angular-docs-cn/modules/@angular/benchpress/test/metric/perflog_metric_spec.ts

/**
 * @license
 * Copyright Google Inc. All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import {Provider} from '@angular/core';
import {AsyncTestCompleter, beforeEach, describe, expect, inject, it} from '@angular/core/testing/testing_internal';

import {Metric, Options, PerfLogEvent, PerfLogFeatures, PerflogMetric, ReflectiveInjector, WebDriverExtension} from '../../index';
import {StringMapWrapper} from '../../src/facade/collection';
import {isPresent} from '../../src/facade/lang';
import {TraceEventFactory} from '../trace_event_factory';

export function main() {
  var commandLog: any[];
  var eventFactory = new TraceEventFactory('timeline', 'pid0');

  function createMetric(
      perfLogs: PerfLogEvent[], perfLogFeatures: PerfLogFeatures,
      {microMetrics, forceGc, captureFrames, receivedData, requestCount}: {
        microMetrics?: {[key: string]: string},
        forceGc?: boolean,
        captureFrames?: boolean,
        receivedData?: boolean,
        requestCount?: boolean
      } = {}): Metric {
    commandLog = [];
    if (!perfLogFeatures) {
      perfLogFeatures =
          new PerfLogFeatures({render: true, gc: true, frameCapture: true, userTiming: true});
    }
    if (!microMetrics) {
      microMetrics = {};
    }
    var providers: Provider[] = [
      Options.DEFAULT_PROVIDERS, PerflogMetric.PROVIDERS,
      {provide: Options.MICRO_METRICS, useValue: microMetrics}, {
        provide: PerflogMetric.SET_TIMEOUT,
        useValue: (fn: Function, millis: number) => {
          commandLog.push(['setTimeout', millis]);
          fn();
        },
      },
      {
        provide: WebDriverExtension,
        useValue: new MockDriverExtension(perfLogs, commandLog, perfLogFeatures)
      }
    ];
    if (isPresent(forceGc)) {
      providers.push({provide: Options.FORCE_GC, useValue: forceGc});
    }
    if (isPresent(captureFrames)) {
      providers.push({provide: Options.CAPTURE_FRAMES, useValue: captureFrames});
    }
    if (isPresent(receivedData)) {
      providers.push({provide: Options.RECEIVED_DATA, useValue: receivedData});
    }
    if (isPresent(requestCount)) {
      providers.push({provide: Options.REQUEST_COUNT, useValue: requestCount});
    }
    return ReflectiveInjector.resolveAndCreate(providers).get(PerflogMetric);
  }

  describe('perflog metric', () => {

    function sortedKeys(stringMap: {[key: string]: any}) {
      var res: string[] = [];
      StringMapWrapper.forEach(stringMap, (_, key) => { res.push(key); });
      res.sort();
      return res;
    }

    it('should describe itself based on the perfLogFeatrues', () => {
      expect(sortedKeys(createMetric([[]], new PerfLogFeatures()).describe())).toEqual([
        'pureScriptTime', 'scriptTime'
      ]);

      expect(
          sortedKeys(createMetric([[]], new PerfLogFeatures({render: true, gc: false})).describe()))
          .toEqual(['pureScriptTime', 'renderTime', 'scriptTime']);

      expect(sortedKeys(createMetric([[]], null).describe())).toEqual([
        'gcAmount', 'gcTime', 'majorGcTime', 'pureScriptTime', 'renderTime', 'scriptTime'
      ]);

      expect(sortedKeys(createMetric([[]], new PerfLogFeatures({render: true, gc: true}), {
                          forceGc: true
                        }).describe()))
          .toEqual([
            'forcedGcAmount', 'forcedGcTime', 'gcAmount', 'gcTime', 'majorGcTime', 'pureScriptTime',
            'renderTime', 'scriptTime'
          ]);


      expect(sortedKeys(createMetric([[]], new PerfLogFeatures({userTiming: true}), {
                          receivedData: true,
                          requestCount: true
                        }).describe()))
          .toEqual(['pureScriptTime', 'receivedData', 'requestCount', 'scriptTime']);
    });

    it('should describe itself based on micro metrics', () => {
      var description =
          createMetric([[]], null, {microMetrics: {'myMicroMetric': 'someDesc'}}).describe();
      expect(description['myMicroMetric']).toEqual('someDesc');
    });

    it('should describe itself if frame capture is requested and available', () => {
      var description = createMetric([[]], new PerfLogFeatures({frameCapture: true}), {
                          captureFrames: true
                        }).describe();
      expect(description['frameTime.mean']).not.toContain('WARNING');
      expect(description['frameTime.best']).not.toContain('WARNING');
      expect(description['frameTime.worst']).not.toContain('WARNING');
      expect(description['frameTime.smooth']).not.toContain('WARNING');
    });

