From: Jérôme Benoit <jerome.benoit@sap.com>
Date: Fri, 4 Feb 2022 15:19:26 +0000 (+0100)
Subject: Introduce JSON type and use it for OCPP and internal message structure
X-Git-Tag: v1.1.45~12
X-Git-Url: https://git.piment-noir.org/?a=commitdiff_plain;h=c3ee95af4edd541595e3873c8aa4c93d38e59474;p=e-mobility-charging-stations-simulator.git

Introduce JSON type and use it for OCPP and internal message structure

Signed-off-by: Jérôme Benoit <jerome.benoit@sap.com>
---

diff --git a/src/charging-station/Bootstrap.ts b/src/charging-station/Bootstrap.ts
index ce5286ac..143bb5c4 100644
--- a/src/charging-station/Bootstrap.ts
+++ b/src/charging-station/Bootstrap.ts
@@ -3,6 +3,7 @@
 import { ChargingStationWorkerData, ChargingStationWorkerMessage, ChargingStationWorkerMessageEvents } from '../types/ChargingStationWorker';
 
 import Configuration from '../utils/Configuration';
+import Statistics from '../types/Statistics';
 import { Storage } from '../performance/storage/Storage';
 import { StorageFactory } from '../performance/storage/StorageFactory';
 import { UIServiceUtils } from './ui-websocket-services/UIServiceUtils';
@@ -17,7 +18,7 @@ import { version } from '../../package.json';
 
 export default class Bootstrap {
   private static instance: Bootstrap | null = null;
-  private workerImplementation: WorkerAbstract | null = null;
+  private workerImplementation: WorkerAbstract<ChargingStationWorkerData> | null = null;
   private readonly uiWebSocketServer!: UIWebSocketServer;
   private readonly storage!: Storage;
   private numberOfChargingStations: number;
@@ -118,11 +119,11 @@ export default class Bootstrap {
         },
         messageHandler: async (msg: ChargingStationWorkerMessage) => {
           if (msg.id === ChargingStationWorkerMessageEvents.STARTED) {
-            this.uiWebSocketServer.chargingStations.add(msg.data.id);
+            this.uiWebSocketServer.chargingStations.add(msg.data.id as string);
           } else if (msg.id === ChargingStationWorkerMessageEvents.STOPPED) {
-            this.uiWebSocketServer.chargingStations.delete(msg.data.id);
+            this.uiWebSocketServer.chargingStations.delete(msg.data.id as string);
           } else if (msg.id === ChargingStationWorkerMessageEvents.PERFORMANCE_STATISTICS) {
-            await this.storage.storePerformanceStatistics(msg.data);
+            await this.storage.storePerformanceStatistics(msg.data as unknown as Statistics);
           }
         }
       });
diff --git a/src/types/ChargingStationWorker.ts b/src/types/ChargingStationWorker.ts
index a48e0768..8bdc9af0 100644
--- a/src/types/ChargingStationWorker.ts
+++ b/src/types/ChargingStationWorker.ts
@@ -19,6 +19,6 @@ export const ChargingStationWorkerMessageEvents = {
 };
 
 
-export interface ChargingStationWorkerMessage extends Omit<WorkerMessage, 'id'> {
+export interface ChargingStationWorkerMessage extends Omit<WorkerMessage<ChargingStationWorkerData>, 'id'> {
   id: ChargingStationWorkerMessageEvents;
 }
diff --git a/src/types/JsonType.ts b/src/types/JsonType.ts
new file mode 100644
index 00000000..2bd219f4
--- /dev/null
+++ b/src/types/JsonType.ts
@@ -0,0 +1,5 @@
+export interface JsonType {
+  [x: string]: string | number | boolean | Date | JsonType | JsonArray;
+}
+
+type JsonArray = Array<string | number | boolean | Date | JsonType | JsonArray>;
diff --git a/src/types/Worker.ts b/src/types/Worker.ts
index 8f47f578..7a963355 100644
--- a/src/types/Worker.ts
+++ b/src/types/Worker.ts
@@ -1,3 +1,4 @@
+import { JsonType } from './JsonType';
 import { PoolOptions } from 'poolifier';
 import { Worker } from 'worker_threads';
 
@@ -16,17 +17,16 @@ export interface WorkerOptions {
   messageHandler?: (message: unknown) => void | Promise<void>;
 }
 
