[INTERNAL] Optimise themeBuild with workerpool via fsinterface (#925)

JIRA: CPOUI5FOUNDATION-614

This change enhances #914 with a
fsInterface like objects that "read" the information through
`postMessages` via `MessageChannel -> MessagePort`

---------

Co-authored-by: Matthias Oßwald <mat.osswald@sap.com>
Co-authored-by: Merlin Beutlberger <m.beutlberger@sap.com>

lib/processors/themeBuilderWorker.js

@@ -0,0 +1,278 @@
+import workerpool from "workerpool";
+import themeBuilder from "./themeBuilder.js";
+import {createResource} from "@ui5/fs/resourceFactory";
+import {Buffer} from "node:buffer";
+
+/**
+ * Task to build library themes.
+ *
+ * @private
+ * @function default
+ * @static
+ *
+ * @param {object} parameters Parameters
+ * @param {MessagePort} parameters.fsInterfacePort
+ * @param {object[]} parameters.themeResources Input array of Uint8Array transferable objects
+ * 	that are the less sources to build upon. By nature those are @ui5/fs/Resource.
+ * @param {object} parameters.options Less compiler options
+ * @returns {Promise<object[]>} Resulting array of Uint8Array transferable objects
+ */
+export default async function execThemeBuild({
+	fsInterfacePort,
+	themeResources = [],
+	options = {}
+}) {
+	const fsThemeResources = deserializeResources(themeResources);
+	const fsReader = new FsWorkerThreadInterface(fsInterfacePort);
+
+	const result = await themeBuilder({
+		resources: fsThemeResources,
+		fs: fsReader,
+		options
+	});
+
+	return serializeResources(result);
+}
+
+/**
+ * Casts @ui5/fs/Resource-s into an Uint8Array transferable object
+ *
+ * @param {@ui5/fs/Resource[]} resourceCollection
+ * @returns {Promise<object[]>}
+ */
+export async function serializeResources(resourceCollection) {
+	return Promise.all(
+		resourceCollection.map(async (res) => ({
+			buffer: await res.getBuffer(),
+			path: res.getPath()
+		}))
+	);
+}
+
+/**
+ * Casts Uint8Array into @ui5/fs/Resource-s transferable object
+ *
+ * @param {Promise<object[]>} resources
+ * @returns {@ui5/fs/Resource[]}
+ */
+export function deserializeResources(resources) {
+	return resources.map((res) => {
+		// res.buffer is an Uint8Array object and needs to be cast
+		// to a Buffer in order to be read correctly.
+		return createResource({path: res.path, buffer: Buffer.from(res.buffer)});
+	});
+}
+
+/**
+ * "@ui5/fs/fsInterface" like class that uses internally
+ * "@ui5/fs/fsInterface", implements its methods, and
+ * sends the results to a MessagePort.
+ *
+ * Used in the main thread in a combination with FsWorkerThreadInterface.
+ */
+export class FsMainThreadInterface {
+	#comPorts = new Set();
+	#fsInterfaceReader = null;
+	#cache = Object.create(null);
+
+	/**
+	 * Constructor
+	 *
+	 * @param {@ui5/fs/fsInterface} fsInterfaceReader Reader for the Resources
+	 */
+	constructor(fsInterfaceReader) {
+		if (!fsInterfaceReader) {
+			throw new Error("fsInterfaceReader is mandatory argument");
+		}
+
+		this.#fsInterfaceReader = fsInterfaceReader;
+	}
+
+	/**
+	 * Adds MessagePort and starts listening for requests on it.
+	 *
+	 * @param {MessagePort} comPort port1 from a {code}MessageChannel{/code}
+	 */
+	startCommunication(comPort) {
+		if (!comPort) {
+			throw new Error("Communication channel is mandatory argument");
+		}
+
+		this.#comPorts.add(comPort);
+		comPort.on("message", (e) => this.#onMessage(e, comPort));
+		comPort.on("close", () => comPort.close());
+	}
+
+	/**
+	 * Ends MessagePort communication.
+	 *
+	 * @param {MessagePort} comPort port1 to remove from handling.
+	 */
+	endCommunication(comPort) {
+		comPort.close();
+		this.#comPorts.delete(comPort);
+	}
+
+	/**
+	 * Destroys the FsMainThreadInterface
+	 */
+	cleanup() {
+		this.#comPorts.forEach((comPort) => comPort.close());
+		this.#cache = null;
+		this.#fsInterfaceReader = null;
+	}
+
+	/**
+	 * Handles messages from the MessagePort
+	 *
+	 * @param {object} e data to construct the request
+	 * @param {string} e.action Action to perform. Corresponds to the names of
+	 * 	the public methods of "@ui5/fs/fsInterface"
+	 * @param {string} e.fsPath Path of the Resource
+	 * @param {object} e.options Options for "readFile" action
+	 * @param {MessagePort} comPort The communication channel
+	 */
+	#onMessage(e, comPort) {
+		switch (e.action) {
+		case "readFile":
+			this.#doRequest(comPort, {action: "readFile", fsPath: e.fsPath, options: e.options});
+			break;
+		case "stat":
