Package org.jcsp.util
Class OverWriteOldestBuffer
- java.lang.Object
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- org.jcsp.util.OverWriteOldestBuffer
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- All Implemented Interfaces:
java.io.Serializable
,java.lang.Cloneable
,ChannelDataStore
public class OverWriteOldestBuffer extends java.lang.Object implements ChannelDataStore, java.io.Serializable
This is used to create a buffered object channel that always accepts input, overwriting its oldest data if full.Description
OverWriteOldestBuffer 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 oldest item left unread in the channel. See the static construction methods ofChannel
(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
,OverWritingBuffer
,OverFlowingBuffer
,InfiniteBuffer
,Channel
, Serialized Form
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Field Summary
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Fields inherited from interface org.jcsp.util.ChannelDataStore
EMPTY, FULL, NONEMPTYFULL
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Constructor Summary
Constructors Constructor Description OverWriteOldestBuffer(int size)
Construct a new OverWriteOldestBuffer with the specified size.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description java.lang.Object
clone()
Returns a new (and EMPTY) OverWriteOldestBuffer with the same creation parameters as this one.void
endGet()
This ends an extended rendezvous by the reader.java.lang.Object
get()
Returns the oldest Object from the OverWriteOldestBuffer and removes it.int
getState()
Returns the current state of the OverWriteOldestBuffer.void
put(java.lang.Object value)
Puts a new Object into the OverWriteOldestBuffer.void
removeAll()
Deletes all items in the buffer, leaving it empty.java.lang.Object
startGet()
Begins an extended rendezvous by the reader.
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Constructor Detail
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OverWriteOldestBuffer
public OverWriteOldestBuffer(int size)
Construct a new OverWriteOldestBuffer with the specified size.- Parameters:
size
- the number of Objects the OverWriteOldestBuffer 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.
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Method Detail
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get
public java.lang.Object get()
Returns the oldest Object from the OverWriteOldestBuffer and removes it.Pre-condition: getState must not currently return EMPTY.
- Specified by:
get
in interfaceChannelDataStore
- Returns:
- the oldest Object from the OverWriteOldestBuffer
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startGet
public java.lang.Object 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 interfaceChannelDataStore
- Returns:
- The oldest value in the buffer at this time
- See Also:
ChannelDataStore.endGet()
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endGet
public void endGet()
This ends an extended rendezvous by the reader.- Specified by:
endGet
in interfaceChannelDataStore
- See Also:
startGet()
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put
public void put(java.lang.Object value)
Puts a new Object into the OverWriteOldestBuffer.If OverWriteOldestBuffer is full, the oldest item left unread in the buffer will be overwritten.
- Specified by:
put
in interfaceChannelDataStore
- Parameters:
value
- the Object to put into the OverWriteOldestBuffer
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getState
public int getState()
Returns the current state of the OverWriteOldestBuffer.- Specified by:
getState
in interfaceChannelDataStore
- Returns:
- the current state of the OverWriteOldestBuffer (EMPTY or NONEMPTYFULL)
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clone
public java.lang.Object clone()
Returns a new (and EMPTY) OverWriteOldestBuffer with the same creation parameters as this one.Note: Only the size and structure of the OverWriteOldestBuffer is cloned, not any stored data.
- Specified by:
clone
in interfaceChannelDataStore
- Overrides:
clone
in classjava.lang.Object
- Returns:
- the cloned instance of this OverWriteOldestBuffer.
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removeAll
public void removeAll()
Description copied from interface:ChannelDataStore
Deletes all items in the buffer, leaving it empty.- Specified by:
removeAll
in interfaceChannelDataStore
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