Class PNCounter

java.lang.Object

com.loomcache.server.datastructures.PNCounter

public class PNCounter
extends Object

Positive-Negative Counter (PN-Counter) CRDT.

Maintains two internal G-Counters so that both increments and decrements are monotonic at the state level:

• P: sum of all positive increments per node
• N: sum of all negative decrements per node

Value = sum(P) - sum(N).

Merges are element-wise max per node and commutative, associative and idempotent — anti-entropy-safe.

Since:

1.0

Constructor Summary

Constructors

Constructor	Description
PNCounter(String name, String nodeId, int instanceNumber)
PNCounter(String name, String nodeId, int instanceNumber, Map<String,Long> restoredPCounters, Map<String,Long> restoredNCounters, Map<String,Long> restoredVectorClock)

Method Summary

Modifier and Type	Method	Description
void	decrement()	Decrement the counter by 1.
void	decrement(long delta)	Decrement the counter by delta.
void	decrementForNode(String contributorId, long delta)	Decrement the counter by delta for a logical contributor.
long	get()	Get the current value of the counter.
long	getLocalN()	Get the local N counter value for this node.
long	getLocalP()	Get the local P counter value for this node.
Map<String,Long>	getNegativeCountersSnapshot()	Snapshot the negative component by contributor id.
int	getNodeCount()	Get the number of nodes that have contributed to this counter.
long	getNodeN(String node)	Get the N counter value for a specific node.
long	getNodeP(String node)	Get the P counter value for a specific node.
long	getNSum()	Get the N (negative) sum across all nodes.
Map<String,Long>	getPositiveCountersSnapshot()	Snapshot the positive component by contributor id.
long	getPSum()	Get the P (positive) sum across all nodes.
Map<String,Long>	getVectorClock()	Get the vector clock version (for diagnostics).
void	increment()	Increment the counter by 1.
void	increment(long delta)	Increment the counter by delta.
void	incrementForNode(String contributorId, long delta)	Increment the counter by delta for a logical contributor.
void	merge(PNCounter other)	Merge another PN-Counter into this one.
void	reset()	Reset is NOT supported for PN-Counters in a distributed context.

Methods inherited from class Object

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

Constructor Details

PNCounter

public PNCounter(String name,
 String nodeId,
 int instanceNumber)

PNCounter

public PNCounter(String name,
 String nodeId,
 int instanceNumber,
 Map<String,Long> restoredPCounters,
 Map<String,Long> restoredNCounters,
 Map<String,Long> restoredVectorClock)

Method Details

increment

public void increment()

Increment the counter by 1.

increment

public void increment(long delta)

Increment the counter by delta.

Parameters:

delta - the amount to add (can be negative for decrement)

incrementForNode

public void incrementForNode(String contributorId,
 long delta)

Increment the counter by delta for a logical contributor.

Wire operations use the client PN-counter session id as the contributor so every Raft replica applies an identical CRDT state, independent of the server node that happened to execute the log entry.

Parameters:

contributorId - logical CRDT contributor/session id

delta - the amount to add (can be negative for decrement)

decrement

public void decrement()

Decrement the counter by 1.

decrement

public void decrement(long delta)

Decrement the counter by delta.

Parameters:

delta - the amount to subtract

decrementForNode

public void decrementForNode(String contributorId,
 long delta)

Decrement the counter by delta for a logical contributor.

Parameters:

contributorId - logical CRDT contributor/session id

delta - the amount to subtract

get

public long get()

Get the current value of the counter. Value = sum(P) - sum(N) across all known nodes.

merge

public void merge(PNCounter other)

Merge another PN-Counter into this one.

getPSum

public long getPSum()

Get the P (positive) sum across all nodes.

getNSum

public long getNSum()

Get the N (negative) sum across all nodes.

getVectorClock

public Map<String,Long> getVectorClock()

Get the vector clock version (for diagnostics).

getPositiveCountersSnapshot

public Map<String,Long> getPositiveCountersSnapshot()

Snapshot the positive component by contributor id.

getNegativeCountersSnapshot

public Map<String,Long> getNegativeCountersSnapshot()

Snapshot the negative component by contributor id.

getNodeCount

public int getNodeCount()

Get the number of nodes that have contributed to this counter.

getLocalP

public long getLocalP()

Get the local P counter value for this node.

getLocalN

public long getLocalN()

Get the local N counter value for this node.

getNodeP

public long getNodeP(String node)

Get the P counter value for a specific node.

getNodeN

public long getNodeN(String node)

Get the N counter value for a specific node.

reset

public void reset()

Reset is NOT supported for PN-Counters in a distributed context.

PN-Counter state must evolve monotonically (element-wise max on merge). A local reset is non-monotonic: if A resets after B merges A's state, a subsequent merge of B into A will silently restore pre-reset values.

Throws:

UnsupportedOperationException - always — reset violates CRDT merge invariants