NEW CD SET 3

What is the difference between wait() and sleep()?

wait() releases the lock and needs notify() to wake up. sleep() keeps its locks and wakes up on its own.

What's the difference between deadlock prevention and deadlock avoidance?

Prevention removes a condition outright, like a fixed lock order. Avoidance checks at runtime if granting a resource could cause deadlock.

What is the semantics of a counting semaphore?

acquire() decrements the permit count, or blocks if it's zero. release() increments it and wakes a waiting thread.

What is object serialization, and how do you implement it?

Serialization turns an object's state into bytes. Implement it via Serializable, a marker interface, or Externalizable, which needs writeExternal() and readExternal().

What is resource ordering, and why does it prevent deadlock?

Every thread acquires locks in the same fixed order, which stops a circular wait from forming.

Why is overuse of threads bad?

Too many threads mean more context-switching and more memory for stacks — use a bounded pool instead.

What is a monitor?

A monitor, like Java's synchronized, gives one thread exclusive access at a time, with a queue for the rest.

What are the three functions/purposes of synchronization in Java?

Synchronization gives mutual exclusion, visibility between threads, and ordering, so instructions aren't reordered across the boundary.

Can a constructor be synchronized? Why or why not?

No — the object isn't visible to other threads until construction finishes, so there's nothing to lock yet.

What is a fair lock, and how do you create one?

new ReentrantLock(true) gives the lock to the longest-waiting thread first, though it costs some throughput.