Documentation Version: 3.3 - Publication Date : Sep 07, 2014

IAtomicLong

Hazelcast IAtomicLong is the distributed implementation of java.util.concurrent.atomic.AtomicLong. It offers most of AtomicLong's operations such as get, set, getAndSet, compareAndSet and incrementAndGet. Since IAtomicLong is a distributed implementation, these operations involve remote calls and hence their performances differ from AtomicLong.

Below sample code creates an instance, increments it by a million and prints the count.

public class Member {
  public static void main( String[] args ) {
    HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();     
    IAtomicLong counter = hazelcastInstance.getAtomicLong( "counter" );
    for ( int k = 0; k < 1000 * 1000; k++ ) {
      if ( k % 500000 == 0 ) {
        System.out.println( "At: " + k );
      }
      counter.incrementAndGet();
    }
    System.out.printf( "Count is %s\n", counter.get() );
  }
}

When you start other instances with the code above, you will see the count as member count times a million.

You can send functions to an IAtomicLong. Function is a Hazelcast owned, single method interface. Below sample Function implementation doubles the original value.

private static class Add2Function implements Function <Long, Long> { 
  @Override
  public Long apply( Long input ) { 
    return input + 2;
  }
}

Below methods can be used to execute functions on IAtomicLong.

• apply: It applies the function to the value in IAtomicLong without changing the actual value and returning the result.
• alter: It alters the value stored in the IAtomicLong by applying the function. It will not send back a result.
• alterAndGet: It alters the value stored in the IAtomicLong by applying the function, storing the result in the IAtomicLong and returning the result.
• getAndAlter: It alters the value stored in the IAtomicLong by applying the function and returning the original value.

Below sample code includes these methods.

public class Member {
  public static void main( String[] args ) {
    HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();         
    IAtomicLong atomicLong = hazelcastInstance.getAtomicLong( "counter" );

    atomicLong.set( 1 );
    long result = atomicLong.apply( new Add2Function() );         
    System.out.println( "apply.result: " + result);         
    System.out.println( "apply.value: " + atomicLong.get() );

    atomicLong.set( 1 );
    atomicLong.alter( new Add2Function() );             
    System.out.println( "alter.value: " + atomicLong.get() );

    atomicLong.set( 1 );
    result = atomicLong.alterAndGet( new Add2Function() );         
    System.out.println( "alterAndGet.result: " + result );         
    System.out.println( "alterAndGet.value: " + atomicLong.get() );

    atomicLong.set( 1 );
    result = atomicLong.getAndAlter( new Add2Function() );         
    System.out.println( "getAndAlter.result: " + result );         
    System.out.println( "getAndAlter.value: " + atomicLong.get() );
  }
}

The reason for using a function instead of a simple code line like atomicLong.set(atomicLong.get() + 2)); is that, read and write operations of IAtomicLong are not atomic. Since it is a distributed implementation, those operations can be remote ones, which may lead to race problems. By using functions, the data is not pulled into the code, but the code is sent to the data. And this makes it more scalable.

ATTENTION: IAtomicLong has 1 synchronous backup and no asynchronous backups. Its backup count is not configurable.