mute-structs
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NodeJS module providing an implementation of the LogootSplit CRDT algorithm
97 lines (93 loc) • 3.91 kB
JavaScript
/*
This file is part of MUTE-structs.
Copyright (C) 2017 Matthieu Nicolas, Victorien Elvinger
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
import { Identifier } from "./identifier";
import { IdentifierTuple } from "./identifiertuple";
import { INT32_BOTTOM, INT32_TOP, isInt32, randomInt32, } from "./int32";
export const INT32_BOTTOM_USER = INT32_BOTTOM + 1;
export const INT32_TOP_USER = INT32_TOP - 1;
export const MIN_TUPLE = new IdentifierTuple(INT32_BOTTOM, 0, 0, 0);
export const MIN_TUPLE_USER = new IdentifierTuple(INT32_BOTTOM_USER, 0, 0, 0);
export const MAX_TUPLE_USER = new IdentifierTuple(INT32_TOP_USER, 0, 0, 0);
export const MAX_TUPLE = new IdentifierTuple(INT32_TOP, 0, 0, 0);
export function createBetweenPosition(id1, id2, replicaNumber, clock) {
console.assert(id1 === null || id2 === null ||
id1.compareTo(id2) === -1 /* Less */, "id1 < id2");
console.assert(isInt32(replicaNumber), "replicaNumber is an int32");
console.assert(isInt32(clock), "clock is an int32");
const seq1 = infiniteSequence(tuplesOf(id1), MIN_TUPLE_USER);
const seq2 = infiniteSequence(tuplesOf(id2), MAX_TUPLE_USER);
const tuples = [];
let tuple1 = seq1.next().value;
let tuple2 = seq2.next().value;
while (tuple1.compareTo(tuple2) === 0 /* Equal */) {
// Cannot insert a new tuple between tuple1 and tuple2
tuples.push(tuple1);
tuple1 = seq1.next().value;
tuple2 = seq2.next().value;
}
if (tuple1.random === INT32_BOTTOM && tuple2.random === INT32_BOTTOM_USER) {
// Special case to avoid problematic scenarios with renaming mechanism
tuples.push(tuple2);
while (tuple1.compareTo(MIN_TUPLE_USER) !== 0 /* Equal */) {
tuple1 = seq1.next().value;
}
tuple2 = seq2.next().value;
}
else if (tuple2.random - tuple1.random <= 1) {
tuples.push(tuple1);
tuple1 = seq1.next().value;
while (tuple2.compareTo(MAX_TUPLE_USER) !== 0 /* Equal */) {
tuple2 = seq2.next().value;
}
}
if (tuple1.random + 1 === INT32_TOP_USER) {
tuples.push(tuple1);
tuple1 = seq1.next().value;
}
const random = randomInt32(tuple1.random + 1, tuple2.random);
// random ∈ ]tuple1.random, tuple2.random[
// tuple1.random exclusion ensures a dense set
// tuple2.random exclusion ensures that newTuple < tuple2
// and thus that newId < id2
tuples.push(new IdentifierTuple(random, replicaNumber, clock, 0));
return new Identifier(tuples);
}
export function createAtPosition(replicaNumber, clock, position, offset) {
console.assert([position, replicaNumber, clock, offset].every(isInt32), "each value ∈ int32");
const tuple = new IdentifierTuple(position, replicaNumber, clock, offset);
return new Identifier([tuple]);
}
/**
* Generate an infinite sequence of tuples
*
* @param values
* @param defaultValue
*/
function* infiniteSequence(values, defaultValue) {
for (const v of values) {
yield v;
}
while (true) {
yield defaultValue;
}
}
/**
* @param id
* @return Tuples of `a' or an empty array if none.
*/
function tuplesOf(id) {
return (id !== null) ? id.tuples : [];
}
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