edu.utah.janos.nodeos
Class CommSpaceHandle

java.lang.Object
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  +--edu.utah.janosvm.sys.ListNode
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        +--edu.utah.janosvm.sys.Importable
              |
              +--edu.utah.janos.nodeos.CommSpaceHandle

public final class CommSpaceHandle

extends edu.utah.janosvm.sys.Importable

A handle on a CommSpace. A CommSpace is an inter-process communication facility based lightly on Linda's "tuples". The space consists of an array of CommSpaceElements. Elements are copied out on read. A thread may write, read, swap, "wait" or "take" any element.

XXX Semantics during a failed take() are probably wrong.

Author:

Janos Ministry of Development

See Also:

CommSpace

Fields inherited from class edu.utah.janosvm.sys.ListNode

pred, succ

Constructor Summary

CommSpaceHandle()
Create an empty handle.

Method Summary

static CommSpaceHandle	newCommSpace(CommSpaceHandle csh, int size) Create a CommSpace and attach it to the given handle.
static CommSpaceHandle	newCommSpace(int size) Create a new CommSpace of the given size and return a handle to it.
CommSpaceElement	read(int index) Read the element at the given index.
int	resize(int newsize) Resize the CommSpace pointed to by this handle to contain the given number of slots.
int	size() Return the number of slots in the CommSpace pointed to by this handle.
CommSpaceElement	swap(int index, CommSpaceElement elem) Swap an element with the one currently in the given index.
CommSpaceElement	take(int index) Take an element from the given index and put a null in its place.
CommSpaceElement	waitToTake(int index) Wait for an element to be placed into the given index.
void	write(int index, CommSpaceElement elem) Write the given element to the given index.

Methods inherited from class edu.utah.janosvm.sys.Importable

clone, equals, pointsTo

Methods inherited from class edu.utah.janosvm.sys.ListNode

append, prepend, remove

Methods inherited from class java.lang.Object

getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CommSpaceHandle

public CommSpaceHandle()

Create an empty handle.

See Also:

newCommSpace(CommSpaceHandle,int)

Method Detail

newCommSpace

public static CommSpaceHandle newCommSpace(int size)

Create a new CommSpace of the given size and return a handle to it.

Parameters:

size - The size of the CommSpace.

Returns:

The handle to the CommSpace.

newCommSpace

public static CommSpaceHandle newCommSpace(CommSpaceHandle csh,
                                           int size)

Create a CommSpace and attach it to the given handle.

Parameters:

csh - The CommSpaceHandle to attach to the newly created CommSpace.

size - The size of the CommSpace.

Returns:

The handle that was passed in.

size

public int size()

Return the number of slots in the CommSpace pointed to by this handle.

resize

public int resize(int newsize)

Resize the CommSpace pointed to by this handle to contain the given number of slots.

XXX what happens when resizing to smaller than current and dropping items?

write

public void write(int index,
                  CommSpaceElement elem)
           throws java.lang.ArrayIndexOutOfBoundsException

Write the given element to the given index. Overwrites whatever is already there.

Parameters:

index - The index in the CommSpace to write into.

elem - The element to copy into the CommSpace.

take

public CommSpaceElement take(int index)
                      throws java.lang.ArrayIndexOutOfBoundsException

Take an element from the given index and put a null in its place. The read and replace are atomic with respect to other take()s at the given index. XXX semantically equivalent to swap(index, null)

Parameters:

index - The index in the CommSpace that we should take.

Returns:

null or the CommSpaceElement that was in the given index.

See Also:

swap(int,CommSpaceElement)

waitToTake

public CommSpaceElement waitToTake(int index)
                            throws java.lang.InterruptedException,
                                   java.lang.ArrayIndexOutOfBoundsException

Wait for an element to be placed into the given index. Then atomically take the element and replace with null.

Parameters:

index - The index in the CommSpace that we should take.

Returns:

the CommSpaceElement that was in the given index.

read

public CommSpaceElement read(int index)
                      throws java.lang.ArrayIndexOutOfBoundsException

Read the element at the given index.

Parameters:

index - The index in the CommSpace that we should take.

Returns:

Null or the CommSpaceElement that was in the given index.

swap

public CommSpaceElement swap(int index,
                             CommSpaceElement elem)
                      throws java.lang.ArrayIndexOutOfBoundsException

Swap an element with the one currently in the given index.

Parameters:

index - The index in the CommSpace that we should take.

elem - The element to swap into the index.

Returns:

Null or the CommSpaceElement that was in the given index.