+			this.#doRequest(comPort, {action: "stat", fsPath: e.fsPath});
+			break;
+		}
+	}
+
+	/**
+	 * Requests a Resource from the "@ui5/fs/fsInterface" and sends it to the worker threads
+	 * via postMessage.
+	 *
+	 * @param {MessagePort} comPort The communication channel
+	 * @param {object} parameters
+	 * @param {string} parameters.action Action to perform. Corresponds to the names of
+	 * 	the public methods of "@ui5/fs/fsInterface" and triggers this method of the
+	 *	"@ui5/fs/fsInterface" instance.
+	 * @param {string} parameters.fsPath Path of the Resource
+	 * @param {object} parameters.options Options for "readFile" action
+	 */
+	async #doRequest(comPort, {action, fsPath, options}) {
+		const cacheKey = `${fsPath}-${action}`;
+		if (!this.#cache[cacheKey]) {
+			this.#cache[cacheKey] = new Promise((res) => {
+				if (action === "readFile") {
+					this.#fsInterfaceReader.readFile(fsPath, options, (error, result) => res({error, result}));
+				} else if (action === "stat") {
+					this.#fsInterfaceReader.stat(fsPath, (error, result) =>
+						// The Stat object has some special methods that sometimes cannot be serialized
+						// properly in the postMessage. In this scenario, we do not need those methods,
+						// but just to check whether stats has resolved to something.
+						res(JSON.parse(JSON.stringify({error, result})))
+					);
+				} else {
+					res({error: new Error(`Action "${action}" is not available.`), result: null});
+				}
+			});
+		}
+
+		const fromCache = await this.#cache[cacheKey];
+		comPort.postMessage({action, fsPath, ...fromCache});
+	}
+}
+
+/**
+ * "@ui5/fs/fsInterface" like class that uses internally
+ * "@ui5/fs/fsInterface", implements its methods, and
+ * requests resources via MessagePort.
+ *
+ * Used in the main thread in a combination with FsMainThreadInterface.
+ */
+export class FsWorkerThreadInterface {
+	#comPort = null;
+	#callbacks = [];
+	#cache = Object.create(null);
+
+	/**
+	 * Constructor
+	 *
+	 * @param {MessagePort} comPort Communication port
+	 */
+	constructor(comPort) {
+		if (!comPort) {
+			throw new Error("Communication port is mandatory argument");
+		}
+
+		this.#comPort = comPort;
+		comPort.on("message", this.#onMessage.bind(this));
+		comPort.on("close", this.#onClose.bind(this));
+	}
+
+	/**
+	 * Handles messages from MessagePort
+	 *
+	 * @param {object} e
+	 * @param {string} e.action Action to perform. Corresponds to the names of
+	 * 	the public methods of "@ui5/fs/fsInterface"
+	 * @param {string} e.fsPath Path of the Resource
+	 * @param {*} e.result Response from the "action".
+	 * @param {object} e.error Error from the "action".
+	 */
+	#onMessage(e) {
+		const cbObject = this.#callbacks.find((cb) => cb.action === e.action && cb.fsPath === e.fsPath);
+
+		if (cbObject) {
+			this.#cache[`${e.fsPath}-${e.action}`] = {error: e.error, result: e.result};
+			this.#callbacks.splice(this.#callbacks.indexOf(cbObject), 1);
+			cbObject.callback(e.error, e.result);
+		} else {
+			throw new Error("No callback found for this message! Possible hang for the thread!", e);
+		}
+	}
+
+	/**
+	 * End communication
+	 */
+	#onClose() {
+		this.#comPort.close();
+		this.#cache = null;
+	}
+
+	/**
+	 * Makes a request via the MessagePort
+	 *
+	 * @param {object} parameters
+	 * @param {string} parameters.action Action to perform. Corresponds to the names of
+	 * 	the public methods.
+	 * @param {string} parameters.fsPath Path of the Resource
+	 * @param {object} parameters.options Options for "readFile" action
+	 * @param {Function} callback Callback to call when the "action" is executed and ready.
+	 */
+	#doRequest({action, fsPath, options}, callback) {
+		const cacheKey = `${fsPath}-${action}`;
+
+		if (this.#cache[cacheKey]) {
+			const {result, error} = this.#cache[cacheKey];
+			callback(error, result);
+		} else {
+			this.#callbacks.push({action, fsPath, callback});
+			this.#comPort.postMessage({action, fsPath, options});
+		}
+	}
+
+	readFile(fsPath, options, callback) {
+		this.#doRequest({action: "readFile", fsPath, options}, callback);
+	}
+
+	stat(fsPath, callback) {
+		this.#doRequest({action: "stat", fsPath}, callback);
+	}
+}
+
+// Test execution via ava is never done on the main thread
+/* istanbul ignore else */
+if (!workerpool.isMainThread) {
+	// Script got loaded through workerpool
+	// => Create a worker and register public functions
+	workerpool.worker({
+		execThemeBuild
+	});
+}