webpack/lib/cache/MemoryWithGcCachePlugin.js

Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/

"use strict";

const Cache = require("../Cache");

/** @typedef {import("webpack-sources").Source} Source */
/** @typedef {import("../Cache").Etag} Etag */
/** @typedef {import("../Compiler")} Compiler */
/** @typedef {import("../Module")} Module */

class MemoryWithGcCachePlugin {
	constructor({ maxGenerations }) {
		this._maxGenerations = maxGenerations;
	}
	/**
	 * Apply the plugin
	 * @param {Compiler} compiler the compiler instance
	 * @returns {void}
	 */
	apply(compiler) {
		const maxGenerations = this._maxGenerations;
		/** @type {Map<string, { etag: Etag | null, data: any }>} */
		const cache = new Map();
		/** @type {Map<string, { entry: { etag: Etag | null, data: any }, until: number }>} */
		const oldCache = new Map();
		let generation = 0;
		let cachePosition = 0;
		const logger = compiler.getInfrastructureLogger("MemoryWithGcCachePlugin");
		compiler.hooks.afterDone.tap("MemoryWithGcCachePlugin", () => {
			generation++;
			let clearedEntries = 0;
			let lastClearedIdentifier;
			for (const [identifier, entry] of oldCache) {
				if (entry.until > generation) break;

				oldCache.delete(identifier);
				if (cache.get(identifier) === undefined) {
					cache.delete(identifier);
					clearedEntries++;
					lastClearedIdentifier = identifier;
				}
			}
			if (clearedEntries > 0 || oldCache.size > 0) {
				logger.log(
					`${cache.size - oldCache.size} active entries, ${
						oldCache.size
					} recently unused cached entries${
						clearedEntries > 0
							? `, ${clearedEntries} old unused cache entries removed e. g. ${lastClearedIdentifier}`
							: ""
					}`
				);
			}
			let i = (cache.size / maxGenerations) | 0;
			let j = cachePosition >= cache.size ? 0 : cachePosition;
			cachePosition = j + i;
			for (const [identifier, entry] of cache) {
				if (j !== 0) {
					j--;
					continue;
				}
				if (entry !== undefined) {
					// We don't delete the cache entry, but set it to undefined instead
					// This reserves the location in the data table and avoids rehashing
					// when constantly adding and removing entries.
					// It will be deleted when removed from oldCache.
					cache.set(identifier, undefined);
					oldCache.delete(identifier);
					oldCache.set(identifier, {
						entry,
						until: generation + maxGenerations
					});
					if (i-- === 0) break;
				}
			}
		});
		compiler.cache.hooks.store.tap(
			{ name: "MemoryWithGcCachePlugin", stage: Cache.STAGE_MEMORY },
			(identifier, etag, data) => {
				cache.set(identifier, { etag, data });
			}
		);
		compiler.cache.hooks.get.tap(
			{ name: "MemoryWithGcCachePlugin", stage: Cache.STAGE_MEMORY },
			(identifier, etag, gotHandlers) => {
				const cacheEntry = cache.get(identifier);
				if (cacheEntry === null) {
					return null;
				} else if (cacheEntry !== undefined) {
					return cacheEntry.etag === etag ? cacheEntry.data : null;
				}
				const oldCacheEntry = oldCache.get(identifier);
				if (oldCacheEntry !== undefined) {
					const cacheEntry = oldCacheEntry.entry;
					if (cacheEntry === null) {
						oldCache.delete(identifier);
						cache.set(identifier, cacheEntry);
						return null;
					} else {
						if (cacheEntry.etag !== etag) return null;
						oldCache.delete(identifier);
						cache.set(identifier, cacheEntry);
						return cacheEntry.data;
					}
				}
				gotHandlers.push((result, callback) => {
					if (result === undefined) {
						cache.set(identifier, null);
					} else {
						cache.set(identifier, { etag, data: result });
					}
					return callback();
				});
			}
		);
		compiler.cache.hooks.shutdown.tap(
			{ name: "MemoryWithGcCachePlugin", stage: Cache.STAGE_MEMORY },
			() => {
				cache.clear();
				oldCache.clear();
			}
		);
	}
}
module.exports = MemoryWithGcCachePlugin;