Core Java 9: Multithreading

Question 1

What is multithreading?

Answer 1

concurrent/parallel programming–a way to have multiple different sets of instructions running at once

Question 2

Why is multithreading useful?

Answer 2

to increase efficiency of application; caveat: for many applications, complexity of multithreading outweighs the benefits

Question 3

Problems Common to Multithreading

Answer 3

multithreading introduces a lot of problems because it’s very easy for different sets of instructions to interfere with one another; maybe they’re competing for a resource, maybe operating in different orders

Question 4

Race conditions

Answer 4

output of application is dependent on order in which threads execute (unpredictable output, may or may not throw exception/error)

Question 5

Deadlock

Answer 5

2 resources acquired in different orders, and threads do not relinquish these resources (a standoff)

Question 6

Starvation

Answer 6

a thread acquires a resource and does not release

Question 7

Livelock

Answer 7

two threads are competing for resources and are trapped in a feedback loop (hot potato)

Question 8

How can issues in multithreading be addressed?

Answer 8

• Frameworks such as Executor
• synchronized keyword
• Thread-safe objects: Collections.synchronizedMap(), Collections.synchronizedList(), StringBuffer, AtomicInteger, etc.
• Checking/changing the order of locks in threads
• Fair locks: ReentrantLock with fair policy set to true is an example
• Design random intervals during which threads attempt to reacquire locks