-// eslint-disable-next-line @typescript-eslint/no-empty-interface
-export interface WorkerData {}
+export type WorkerData = JsonType;
 
 export interface WorkerSetElement {
   worker: Worker;
   numberOfWorkerElements: number;
 }
 
-export interface WorkerMessage {
+export interface WorkerMessage<T extends WorkerData> {
   id: WorkerMessageEvents;
-  data: any;
+  data: T;
 }
 
 export enum WorkerMessageEvents {
diff --git a/src/types/ocpp/1.6/ChargingProfile.ts b/src/types/ocpp/1.6/ChargingProfile.ts
index 5d72a7ac..6416bf5d 100644
--- a/src/types/ocpp/1.6/ChargingProfile.ts
+++ b/src/types/ocpp/1.6/ChargingProfile.ts
@@ -1,4 +1,6 @@
-export interface OCPP16ChargingProfile {
+import { JsonType } from '../../JsonType';
+
+export interface OCPP16ChargingProfile extends JsonType {
   chargingProfileId: number;
   transactionId?: number;
   stackLevel: number;
@@ -10,7 +12,7 @@ export interface OCPP16ChargingProfile {
   chargingSchedule: ChargingSchedule;
 }
 
-export interface ChargingSchedule {
+export interface ChargingSchedule extends JsonType {
   duration?: number;
   startSchedule?: Date;
   chargingRateUnit: ChargingRateUnitType;
@@ -18,7 +20,7 @@ export interface ChargingSchedule {
   minChargeRate?: number;
 }
 
-export interface ChargingSchedulePeriod {
+export interface ChargingSchedulePeriod extends JsonType {
   startPeriod: number;
   limit: number;
   numberPhases?: number;
diff --git a/src/types/ocpp/1.6/MeterValues.ts b/src/types/ocpp/1.6/MeterValues.ts
index d3038e63..97a7d24c 100644
--- a/src/types/ocpp/1.6/MeterValues.ts
+++ b/src/types/ocpp/1.6/MeterValues.ts
@@ -1,4 +1,5 @@
 import { EmptyObject } from '../../EmptyObject';
+import { JsonType } from '../../JsonType';
 
 export enum MeterValueUnit {
   WATT_HOUR = 'Wh',
@@ -81,7 +82,7 @@ export enum MeterValueFormat {
   SIGNED_DATA = 'SignedData',
 }
 
-export interface OCPP16SampledValue {
+export interface OCPP16SampledValue extends JsonType {
   value?: string;
   unit?: MeterValueUnit;
   context?: MeterValueContext;
@@ -91,12 +92,12 @@ export interface OCPP16SampledValue {
   format?: MeterValueFormat;
 }
 
-export interface OCPP16MeterValue {
+export interface OCPP16MeterValue extends JsonType {
   timestamp: string;
   sampledValue: OCPP16SampledValue[];
 }
 
-export interface MeterValuesRequest {
+export interface MeterValuesRequest extends JsonType {
   connectorId: number;
   transactionId?: number;
   meterValue: OCPP16MeterValue[];
diff --git a/src/types/ocpp/1.6/Requests.ts b/src/types/ocpp/1.6/Requests.ts
index d83417b0..97b5d756 100644
--- a/src/types/ocpp/1.6/Requests.ts
+++ b/src/types/ocpp/1.6/Requests.ts
@@ -1,6 +1,7 @@
 import { ChargingProfilePurposeType, OCPP16ChargingProfile } from './ChargingProfile';
 
 import { EmptyObject } from '../../EmptyObject';
+import { JsonType } from '../../JsonType';
 import { OCPP16ChargePointErrorCode } from './ChargePointErrorCode';
 import { OCPP16ChargePointStatus } from './ChargePointStatus';
 import { OCPP16DiagnosticsStatus } from './DiagnosticsStatus';
@@ -35,7 +36,7 @@ export enum OCPP16IncomingRequestCommand {
 
 export type HeartbeatRequest = EmptyObject;
 
-export interface OCPP16BootNotificationRequest {
+export interface OCPP16BootNotificationRequest extends JsonType {
   chargeBoxSerialNumber?: string;
   chargePointModel: string;
   chargePointSerialNumber?: string;
@@ -47,7 +48,7 @@ export interface OCPP16BootNotificationRequest {
   meterType?: string;
 }
 
