphore for the table, T. Initialize the smokers' semaphores to zero and the table's semaphore to 1. Then the arbiter's code is


time.sleep(T) # choose smokers i and j nondeterministically, # making the third smoker k signal(A)

and the code for smoker i is

while true: time.sleep(A) # make a cigarette signal(T) # smoke the cigarette

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