Package protocols.apps.canvas

Class PaintOp

java.lang.Object

protocols.apps.canvas.PaintOp

public final class PaintOp
extends Object

A single paint operation: "cell (x,y) becomes colour argb". This is the atomic unit the canvas disseminates by gossip and the unit it stores per cell.

Last-writer-wins (why the canvas converges)

Each op carries a timestamp (the painter's wall clock at paint time) and the painter's originId. A cell keeps whichever op is the winner under the total order in isNewerThan(protocols.apps.canvas.PaintOp): higher timestamp first, ties broken by originId then opId. Because that order is total and deterministic, any two nodes that have applied the same set of ops hold the identical winner in every cell — independent of the order the gossip waves delivered them. Convergence is therefore a property of dissemination completeness alone, which is exactly what the experiments harness measures.

opId is a globally-unique identifier for the op, assigned once at the origin. It is the final tie-breaker, and the stable key the telemetry uses to correlate "broadcast on node A" with "delivered on node B".

Constructor Summary

Constructors

Constructor	Description
PaintOp(int x, int y, int argb, long timestamp, String originId, UUID opId)

Method Summary

Modifier and Type	Method	Description
int	getArgb()
UUID	getOpId()
String	getOriginId()
long	getTimestamp()
int	getX()
int	getY()
boolean	isNewerThan(PaintOp other)	Total, deterministic last-writer-wins order: this op beats other iff it has a strictly higher timestamp, or an equal timestamp and a greater originId, or equal on both and a greater opId.
static PaintOp	readFrom(DataInputStream in)	Read one op previously written by writeTo(java.io.DataOutputStream).
String	toString()
void	writeTo(DataOutputStream out)	Append this op to out (see readFrom(java.io.DataInputStream) for the inverse).

Methods inherited from class java.lang.Object

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

Constructor Details

PaintOp

public PaintOp(int x,
 int y,
 int argb,
 long timestamp,
 String originId,
 UUID opId)

Method Details

getX

public int getX()

getY

public int getY()

getArgb

public int getArgb()

getTimestamp

public long getTimestamp()

getOriginId

public String getOriginId()

getOpId

public UUID getOpId()

isNewerThan

public boolean isNewerThan(PaintOp other)

Total, deterministic last-writer-wins order: this op beats other iff it has a strictly higher timestamp, or an equal timestamp and a greater originId, or equal on both and a greater opId. other may be null (an empty cell), which this always wins.

writeTo

public void writeTo(DataOutputStream out)
             throws IOException

Append this op to out (see readFrom(java.io.DataInputStream) for the inverse).

Throws:

IOException

readFrom

public static PaintOp readFrom(DataInputStream in)
                        throws IOException

Read one op previously written by writeTo(java.io.DataOutputStream).

Throws:

IOException

toString

public String toString()

Overrides:

toString in class Object