Post Office Simulation

A Post Office simulation in Java

You must use Java Threads and Java Semaphores (java.util.concurrent.Semaphore). You should not use the synchronized keyword in Java. You should not use any Java classes that have built-in mutual exclusion.

A Post Office is simulated by using threads to model customer and employee behavior.

The following rules apply:

Customer:

1)50 customers visit the Post Office (1 thread per customer up to 50), all created initially.

2)Only 10 customers can be inside the Post Office at a time.

3)Each customer upon creation is randomly assigned one of the following tasks:

a)buy stamps

b)mail a letter

c)mail a package

4)Times for each task are defined in the task table.

Postal Worker:

1)3 created initially, one thread each.

2)Serves next customer in line.

3)Service time varies depending on customer task.

Scales:

1)Used by the postal worker when mailing a package.

2)There is only one, which can only be used one at a time.

3)The scales are not a thread. They are just a resource the postal worker threads use.

Other rules:

1)A thread should sleep 1 second in the program for each 60 seconds listed in the table.

2)All mutual exclusion and coordination must be achieved with semaphores.

3)A thread may not use sleeping as a means of coordination.

4)Busy waiting (polling) is not allowed.

5)Mutual exclusion should be kept to a minimum to allow the most concurrency.

6)Each thread should print when it is created and when it is joined.

7)Each thread should only print its own activities. The customer threads prints customer actions and the postal worker threads prints postal worker actions.

8)Your output must include the same information and the same set of steps as the sample output.

Output:

1)Each step of each task of each thread should be printed to the screen with identifying numbers so it is clear which threads are involved.

2)Thread output sample. The wording in your output should exactly match the sample.

Simulating Post Office with 50 customers and 3 postal workers

Postal worker 0 created

Postal worker 2 created

Postal worker 1 created

Customer 0 created

Customer 0 enters post office

Customer 9 created

Customer 9 enters post office

Customer 10 created

Postal worker 0 serving customer 0

Customer 11 created

Postal worker 2 serving customer 1

Postal worker 1 serving customer 2

Customer 0 asks postal worker 0 to buy stamps

Customer 2 asks postal worker 1 to mail a package

Customer 1 asks postal worker 2 to mail a package

Scales in use by postal worker 1

Postal worker 0 finished serving customer 0

Customer 0 finished buying stamps

Postal worker 0 serving customer 3

Customer 3 asks postal worker 0 to mail a letter

Customer 0 leaves post office

Customer 10 enters post office

Joined customer 0

Scales released by postal worker 1

Postal worker 1 finished serving customer 2

Customer 5 asks postal worker 1 to mail a package

Scales in use by postal worker 2

Customer 2 finished mailing a package

Postal worker 1 serving customer 5

Customer 2 leaves post office

Postal worker 0 finished serving customer 3

Customer 3 finished mailing a letter

Postal worker 0 serving customer 4

Customer 4 asks postal worker 0 to mail a letter

Customer 3 leaves post office

Scales released by postal worker 2

Postal worker 2 finished serving customer 1

Scales in use by postal worker 1

Customer 1 finished mailing a package

Customer 1 leaves post office

Joined customer 1

Joined customer 2

Joined customer 3