think about your possible case about process synchronization, and give out a solution for the problem.

bounded buffer problem

This problem is generalised in terms of the Producer Consumer problem, where a finite buffer pool is used to exchange messages between producer and consumer processes. Because the buffer pool has a maximum size, this problem is often called the Bounded buffer problem.

Solution to this problem is, creating two counting semaphores "full" and "empty" to keep track of the current number of full and empty buffers respectively.

solution

One solution of this problem is to use semaphores. The semaphores which will be used here are:

m, a binary semaphore which is used to acquire and release the lock. empty, a counting semaphore whose initial value is the number of slots in the buffer, since, initially all slots are empty. full, a counting semaphore whose initial value is 0. At any instant, the current value of empty represents the number of empty slots in the buffer and full represents the number of occupied slots in the buffer.

Dining Philosophers Problem

The dining philosopher's problem involves the allocation of limited resources to a group of processes in a deadlock-free and starvation-free manner. There are five philosophers sitting around a table, in which there are five chopsticks/forks kept beside them and a bowl of rice in the centre, When a philosopher wants to eat, he uses two chopsticks - one from their left and one from their right. When a philosopher wants to think, he keeps down both chopsticks at their original place.

solution

When a philosopher wants to eat the rice, he will wait for the chopstick at his left and picks up that chopstick. Then he waits for the right chopstick to be available, and then picks it too. After eating, he puts both the chopsticks down.

But if all five philosophers are hungry simultaneously, and each of them pickup one chopstick, then a deadlock situation occurs because they will be waiting for another chopstick forever. The possible solutions for this are:

A philosopher must be allowed to pick up the chopsticks only if both the left and right chopsticks are available. Allow only four philosophers to sit at the table. That way, if all the four philosophers pick up four chopsticks, there will be one chopstick left on the table. So, one philosopher can start eating and eventually, two chopsticks will be available. In this way, deadlocks can be avoided.

The Readers Writers Problem

In this problem there are some processes(called readers) that only read the shared data, and never change it, and there are other processes(called writers) who may change the data in addition to reading, or instead of reading it. There are various type of readers-writers problem, most centred on relative priorities of readers and writers.

solution

From the above problem statement, it is evident that readers have higher priority than writer. If a writer wants to write to the resource, it must wait until there are no readers currently accessing that resource.

Here, we use one mutex m and a semaphore w. An integer variable read_count is used to maintain the number of readers currently accessing the resource. The variable read_count is initialized to 0. A value of 1 is given initially to m and w.

Instead of having the process to acquire lock on the shared resource, we use the mutex m to make the process to acquire and release lock whenever it is updating the read_count variable.