What backpressure strategies exist when the queue overflows?

When a queue overflows in Java and other data streaming systems, the following backpressure strategies are used:

1. Blocking the sender — the thread trying to add an element to a full queue is blocked until space is freed.
2. Dropping new elements — new incoming elements are discarded when overflow occurs.
3. Dropping the oldest elements — old elements are removed from the queue to make room for new ones.
4. Buffering with a limit — elements are buffered up to a certain limit, after which other strategies are applied.
5. Backpressure signal to the source — the data source receives a signal to slow down or stop generating new elements.

In Java, for example, reactive libraries (Reactor, RxJava) implement backpressure through special interfaces that allow controlling the data consumption rate. In traditional queues, blocking methods or custom discard logic can be used.

Example with a blocking queue:

BlockingQueue<String> queue = new ArrayBlockingQueue<>(100);

// producer thread
queue.put(item); // blocks if the queue is full

// consumer thread
String item = queue.take();

If a discard strategy is needed, offer methods with timeout or checking the queue size before adding can be used.