com.hazelcast.crdt.pncounter

Interface PNCounter

All Superinterfaces:

DistributedObject

public interface PNCounter
extends DistributedObject

PN (Positive-Negative) CRDT counter.

The counter supports adding and subtracting values as well as retrieving the current counter value. Each replica of this counter can perform operations locally without coordination with the other replicas, thus increasing availability. The counter guarantees that whenever two nodes have received the same set of updates, possibly in a different order, their state is identical, and any conflicting updates are merged automatically. If no new updates are made to the shared state, all nodes that can communicate will eventually have the same data.

The updates to this counter are applied locally when invoked on a CRDT replica. A replica can be any hazelcast instance which is not a client or a lite member. The number of replicas in the cluster is determined by the PNCounterConfig.getReplicaCount() configuration value.

When invoking updates from non-replica instance, the invocation is remote. This may lead to indeterminate state - the update may be applied but the response has not been received. In this case, the caller will be notified with a TargetDisconnectedException when invoking from a client or a MemberLeftException when invoked from a member.

The read and write methods provide monotonic read and RYW (read-your-write) guarantees. These guarantees are session guarantees which means that if no replica with the previously observed state is reachable, the session guarantees are lost and the method invocation will throw a ConsistencyLostException. This does not mean that an update is lost. All the updates are part of some replica and will be eventually reflected in the state of all other replicas. This exception just means that you cannot observe your own writes because all replicas that contain your updates are currently unreachable. After you have received a ConsistencyLostException, you can either wait for a sufficiently up-to-date replica to become reachable in which case the session can be continued, or you can reset the session by calling the reset() method. If you have called the reset() method, a new session is started with the next invocation to a CRDT replica.

If the PN Counter is used through a client, the invocations might throw TargetNotMemberException, indicating that the invocation targets are not members of the cluster anymore. That might happen when the client is connected to a new cluster, but the member list is not updated yet, or all the replica members of the PN Counter is dead but the corresponding member list update is not received yet. Upon receiving the exception, one has to wait until the member list is updated on the client side and try again.

NOTE: The CRDT state is kept entirely on non-lite (data) members. If there aren't any and the methods here are invoked on a lite member, they will fail with an NoDataMemberInClusterException.

Since:

3.10

Method Summary

Modifier and Type	Method and Description
long	addAndGet(long delta) Adds the given value to the current value.
long	decrementAndGet() Decrements by one the current value.
long	get() Returns the current value of the counter.
long	getAndAdd(long delta) Adds the given value to the current value.
long	getAndDecrement() Decrements by one the current value.
long	getAndIncrement() Increments by one the current value.
long	getAndSubtract(long delta) Subtracts the given value from the current value.
long	incrementAndGet() Increments by one the current value.
void	reset() Resets the observed state by this PN counter.
long	subtractAndGet(long delta) Subtracts the given value from the current value.

Methods inherited from interface com.hazelcast.core.DistributedObject

destroy, getDestroyContextForTenant, getName, getPartitionKey, getServiceName

Method Detail

get

long get()

Returns the current value of the counter.

Throws:

NoDataMemberInClusterException - if the cluster does not contain any data members

ConsistencyLostException - if the session guarantees have been lost (see class level javadoc)

See Also:

Cluster.getClusterVersion()

getAndAdd

long getAndAdd(long delta)

Adds the given value to the current value.

Parameters:

delta - the value to add

Returns:

the previous value

Throws:

NoDataMemberInClusterException - if the cluster does not contain any data members

ConsistencyLostException - if the session guarantees have been lost (see class level javadoc)

See Also:

Cluster.getClusterVersion()

addAndGet

long addAndGet(long delta)

Adds the given value to the current value.

Parameters:

delta - the value to add

Returns:

the updated value

Throws:

NoDataMemberInClusterException - if the cluster does not contain any data members

ConsistencyLostException - if the session guarantees have been lost (see class level javadoc)

See Also:

Cluster.getClusterVersion()

getAndSubtract

long getAndSubtract(long delta)

Subtracts the given value from the current value.

Parameters:

delta - the value to add

Returns:

the previous value

Throws:

NoDataMemberInClusterException - if the cluster does not contain any data members

ConsistencyLostException - if the session guarantees have been lost (see class level javadoc)

See Also:

Cluster.getClusterVersion()

subtractAndGet

long subtractAndGet(long delta)

Subtracts the given value from the current value.

Parameters:

delta - the value to subtract

Returns:

the updated value

Throws:

NoDataMemberInClusterException - if the cluster does not contain any data members

ConsistencyLostException - if the session guarantees have been lost (see class level javadoc)

See Also:

Cluster.getClusterVersion()

decrementAndGet

long decrementAndGet()

Decrements by one the current value.

Returns:

the updated value

Throws:

NoDataMemberInClusterException - if the cluster does not contain any data members

ConsistencyLostException - if the session guarantees have been lost (see class level javadoc)

See Also:

Cluster.getClusterVersion()

incrementAndGet

long incrementAndGet()

Increments by one the current value.

Returns:

the updated value

Throws:

NoDataMemberInClusterException - if the cluster does not contain any data members

ConsistencyLostException - if the session guarantees have been lost (see class level javadoc)

See Also:

Cluster.getClusterVersion()

getAndDecrement

long getAndDecrement()

Decrements by one the current value.

Returns:

the previous value

Throws:

NoDataMemberInClusterException - if the cluster does not contain any data members

ConsistencyLostException - if the session guarantees have been lost (see class level javadoc)

See Also:

Cluster.getClusterVersion()

getAndIncrement

long getAndIncrement()

Increments by one the current value.

Returns:

the previous value

Throws:

NoDataMemberInClusterException - if the cluster does not contain any data members

ConsistencyLostException - if the session guarantees have been lost (see class level javadoc)

See Also:

Cluster.getClusterVersion()

reset

void reset()

Resets the observed state by this PN counter. This method may be used after a method invocation has thrown a ConsistencyLostException to reset the proxy and to be able to start a new session.