org.apache.curator.framework.recipes.atomic

Class DistributedAtomicValue

java.lang.Object

org.apache.curator.framework.recipes.atomic.DistributedAtomicValue

public class DistributedAtomicValue
extends Object

A distributed value that attempts atomic sets. It first tries uses optimistic locking. If that fails, an optional InterProcessMutex is taken. For both optimistic and mutex, a retry policy is used to retry the increment.

The various methods return an AtomicValue object. You must always check AtomicValue.succeeded(). None of the methods (other than get()) are guaranteed to succeed.

Constructor Summary

Constructors

Constructor and Description
DistributedAtomicValue(org.apache.curator.framework.CuratorFramework client, String path, org.apache.curator.RetryPolicy retryPolicy) Creates in optimistic mode only - i.e.
DistributedAtomicValue(org.apache.curator.framework.CuratorFramework client, String path, org.apache.curator.RetryPolicy retryPolicy, PromotedToLock promotedToLock) Creates in mutex promotion mode.

Method Summary

Modifier and Type	Method and Description
AtomicValue<byte[]>	compareAndSet(byte[] expectedValue, byte[] newValue) Atomically sets the value to the given updated value if the current value == the expected value.
void	forceSet(byte[] newValue) Forcibly sets the value any guarantees of atomicity.
AtomicValue<byte[]>	get() Returns the current value of the counter.
boolean	initialize(byte[] value) Atomic values are initially set to the equivalent of NULL in a database.
AtomicValue<byte[]>	trySet(byte[] newValue) Attempt to atomically set the value to the given value.

Methods inherited from class java.lang.Object

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

Constructor Detail

DistributedAtomicValue

public DistributedAtomicValue(org.apache.curator.framework.CuratorFramework client,
                              String path,
                              org.apache.curator.RetryPolicy retryPolicy)

Creates in optimistic mode only - i.e. the promotion to a mutex is not done

Parameters:

client - the client

path - path to hold the value

retryPolicy - the retry policy to use

DistributedAtomicValue

public DistributedAtomicValue(org.apache.curator.framework.CuratorFramework client,
                              String path,
                              org.apache.curator.RetryPolicy retryPolicy,
                              PromotedToLock promotedToLock)

Creates in mutex promotion mode. The optimistic lock will be tried first using the given retry policy. If the increment does not succeed, a InterProcessMutex will be tried with its own retry policy

Parameters:

client - the client

path - path to hold the value

retryPolicy - the retry policy to use

promotedToLock - the arguments for the mutex promotion

Method Detail

get

public AtomicValue<byte[]> get()
                        throws Exception

Returns the current value of the counter. NOTE: if the value has never been set, 0 is returned.

Returns:

value info

Throws:

Exception - ZooKeeper errors

forceSet

public void forceSet(byte[] newValue)
              throws Exception

Forcibly sets the value any guarantees of atomicity.

Parameters:

newValue - the new value

Throws:

Exception - ZooKeeper errors

compareAndSet

public AtomicValue<byte[]> compareAndSet(byte[] expectedValue,
                                         byte[] newValue)
                                  throws Exception

Atomically sets the value to the given updated value if the current value == the expected value. Remember to always check AtomicValue.succeeded().

Parameters:

expectedValue - the expected value

newValue - the new value

Returns:

value info

Throws:

Exception - ZooKeeper errors

trySet

public AtomicValue<byte[]> trySet(byte[] newValue)
                           throws Exception

Attempt to atomically set the value to the given value. Remember to always check AtomicValue.succeeded().

Parameters:

newValue - the value to set

Returns:

value info

Throws:

Exception - ZooKeeper errors

initialize

public boolean initialize(byte[] value)
                   throws Exception

Atomic values are initially set to the equivalent of NULL in a database. Use this method to initialize the value. The value will be set if and only iff the node does not exist.

Parameters:

value - the initial value to set

Returns:

true if the value was set, false if the node already existed

Throws:

Exception - ZooKeeper errors