This assignment aims to give you experience in thread (and, by extension, process) synchronization using semaphores. In this project, you will write multithreaded programs in Java to solve three classic synchronization problems, using only semaphores. A secondary aim is to give you experience in reading, understanding and correcting existing code. The assignment is in three parts, increasing in difficulty. The first part is described below.

1 Part I: Simple barrier with semaphores

In this first part of the assignment, you will implement a simple barrier in Java, using only semaphores.

A barrier is a synchronization construct that forces threads to wait until a fixed number of threads (n) have arrived at the barrier, whereupon they may all continue with their next step.

The synchronization requirement is that no thread may proceed until n threads have reached the barrier. When the first n-1 threads arrive, they should block until the nth thread arrives, whereupon all threads may proceed.

Note that for this task you must only implement a simple barrier, not a reusable barrier. The barrier implemented must be deadlock free.

1.1 Code skeleton: BarrierS

You must use and extend the BarrierS package provided, correctly implementing the Barrier class (and the b_wait() method), so that the BarrierTest class will execute correctly, always. This will not require many lines of code. Do not alter the BarrierTest or the BThread classes in the package (although you must submit them). You will need to inspect the various classes to see how they work this is part of the assignment and no explanation other than the code will be given.

An example of a correct execution of BarrierTest is:

• java BarrierS.BarrierTest 5 5

Starting simulation with 5 threads, barrier size 5

Parent thread completed

Thread 1 waiting at barrier.

Thread 3 waiting at barrier.

Thread 0 waiting at barrier.

Thread 2 waiting at barrier.

Thread 4 waiting at barrier.

Thread 4 passed barrier.

Thread 1 passed barrier.

Thread 2 passed barrier.

Thread 0 passed barrier.

Thread 3 passed barrier.

1 Code requirements

You will code your solutions in Java, adding to the skeleton code provided.

You may only use the Semaphore class in the java.util.concurrent library: no other Java synchronization constructs at all.

All code must be deadlock free.

The output must comply with the stated synchronization constraints and with the examples shown.