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Classical Problems of Synchronization with Semaphore Solution

Last Updated : 03 Nov, 2023
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In this article, we will see a number of classical problems of synchronization as examples of a large class of concurrency-control problems. In our solutions to the problems, we use semaphores for synchronization, since that is the traditional way to present such solutions. However, actual implementations of these solutions could use mutex locks instead of binary semaphores. 

Synchronization Problems

These problems are used for testing nearly every newly proposed synchronization scheme. The following problems of synchronization are considered as classical problems: 

1. Bounded-buffer (or Producer-Consumer) Problem,
2. Dining-Philosophers Problem,
3. Readers and Writers Problem,
4. Sleeping Barber Problem

These are summarized, for detailed explanation, you can view the linked articles for each. 

Bounded-Buffer (or Producer-Consumer) Problem

The Bounded Buffer problem is also called the producer-consumer problem. This problem is generalized in terms of the Producer-Consumer problem. The solution to this problem is, to create two counting semaphores “full” and “empty” to keep track of the current number of full and empty buffers respectively. Producers produce a product and consumers consume the product, but both use of one of the containers each time. 

Dining-Philosophers Problem

The Dining Philosopher Problem states that K philosophers seated around a circular table with one chopstick between each pair of philosophers. There is one chopstick between each philosopher. A philosopher may eat if he can pickup the two chopsticks adjacent to him. One chopstick may be picked up by any one of its adjacent followers but not both. This problem involves the allocation of limited resources to a group of processes in a deadlock-free and starvation-free manner. 


Readers and Writers Problem

Suppose that a database is to be shared among several concurrent processes. Some of these processes may want only to read the database, whereas others may want to update (that is, to read and write) the database. We distinguish between these two types of processes by referring to the former as readers and to the latter as writers. Precisely in OS we call this situation as the readers-writers problem. Problem parameters: 

  • One set of data is shared among a number of processes. 
  • Once a writer is ready, it performs its write. Only one writer may write at a time. 
  • If a process is writing, no other process can read it. 
  • If at least one reader is reading, no other process can write. 
  • Readers may not write and only read. 

Sleeping Barber Problem

  • Barber shop with one barber, one barber chair and N chairs to wait in. When no customers the barber goes to sleep in barber chair and must be woken when a customer comes in. When barber is cutting hair new customers take empty seats to wait, or leave if no vacancy. This is basically the Sleeping Barber Problem.

Sleeping Barber Problem

Frequently Asked Questions

1. What is the purpose of using semaphores or mutex locks for synchronization in these synchronization problems?

Semaphores and mutex locks are synchronization primitives used to coordinate access to shared resources among concurrent processes or threads. They help ensure that multiple processes or threads can access shared resources in a controlled and orderly manner, avoiding conflicts and maintaining data integrity.

2. Can the solutions to these synchronization problems be implemented using mutex locks instead of semaphores?

Yes, the solutions to these synchronization problems can be implemented using either semaphores or mutex locks. Semaphores and mutex locks are interchangeable in many cases and can be used to achieve similar synchronization goals. The choice between them often depends on the specific requirements of the problem and the programming language or framework being used.

3. Are these synchronization problems applicable only in multi-threaded or multi-process environments?

Yes, these synchronization problems are typically encountered in multi-threaded or multi-process environments where multiple entities need to access shared resources concurrently. In single-threaded or single-process scenarios, these synchronization problems may not be relevant or may have simpler solutions.

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