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Java Concurrency API.md

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Java Concurrency API

Types in the Java Concurrency Utilities (APIs) are organized into small frameworks:

  • Executor framework
  • Synchronizers
  • Concurrent collections
  • Locks
  • Atomic variables
  • Fork/Join

Concurrent Collections

  • BlockingQueue
  • BlockingDeque
  • ConcurrentMap

BlockingQueue (put(NonNull e),take()) {ArrayBlockingQueue (bounded), LinkedBlockingQueue (unbounded), DelayQueue (unbounded), SynchronousQueue (unbounded), PriorityBlockingQueue, LinkedTransferQueue}

throws exception: add(e) remove() element()

special value: offer(e) poll() peek()

blocking methods: put(e) take()

times out: offer(e,longtime,unit) poll(longtime,unit)

BlockingDeque (put(NonNull e),take()) {LinkedBlockingDeque (opetionally bounded)}

method names: the names of methods of BlockingQueue+{First/Last}

put() = putLast() take() = takeFirst() element() = getFirst() peek() = peekFirst()

ConcurrentMap (NonNull keys, NonNull values, Failsafe iterator)

Segment = HashEntry[] Map = Segment[]

public V putIfAbsent(K key, V value) boolean remove(Object key, Object value) public V replace(K key, V value) public V replace(K key, V oldValue, V newValue)

ConcurrentNavigableMap (headMap(key), subMap(k1,k2), tailMap(key), navigableKeySet(), descendingMap(), descendingKeySet())

ConcurrentskipListMap (entries sorted by natural order of key type) (O(log n) getters)

CopyOnWriteArrayList (failsafe iterator, iterator does not support remove())

Synchronizers

Semaphores (mutex(binary semaphore), counting semaphore)

acquire() tryAcquire() acquireUninterruptibly()

CountDownLatch

Multiplayer scenario: Waiting for the last player to come in, to start gameplay.

  • await()
  • countDown()

CyclicBarrier

  • CyclicBarrier(int nThreads)
  • CyclicBarrier(int nThreads, Runnable barrierAction)
  • await()
  • reset()

Exchanger

a bidirectional form of SynchronousQueue

  • exchange(Object o) this.object = this.exchanger.exchange(this.object); // in a participating thread

Phaser

  • phase number

  • dynamic number of unarrived parties

  • register()

  • onAdvance()

  • arriveAndAwaitAdvance()

  • arriveAndDeregister()

  • isTerminated()

Failsafe Iterators