All files / ima/storage WeakMapStorage.js

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85.71% Branches 12/14
80% Functions 8/10
84.38% Lines 27/32
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import ns from '../namespace';
import MapStorage from './MapStorage';
 
ns.namespace('ima.storage');
 
/**
 * A specialization of the {@codelink MapStorage} storage mimicking the native
 * {@code WeakMap} using its internal garbage collector used once the size of
 * the storage reaches the configured threshold.
 */
export default class WeakMapStorage extends MapStorage {
  /**
	 * Initializes the storage.
	 *
	 * @param {{entryTtl: number}} config Weak map storage configuration. The
	 *        fields have the following meaning:
	 *        - entryTtl The time-to-live of a storage entry in milliseconds.
	 */
  constructor(config) {
    super();
 
    /**
		 * The time-to-live of a storage entry in milliseconds.
		 *
		 * @type {number}
		 */
    this._entryTtl = config.entryTtl;
  }
 
  /**
	 * @inheritdoc
	 */
  has(key) {
    this._discardExpiredEntries();
 
    return super.has(key);
  }
 
  /**
	 * @inheritdoc
	 */
  get(key) {
    this._discardExpiredEntries();
 
    if (!super.has(key)) {
      return undefined;
    }
 
    return super.get(key).target;
  }
 
  /**
	 * @inheritdoc
	 */
  set(key, value) {
    this._discardExpiredEntries();
 
    return super.set(key, new WeakRef(value, this._entryTtl));
  }
 
  /**
	 * @inheritdoc
	 */
  delete(key) {
    this._discardExpiredEntries();
 
    return super.delete(key);
  }
 
  /**
	 * @inheritdoc
	 */
  keys() {
    this._discardExpiredEntries();
 
    return super.keys();
  }
 
  /**
	 * @inheritdoc
	 */
  size() {
    this._discardExpiredEntries();
 
    return super.size();
  }
 
  /**
	 * Deletes all expired entries from this storage.
	 */
  _discardExpiredEntries() {
    for (let key of super.keys()) {
      let targetReference = super.get(key);
      if (!targetReference.target) {
        // the reference has died
        super.delete(key);
      }
    }
  }
}
 
ns.ima.storage.WeakMapStorage = WeakMapStorage;
 
/**
 * A simple reference wrapper that emulates a weak reference. We seem to have
 * no other option, since WeakMap and WeakSet are not enumerable (so what is
 * the point of WeakMap and WeakSet if you still need to manage the keys?!) and
 * there is no native way to create a weak reference.
 */
class WeakRef {
  /**
	 * Initializes the weak reference to the target reference.
	 *
	 * @param {Object} target The target reference that should be referenced by
	 *        this weak reference.
	 * @param {number} ttl The maximum number of milliseconds the weak
	 *        reference should be kept. The reference will be discarded once
	 *        ACCESSED after the specified timeout.
	 */
  constructor(target, ttl) {
    Eif ($Debug) {
      if (!(target instanceof Object)) {
        throw new TypeError(
          'The target reference must point to an object, ' +
            'primitive values are not allowed'
        );
      }
      Iif (ttl <= 0) {
        throw new Error('The time-to-live must be positive');
      }
    }
 
    /**
		 * The actual target reference, or {@code null} if the reference has
		 * been already discarded.
		 *
		 * @type {?Object}
		 */
    this._reference = target;
 
    /**
		 * The UNIX timestamp with millisecond precision marking the moment at
		 * or after which the reference will be discarded.
		 *
		 * @type {number}
		 */
    this._expiration = Date.now() + ttl;
  }
 
  /**
	 * Returns the target reference, provided that the target reference is
	 * still alive. Returns {@code null} if the reference has been discarded.
	 *
	 * @return {?Object} The target reference, or {@code null} if the reference
	 *         has been discarded by the garbage collector.
	 */
  get target() {
    if (this._reference && Date.now() >= this._expiration) {
      this._reference = null; // let the GC do its job
    }
 
    return this._reference;
  }
}