Question

The messages exchanged by communicating processes reside in a temporary queu
E. Such queue cannot be implemented in the following way :

• A. Zero capacity
• B. Blocking capacity
• C. Bounded capacity
• D. Unbounded capacity

Hint:

Remember the three 'ZBU' rules for buffering: Zero, Bounded, and Unbounded. Blocking and Non-blocking refer to how the process behaves, not how the queue is sized.

Answer 1

The Correct Option is B

Concept:
• Message passing systems utilize a temporary queue to hold messages during inter-process communication (IPC).
• These queues are primarily characterized by their "Capacity", which defines the maximum number of messages they can hold.
• Communication synchronization (blocking vs. non-blocking) is a behavioral property, not a structural implementation of queue capacity.

Step 1: Analyze standard implementations of message queues

• Zero capacity: The queue has a maximum length of zero. The sender must block until the recipient receives the message. This is known as "rendezvous".
• Bounded capacity: The queue has a finite length \(n\). If the queue is not full, the sender can continue; if it is full, the sender must block.
• Unbounded capacity: The queue has potentially infinite length. The sender never has to block for space.

Step 2: Evaluate the term "Blocking capacity"
"Blocking" refers to the synchronization policy of the sender/receiver (e.g., synchronous vs. asynchronous).
While queues can cause a process to block, there is no such physical implementation called "Blocking capacity".
It is a mix-up of terminology between the "capacity" of the buffer and the "synchronization" of the primitive.