org.apache.tomcat.jdbc.pool

## Class FairBlockingQueue<E>

- java.lang.Object
- - org.apache.tomcat.jdbc.pool.FairBlockingQueue<E>

- All Implemented Interfaces:
    Iterable<E>, Collection<E>, BlockingQueue<E>, Queue<E>

      public class FairBlockingQueue<E>
      extends Object
      implements BlockingQueue<E>

  A simple implementation of a blocking queue with fairness waiting. invocations to method poll(...) will get handed out in the order they were received. Locking is fine grained, a shared lock is only used during the first level of contention, waiting is done in a lock per thread basis so that order is guaranteed once the thread goes into a suspended monitor state.
  Not all of the methods of the `BlockingQueue` are implemented.
  Author:
    Filip Hanik

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `protected class` | `FairBlockingQueue.ExchangeCountDownLatch<T>`
    `protected class` | `FairBlockingQueue.FairIterator`
    `protected class` | `FairBlockingQueue.ItemFuture<T>`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `FairBlockingQueue()` Creates a new fair blocking queue.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `boolean` | `add(E e)`
    `boolean` | `addAll(Collection<? extends E> c)`
    `void` | `clear()`
    `boolean` | `contains(Object e)`
    `boolean` | `containsAll(Collection<?> c)`
    `int` | `drainTo(Collection<? super E> c)`
    `int` | `drainTo(Collection<? super E> c, int maxElements)`
    `E` | `element()`
    `boolean` | `isEmpty()`
    `Iterator<E>` | `iterator()`
    `boolean` | `offer(E e)` Will always return true, queue is unbounded.
    `boolean` | `offer(E e, long timeout, TimeUnit unit)` Will never timeout, as it invokes the `offer(Object)` method.
    `E` | `peek()`
    `E` | `poll()`
    `E` | `poll(long timeout, TimeUnit unit)` Fair retrieval of an object in the queue.
    `Future<E>` | `pollAsync()` Request an item from the queue asynchronously
    `void` | `put(E e)`
    `int` | `remainingCapacity()`
    `E` | `remove()`
    `boolean` | `remove(Object e)`
    `boolean` | `removeAll(Collection<?> c)`
    `boolean` | `retainAll(Collection<?> c)`
    `int` | `size()`
    `E` | `take()`
    `Object[]` | `toArray()`
    `<T> T[]` | `toArray(T[] a)`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

    - ### Methods inherited from interface java.util.Collection

      `equals, hashCode`

- - ### Constructor Detail

    - #### FairBlockingQueue

          public FairBlockingQueue()

      Creates a new fair blocking queue.

  - ### Method Detail

    - #### offer

          public boolean offer(E e)

      Will always return true, queue is unbounded.
      Specified by:
        `offer` in interface `BlockingQueue<E>`
      Specified by:
        `offer` in interface `Queue<E>`

    - #### offer

          public boolean offer(E e,
                      long timeout,
                      TimeUnit unit)
                        throws InterruptedException

      Will never timeout, as it invokes the `offer(Object)` method. Once a lock has been acquired, the
      Specified by:
        `offer` in interface `BlockingQueue<E>`
      Throws:
        `InterruptedException`

    - #### poll

          public E poll(long timeout,
               TimeUnit unit)
                 throws InterruptedException

      Fair retrieval of an object in the queue. Objects are returned in the order the threads requested them.
      Specified by:
        `poll` in interface `BlockingQueue<E>`
      Throws:
        `InterruptedException`

    - #### pollAsync

          public Future<E> pollAsync()

      Request an item from the queue asynchronously
      Returns:
        - a future pending the result from the queue poll request

    - #### remove

          public boolean remove(Object e)

      Specified by:
        `remove` in interface `Collection<E>`
      Specified by:
        `remove` in interface `BlockingQueue<E>`

    - #### size

          public int size()

      Specified by:
        `size` in interface `Collection<E>`

    - #### iterator

          public Iterator<E> iterator()

      Specified by:
        `iterator` in interface `Iterable<E>`
      Specified by:
        `iterator` in interface `Collection<E>`

    - #### poll

          public E poll()

      Specified by:
        `poll` in interface `Queue<E>`

    - #### contains

          public boolean contains(Object e)

      Specified by:
        `contains` in interface `Collection<E>`
      Specified by:
        `contains` in interface `BlockingQueue<E>`

    - #### add

          public boolean add(E e)

      Specified by:
        `add` in interface `Collection<E>`
      Specified by:
        `add` in interface `BlockingQueue<E>`
      Specified by:
        `add` in interface `Queue<E>`

    - #### drainTo

          public int drainTo(Collection<? super E> c,
                    int maxElements)

      Specified by:
        `drainTo` in interface `BlockingQueue<E>`
      Throws:
        `UnsupportedOperationException` - - this operation is not supported

    - #### drainTo

          public int drainTo(Collection<? super E> c)

      Specified by:
        `drainTo` in interface `BlockingQueue<E>`
      Throws:
        `UnsupportedOperationException` - - this operation is not supported

    - #### put

          public void put(E e)
                   throws InterruptedException

      Specified by:
        `put` in interface `BlockingQueue<E>`
      Throws:
        `InterruptedException`

    - #### remainingCapacity

          public int remainingCapacity()

      Specified by:
        `remainingCapacity` in interface `BlockingQueue<E>`

    - #### take

          public E take()
                 throws InterruptedException

      Specified by:
        `take` in interface `BlockingQueue<E>`
      Throws:
        `InterruptedException`

    - #### addAll

          public boolean addAll(Collection<? extends E> c)

      Specified by:
        `addAll` in interface `Collection<E>`

    - #### clear

          public void clear()

      Specified by:
        `clear` in interface `Collection<E>`
      Throws:
        `UnsupportedOperationException` - - this operation is not supported

    - #### containsAll

          public boolean containsAll(Collection<?> c)

      Specified by:
        `containsAll` in interface `Collection<E>`
      Throws:
        `UnsupportedOperationException` - - this operation is not supported

    - #### isEmpty

          public boolean isEmpty()

      Specified by:
        `isEmpty` in interface `Collection<E>`

    - #### removeAll

          public boolean removeAll(Collection<?> c)

      Specified by:
        `removeAll` in interface `Collection<E>`
      Throws:
        `UnsupportedOperationException` - - this operation is not supported

    - #### retainAll

          public boolean retainAll(Collection<?> c)

      Specified by:
        `retainAll` in interface `Collection<E>`
      Throws:
        `UnsupportedOperationException` - - this operation is not supported

    - #### toArray

          public Object[] toArray()

      Specified by:
        `toArray` in interface `Collection<E>`
      Throws:
        `UnsupportedOperationException` - - this operation is not supported

    - #### toArray

          public <T> T[] toArray(T[] a)

      Specified by:
        `toArray` in interface `Collection<E>`
      Throws:
        `UnsupportedOperationException` - - this operation is not supported

    - #### element

          public E element()

      Specified by:
        `element` in interface `Queue<E>`
      Throws:
        `UnsupportedOperationException` - - this operation is not supported

    - #### peek

          public E peek()

      Specified by:
        `peek` in interface `Queue<E>`
      Throws:
        `UnsupportedOperationException` - - this operation is not supported

    - #### remove

          public E remove()

      Specified by:
        `remove` in interface `Queue<E>`
      Throws:
        `UnsupportedOperationException` - - this operation is not supported

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