BlockingQueue

1. Purpose

BlockingQueue combines a queue with waiting semantics for producers/consumers.

Typical method families:

Action	exception	special value	block	timed
insert	add	offer	put	offer(timeout)
remove	remove	poll	take	poll(timeout)
examine	element	peek	—	—

2. Backpressure

A bounded queue is an important overload-control mechanism. When full, producers either wait, time out, reject, or apply another policy.

An effectively unbounded queue can hide overload until latency/memory becomes unacceptable.

3. Implementations

• ArrayBlockingQueue — bounded array, one fixed capacity;
• LinkedBlockingQueue — linked nodes, optionally bounded, default capacity is very large;
• PriorityBlockingQueue — priority heap, logically unbounded, no FIFO guarantee across priorities;
• SynchronousQueue — zero-capacity handoff: producer and consumer rendezvous.

4. Memory Semantics

Actions before putting an element into a concurrent queue happen-before actions after another thread removes/accesses that element through the documented queue handoff.