CSP for Java
(JCSP) 1.1-rc4

org.jcsp.util
Class OverWritingBuffer

java.lang.Object
  extended by org.jcsp.util.OverWritingBuffer
All Implemented Interfaces:
Serializable, Cloneable, ChannelDataStore

public class OverWritingBuffer
extends Object
implements ChannelDataStore, 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.

Author:
P.D. Austin
See Also:
ZeroBuffer, Buffer, OverWriteOldestBuffer, OverFlowingBuffer, InfiniteBuffer, Channel, Serialized Form

Field Summary
 
Fields inherited from interface org.jcsp.util.ChannelDataStore
EMPTY, FULL, NONEMPTYFULL
 
Constructor Summary
OverWritingBuffer(int size)
          Construct a new OverWritingBuffer with the specified size.
 
Method Summary
 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.
 Object get()
          Returns the oldest Object from the OverWritingBuffer and removes it.
 int getState()
          Returns the current state of the OverWritingBuffer.
 void put(Object value)
          Puts a new Object into the OverWritingBuffer.
 void removeAll()
          Deletes all items in the buffer, leaving it empty.
 Object 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
 

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 Object 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
Returns:
the oldest Object from the OverWritingBuffer

put

public void put(Object 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
Parameters:
value - the Object to put into the OverWritingBuffer

startGet

public Object 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
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
See Also:
startGet()

getState

public int getState()
Returns the current state of the OverWritingBuffer.

Specified by:
getState in interface ChannelDataStore
Returns:
the current state of the OverWritingBuffer (EMPTY or NONEMPTYFULL)

clone

public 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
Overrides:
clone in class 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

CSP for Java
(JCSP) 1.1-rc4

Submit a bug or feature to jcsp-team@kent.ac.uk
Version 1.1-rc4 of the JCSP API Specification (Copyright 1997-2008 P.D.Austin and P.H.Welch - All Rights Reserved)
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