Question

Consider a binary semaphore, counting semaphore, queues, and mailboxes. Any three can be implemented with the fourth. Show how one can be used to implement the other for the following using data flow diagrams :

Binary semaphores for implementing mailboxes

Answer 1

Mailboxes can be implemented using a binary semaphore and a queue data structure. The binary semaphore serves as a lock to ensure thread-safety, while the queue maintains the order of the messages.

Step-by-step explanation:

To implement mailboxes using binary semaphores, we can use a queue data structure. A queue is a collection of items that follows the FIFO (First In, First Out) principle. We can use the binary semaphore as a lock to ensure that only one process can access the queue at a time, ensuring thread-safety.

Whenever a process wants to send a message to a mailbox, it first acquires the binary semaphore. It then enqueues the message in the queue. To receive a message, a process acquires the binary semaphore, dequeues the message from the queue, and releases the semaphore.

This implementation ensures that messages are processed in the order they are received, and the binary semaphore provides the necessary synchronization to avoid race conditions.