org.jgroups.util

Class Queue

java.lang.Object

org.jgroups.util.Queue

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).

Author:

Bela Ban

Field Summary

Fields

Modifier and Type	Field and Description
protected static Log	log

Constructor Summary

Constructors

Constructor and Description
Queue() creates an empty queue

Method Summary

Modifier and Type	Method and Description
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(java.util.List<java.lang.Object> list)
void	clear() Removes all elements from the queue.
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.
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.
java.lang.Object	removeWait(long timeout)
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

log

protected static final 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.

getLast

public java.lang.Object getLast()

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

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.

Returns:

true if the queue has been closed

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.

Parameters:

obj - - the object to be added to the queue

Throws:

QueueClosedException - exception if closed() returns true

addAll

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

Throws:

QueueClosedException

addAll

public void addAll(java.util.List<java.lang.Object> list)
            throws QueueClosedException

Throws:

QueueClosedException

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

Returns:

the first element to be taken of the queue

Throws:

QueueClosedException

remove

public java.lang.Object remove(long timeout)
                        throws QueueClosedException,
                               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 (bela Aug 2009) Note that the semantics of remove(long timeout) are weird - the method waits until an element has been added, but doesn't do so in a loop ! So if we have 10 threads waiting on an empty queue, and 1 thread adds an element, all 10 threads will return (but only 1 will have the element), therefore 9 will throw a TimeoutException ! If I change this to the 'correct' semantics, however (e.g. the method removeWait() below), GMS.ViewHandler doesn't work correctly anymore. I won't change this now, as Queue will get removed anyway in 3.0.

Parameters:

timeout - - the number of milli seconds this operation will wait before it times out

Returns:

the first object in the queue

Throws:

QueueClosedException

TimeoutException

removeWait

public java.lang.Object removeWait(long timeout)
                            throws QueueClosedException,
                                   TimeoutException

Throws:

QueueClosedException

TimeoutException

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.

Parameters:

obj - the actual object to be removed from the queue

Throws:

QueueClosedException

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

Returns:

the first object on the queue

Throws:

QueueClosedException

peek

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

Parameters:

timeout - how long in milli seconds will this operation wait for an object to be added to the queue before it times out

Returns:

the first object on the queue

Throws:

QueueClosedException

TimeoutException

clear

public void clear()

Removes all elements from the queue. This method can succeed even when the queue is closed

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.

Parameters:

flush_entries - When true, a end-of-entries marker is added to the end of the queue. Entries may be added and removed, but when the end-of-entries marker is encountered, the queue is marked as closed. This allows to flush pending messages before closing the queue.

waitUntilClosed

public void waitUntilClosed(long timeout)

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

Parameters:

timeout - Number of milliseconds to wait. A value <= 0 means to wait forever

reset

public void reset()

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

values

public java.util.LinkedList values()

Returns all the elements of the queue

Returns:

A copy of the queue

size

public int size()

returns the number of objects that are currently in the queue

toString

public java.lang.String toString()

prints the size of the queue

Overrides:

toString in class java.lang.Object