org.jcsp.util.ints
Class OverWriteOldestBufferInt

java.lang.Object
  org.jcsp.util.ints.OverWriteOldestBufferInt

All Implemented Interfaces:

Serializable, Cloneable, ChannelDataStoreInt

public class OverWriteOldestBufferInt
extends Object
implements ChannelDataStoreInt, Serializable

This is used to create a buffered integer channel that always accepts input, overwriting its oldest data if full.

Description

OverWriteOldestBufferInt is an implementation of ChannelDataStoreInt that yields a FIFO buffered semantics for a channel. When empty, the channel blocks readers. When full, a writer will overwrite the oldest item left unread in the channel. See the static construction methods of Channel (Channel.one2oneInt(org.jcsp.util.ints.ChannelDataStoreInt) etc.).

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

Author:

P.D. Austin

See Also:

ZeroBufferInt, BufferInt, OverWritingBufferInt, OverFlowingBufferInt, InfiniteBufferInt, ChannelInt, Serialized Form

Field Summary

Fields inherited from interface org.jcsp.util.ints.ChannelDataStoreInt

EMPTY, FULL, NONEMPTYFULL

Constructor Summary

OverWriteOldestBufferInt(int size)
Construct a new OverWriteOldestBufferInt with the specified size.

Method Summary

Object	clone() Returns a new (and EMPTY) OverWriteOldestBufferInt with the same creation parameters as this one.
void	endGet() See startGet() for a description of the semantics of this method.
int	get() Returns the oldest int from the OverWriteOldestBufferInt and removes it.
int	getState() Returns the current state of the OverWriteOldestBufferInt.
void	put(int value) Puts a new int into the OverWriteOldestBufferInt.
void	removeAll()
int	startGet() 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

OverWriteOldestBufferInt

public OverWriteOldestBufferInt(int size)

Construct a new OverWriteOldestBufferInt with the specified size.

Parameters:

size - the number of ints the OverWriteOldestBufferInt can store.

Throws:

BufferIntSizeError - 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 int get()

Returns the oldest int from the OverWriteOldestBufferInt and removes it.

Pre-condition: getState must not currently return EMPTY.

Specified by:

get in interface ChannelDataStoreInt

Returns:

the oldest int from the OverWriteOldestBufferInt

startGet

public int startGet()

Begins an extended rendezvous by the reader. The semantics of an extended rendezvous on an overwrite-oldest buffer are slightly complicated, but hopefully intuitive. When a reader begins an extended rendezvous, the oldest value is returned from the buffer (as it would be for a call to get()). While an extended rendezvous is ongoing, the writer may (repeatedly) write to the buffer, without ever blocking. When the reader finishes an extended rendezvous, the following options are possible:

• The writer has not written to the channel during the rendezvous. In this case, the value that was read at the start of the rendezvous is removed from the buffer.
• The writer has written to the channel during the rendezvous, but has not over-written the value that was read at the start of the rendezvous. In this case, the value that was read at the start of the rendezvous is removed from the buffer.
• The writer has written to the channel during the rendezvous, and has over-written (perhaps repeatedly) the value that was read at the start of the rendezvous. In this case, the value that was read at the start of the rendezvous is no longer in the buffer, and hence nothing is removed.

Specified by:

startGet in interface ChannelDataStoreInt

Returns:

The oldest value in the buffer at this time

See Also:

ChannelDataStoreInt.endGet()

endGet

public void endGet()

See startGet() for a description of the semantics of this method.

Specified by:

endGet in interface ChannelDataStoreInt

See Also:

ChannelDataStoreInt.startGet()

put

public void put(int value)

Puts a new int into the OverWriteOldestBufferInt.

If OverWriteOldestBufferInt is full, the oldest item left unread in the buffer will be overwritten.

Specified by:

put in interface ChannelDataStoreInt

Parameters:

value - the int to put into the OverWriteOldestBufferInt

getState

public int getState()

Returns the current state of the OverWriteOldestBufferInt.

Specified by:

getState in interface ChannelDataStoreInt

Returns:

the current state of the OverWriteOldestBufferInt (EMPTY or NONEMPTYFULL)

clone

public Object clone()

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

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

Specified by:

clone in interface ChannelDataStoreInt

Overrides:

clone in class Object

Returns:

the cloned instance of this OverWriteOldestBufferInt.

removeAll

public void removeAll()

Specified by:

removeAll in interface ChannelDataStoreInt