com.hazelcast.internal.util.counters

Class SwCounter

java.lang.Object

com.hazelcast.internal.util.counters.SwCounter

All Implemented Interfaces:

Counter

public abstract class SwCounter
extends Object
implements Counter

A Counter that is made to be used by a single writing thread.

It makes use of the lazySet to provide a lower overhead than a volatile write on X86 systems. The volatile write requires waiting for the store buffer to be drained which isn't needed for the lazySet.

This counter does not provide padding to prevent false sharing.

One might wonder why not use the AtomicLong.inc. The problem here is that AtomicLong requires a full fence, so there is waiting for store and load buffers to be drained. This is more expensive.

One might also wonder why not use the following:

     atomicLong.lazySet(atomicLong.get()+1)
 

This causes a lot of syntactic noise due to lack of abstraction. A counter.inc() gives a better clue what the intent is.

Method Summary

Modifier and Type	Method and Description
static SwCounter	newSwCounter() Creates a new SwCounter with 0 as initial value.
static SwCounter	newSwCounter(long initialValue) Creates a new SwCounter with the given initial value.

Methods inherited from class java.lang.Object

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

Methods inherited from interface com.hazelcast.internal.util.counters.Counter

get, inc, inc

Method Detail

newSwCounter

public static SwCounter newSwCounter()

Creates a new SwCounter with 0 as initial value.

Returns:

the created SwCounter, set to zero.

newSwCounter

public static SwCounter newSwCounter(long initialValue)

Creates a new SwCounter with the given initial value.

Parameters:

initialValue - the initial value for the SwCounter.

Returns:

the created SwCounter.