Package org.jcsp.util

Class OverWriteOldestBuffer<T>

java.lang.Object
org.jcsp.util.OverWriteOldestBuffer<T>
All Implemented Interfaces:
Serializable, Cloneable, ChannelDataStore<T>

public class OverWriteOldestBuffer<T> extends Object implements ChannelDataStore<T>, 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 of Channel (Channel.one2one(org.jcsp.util.ChannelDataStore) etc.).

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

See Also:
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private final T[]
    The storage for the buffered Objects
    private int
    The number of Objects stored in the Buffer
    private 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
  • Constructor Summary

    Constructors
    Constructor
    Description
    Construct a new OverWriteOldestBuffer with the specified size.
  • Method Summary

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

    • 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 invalid input: '<' buffer.length)
    • valueWrittenWhileFull

      private boolean valueWrittenWhileFull
  • Constructor Details

    • 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.
  • Method Details

    • get

      public T get()
      Returns the oldest Object from the OverWriteOldestBuffer and removes it.

      Pre-condition: getState must not currently return EMPTY.

      Specified by:
      get in interface ChannelDataStore<T>
      Returns:
      the oldest Object from the OverWriteOldestBuffer
    • startGet

      public T 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 ChannelDataStore<T>
      Returns:
      The oldest value in the buffer at this time
      See Also:
    • endGet

      public void endGet()
      This ends an extended rendezvous by the reader.
      Specified by:
      endGet in interface ChannelDataStore<T>
      See Also:
    • put

      public void put(T 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 interface ChannelDataStore<T>
      Parameters:
      value - the Object to put into the OverWriteOldestBuffer
    • getState

      public int getState()
      Returns the current state of the OverWriteOldestBuffer.
      Specified by:
      getState in interface ChannelDataStore<T>
      Returns:
      the current state of the OverWriteOldestBuffer (EMPTY or NONEMPTYFULL)
    • clone

      public 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 interface ChannelDataStore<T>
      Overrides:
      clone in class Object
      Returns:
      the cloned instance of this OverWriteOldestBuffer.
    • 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>