electron/atom/browser/lib/objects-registry.js

'use strict';

const EventEmitter = require('events').EventEmitter;
const v8Util = process.atomBinding('v8_util');

class ObjectsRegistry extends EventEmitter {
  constructor() {
    super();

    this.setMaxListeners(Number.MAX_VALUE);
    this.nextId = 0;

    // Stores all objects by ref-counting.
    // (id) => {object, count}
    this.storage = {};

    // Stores the IDs of objects referenced by WebContents.
    // (webContentsId) => [id]
    this.owners = {};
  }

  // Register a new object and return its assigned ID. If the object is already
  // registered then the already assigned ID would be returned.
  add(webContentsId, obj) {
    // Get or assign an ID to the object.
    let id = this.saveToStorage(obj);

    // Add object to the set of referenced objects.
    let owner = this.owners[webContentsId];
    if (!owner)
      owner = this.owners[webContentsId] = new Set();
    if (!owner.has(id)) {
      owner.add(id);
      // Increase reference count if not referenced before.
      this.storage[id].count++;
    }
    return id;
  }

  // Get an object according to its ID.
  get(id) {
    return this.storage[id].object;
  }

  // Dereference an object according to its ID.
  remove(webContentsId, id) {
    // Dereference from the storage.
    this.dereference(id);

    // Also remove the reference in owner.
    this.owners[webContentsId].delete(id);
  }

  // Clear all references to objects refrenced by the WebContents.
  clear(webContentsId) {
    this.emit(`clear-${webContentsId}`);

    let owner = this.owners[webContentsId];
    if (!owner)
      return;
    for (let id of owner)
      this.dereference(id);
    delete this.owners[webContentsId];
  }

  // Private: Saves the object into storage and assigns an ID for it.
  saveToStorage(object) {
    let id = v8Util.getHiddenValue(object, 'atomId');
    if (!id) {
      id = ++this.nextId;
      this.storage[id] = {
        count: 0,
        object: object
      };
      v8Util.setHiddenValue(object, 'atomId', id);
    }
    return id;
  }

  // Private: Dereference the object from store.
  dereference(id) {
    let pointer = this.storage[id];
    if (pointer == null) {
      return;
    }
    pointer.count -= 1;
    if (pointer.count === 0) {
      v8Util.deleteHiddenValue(pointer.object, 'atomId');
      return delete this.storage[id];
    }
  }
}

module.exports = new ObjectsRegistry;