-export interface StatusNotificationRequest {
+export interface StatusNotificationRequest extends JsonType {
   connectorId: number;
   errorCode: OCPP16ChargePointErrorCode;
   info?: string;
@@ -57,26 +58,26 @@ export interface StatusNotificationRequest {
   vendorErrorCode?: string;
 }
 
-export interface ChangeConfigurationRequest {
+export interface ChangeConfigurationRequest extends JsonType {
   key: string | OCPP16StandardParametersKey;
   value: string;
 }
 
-export interface RemoteStartTransactionRequest {
+export interface RemoteStartTransactionRequest extends JsonType {
   connectorId: number;
   idTag: string;
   chargingProfile?: OCPP16ChargingProfile;
 }
 
-export interface RemoteStopTransactionRequest {
+export interface RemoteStopTransactionRequest extends JsonType {
   transactionId: number;
 }
 
-export interface UnlockConnectorRequest {
+export interface UnlockConnectorRequest extends JsonType {
   connectorId: number;
 }
 
-export interface GetConfigurationRequest {
+export interface GetConfigurationRequest extends JsonType {
   key?: string | OCPP16StandardParametersKey[];
 }
 
@@ -85,11 +86,11 @@ export enum ResetType {
   SOFT = 'Soft'
 }
 
-export interface ResetRequest {
+export interface ResetRequest extends JsonType {
   type: ResetType;
 }
 
-export interface SetChargingProfileRequest {
+export interface SetChargingProfileRequest extends JsonType {
   connectorId: number;
   csChargingProfiles: OCPP16ChargingProfile;
 }
@@ -99,19 +100,19 @@ export enum OCPP16AvailabilityType {
   OPERATIVE = 'Operative'
 }
 
-export interface ChangeAvailabilityRequest {
+export interface ChangeAvailabilityRequest extends JsonType {
   connectorId: number;
   type: OCPP16AvailabilityType;
 }
 
-export interface ClearChargingProfileRequest {
+export interface ClearChargingProfileRequest extends JsonType {
   id?: number;
   connectorId?: number;
   chargingProfilePurpose?: ChargingProfilePurposeType;
   stackLevel?: number;
 }
 
-export interface GetDiagnosticsRequest {
+export interface GetDiagnosticsRequest extends JsonType {
   location: string;
   retries?: number;
   retryInterval?: number;
@@ -119,7 +120,7 @@ export interface GetDiagnosticsRequest {
   stopTime?: Date;
 }
 
-export interface DiagnosticsStatusNotificationRequest {
+export interface DiagnosticsStatusNotificationRequest extends JsonType {
   status: OCPP16DiagnosticsStatus
 }
 
@@ -132,7 +133,7 @@ export enum MessageTrigger {
   StatusNotification = 'StatusNotification'
 }
 
-export interface OCPP16TriggerMessageRequest {
+export interface OCPP16TriggerMessageRequest extends JsonType {
   requestedMessage: MessageTrigger;
   connectorId?: number
 }
diff --git a/src/types/ocpp/1.6/Responses.ts b/src/types/ocpp/1.6/Responses.ts
index 4f526b94..7d3487ba 100644
--- a/src/types/ocpp/1.6/Responses.ts
+++ b/src/types/ocpp/1.6/Responses.ts
@@ -1,7 +1,8 @@
 import { EmptyObject } from '../../EmptyObject';
+import { JsonType } from '../../JsonType';
 import { OCPPConfigurationKey } from '../Configuration';
 
-export interface HeartbeatResponse {
+export interface HeartbeatResponse extends JsonType {
   currentTime: string;
 }
 
@@ -11,7 +12,7 @@ export enum OCPP16UnlockStatus {
   NOT_SUPPORTED = 'NotSupported'
 }
 
-export interface UnlockConnectorResponse {
+export interface UnlockConnectorResponse extends JsonType {
   status: OCPP16UnlockStatus;
 }
 
@@ -22,7 +23,7 @@ export enum OCPP16ConfigurationStatus {
   NOT_SUPPORTED = 'NotSupported'
 }
 
-export interface ChangeConfigurationResponse {
+export interface ChangeConfigurationResponse extends JsonType {
   status: OCPP16ConfigurationStatus;
 }
 
