Consider a system with three smoker processes and one agent process. Each smoker continuously rolls a cigarette and then smokes it. But to roll and smoke a cigarette, the smoker needs three ingredients: tobacco, paper and matches. One of the smoker processes has paper, another has tobacco and the third has the matches. The agent has an infinite supply of all three materials. The agent places two of the ingredients on the table. The smoker who has the remaining ingredient then makes and smokes a cigarette, signaling the agent on completion. The agent then puts out another two of the three ingredients, and the cycle repeats. Given below is a solution to the Cigarette-Smokers Problem. Give initial conditions for the semaphores as well as plausible values for the variables i & j and r & s, such that the agent and smokers are synchronized. Write a couple of sentences on why these initial conditions are necessary and sufficient. Solution: var a: array [0..2] of semaphore (initial condition = } agent: semaphore { initial condition = } agent code rep repeat Set i,j to a value = wait(agent); signal(a[i]); signal(a[j]); until false; smoker code rep repeat Set r,s to a value = wait(a[r]); wait(a[s]); "smoke" signal(agent); until false; Explanation (brief):
Consider a system with three smoker processes and one agent process. Each smoker continuously rolls a cigarette and then smokes it. But to roll and smoke a cigarette, the smoker needs three ingredients: tobacco, paper and matches. One of the smoker processes has paper, another has tobacco and the third has the matches. The agent has an infinite supply of all three materials. The agent places two of the ingredients on the table. The smoker who has the remaining ingredient then makes and smokes a cigarette, signaling the agent on completion. The agent then puts out another two of the three ingredients, and the cycle repeats. Given below is a solution to the Cigarette-Smokers Problem. Give initial conditions for the semaphores as well as plausible values for the variables i & j and r & s, such that the agent and smokers are synchronized. Write a couple of sentences on why these initial conditions are necessary and sufficient. Solution: var a: array [0..2] of semaphore (initial condition = } agent: semaphore { initial condition = } agent code rep repeat Set i,j to a value = wait(agent); signal(a[i]); signal(a[j]); until false; smoker code rep repeat Set r,s to a value = wait(a[r]); wait(a[s]); "smoke" signal(agent); until false; Explanation (brief):
Operations Research : Applications and Algorithms
4th Edition
ISBN:9780534380588
Author:Wayne L. Winston
Publisher:Wayne L. Winston
Chapter17: Markov Chains
Section17.4: Classification Of States In A Markov Chain
Problem 1P
Related questions
Question
![Consider a system with three smoker processes and one agent process. Each smoker
continuously rolls a cigarette and then smokes it. But to roll and smoke a cigarette, the smoker
needs three ingredients: tobacco, paper and matches. One of the smoker processes has paper,
another has tobacco and the third has the matches. The agent has an infinite supply of all three
materials. The agent places two of the ingredients on the table. The smoker who has the
remaining ingredient then makes and smokes a cigarette, signaling the agent on completion. The
agent then puts out another two of the three ingredients, and the cycle repeats.
Given below is a solution to the Cigarette-Smokers Problem. Give initial conditions for the semaphores as
well as plausible values for the variables i & j and r & s, such that the agent and smokers are synchronized.
Write a couple of sentences on why these initial conditions are necessary and sufficient.
Solution:
var a: array [0..2] of semaphore (initial condition = }
agent: semaphore { initial condition = }
agent code
rep
repeat
Set i,j to a value =
wait(agent);
signal(a[i]);
signal(a[j]);
until false;
smoker code
rep
repeat
Set r,s to a value =
wait(a[r]);
wait(a[s]);
"smoke"
signal(agent);
until false;
Explanation (brief):](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F95069adb-9da5-447d-9aa1-8b7142418c79%2Fb60577e0-2c0f-49c6-a14f-98ad0cd7245c%2Fdnduxdd_processed.png&w=3840&q=75)
Transcribed Image Text:Consider a system with three smoker processes and one agent process. Each smoker
continuously rolls a cigarette and then smokes it. But to roll and smoke a cigarette, the smoker
needs three ingredients: tobacco, paper and matches. One of the smoker processes has paper,
another has tobacco and the third has the matches. The agent has an infinite supply of all three
materials. The agent places two of the ingredients on the table. The smoker who has the
remaining ingredient then makes and smokes a cigarette, signaling the agent on completion. The
agent then puts out another two of the three ingredients, and the cycle repeats.
Given below is a solution to the Cigarette-Smokers Problem. Give initial conditions for the semaphores as
well as plausible values for the variables i & j and r & s, such that the agent and smokers are synchronized.
Write a couple of sentences on why these initial conditions are necessary and sufficient.
Solution:
var a: array [0..2] of semaphore (initial condition = }
agent: semaphore { initial condition = }
agent code
rep
repeat
Set i,j to a value =
wait(agent);
signal(a[i]);
signal(a[j]);
until false;
smoker code
rep
repeat
Set r,s to a value =
wait(a[r]);
wait(a[s]);
"smoke"
signal(agent);
until false;
Explanation (brief):
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