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LimitChunkCountPlugin.js
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Thu, Feb 13, 18:58

LimitChunkCountPlugin.js
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/*
MIT License http://www.opensource.org/licenses/mit-license.php
Author Tobias Koppers @sokra
*/
"use strict";
const { validate } = require("schema-utils");
const schema = require("../../schemas/plugins/optimize/LimitChunkCountPlugin.json");
const { STAGE_ADVANCED } = require("../OptimizationStages");
const LazyBucketSortedSet = require("../util/LazyBucketSortedSet");
const { compareChunks } = require("../util/comparators");
/** @typedef {import("../Chunk")} Chunk */
/** @typedef {import("../Compiler")} Compiler */
/** @typedef {import("../../declarations/plugins/optimize/LimitChunkCountPlugin").LimitChunkCountPluginOptions} LimitChunkCountPluginOptions */
/**
* @typedef {Object} ChunkCombination
* @property {boolean} deleted this is set to true when combination was removed
* @property {number} sizeDiff
* @property {number} integratedSize
* @property {Chunk} a
* @property {Chunk} b
* @property {number} aIdx
* @property {number} bIdx
* @property {number} aSize
* @property {number} bSize
*/
const addToSetMap = (map, key, value) => {
const set = map.get(key);
if (set === undefined) {
map.set(key, new Set([value]));
} else {
set.add(value);
}
};
class LimitChunkCountPlugin {
/**
* @param {LimitChunkCountPluginOptions=} options options object
*/
constructor(options) {
validate(schema, options, {
name: "Limit Chunk Count Plugin",
baseDataPath: "options"
});
this.options = options;
}
/**
* @param {Compiler} compiler the webpack compiler
* @returns {void}
*/
apply(compiler) {
const options = this.options;
compiler.hooks.compilation.tap("LimitChunkCountPlugin", compilation => {
compilation.hooks.optimizeChunks.tap(
{
name: "LimitChunkCountPlugin",
stage: STAGE_ADVANCED
},
chunks => {
const chunkGraph = compilation.chunkGraph;
const maxChunks = options.maxChunks;
if (!maxChunks) return;
if (maxChunks < 1) return;
if (compilation.chunks.size <= maxChunks) return;
let remainingChunksToMerge = compilation.chunks.size - maxChunks;
// order chunks in a deterministic way
const compareChunksWithGraph = compareChunks(chunkGraph);
const orderedChunks = Array.from(chunks).sort(compareChunksWithGraph);
// create a lazy sorted data structure to keep all combinations
// this is large. Size = chunks * (chunks - 1) / 2
// It uses a multi layer bucket sort plus normal sort in the last layer
// It's also lazy so only accessed buckets are sorted
const combinations = new LazyBucketSortedSet(
// Layer 1: ordered by largest size benefit
c => c.sizeDiff,
(a, b) => b - a,
// Layer 2: ordered by smallest combined size
c => c.integratedSize,
(a, b) => a - b,
// Layer 3: ordered by position difference in orderedChunk (-> to be deterministic)
c => c.bIdx - c.aIdx,
(a, b) => a - b,
// Layer 4: ordered by position in orderedChunk (-> to be deterministic)
(a, b) => a.bIdx - b.bIdx
);
// we keep a mapping from chunk to all combinations
// but this mapping is not kept up-to-date with deletions
// so `deleted` flag need to be considered when iterating this
/** @type {Map<Chunk, Set<ChunkCombination>>} */
const combinationsByChunk = new Map();
orderedChunks.forEach((b, bIdx) => {
// create combination pairs with size and integrated size
for (let aIdx = 0; aIdx < bIdx; aIdx++) {
const a = orderedChunks[aIdx];
// filter pairs that can not be integrated!
if (!chunkGraph.canChunksBeIntegrated(a, b)) continue;
const integratedSize = chunkGraph.getIntegratedChunksSize(
a,
b,
options
);
const aSize = chunkGraph.getChunkSize(a, options);
const bSize = chunkGraph.getChunkSize(b, options);
const c = {
deleted: false,
sizeDiff: aSize + bSize - integratedSize,
integratedSize,
a,
b,
aIdx,
bIdx,
aSize,
bSize
};
combinations.add(c);
addToSetMap(combinationsByChunk, a, c);
addToSetMap(combinationsByChunk, b, c);
}
return combinations;
});
// list of modified chunks during this run
// combinations affected by this change are skipped to allow
// further optimizations
/** @type {Set<Chunk>} */
const modifiedChunks = new Set();
let changed = false;
// eslint-disable-next-line no-constant-condition
loop: while (true) {
const combination = combinations.popFirst();
if (combination === undefined) break;
combination.deleted = true;
const { a, b, integratedSize } = combination;
// skip over pair when
// one of the already merged chunks is a parent of one of the chunks
if (modifiedChunks.size > 0) {
const queue = new Set(a.groupsIterable);
for (const group of b.groupsIterable) {
queue.add(group);
}
for (const group of queue) {
for (const mChunk of modifiedChunks) {
if (mChunk !== a && mChunk !== b && mChunk.isInGroup(group)) {
// This is a potential pair which needs recalculation
// We can't do that now, but it merge before following pairs
// so we leave space for it, and consider chunks as modified
// just for the worse case
remainingChunksToMerge--;
if (remainingChunksToMerge <= 0) break loop;
modifiedChunks.add(a);
modifiedChunks.add(b);
continue loop;
}
}
for (const parent of group.parentsIterable) {
queue.add(parent);
}
}
}
// merge the chunks
if (a.integrate(b, "limit")) {
compilation.chunks.delete(b);
// flag chunk a as modified as further optimization are possible for all children here
modifiedChunks.add(a);
changed = true;
remainingChunksToMerge--;
if (remainingChunksToMerge <= 0) break;
// Update all affected combinations
// delete all combination with the removed chunk
// we will use combinations with the kept chunk instead
for (const combination of combinationsByChunk.get(a)) {
if (combination.deleted) continue;
combination.deleted = true;
combinations.delete(combination);
}
// Update combinations with the kept chunk with new sizes
for (const combination of combinationsByChunk.get(b)) {
if (combination.deleted) continue;
if (combination.a === b) {
if (!chunkGraph.canChunksBeIntegrated(a, combination.b)) {
combination.deleted = true;
combinations.delete(combination);
continue;
}
// Update size
const newIntegratedSize = a.integratedSize(
combination.b,
options
);
const finishUpdate = combinations.startUpdate(combination);
combination.a = a;
combination.integratedSize = newIntegratedSize;
combination.aSize = integratedSize;
combination.sizeDiff =
combination.bSize + integratedSize - newIntegratedSize;
finishUpdate();
} else if (combination.b === b) {
if (!chunkGraph.canChunksBeIntegrated(combination.a, a)) {
combination.deleted = true;
combinations.delete(combination);
continue;
}
// Update size
const newIntegratedSize = combination.a.integratedSize(
a,
options
);
const finishUpdate = combinations.startUpdate(combination);
combination.b = a;
combination.integratedSize = newIntegratedSize;
combination.bSize = integratedSize;
combination.sizeDiff =
integratedSize + combination.aSize - newIntegratedSize;
finishUpdate();
}
}
combinationsByChunk.set(a, combinationsByChunk.get(b));
combinationsByChunk.delete(b);
}
}
if (changed) return true;
}
);
});
}
}
module.exports = LimitChunkCountPlugin;

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