    it('should describe itself if frame capture is requested and not available', () => {
      var description = createMetric([[]], new PerfLogFeatures({frameCapture: false}), {
                          captureFrames: true
                        }).describe();
      expect(description['frameTime.mean']).toContain('WARNING');
      expect(description['frameTime.best']).toContain('WARNING');
      expect(description['frameTime.worst']).toContain('WARNING');
      expect(description['frameTime.smooth']).toContain('WARNING');
    });

    describe('beginMeasure', () => {

      it('should not force gc and mark the timeline',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           var metric = createMetric([[]], null);
           metric.beginMeasure().then((_) => {
             expect(commandLog).toEqual([['timeBegin', 'benchpress0']]);

             async.done();
           });
         }));

      it('should force gc and mark the timeline',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           var metric = createMetric([[]], null, {forceGc: true});
           metric.beginMeasure().then((_) => {
             expect(commandLog).toEqual([['gc'], ['timeBegin', 'benchpress0']]);

             async.done();
           });
         }));

    });

    describe('endMeasure', () => {

      it('should mark and aggregate events in between the marks',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           var events = [[
             eventFactory.markStart('benchpress0', 0), eventFactory.start('script', 4),
             eventFactory.end('script', 6), eventFactory.markEnd('benchpress0', 10)
           ]];
           var metric = createMetric(events, null);
           metric.beginMeasure().then((_) => metric.endMeasure(false)).then((data) => {
             expect(commandLog).toEqual([
               ['timeBegin', 'benchpress0'], ['timeEnd', 'benchpress0', null], 'readPerfLog'
             ]);
             expect(data['scriptTime']).toBe(2);

             async.done();
           });
         }));

      it('should mark and aggregate events since navigationStart',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           var events = [[
             eventFactory.markStart('benchpress0', 0), eventFactory.start('script', 4),
             eventFactory.end('script', 6), eventFactory.instant('navigationStart', 7),
             eventFactory.start('script', 8), eventFactory.end('script', 9),
             eventFactory.markEnd('benchpress0', 10)
           ]];
           var metric = createMetric(events, null);
           metric.beginMeasure().then((_) => metric.endMeasure(false)).then((data) => {
             expect(data['scriptTime']).toBe(1);

             async.done();
           });
         }));

      it('should restart timing', inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           var events = [
             [
               eventFactory.markStart('benchpress0', 0),
               eventFactory.markEnd('benchpress0', 1),
               eventFactory.markStart('benchpress1', 2),
             ],
             [eventFactory.markEnd('benchpress1', 3)]
           ];
           var metric = createMetric(events, null);
           metric.beginMeasure()
               .then((_) => metric.endMeasure(true))
               .then((_) => metric.endMeasure(true))
               .then((_) => {
                 expect(commandLog).toEqual([
                   ['timeBegin', 'benchpress0'], ['timeEnd', 'benchpress0', 'benchpress1'],
                   'readPerfLog', ['timeEnd', 'benchpress1', 'benchpress2'], 'readPerfLog'
                 ]);

                 async.done();
               });
         }));

      it('should loop and aggregate until the end mark is present',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           var events = [
             [eventFactory.markStart('benchpress0', 0), eventFactory.start('script', 1)],
             [eventFactory.end('script', 2)],
             [
               eventFactory.start('script', 3), eventFactory.end('script', 5),
               eventFactory.markEnd('benchpress0', 10)
             ]
           ];
           var metric = createMetric(events, null);
           metric.beginMeasure().then((_) => metric.endMeasure(false)).then((data) => {
             expect(commandLog).toEqual([
               ['timeBegin', 'benchpress0'], ['timeEnd', 'benchpress0', null], 'readPerfLog',
               ['setTimeout', 100], 'readPerfLog', ['setTimeout', 100], 'readPerfLog'
             ]);
             expect(data['scriptTime']).toBe(3);

             async.done();
           });
         }));

      it('should store events after the end mark for the next call',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           var events = [
             [
               eventFactory.markStart('benchpress0', 0), eventFactory.markEnd('benchpress0', 1),
               eventFactory.markStart('benchpress1', 1), eventFactory.start('script', 1),
               eventFactory.end('script', 2)
             ],
             [
               eventFactory.start('script', 3), eventFactory.end('script', 5),
               eventFactory.markEnd('benchpress1', 6)
             ]
           ];
           var metric = createMetric(events, null);
           metric.beginMeasure()
               .then((_) => metric.endMeasure(true))
               .then((data) => {
                 expect(data['scriptTime']).toBe(0);
                 return metric.endMeasure(true);
               })
               .then((data) => {
                 expect(commandLog).toEqual([
                   ['timeBegin', 'benchpress0'], ['timeEnd', 'benchpress0', 'benchpress1'],
                   'readPerfLog', ['timeEnd', 'benchpress1', 'benchpress2'], 'readPerfLog'
                 ]);
                 expect(data['scriptTime']).toBe(3);