@@ -32,7 +33,7 @@ export enum OCPP16RegistrationStatus {
   REJECTED = 'Rejected'
 }
 
-export interface OCPP16BootNotificationResponse {
+export interface OCPP16BootNotificationResponse extends JsonType {
   status: OCPP16RegistrationStatus;
   currentTime: string;
   interval: number;
@@ -40,7 +41,7 @@ export interface OCPP16BootNotificationResponse {
 
 export type StatusNotificationResponse = EmptyObject;
 
-export interface GetConfigurationResponse {
+export interface GetConfigurationResponse extends JsonType {
   configurationKey: OCPPConfigurationKey[];
   unknownKey: string[];
 }
@@ -51,7 +52,7 @@ export enum OCPP16ChargingProfileStatus {
   NOT_SUPPORTED = 'NotSupported',
 }
 
-export interface SetChargingProfileResponse {
+export interface SetChargingProfileResponse extends JsonType {
   status: OCPP16ChargingProfileStatus;
 }
 
@@ -61,7 +62,7 @@ export enum OCPP16AvailabilityStatus {
   SCHEDULED = 'Scheduled'
 }
 
-export interface ChangeAvailabilityResponse {
+export interface ChangeAvailabilityResponse extends JsonType {
   status: OCPP16AvailabilityStatus;
 }
 
@@ -70,11 +71,11 @@ export enum OCPP16ClearChargingProfileStatus {
   UNKNOWN = 'Unknown'
 }
 
-export interface ClearChargingProfileResponse {
+export interface ClearChargingProfileResponse extends JsonType {
   status: OCPP16ClearChargingProfileStatus;
 }
 
-export interface GetDiagnosticsResponse {
+export interface GetDiagnosticsResponse extends JsonType {
   fileName?: string;
 }
 
@@ -86,6 +87,6 @@ export enum OCPP16TriggerMessageStatus {
   NOT_IMPLEMENTED = 'NotImplemented'
 }
 
-export interface OCPP16TriggerMessageResponse {
+export interface OCPP16TriggerMessageResponse extends JsonType {
   status: OCPP16TriggerMessageStatus
 }
diff --git a/src/types/ocpp/1.6/Transaction.ts b/src/types/ocpp/1.6/Transaction.ts
index 41bd344e..bf237777 100644
--- a/src/types/ocpp/1.6/Transaction.ts
+++ b/src/types/ocpp/1.6/Transaction.ts
@@ -1,3 +1,4 @@
+import { JsonType } from '../../JsonType';
 import { OCPP16MeterValue } from './MeterValues';
 
 export enum OCPP16StopTransactionReason {
@@ -23,21 +24,21 @@ export enum OCPP16AuthorizationStatus {
   CONCURRENT_TX = 'ConcurrentTx'
 }
 
-export interface IdTagInfo {
+export interface IdTagInfo extends JsonType {
   status: OCPP16AuthorizationStatus;
   parentIdTag?: string;
   expiryDate?: Date;
 }
 
-export interface AuthorizeRequest {
+export interface AuthorizeRequest extends JsonType {
   idTag: string;
 }
 
-export interface OCPP16AuthorizeResponse {
+export interface OCPP16AuthorizeResponse extends JsonType {
   idTagInfo: IdTagInfo;
 }
 
-export interface StartTransactionRequest {
+export interface StartTransactionRequest extends JsonType {
   connectorId: number;
   idTag: string;
   meterStart: number;
@@ -45,12 +46,12 @@ export interface StartTransactionRequest {
   timestamp: string;
 }
 
-export interface OCPP16StartTransactionResponse {
+export interface OCPP16StartTransactionResponse extends JsonType {
   idTagInfo: IdTagInfo;
   transactionId: number;
 }
 
-export interface StopTransactionRequest {
+export interface StopTransactionRequest extends JsonType {
   idTag?: string;
   meterStop: number;
   timestamp: string;
@@ -59,6 +60,6 @@ export interface StopTransactionRequest {
   transactionData?: OCPP16MeterValue[];
 }
 
-export interface OCPP16StopTransactionResponse {
+export interface OCPP16StopTransactionResponse extends JsonType {
   idTagInfo?: IdTagInfo;
 }
diff --git a/src/types/ocpp/Configuration.ts b/src/types/ocpp/Configuration.ts
index b55c2121..b13a24ba 100644
--- a/src/types/ocpp/Configuration.ts
+++ b/src/types/ocpp/Configuration.ts
@@ -1,5 +1,7 @@
 import { OCPP16StandardParametersKey, OCPP16SupportedFeatureProfiles, OCPP16VendorDefaultParametersKey } from './1.6/Configuration';
 
