Difference between wait() and sleep()

Question

What is the difference between a wait() and sleep() in Threads?

Is my understanding that a wait()-ing Thread is still in runni

Answer 1

In my opinion, the main difference between both mechanisms is that sleep/interrupt is the most basic way of handling threads, whereas wait/notify is an abstraction aimed to do thread inter-communication easier. This means that sleep/interrupt can do anything, but that this specific task is harder to do.

Why is wait/notify more suitable? Here are some personal considerations:

1. It enforces centralization. It allows to coordinate the communication between a group of threads with a single shared object. This simplifies the work a lot.

2. It enforces synchronization. Because it makes the programmer wrap the call to wait/notify in a synchronized block.

3. It's independent of the thread origin and number. With this approach you can add more threads arbitrarily without editing the other threads or keeping a track of the existing ones. If you used sleep/interrupt, first you would need to keep the references to the sleeping threads, and then interrupt them one by one, by hand.

An example from the real life that is good to explain this is a classic restaurant and the method that the personnel use to communicate among them: The waiters leave the customer requests in a central place (a cork board, a table, etc.), ring a bell, and the workers from the kitchen come to take such requests. Once that there is any course ready, the kitchen personnel ring the bell again so that the waiters are aware and take them to the customers.