org.apache.tomcat.jdbc.pool
Class FairBlockingQueue<E>

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

All Implemented Interfaces:

java.lang.Iterable<E>, java.util.Collection<E>, java.util.concurrent.BlockingQueue<E>, java.util.Queue<E>

public class FairBlockingQueue<E>
extends java.lang.Object
implements java.util.concurrent.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

protected class	FairBlockingQueue.ExchangeCountDownLatch<T>
protected class	FairBlockingQueue.FairIterator
protected class	FairBlockingQueue.ItemFuture<T>

Constructor Summary

FairBlockingQueue()
Creates a new fair blocking queue.

Method Summary

boolean	add(E e)
boolean	addAll(java.util.Collection<? extends E> c)
void	clear()
boolean	contains(java.lang.Object e)
boolean	containsAll(java.util.Collection<?> c)
int	drainTo(java.util.Collection<? super E> c)
int	drainTo(java.util.Collection<? super E> c, int maxElements)
E	element()
boolean	isEmpty()
java.util.Iterator<E>	iterator()
boolean	offer(E e) Will always return true, queue is unbounded.
boolean	offer(E e, long timeout, java.util.concurrent.TimeUnit unit) Will never timeout, as it invokes the offer(Object) method.
E	peek()
E	poll()
E	poll(long timeout, java.util.concurrent.TimeUnit unit) Fair retrieval of an object in the queue.
java.util.concurrent.Future<E>	pollAsync() Request an item from the queue asynchronously
void	put(E e)
int	remainingCapacity()
E	remove()
boolean	remove(java.lang.Object e)
boolean	removeAll(java.util.Collection<?> c)
boolean	retainAll(java.util.Collection<?> c)
int	size()
E	take()
java.lang.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 java.util.concurrent.BlockingQueue<E>

Specified by:

offer in interface java.util.Queue<E>

offer

public boolean offer(E e,
                     long timeout,
                     java.util.concurrent.TimeUnit unit)
              throws java.lang.InterruptedException

Will never timeout, as it invokes the offer(Object) method. Once a lock has been acquired, the

Specified by:

offer in interface java.util.concurrent.BlockingQueue<E>

Throws:

java.lang.InterruptedException

poll

public E poll(long timeout,
              java.util.concurrent.TimeUnit unit)
       throws java.lang.InterruptedException

Fair retrieval of an object in the queue. Objects are returned in the order the threads requested them.

Specified by:

poll in interface java.util.concurrent.BlockingQueue<E>

Throws:

java.lang.InterruptedException

pollAsync

public java.util.concurrent.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(java.lang.Object e)

Specified by:

remove in interface java.util.Collection<E>

Specified by:

remove in interface java.util.concurrent.BlockingQueue<E>

size

public int size()

Specified by:

size in interface java.util.Collection<E>

iterator

public java.util.Iterator<E> iterator()

Specified by:

iterator in interface java.lang.Iterable<E>

Specified by:

iterator in interface java.util.Collection<E>

poll

public E poll()

Specified by:

poll in interface java.util.Queue<E>

contains

public boolean contains(java.lang.Object e)

Specified by:

contains in interface java.util.Collection<E>

Specified by:

contains in interface java.util.concurrent.BlockingQueue<E>

add

public boolean add(E e)

Specified by:

add in interface java.util.Collection<E>

Specified by:

add in interface java.util.concurrent.BlockingQueue<E>

Specified by:

add in interface java.util.Queue<E>

drainTo

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

Specified by:

drainTo in interface java.util.concurrent.BlockingQueue<E>

Throws:

java.lang.UnsupportedOperationException - - this operation is not supported

drainTo

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

Specified by:

drainTo in interface java.util.concurrent.BlockingQueue<E>

Throws:

java.lang.UnsupportedOperationException - - this operation is not supported

put

public void put(E e)
         throws java.lang.InterruptedException

Specified by:

put in interface java.util.concurrent.BlockingQueue<E>

Throws:

java.lang.InterruptedException

remainingCapacity

public int remainingCapacity()

Specified by:

remainingCapacity in interface java.util.concurrent.BlockingQueue<E>

take

public E take()
       throws java.lang.InterruptedException

Specified by:

take in interface java.util.concurrent.BlockingQueue<E>

Throws:

java.lang.InterruptedException

addAll

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

Specified by:

addAll in interface java.util.Collection<E>

clear

public void clear()

Specified by:

clear in interface java.util.Collection<E>

Throws:

java.lang.UnsupportedOperationException - - this operation is not supported

containsAll

public boolean containsAll(java.util.Collection<?> c)

Specified by:

containsAll in interface java.util.Collection<E>

Throws:

java.lang.UnsupportedOperationException - - this operation is not supported

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface java.util.Collection<E>

removeAll

public boolean removeAll(java.util.Collection<?> c)

Specified by:

removeAll in interface java.util.Collection<E>

Throws:

java.lang.UnsupportedOperationException - - this operation is not supported

retainAll

public boolean retainAll(java.util.Collection<?> c)

Specified by:

retainAll in interface java.util.Collection<E>

Throws:

java.lang.UnsupportedOperationException - - this operation is not supported

toArray

public java.lang.Object[] toArray()

Specified by:

toArray in interface java.util.Collection<E>

Throws:

java.lang.UnsupportedOperationException - - this operation is not supported

toArray

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

Specified by:

toArray in interface java.util.Collection<E>

Throws:

java.lang.UnsupportedOperationException - - this operation is not supported

element

public E element()

Specified by:

element in interface java.util.Queue<E>

Throws:

java.lang.UnsupportedOperationException - - this operation is not supported

peek

public E peek()

Specified by:

peek in interface java.util.Queue<E>

Throws:

java.lang.UnsupportedOperationException - - this operation is not supported

remove

public E remove()

Specified by:

remove in interface java.util.Queue<E>

Throws:

java.lang.UnsupportedOperationException - - this operation is not supported