+import { JsonType } from '../JsonType';
+
 export type StandardParametersKey = OCPP16StandardParametersKey;
 
 export const StandardParametersKey = {
@@ -29,7 +31,7 @@ export enum ConnectorPhaseRotation {
   TSR = 'TSR'
 }
 
-export interface OCPPConfigurationKey {
+export interface OCPPConfigurationKey extends JsonType {
   key: string | StandardParametersKey;
   readonly: boolean;
   value?: string;
diff --git a/src/worker/WorkerAbstract.ts b/src/worker/WorkerAbstract.ts
index fa28597c..7c662d9d 100644
--- a/src/worker/WorkerAbstract.ts
+++ b/src/worker/WorkerAbstract.ts
@@ -1,7 +1,7 @@
 import Constants from '../utils/Constants';
 import { WorkerData } from '../types/Worker';
 
-export default abstract class WorkerAbstract {
+export default abstract class WorkerAbstract<T extends WorkerData> {
   protected readonly workerScript: string;
   protected readonly workerStartDelay: number;
   public abstract readonly size: number;
@@ -20,5 +20,5 @@ export default abstract class WorkerAbstract {
 
   public abstract start(): Promise<void>;
   public abstract stop(): Promise<void>;
-  public abstract addElement(elementData: WorkerData): Promise<void>;
+  public abstract addElement(elementData: T): Promise<void>;
 }
diff --git a/src/worker/WorkerDynamicPool.ts b/src/worker/WorkerDynamicPool.ts
index e2dd3b1e..37b6ddd1 100644
--- a/src/worker/WorkerDynamicPool.ts
+++ b/src/worker/WorkerDynamicPool.ts
@@ -6,7 +6,7 @@ import WorkerAbstract from './WorkerAbstract';
 import { WorkerData } from '../types/Worker';
 import { WorkerUtils } from './WorkerUtils';
 
-export default class WorkerDynamicPool<T> extends WorkerAbstract {
+export default class WorkerDynamicPool extends WorkerAbstract<WorkerData> {
   private readonly pool: DynamicThreadPool<WorkerData>;
 
   /**
@@ -56,7 +56,7 @@ export default class WorkerDynamicPool<T> extends WorkerAbstract {
    * @returns
    * @public
    */
-  public async addElement(elementData: T): Promise<void> {
+  public async addElement(elementData: WorkerData): Promise<void> {
     await this.pool.execute(elementData);
     // Start worker sequentially to optimize memory at startup
     await Utils.sleep(this.workerStartDelay);
diff --git a/src/worker/WorkerFactory.ts b/src/worker/WorkerFactory.ts
index 8b979d06..76da7a20 100644
--- a/src/worker/WorkerFactory.ts
+++ b/src/worker/WorkerFactory.ts
@@ -1,5 +1,5 @@
 import { Worker, isMainThread } from 'worker_threads';
-import { WorkerOptions, WorkerProcessType } from '../types/Worker';
+import { WorkerData, WorkerOptions, WorkerProcessType } from '../types/Worker';
 
 import Constants from '../utils/Constants';
 import { PoolOptions } from 'poolifier';
@@ -13,7 +13,7 @@ export default class WorkerFactory {
     // This is intentional
   }
 