                 async.done();
               });
         }));

      describe('with forced gc', () => {
        var events: PerfLogEvent[][];
        beforeEach(() => {
          events = [[
            eventFactory.markStart('benchpress0', 0), eventFactory.start('script', 4),
            eventFactory.end('script', 6), eventFactory.markEnd('benchpress0', 10),
            eventFactory.markStart('benchpress1', 11),
            eventFactory.start('gc', 12, {'usedHeapSize': 2500}),
            eventFactory.end('gc', 15, {'usedHeapSize': 1000}),
            eventFactory.markEnd('benchpress1', 20)
          ]];
        });

        it('should measure forced gc', inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             var metric = createMetric(events, null, {forceGc: true});
             metric.beginMeasure().then((_) => metric.endMeasure(false)).then((data) => {
               expect(commandLog).toEqual([
                 ['gc'], ['timeBegin', 'benchpress0'], ['timeEnd', 'benchpress0', 'benchpress1'],
                 'readPerfLog', ['gc'], ['timeEnd', 'benchpress1', null], 'readPerfLog'
               ]);
               expect(data['forcedGcTime']).toBe(3);
               expect(data['forcedGcAmount']).toBe(1.5);

               async.done();
             });
           }));

        it('should restart after the forced gc if needed',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             var metric = createMetric(events, null, {forceGc: true});
             metric.beginMeasure().then((_) => metric.endMeasure(true)).then((data) => {
               expect(commandLog[5]).toEqual(['timeEnd', 'benchpress1', 'benchpress2']);

               async.done();
             });
           }));

      });

    });

    describe('aggregation', () => {

      function aggregate(events: any[], {microMetrics, captureFrames, receivedData, requestCount}: {
        microMetrics?: {[key: string]: string},
        captureFrames?: boolean,
        receivedData?: boolean,
        requestCount?: boolean
      } = {}) {
        events.unshift(eventFactory.markStart('benchpress0', 0));
        events.push(eventFactory.markEnd('benchpress0', 10));
        var metric = createMetric([events], null, {
          microMetrics: microMetrics,
          captureFrames: captureFrames,
          receivedData: receivedData,
          requestCount: requestCount
        });
        return metric.beginMeasure().then((_) => metric.endMeasure(false));
      }

      describe('frame metrics', () => {
        it('should calculate mean frame time',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             aggregate(
                 [
                   eventFactory.markStart('frameCapture', 0), eventFactory.instant('frame', 1),
                   eventFactory.instant('frame', 3), eventFactory.instant('frame', 4),
                   eventFactory.markEnd('frameCapture', 5)
                 ],
                 {captureFrames: true})
                 .then((data) => {
                   expect(data['frameTime.mean']).toBe(((3 - 1) + (4 - 3)) / 2);
                   async.done();
                 });
           }));

        it('should throw if no start event',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {

             aggregate(
                 [eventFactory.instant('frame', 4), eventFactory.markEnd('frameCapture', 5)],
                 {captureFrames: true})
                 .catch((err): any => {
                   expect(() => {
                     throw err;
                   }).toThrowError('missing start event for frame capture');
                   async.done();
                 });
           }));

        it('should throw if no end event',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {

             aggregate(
                 [eventFactory.markStart('frameCapture', 3), eventFactory.instant('frame', 4)],
                 {captureFrames: true})
                 .catch((err): any => {
                   expect(() => { throw err; }).toThrowError('missing end event for frame capture');
                   async.done();
                 });
           }));

        it('should throw if trying to capture twice',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {

             aggregate(
                 [
                   eventFactory.markStart('frameCapture', 3),
                   eventFactory.markStart('frameCapture', 4)
                 ],
                 {captureFrames: true})
                 .catch((err): any => {
                   expect(() => {
                     throw err;
                   }).toThrowError('can capture frames only once per benchmark run');
                   async.done();
                 });
           }));

        it('should throw if trying to capture when frame capture is disabled',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             aggregate([eventFactory.markStart('frameCapture', 3)]).catch((err) => {
               expect(() => { throw err; })
                   .toThrowError(
                       'found start event for frame capture, but frame capture was not requested in benchpress');
               async.done();
               return null;
             });
           }));

