Using the threads, you have implemented, implement semaphores. Since the threads are nonpreemptive, you do not need to ensure atomicity of the semaphores (they are already atomic).
Implement the following: (in a file called sem.h)
1. Semaphore data structure: A value field and a queue of TCBs.
2. InitSem(semaphore, value): Initializes the value field with the specified value.
3. P(semaphore): The P routine decrements the semaphore, and if the value is less than zero then blocks the process in the queue associated with the semaphore.
4. V(semaphore): The V routine increments the semaphore, and if the value is 0 or negative, then takes a PCB out of the semaphore queue and puts it into the run queue.
Note: The V routine also “yields” to the next runnable process. //this is important.
5. Implement a set of thread to test the semaphores. You can choose one of two methods, preferably the second method – the second method will have a few extra credits:
Method 1:
Each thread is an infinite loop, and has a critical section using a mutex semaphore. The thread gets into the CS, prints values of global and local variables (like proj1), sleeps and exists the CS. Then it prints a message and sleeps and then repeats.
Method 2:
Write a producer consumer solution, using the code given in class (see notes). Run 2
producers and 2 consumers. You will have to work out some details. If you choose to do this you really should do method 1 first. Also, doing this will make it easier for you to do project 4.
If your threads work, but fails when you add semaphores …specially if prod/cons causes trouble:
