xapi.util.impl

Class Bitwise

java.lang.Object

xapi.util.impl.Bitwise

public final class Bitwise
extends Object

Need 32 boolean fields? At one int-per-pointer for boolean fields, that's 128 bytes of heap. Using one int value and one pointer to a Bitwise instance saves heap space, at the price of some bitwise math and synchronization code. All bitwise add and remove operations are synchronized (and volatile). All set and get operations are only volatile. This class may incur slight overhead in single-threaded implementations, (provided the jvm doesn't delete locking code because it knows it's unithread) but if used to represent multiple volatile synchronized boolean fields, it can be a very effective means to share state between multiple threads. Note that this class will enforce a happens-before relationship between threads writing to or reading from this value. If you have multiple sets of bools which should not enforce synchronicity between each other, you should use separate Bitwise objects for each. (This will also reduce the size of your bytecode constant pool, by encouraging the reuse of 1,2,4,8,16, instead of 0x1->0xFFFFF)

Author:

"James X. Nelson (james@wetheinter.net)"

Constructor Summary

Constructors

Constructor and Description
Bitwise(int initialValue)

Method Summary

Methods

Modifier and Type	Method and Description
int	getValue()
boolean	isFalse(int pos)
boolean	isTrue(int pos)
Bitwise	setFalse(int bitwise) Applies the int value using bitwise &~ (NOR) This method is synchronized to allow deterministic, concurrent access.
Bitwise	setTrue(int bitwise) Applies the int value using bitwise | This method is synchronized to allow deterministic, concurrent access.
void	setValue(int value) This is the fastest way to set a value, as it is not synchronized.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Bitwise

public Bitwise(int initialValue)

Method Detail

isTrue

public boolean isTrue(int pos)

isFalse

public boolean isFalse(int pos)

setTrue

public Bitwise setTrue(int bitwise)

Applies the int value using bitwise | This method is synchronized to allow deterministic, concurrent access. For known single-threaded operations, (getValue() | bitwise) is faster.

Parameters:

bitwise - - Binary flags to set to true.

Returns:

this, for chaining

setFalse

public Bitwise setFalse(int bitwise)

Applies the int value using bitwise &~ (NOR) This method is synchronized to allow deterministic, concurrent access. For known single-threaded operations, (getValue() &~ bitwise) is faster.

Parameters:

bitwise - - Binary flags to set to true.

Returns:

this, for chaining

getValue

public int getValue()

Returns:

The value stored in this register

setValue

public void setValue(int value)

This is the fastest way to set a value, as it is not synchronized. If you already know the or'd | together value, prefer .setValue() as it only performs one volatile write, instead of a synchronized, volatile read and write. If you are interleaving an overwrite and bitwise or operations concurrently, you deserve undeterministic behavior; synchro won't save you! :)

Parameters:

value - - The new value to use.