Concurrency II

Question 1

What does join() do

Answer 1

Allows one thread to wait for the completion of another

Can respond to an interrupt

Question 2

What does yield() do?

Answer 2

Pauses currently executing thread and allows other threads of other priorities to execute

Question 3

Name the 5 states in the lifecycle of a thread

Answer 3

New => Initializing the thread

Runnable => start() must be called to get to this state, runnable is when the thread is ready to be run by waiting for CPU time to run

Running => Currently being processed by CPU. Changing from runnable to running state is OS dependent, since this is what schedules thread timeslices.

Dead => thread execution complete

Waiting/ Sleeping/ Blocking => when the thread in running state. One of the methods stated are called, must wait to be notified/ sleep time to be finished before going back to runnable state.

Question 4

Give 3 differences between wait and sleep

Answer 4

Wait: must be in a block that is synchronized to the monitor object
Sleep: doesn’t need to occur in a synchronized block

Wait: releases the lock when called (doesn’t sacrifice remainder timeslice)
Sleep: Retains the lock and sacrifices the remainder of its timeslice

Wait: Wakes up when notified
Sleep: Woken up by an interruption

Question 5

What do the methods wait() and notify() do

Answer 5

Objects are monitored using a lock; wait() releases the lock, notify() hands the lock to the waiting thread once the block that notified the thread completes execution

wait() => waits for a condition to occur, must call from synchronized methods

notify() => notifies a waiting thread that a condition has occurred

Question 6

What is livelock

Answer 6

When two threads are too busy responding to each other to do work

Question 7

1) What is starvation

When does it occur most often

Answer 7

1) When a thread can’t gain access to shared resources because another thread is frequently calling the objects’ method.
2) When a thread is synchronized with methods that has faster execution times

Question 8

What is a deadlock

Answer 8

Occurs when two or more processes are waiting for each other to release a resource

Question 9

Give 3 differences between wait and sleep

Answer 9

Wait: must be in a block that is synchronized to the monitor object
Sleep: doesn’t need to occur in a synchronized block

Wait: releases the lock when called (doesn’t sacrifice remainder timeslice)
Sleep: Retains the lock and sacrifices the remainder of its timeslice

Wait: Wakes up when notified
Sleep: Woken up by an interruption