Challenge Problems

Implementing Barriers with Semaphores ( intro to OS )

You are given a system that has semaphores, like the ones that we have studied in class. These semaphores have three functions you can call:

sem_init: Sets the initial value of the semaphore. Note that it can be called only once, and must be before any other operation is done on that semaphore.

sem_P(): the normal semaphore P operation.

sem_V(): the normal semaphore V operation.

Using semaphores, you are to implement barriers, an important type of synchronization used in parallel computing systems. You will define a new type called barrier and write the code for the initialization (init_barrier) and arrive_barrier functions.

The initialization function, init_barrier(N) is called to set the number of processes that will use the barrier. A barrier is a way of synchronizing a fixed group of N processes (which is a group where you know the number, N of the processes involved in advance. Each process calls the arrive_barrier() operation and blocks until all N processes do the same. At that point, all the processes should be free to continue. Also, at this point, the barrier is reset and ready to use again.

// declare semaphores and state variables here: void init_barrier (int val) { } void arrive_barrier () { }

Please comment heavily for me to understand.