        it('should throw if frame capture is enabled, but nothing is captured',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             aggregate([], {captureFrames: true}).catch((err): any => {
               expect(() => { throw err; })
                   .toThrowError(
                       'frame capture requested in benchpress, but no start event was found');
               async.done();
             });
           }));

        it('should calculate best and worst frame time',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             aggregate(
                 [
                   eventFactory.markStart('frameCapture', 0), eventFactory.instant('frame', 1),
                   eventFactory.instant('frame', 9), eventFactory.instant('frame', 15),
                   eventFactory.instant('frame', 18), eventFactory.instant('frame', 28),
                   eventFactory.instant('frame', 32), eventFactory.markEnd('frameCapture', 10)
                 ],
                 {captureFrames: true})
                 .then((data) => {
                   expect(data['frameTime.worst']).toBe(10);
                   expect(data['frameTime.best']).toBe(3);
                   async.done();
                 });
           }));

        it('should calculate percentage of smoothness to be good',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             aggregate(
                 [
                   eventFactory.markStart('frameCapture', 0), eventFactory.instant('frame', 1),
                   eventFactory.instant('frame', 2), eventFactory.instant('frame', 3),
                   eventFactory.markEnd('frameCapture', 4)
                 ],
                 {captureFrames: true})
                 .then((data) => {
                   expect(data['frameTime.smooth']).toBe(1.0);
                   async.done();
                 });
           }));

        it('should calculate percentage of smoothness to be bad',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             aggregate(
                 [
                   eventFactory.markStart('frameCapture', 0), eventFactory.instant('frame', 1),
                   eventFactory.instant('frame', 2), eventFactory.instant('frame', 22),
                   eventFactory.instant('frame', 23), eventFactory.instant('frame', 24),
                   eventFactory.markEnd('frameCapture', 4)
                 ],
                 {captureFrames: true})
                 .then((data) => {
                   expect(data['frameTime.smooth']).toBe(0.75);
                   async.done();
                 });
           }));

      });

      it('should report a single interval',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           aggregate([
             eventFactory.start('script', 0), eventFactory.end('script', 5)
           ]).then((data) => {
             expect(data['scriptTime']).toBe(5);
             async.done();
           });
         }));

      it('should sum up multiple intervals',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           aggregate([
             eventFactory.start('script', 0), eventFactory.end('script', 5),
             eventFactory.start('script', 10), eventFactory.end('script', 17)
           ]).then((data) => {
             expect(data['scriptTime']).toBe(12);
             async.done();
           });
         }));

      it('should ignore not started intervals',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           aggregate([eventFactory.end('script', 10)]).then((data) => {
             expect(data['scriptTime']).toBe(0);
             async.done();
           });
         }));

      it('should ignore not ended intervals',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           aggregate([eventFactory.start('script', 10)]).then((data) => {
             expect(data['scriptTime']).toBe(0);
             async.done();
           });
         }));

      it('should ignore nested intervals',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           aggregate([
             eventFactory.start('script', 0), eventFactory.start('script', 5),
             eventFactory.end('script', 10), eventFactory.end('script', 17)
           ]).then((data) => {
             expect(data['scriptTime']).toBe(17);
             async.done();
           });
         }));

      it('should ignore events from different processed as the start mark',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           var otherProcessEventFactory = new TraceEventFactory('timeline', 'pid1');
           var metric = createMetric(
               [[
                 eventFactory.markStart('benchpress0', 0), eventFactory.start('script', 0, null),
                 eventFactory.end('script', 5, null),
                 otherProcessEventFactory.start('script', 10, null),
                 otherProcessEventFactory.end('script', 17, null),
                 eventFactory.markEnd('benchpress0', 20)
               ]],
               null);
           metric.beginMeasure().then((_) => metric.endMeasure(false)).then((data) => {
             expect(data['scriptTime']).toBe(5);
             async.done();
           });
         }));

      it('should support scriptTime metric',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           aggregate([
             eventFactory.start('script', 0), eventFactory.end('script', 5)
           ]).then((data) => {
             expect(data['scriptTime']).toBe(5);
             async.done();
           });
         }));

      it('should support renderTime metric',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           aggregate([
             eventFactory.start('render', 0), eventFactory.end('render', 5)
           ]).then((data) => {
             expect(data['renderTime']).toBe(5);
             async.done();
           });
         }));

      it('should support gcTime/gcAmount metric',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           aggregate([
             eventFactory.start('gc', 0, {'usedHeapSize': 2500}),
             eventFactory.end('gc', 5, {'usedHeapSize': 1000})
           ]).then((data) => {
             expect(data['gcTime']).toBe(5);
             expect(data['gcAmount']).toBe(1.5);
             expect(data['majorGcTime']).toBe(0);
             async.done();
           });
         }));

