Batch AsyncStorage.multiGet calls

Reviewed By: javache

Differential Revision: D2636553

fb-gh-sync-id: d6351b67c615d8c01c11c10e32321a9764c54c67

Libraries/Storage/AsyncStorage.js

@@ -33,6 +33,10 @@ var RCTAsyncStorage = RCTAsyncRocksDBStorage || RCTAsyncSQLiteStorage || RCTAsyn
 * method returns a `Promise` object.
 */
var AsyncStorage = {
  _getRequests: ([]: Array<any>),
  _getKeys: ([]: Array<string>),
  _immediate: (null: ?number),

  /**
   * Fetches `key` and passes the result to `callback`, along with an `Error` if
   * there is any. Returns a `Promise` object.
@@ -164,6 +168,32 @@ var AsyncStorage = {
   * indicate which key caused the error.
   */

  /** Flushes any pending requests using a single multiget */
  flushGetRequests: function(): void {
    const getRequests = this._getRequests;
    const getKeys = this._getKeys;

    this._getRequests = [];
    this._getKeys = [];

    RCTAsyncStorage.multiGet(getKeys, function(errors, result) {
      // Even though the runtime complexity of this is theoretically worse vs if we used a map,
      // it's much, much faster in practice for the data sets we deal with (we avoid
      // allocating result pair arrays). This was heavily benchmarked.
      const reqLength = getRequests.length;
      for (let i = 0; i < reqLength; i++) {
        const request = getRequests[i];
        const requestKeys = request.keys;
        var requestResult = result.filter(function(resultPair) {
          return requestKeys.indexOf(resultPair[0]) !== -1;
        });

        request.callback && request.callback(null, requestResult);
        request.resolve && request.resolve(requestResult);
      }
    });
  },

  /**
   * multiGet invokes callback with an array of key-value pair arrays that
   * matches the input format of multiSet. Returns a `Promise` object.
@@ -174,17 +204,30 @@ var AsyncStorage = {
    keys: Array<string>,
    callback?: ?(errors: ?Array<Error>, result: ?Array<Array<string>>) => void
  ): Promise {
    return new Promise((resolve, reject) => {
      RCTAsyncStorage.multiGet(keys, function(errors, result) {
        var error = convertErrors(errors);
        callback && callback(error, result);
        if (error) {
          reject(error);
        } else {
          resolve(result);
        }
    if (!this._immediate) {
      this._immediate = setImmediate(() => {
        this._immediate = null;
        this.flushGetRequests();
      });
    }

    var getRequest = {
      keys: keys,
      callback: callback,
      keyIndex: this._getKeys.length,
      resolve: null,
      reject: null,
    };

    var promiseResult = new Promise((resolve, reject) => {
      getRequest.resolve = resolve;
      getRequest.reject = reject;
    });

    this._getRequests.push(getRequest);
    this._getKeys.push.apply(this._getKeys, keys);

    return promiseResult;
  },

  /**