What is the Difference between ArrayBlockingQueue and LinkedBlockingQueue

Question

1. What scenarios is it better to use an ArrayBlockingQueue and when is it better to use a LinkedBlockingQueue?
2. If LinkedBlockingQueue default capacity is equal to M

Answer 1

ArrayBlockingQueue :

ArrayBlockingQueue is a bounded, blocking queue that stores the elements internally in an array. That it is bounded means that it cannot store unlimited amounts of elements. There is an upper bound on the number of elements it can store at the same time. You set the upper bound at instantiation time, and after that it cannot be changed.

LinkedBlockingQueue

The LinkedBlockingQueue keeps the elements internally in a linked structure (linked nodes). This linked structure can optionally have an upper bound if desired. If no upper bound is specified, Integer.MAX_VALUE is used as the upper bound.

Similarity

The ArrayBlockingQueue/LinkedBlockingQueue stores the elements internally in FIFO (First In, First Out) order. The head of the queue is the element which has been in queue the longest time, and the tail of the queue is the element which has been in the queue the shortest time.

Differences

• LinkedBlockingQueue has a putLock and a takeLock for insertion and removal respectively but ArrayBlockingQueue uses only 1 lock.
• ArrayBlockingQueue uses single-lock double condition algorithm and LinkedBlockingQueue is variant of the "two lock queue" algorithm and it has 2 locks 2 conditions ( takeLock , putLock).

Two Lock Queue algorithm is being used by LinkedBlockingQueue Implementation.Thus LinkedBlockingQueue's take and put can work concurrently, but this is not the case with ArrayBlockingQueue. The reason for using a single lock in ArrayBlockingQueue is ,ArrayBlockingQueue has to avoid overwriting entries so that it needs to know where the start and the end is. A LinkedBlockQueue doesn't need to know this as it lets the GC worry about cleaning up Nodes in the queue.