CS604 Operating Systems assignment 3 Fall2011

Operating Systems (CS604)

Assignment # 3

Fall 2011

IDEA SOLUTION:

# These three are mutexes (only 0 or 1 possible)

Semaphore contractorReady = 0         # if 1, at least one contractor is ready

Semaphore ministerReady = 0

Semaphore accessWRSeats = 1       # if 1, the # of seats in the waiting room can be incremented or decremented

int numberOfFreeWRSeats = N     # total number of seats in the waiting room

def minister():

  while true:                   # Run in an infinite loop.

    wait(contractorReady)             # Try to acquire a contractor - if none is available, go to sleep. 

    wait(accessWRSeats)         # Awake - try to get access to modify # of available seats, otherwise sleep.

    numberOfFreeWRSeats++       # One waiting room chair becomes afree.

    signal(ministerReady)         # I am ready.

    signal(accessWRSeats)       # Don't need the lock on the chairs anymore.

    # (Enter Door 1.)

def Contractor():

  while true:                   # Run in an infinite loop.

wait(accessWRSeats)         # Try to get access to the waiting room chairs.
 if numberOfFreeWRSeats > 0: # If there are any free seats:

      numberOfFreeWRSeats--     #   sit down in a chair

   signal(contractorReady)         #   notify the minister, who's waiting until there is a contractor

      signal(accessWRSeats)     #   don't need to lock the chairs anymore

      wait(ministerReady)         #   wait until the minister is ready

      # (Finish the meeting here.)

    else:                      

# otherwise, there are no free seats;

      signal(accessWRSeats)     #   but don't forget to release the lock on the seats!

      # (Leave without a meeting with minister.)

      if minister=busy

      close D1;

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Consult from this Example

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