Package org.apache.tomcat.jdbc.pool

Class FairBlockingQueue<E>

java.lang.Object

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

Type Parameters:

E - Type of element in the queue

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.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
protected class	FairBlockingQueue.ExchangeCountDownLatch<T>
protected class	FairBlockingQueue.FairIterator
protected class	FairBlockingQueue.ItemFuture<T>

Constructor Summary

Constructors

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

Method Summary

Modifier and Type	Method	Description
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, parallelStream, removeIf, spliterator, stream, toArray

Methods inherited from interface java.lang.Iterable

forEach

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.concurrent.BlockingQueue<E>

Specified by:

remove in interface java.util.Collection<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.util.Collection<E>

Specified by:

iterator in interface java.lang.Iterable<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.concurrent.BlockingQueue<E>

Specified by:

contains in interface java.util.Collection<E>

add

public boolean add(E e)

Specified by:

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

Specified by:

add in interface java.util.Collection<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