Package org.jcsp.util

Class OverWritingBuffer<T>

java.lang.Object

org.jcsp.util.OverWritingBuffer<T>

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, ChannelDataStore<T>

public class OverWritingBuffer<T>
extends java.lang.Object
implements ChannelDataStore<T>, java.io.Serializable

This is used to create a buffered object channel that always accepts input, overwriting its last entered data if full.

Description

It is an implementation of ChannelDataStore that yields a FIFO buffered semantics for a channel. When empty, the channel blocks readers. When full, a writer will overwrite the latest item written to the channel. See the static construction methods of Channel (Channel.one2one(org.jcsp.util.ChannelDataStore) etc.).

The getState method returns EMPTY or NONEMPTYFULL, but never FULL.

See Also:

ZeroBuffer, Buffer, OverWriteOldestBuffer, OverFlowingBuffer, InfiniteBuffer, Channel, Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
private T[]	buffer	The storage for the buffered Objects
private int	counter	The number of Objects stored in the Buffer
private int	firstIndex	The index of the oldest element (when counter > 0)
private int	lastIndex	The index of the next free element (when counter < buffer.length)
private boolean	valueWrittenWhileFull

Fields inherited from interface org.jcsp.util.ChannelDataStore

EMPTY, FULL, NONEMPTYFULL

Constructor Summary

Constructors

Constructor	Description
OverWritingBuffer(int size)	Construct a new OverWritingBuffer with the specified size.

Method Summary

Modifier and Type	Method	Description
java.lang.Object	clone()	Returns a new (and EMPTY) OverWritingBuffer with the same creation parameters as this one.
void	endGet()	This ends an extended rendezvous by the reader.
T	get()	Returns the oldest Object from the OverWritingBuffer and removes it.
int	getState()	Returns the current state of the OverWritingBuffer.
void	put(T value)	Puts a new Object into the OverWritingBuffer.
void	removeAll()	Deletes all items in the buffer, leaving it empty.
T	startGet()	This begins an extended rendezvous by the reader.

Methods inherited from class java.lang.Object

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

Field Detail

buffer

private final T[] buffer

The storage for the buffered Objects

counter

private int counter

The number of Objects stored in the Buffer

firstIndex

private int firstIndex

The index of the oldest element (when counter > 0)

lastIndex

private int lastIndex

The index of the next free element (when counter < buffer.length)

valueWrittenWhileFull

private boolean valueWrittenWhileFull

Constructor Detail

OverWritingBuffer

public OverWritingBuffer(int size)

Construct a new OverWritingBuffer with the specified size.

Parameters:

size - the number of Objects the OverWritingBuffer can store.

Throws:

BufferSizeError - if size is zero or negative. Note: no action should be taken to try/catch this exception - application code generating it is in error and needs correcting.

Method Detail

get

public T get()

Returns the oldest Object from the OverWritingBuffer and removes it.

Pre-condition: getState must not currently return EMPTY.

Specified by:

get in interface ChannelDataStore<T>

Returns:

the oldest Object from the OverWritingBuffer

put

public void put(T value)

Puts a new Object into the OverWritingBuffer.

If OverWritingBuffer is full, the last item previously put into the buffer will be overwritten.

Specified by:

put in interface ChannelDataStore<T>

Parameters:

value - the Object to put into the OverWritingBuffer

startGet

public T startGet()

This begins an extended rendezvous by the reader. The semantics of an extended rendezvous on an overwrite-newest buffer are slightly complicated, but hopefully intuitive.

If the buffer is of size 2 or larger, the semantics are as follows. Beginning an extended rendezvous will return the oldest value in the buffer, but not remove it. If the writer writes to the buffer during the rendezvous, it will grow the buffer and end up overwriting the newest value as normal. At the end of the extended rendezvous, the oldest value is removed.

If the buffer is of size 1, the semantics are identical to those of an OverWriteOldestBuffer. For a complete description, refer to the documentation for the OverWriteOldestBuffer.startGet() method.

Specified by:

startGet in interface ChannelDataStore<T>

Returns:

The oldest value in the buffer at this time

See Also:

ChannelDataStore.endGet()

endGet

public void endGet()

This ends an extended rendezvous by the reader.

Specified by:

endGet in interface ChannelDataStore<T>

See Also:

startGet()

getState

public int getState()

Returns the current state of the OverWritingBuffer.

Specified by:

getState in interface ChannelDataStore<T>

Returns:

the current state of the OverWritingBuffer (EMPTY or NONEMPTYFULL)

clone

public java.lang.Object clone()

Returns a new (and EMPTY) OverWritingBuffer with the same creation parameters as this one.

Note: Only the size and structure of the OverWritingBuffer is cloned, not any stored data.

Specified by:

clone in interface ChannelDataStore<T>

Overrides:

clone in class java.lang.Object

Returns:

the cloned instance of this OverWritingBuffer.

removeAll

public void removeAll()

Description copied from interface: ChannelDataStore

Deletes all items in the buffer, leaving it empty.

Specified by:

removeAll in interface ChannelDataStore<T>