      it('should support majorGcTime metric',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           aggregate([
             eventFactory.start('gc', 0, {'usedHeapSize': 2500}),
             eventFactory.end('gc', 5, {'usedHeapSize': 1000, 'majorGc': true})
           ]).then((data) => {
             expect(data['gcTime']).toBe(5);
             expect(data['majorGcTime']).toBe(5);
             async.done();
           });
         }));

      it('should support pureScriptTime = scriptTime-gcTime-renderTime',
         inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
           aggregate([
             eventFactory.start('script', 0), eventFactory.start('gc', 1, {'usedHeapSize': 1000}),
             eventFactory.end('gc', 4, {'usedHeapSize': 0}), eventFactory.start('render', 4),
             eventFactory.end('render', 5), eventFactory.end('script', 6)
           ]).then((data) => {
             expect(data['scriptTime']).toBe(6);
             expect(data['pureScriptTime']).toBe(2);
             async.done();
           });
         }));

      describe('receivedData', () => {
        it('should report received data since last navigationStart',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             aggregate(
                 [
                   eventFactory.instant('receivedData', 0, {'encodedDataLength': 1}),
                   eventFactory.instant('navigationStart', 1),
                   eventFactory.instant('receivedData', 2, {'encodedDataLength': 2}),
                   eventFactory.instant('navigationStart', 3),
                   eventFactory.instant('receivedData', 4, {'encodedDataLength': 4}),
                   eventFactory.instant('receivedData', 5, {'encodedDataLength': 8})
                 ],
                 {receivedData: true})
                 .then((data) => {
                   expect(data['receivedData']).toBe(12);
                   async.done();
                 });
           }));
      });

      describe('requestCount', () => {
        it('should report count of requests sent since last navigationStart',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             aggregate(
                 [
                   eventFactory.instant('sendRequest', 0),
                   eventFactory.instant('navigationStart', 1),
                   eventFactory.instant('sendRequest', 2),
                   eventFactory.instant('navigationStart', 3),
                   eventFactory.instant('sendRequest', 4), eventFactory.instant('sendRequest', 5)
                 ],
                 {requestCount: true})
                 .then((data) => {
                   expect(data['requestCount']).toBe(2);
                   async.done();
                 });
           }));
      });

      describe('microMetrics', () => {

        it('should report micro metrics',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             aggregate(
                 [
                   eventFactory.markStart('mm1', 0),
                   eventFactory.markEnd('mm1', 5),
                 ],
                 {microMetrics: {'mm1': 'micro metric 1'}})
                 .then((data) => {
                   expect(data['mm1']).toBe(5.0);
                   async.done();
                 });
           }));

        it('should ignore micro metrics that were not specified',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             aggregate([
               eventFactory.markStart('mm1', 0),
               eventFactory.markEnd('mm1', 5),
             ]).then((data) => {
               expect(data['mm1']).toBeFalsy();
               async.done();
             });
           }));

        it('should report micro metric averages',
           inject([AsyncTestCompleter], (async: AsyncTestCompleter) => {
             aggregate(
                 [
                   eventFactory.markStart('mm1*20', 0),
                   eventFactory.markEnd('mm1*20', 5),
                 ],
                 {microMetrics: {'mm1': 'micro metric 1'}})
                 .then((data) => {
                   expect(data['mm1']).toBe(5 / 20);
                   async.done();
                 });
           }));

      });

    });

  });
}

class MockDriverExtension extends WebDriverExtension {
  constructor(
      private _perfLogs: any[], private _commandLog: any[],
      private _perfLogFeatures: PerfLogFeatures) {
    super();
  }

  timeBegin(name: string): Promise<any> {
    this._commandLog.push(['timeBegin', name]);
    return Promise.resolve(null);
  }

  timeEnd(name: string, restartName: string): Promise<any> {
    this._commandLog.push(['timeEnd', name, restartName]);
    return Promise.resolve(null);
  }

  perfLogFeatures(): PerfLogFeatures { return this._perfLogFeatures; }

  readPerfLog(): Promise<any> {
    this._commandLog.push('readPerfLog');
    if (this._perfLogs.length > 0) {
      var next = this._perfLogs[0];
      this._perfLogs.shift();
      return Promise.resolve(next);
    } else {
      return Promise.resolve([]);
    }
  }

  gc(): Promise<any> {
    this._commandLog.push(['gc']);
    return Promise.resolve(null);
  }
}