-  public static getWorkerImplementation<T>(workerScript: string, workerProcessType: WorkerProcessType, options?: WorkerOptions): WorkerAbstract | null {
+  public static getWorkerImplementation<T extends WorkerData>(workerScript: string, workerProcessType: WorkerProcessType, options?: WorkerOptions): WorkerAbstract<T> | null {
     if (!isMainThread) {
       throw new Error('Trying to get a worker implementation outside the main thread');
     }
@@ -21,20 +21,20 @@ export default class WorkerFactory {
     options.startDelay = options?.startDelay ?? Constants.WORKER_START_DELAY;
     options.poolOptions = options?.poolOptions ?? {} as PoolOptions<Worker>;
     options?.messageHandler && (options.poolOptions.messageHandler = options.messageHandler);
-    let workerImplementation: WorkerAbstract = null;
+    let workerImplementation: WorkerAbstract<T> = null;
     switch (workerProcessType) {
       case WorkerProcessType.WORKER_SET:
         options.elementsPerWorker = options.elementsPerWorker ?? Constants.DEFAULT_CHARGING_STATIONS_PER_WORKER;
-        workerImplementation = new WorkerSet<T>(workerScript, options.elementsPerWorker, options.startDelay, options);
+        workerImplementation = new WorkerSet(workerScript, options.elementsPerWorker, options.startDelay, options);
         break;
       case WorkerProcessType.STATIC_POOL:
         options.poolMaxSize = options.poolMaxSize ?? Constants.DEFAULT_WORKER_POOL_MAX_SIZE;
-        workerImplementation = new WorkerStaticPool<T>(workerScript, options.poolMaxSize, options.startDelay, options.poolOptions);
+        workerImplementation = new WorkerStaticPool(workerScript, options.poolMaxSize, options.startDelay, options.poolOptions);
         break;
       case WorkerProcessType.DYNAMIC_POOL:
         options.poolMinSize = options.poolMinSize ?? Constants.DEFAULT_WORKER_POOL_MIN_SIZE;
         options.poolMaxSize = options.poolMaxSize ?? Constants.DEFAULT_WORKER_POOL_MAX_SIZE;
-        workerImplementation = new WorkerDynamicPool<T>(workerScript, options.poolMinSize, options.poolMaxSize, options.startDelay, options.poolOptions);
+        workerImplementation = new WorkerDynamicPool(workerScript, options.poolMinSize, options.poolMaxSize, options.startDelay, options.poolOptions);
         break;
       default:
         throw new Error(`Worker implementation type '${workerProcessType}' not found`);
diff --git a/src/worker/WorkerSet.ts b/src/worker/WorkerSet.ts
index d179608d..64399c87 100644
--- a/src/worker/WorkerSet.ts
+++ b/src/worker/WorkerSet.ts
@@ -1,13 +1,13 @@
 // Partial Copyright Jerome Benoit. 2021. All Rights Reserved.
 
-import { WorkerMessageEvents, WorkerOptions, WorkerSetElement } from '../types/Worker';
+import { WorkerData, WorkerMessageEvents, WorkerOptions, WorkerSetElement } from '../types/Worker';
 
 import Utils from '../utils/Utils';
 import { Worker } from 'worker_threads';
 import WorkerAbstract from './WorkerAbstract';
 import { WorkerUtils } from './WorkerUtils';
 
-export default class WorkerSet<T> extends WorkerAbstract {
+export default class WorkerSet extends WorkerAbstract<WorkerData> {
   public readonly maxElementsPerWorker: number;
   private readonly messageHandler: (message: unknown) => void | Promise<void>;
   private readonly workerSet: Set<WorkerSetElement>;
@@ -37,7 +37,7 @@ export default class WorkerSet<T> extends WorkerAbstract {
    * @returns
    * @public
    */
-  public async addElement(elementData: T): Promise<void> {
+  public async addElement(elementData: WorkerData): Promise<void> {
     if (!this.workerSet) {
       throw new Error('Cannot add a WorkerSet element: workers\' set does not exist');
     }
diff --git a/src/worker/WorkerStaticPool.ts b/src/worker/WorkerStaticPool.ts
index d5d6390c..1cbd18e8 100644
--- a/src/worker/WorkerStaticPool.ts
+++ b/src/worker/WorkerStaticPool.ts
@@ -6,7 +6,7 @@ import WorkerAbstract from './WorkerAbstract';
 import { WorkerData } from '../types/Worker';
 import { WorkerUtils } from './WorkerUtils';
 
-export default class WorkerStaticPool<T> extends WorkerAbstract {
+export default class WorkerStaticPool extends WorkerAbstract<WorkerData> {
   private readonly pool: FixedThreadPool<WorkerData>;
 
   /**
@@ -55,7 +55,7 @@ export default class WorkerStaticPool<T> extends WorkerAbstract {
    * @returns
    * @public
    */
-  public async addElement(elementData: T): Promise<void> {
+  public async addElement(elementData: WorkerData): Promise<void> {
     await this.pool.execute(elementData);
     // Start worker sequentially to optimize memory at startup
     await Utils.sleep(this.workerStartDelay);