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org.jgroups.util
Class Queue  

java.lang.Object
  org.jgroups.util.Queue

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public class Queue

extends java.lang.Object

Elements are added at the tail and removed from the head. Class is thread-safe in that 1 producer and 1 consumer may add/remove elements concurrently. The class is not explicitely designed for multiple producers or consumers. Implemented as a linked list, so that removal of an element at the head does not cause a right-shift of the remaining elements (as in a Vector-based implementation).

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Nested Class Summary
(package private) static class	Queue.Element           the class Element indicates an object in the queue.

 

Field Summary
private  boolean	closed
private static java.lang.Object	endMarker           if the queue closes during the runtime an endMarker object is added to the end of the queue to indicate that the queue will close automatically when the end marker is encountered This allows for a "soft" close.
private  Queue.Element	head
protected static org.apache.commons.logging.Log	log
private  java.lang.Object	mutex
private  int	num_markers           Lock object for syncing on removes.
private  int	size
private  Queue.Element	tail

 

Constructor Summary

Queue()           creates an empty queue

 

Method Summary
void	add(java.lang.Object obj)           adds an object to the tail of this queue If the queue has been closed with close(true) no exception will be thrown if the queue has not been flushed yet.
void	addAll(java.util.Collection c)
void	addAll(List l)
void	addAtHead(java.lang.Object obj)           Adds a new object to the head of the queue basically (obj.equals(queue.remove(queue.add(obj)))) returns true If the queue has been closed with close(true) no exception will be thrown if the queue has not been flushed yet.
private  void	addInternal(java.lang.Object obj)
void	close(boolean flush_entries)           Marks the queues as closed.
boolean	closed()           returns true if the Queue has been closed however, this method will return false if the queue has been closed using the close(true) method and the last element has yet not been received.
private  void	decrementSize()           Doesn't need to be synchronized; is always called from synchronized methods
java.lang.Object	getFirst()           Returns the first element.
java.lang.Object	getLast()           Returns the last element.
java.lang.Object	peek()           returns the first object on the queue, without removing it.
java.lang.Object	peek(long timeout)           returns the first object on the queue, without removing it.
java.lang.Object	remove()           Removes 1 element from head or blocks until next element has been added or until queue has been closed
java.lang.Object	remove(long timeout)           Removes 1 element from the head.
void	removeElement(java.lang.Object obj)           removes a specific object from the queue.
private  java.lang.Object	removeInternal()           Removes the first element.
void	reset()           resets the queue.
int	size()           returns the number of objects that are currently in the queue
java.lang.String	toString()           prints the size of the queue
java.util.LinkedList	values()           Returns all the elements of the queue
void	waitUntilClosed(long timeout)           Waits until the queue has been closed.

 

Methods inherited from class java.lang.Object

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

 

Field Detail

head

private Queue.Element head

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tail

private Queue.Element tail

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closed

private boolean closed

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size

private int size

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mutex

private final java.lang.Object mutex

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num_markers

private int num_markers

Lock object for syncing on removes. It is notified when an object is removed

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endMarker

private static final java.lang.Object endMarker

if the queue closes during the runtime an endMarker object is added to the end of the queue to indicate that the queue will close automatically when the end marker is encountered This allows for a "soft" close.

See Also:

close(boolean) 55

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log

protected static final org.apache.commons.logging.Log log

Constructor Detail

Queue

public Queue()

creates an empty queue

Method Detail

getFirst

public java.lang.Object getFirst()

Returns the first element. Returns null if no elements are available.

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getLast

public java.lang.Object getLast()

Returns the last element. Returns null if no elements are available.

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closed

public boolean closed()

returns true if the Queue has been closed however, this method will return false if the queue has been closed using the close(true) method and the last element has yet not been received.

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add

public void add(java.lang.Object obj)
         throws QueueClosedException

adds an object to the tail of this queue If the queue has been closed with close(true) no exception will be thrown if the queue has not been flushed yet.

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addAll

public void addAll(java.util.Collection c)
            throws QueueClosedException

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addAll

public void addAll(List l)
            throws QueueClosedException

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addAtHead

public void addAtHead(java.lang.Object obj)
               throws QueueClosedException

Adds a new object to the head of the queue basically (obj.equals(queue.remove(queue.add(obj)))) returns true If the queue has been closed with close(true) no exception will be thrown if the queue has not been flushed yet.

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remove

public java.lang.Object remove()
                        throws QueueClosedException

Removes 1 element from head or blocks until next element has been added or until queue has been closed

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remove

public java.lang.Object remove(long timeout)
                        throws QueueClosedException,
                               org.jgroups.TimeoutException

Removes 1 element from the head. If the queue is empty the operation will wait for timeout ms. if no object is added during the timeout time, a Timout exception is thrown

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removeElement

public void removeElement(java.lang.Object obj)
                   throws QueueClosedException

removes a specific object from the queue. the object is matched up using the Object.equals method.

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peek

public java.lang.Object peek()
                      throws QueueClosedException

returns the first object on the queue, without removing it. If the queue is empty this object blocks until the first queue object has been added

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peek

public java.lang.Object peek(long timeout)
                      throws QueueClosedException,
                             org.jgroups.TimeoutException

returns the first object on the queue, without removing it. If the queue is empty this object blocks until the first queue object has been added or the operation times out

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close

public void close(boolean flush_entries)

Marks the queues as closed. When an add or remove operation is attempted on a closed queue, an exception is thrown.

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waitUntilClosed

public void waitUntilClosed(long timeout)

Waits until the queue has been closed. Returns immediately if already closed

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reset

public void reset()

resets the queue. This operation removes all the objects in the queue and marks the queue open

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values

public java.util.LinkedList values()

Returns all the elements of the queue

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size

public int size()

returns the number of objects that are currently in the queue

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toString

public java.lang.String toString()

prints the size of the queue

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addInternal

private final void addInternal(java.lang.Object obj)

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removeInternal

private java.lang.Object removeInternal()

Removes the first element. Returns null if no elements in queue. Always called with mutex locked (we don't have to lock mutex ourselves)

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decrementSize

private final void decrementSize()

Doesn't need to be synchronized; is always called from synchronized methods

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