Interface PNCounter
- All Superinterfaces:
DistributedObject
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 TypeMethodDescriptionlong
addAndGet
(long delta) Adds the given value to the current value.long
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
Decrements by one the current value.long
Increments by one the current value.long
getAndSubtract
(long delta) Subtracts the given value from the current value.long
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 Details
-
get
long get()Returns the current value of the counter.- Throws:
NoDataMemberInClusterException
- if the cluster does not contain any data membersConsistencyLostException
- if the session guarantees have been lost (see class level javadoc)- See Also:
-
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 membersConsistencyLostException
- if the session guarantees have been lost (see class level javadoc)- See Also:
-
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 membersConsistencyLostException
- if the session guarantees have been lost (see class level javadoc)- See Also:
-
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 membersConsistencyLostException
- if the session guarantees have been lost (see class level javadoc)- See Also:
-
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 membersConsistencyLostException
- if the session guarantees have been lost (see class level javadoc)- See Also:
-
decrementAndGet
long decrementAndGet()Decrements by one the current value.- Returns:
- the updated value
- Throws:
NoDataMemberInClusterException
- if the cluster does not contain any data membersConsistencyLostException
- if the session guarantees have been lost (see class level javadoc)- See Also:
-
incrementAndGet
long incrementAndGet()Increments by one the current value.- Returns:
- the updated value
- Throws:
NoDataMemberInClusterException
- if the cluster does not contain any data membersConsistencyLostException
- if the session guarantees have been lost (see class level javadoc)- See Also:
-
getAndDecrement
long getAndDecrement()Decrements by one the current value.- Returns:
- the previous value
- Throws:
NoDataMemberInClusterException
- if the cluster does not contain any data membersConsistencyLostException
- if the session guarantees have been lost (see class level javadoc)- See Also:
-
getAndIncrement
long getAndIncrement()Increments by one the current value.- Returns:
- the previous value
- Throws:
NoDataMemberInClusterException
- if the cluster does not contain any data membersConsistencyLostException
- if the session guarantees have been lost (see class level javadoc)- See Also:
-
reset
void reset()Resets the observed state by this PN counter. This method may be used after a method invocation has thrown aConsistencyLostException
to reset the proxy and to be able to start a new session.
-