com.webmethods.rtl.event

Class WindowQueue

java.lang.Object

com.webmethods.rtl.event.WindowQueue

All Implemented Interfaces:

Cloneable

public class WindowQueue
extends Object
implements Cloneable

A queue implemented using a cicular buffer that holds a finite number of elements. When an item is added to the queue and the queue is full, the first element is removed to make room. This simulates a sliding window queue. On the get() method, the call is blocked if the queue is empty until data is added.

All methods in this class run explicitly or implicitly synchronized on the object.

Most of the methods in this class are also declared final so they can be more readily in-lined by the compiler.

Copyright (c) 2002-2005 webMethods, Inc. This class is based largely on the WindowQueue class

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	WindowQueue.ShutdownException The exception to be throw to kick the blocking get() call when the queue is shutdown().

Constructor Summary

Constructors

Constructor and Description
WindowQueue() Contructs a windowed queue with a default beginning size.
WindowQueue(int size) Contructs a queue with an initial size.

Method Summary

Modifier and Type	Method and Description
protected Object	clone() Clones this object.
Object	get() Gets an object from the queue.
Object	get(int timeoutMs) Gets an object from the queue.
boolean	isEmpty() Tests if the queue is empty.
boolean	isFull() Tests if the queue is full.
Object	peek() Peeks an object from the queue.
void	put(Object obj) Adds an object to the queue.
void	shutdown() Shuts down the queue.

Methods inherited from class java.lang.Object

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

Constructor Detail

WindowQueue

public WindowQueue()

Contructs a windowed queue with a default beginning size.

WindowQueue

public WindowQueue(int size)

Contructs a queue with an initial size.

Parameters:

size - the size of the queue, must be > 0. If it is <=0, it is ignored and the default size is used

Method Detail

clone

protected Object clone()

Clones this object.

Overrides:

clone in class Object

Returns:

a copy of this queue

put

public final void put(Object obj)

Adds an object to the queue. If the queue is full, the queue is expanded if it is resizable. If the queue if not resizable, or if there is no more memory to expand the queue, the calling thread is blocked until items has been removed from the queue by another thread calling get().

If this call is interrupted/terminated by shutdown(), the object may be discarded and the call returns without put it on the queue.

Parameters:

obj - the Object to add to the queue

get

public final Object get()
                 throws WindowQueue.ShutdownException

Gets an object from the queue. If queue is empty, the calling thread is blocked until an entry is added to the queue by another thread.

Returns:

the next object on the queue

Throws:

WindowQueue.ShutdownException - WindowQueue.ShutdownException, if this call is interrupted/terminated by shutdown()

get

public final Object get(int timeoutMs)
                 throws WindowQueue.ShutdownException

Gets an object from the queue. If queue is empty, the calling thread is blocked until an entry is added to the queue by another thread or the specified timeout is exceeded

Parameters:

timeoutMs - - maximum time to wait before returning (null is returned for timeout)

Returns:

the next object on the queue

Throws:

WindowQueue.ShutdownException - WindowQueue.ShutdownException, if this call is interrupted/terminated by shutdown()

peek

public final Object peek()
                  throws WindowQueue.ShutdownException

Peeks an object from the queue. If queue is empty, the calling thread is blocked until an entry is added to the queue by another thread. As opposed to get() function peek() won't remove an item from the queue

Returns:

the next object on the queue

Throws:

WindowQueue.ShutdownException - WindowQueue.ShutdownException, if this call is interrupted/terminated by shutdown()

isFull

public final boolean isFull()

Tests if the queue is full.

Returns:

true if the queue is full

isEmpty

public final boolean isEmpty()

Tests if the queue is empty.

Returns:

true if the queue is empty

shutdown

public void shutdown()

Shuts down the queue. It sets the internal shutdown flag of the queue, then wakes up all threads waiting to put(java.lang.Object) or get() which would then abort their current operation.