Hints on Homework 2: The Smokers Problem

• The whole program is a ParBegin .. ParEnd statement within which are six statements. Each of these six statements represents a smoker or an agent.

• The statement representing a smoker is an infinite loop.

• The statement representing an agent is an infinite loop.

• The problem can be solved in one of two ways:
  • In a Push form: The agents push their stuff. This means that there are global variables indicating what is on the table. The agents set these variables and the smokers, depending on the value of the variables, pick up the ingredients.
  • In a Pull form: The smokers pull the stuff. This means that there are global variables indicating what ingredients are being requested. The smokers set these variables and the agents, depending on the value of the variables, put down the appropriate ingredients.

  Solve the problem in the Pull form.

• The table can be managed in many ways. Among them:
  • Only one copy of one ingredient can be on the table at one time;
  • Only one copy of any number of ingredients can be on the table at one time;
  • At most M copies (where M is 2 or 3 or ..) of each ingredient can be on the table at one time;
  • At most M copies (where M is 4 or 5 or ..) of ingredients can be on the table at one time;
  • Any number of copies of one ingredient can be on the table at one time;
  • Any number of copies of any number of ingredient can be on the table at one time.

  It is up to you to choose which of these ways to implement. But your choice must be consistent with the Pull mode of operation. Say what is your choice.

• You will need a mutual exclusion semaphore to control the table.

• You will need semaphores for the specific smokers to sleep in while they wait for missing ingredients.

• You may need semaphores for the agents to sleep on.