Package org.jcsp.util

Class OverWritingBuffer

java.lang.Object
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:
  • Field Summary

    Fields inherited from interface org.jcsp.util.ChannelDataStore

    EMPTY, FULL, NONEMPTYFULL
  • Constructor Summary

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

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

    • 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 Details

    • 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:
    • endGet

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