Package org.jcsp.util
Class OverWriteOldestBuffer<T>
java.lang.Object
org.jcsp.util.OverWriteOldestBuffer<T>
- All Implemented Interfaces:
Serializable
,Cloneable
,ChannelDataStore<T>
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.
- See Also:
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Field Summary
FieldsModifier and TypeFieldDescriptionprivate final T[]
The storage for the buffered Objectsprivate int
The number of Objects stored in the Bufferprivate int
The index of the oldest element (when counter > 0)private int
The index of the next free element (when counter invalid input: '<' buffer.length)private boolean
Fields inherited from interface org.jcsp.util.ChannelDataStore
EMPTY, FULL, NONEMPTYFULL
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Constructor Summary
ConstructorsConstructorDescriptionOverWriteOldestBuffer
(int size) Construct a new OverWriteOldestBuffer with the specified size. -
Method Summary
Modifier and TypeMethodDescriptionclone()
Returns a new (and EMPTY) OverWriteOldestBuffer with the same creation parameters as this one.void
endGet()
This ends an extended rendezvous by the reader.get()
Returns the oldest Object from the OverWriteOldestBuffer and removes it.int
getState()
Returns the current state of the OverWriteOldestBuffer.void
Puts a new Object into the OverWriteOldestBuffer.void
Deletes all items in the buffer, leaving it empty.startGet()
Begins an extended rendezvous by the reader.
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Field Details
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buffer
The storage for the buffered Objects -
counter
private int counterThe number of Objects stored in the Buffer -
firstIndex
private int firstIndexThe index of the oldest element (when counter > 0) -
lastIndex
private int lastIndexThe index of the next free element (when counter invalid input: '<' buffer.length) -
valueWrittenWhileFull
private boolean valueWrittenWhileFull
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Constructor Details
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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 Details
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get
Returns the oldest Object from the OverWriteOldestBuffer and removes it.Pre-condition: getState must not currently return EMPTY.
- Specified by:
get
in interfaceChannelDataStore<T>
- Returns:
- the oldest Object from the OverWriteOldestBuffer
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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<T>
- Returns:
- The oldest value in the buffer at this time
- See Also:
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endGet
public void endGet()This ends an extended rendezvous by the reader.- Specified by:
endGet
in interfaceChannelDataStore<T>
- See Also:
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put
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<T>
- 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<T>
- Returns:
- the current state of the OverWriteOldestBuffer (EMPTY or NONEMPTYFULL)
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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<T>
- Overrides:
clone
in classObject
- 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<T>
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