Understanding Threads and Locks

Question 1

What is deadlock?

Answer 1

Deadlock is when two or more threads become blocked, because they are each waiting for something the other thread has. This reliance is a mutual dependancy between the two.

Question 2

What is lock overhead?

Answer 2

Locking is storage expensive, as it is another variable that needs to be maintained. This required storage is called lock overhead.

Question 3

How can you mitigate lock overhead?

Answer 3

If there’s a cost associated to a lock, reduce overhead by having fewer locks. You can decrease the number of locks by locking larger amounts of code

Question 4

What is lock contention?

Answer 4

Lock contention is the time spent waiting for another thread to give up a lock, so work can be continued

Question 5

How can you mitigate lock contention?

Answer 5

You can reduce lock contention by placing locks on smaller amounts of code. This means less code has to be completed before a lock is given up.

Question 6

What is a thread pool?

Answer 6

You can create multiple threads to begin with, and assign them tasks, rather than creating threads as you go along

Question 7

What is an advantage of thread pools?

Answer 7

There is no overhead for creating new threads, you just use ones from the pool

Question 8

What are 2 disadvantages of thread pools?

Answer 8

1) Deadlock may happen if you run out of threads (a locked action will not unlock until right amount of threads available for task completion) 2) Thread leakage, if a thread has an exception not dealt with, the thread cannot be used

Question 9

What is the difference between threads and co-routines?

Answer 9

1) Threading offers concurrency and parallelism. Coroutines offer concurrency but not necessarily parallelism. 2) Coroutines yield control at fixed points, Threading does not, leaves that to the processor.