vscode源码分析【六】服务实例化和单例的实现

		services.set(ILifecycleService, new SyncDescriptor(LifecycleService));
		services.set(IStateService, new SyncDescriptor(StateService));
		services.set(IRequestService, new SyncDescriptor(RequestService));
		services.set(IDiagnosticsService, new SyncDescriptor(DiagnosticsService));
		services.set(IThemeMainService, new SyncDescriptor(ThemeMainService));
		services.set(ISignService, new SyncDescriptor(SignService));

export class SyncDescriptor<T> {
	readonly ctor: any;
	readonly staticArguments: any[];
	readonly supportsDelayedInstantiation: boolean;
	constructor(ctor: new (...args: any[]) => T, staticArguments: any[] = [], supportsDelayedInstantiation: boolean = false) {
		this.ctor = ctor;
		this.staticArguments = staticArguments;
		this.supportsDelayedInstantiation = supportsDelayedInstantiation;
	}
}

			await instantiationService.invokeFunction(async accessor => {
				const environmentService = accessor.get(IEnvironmentService);
				const configurationService = accessor.get(IConfigurationService);
				const stateService = accessor.get(IStateService);
				try {
					await this.initServices(environmentService, configurationService as ConfigurationService, stateService as StateService);
				} catch (error) {

					// Show a dialog for errors that can be resolved by the user
					this.handleStartupDataDirError(environmentService, error);

					throw error;
				}
			});

				get: <T>(id: ServiceIdentifier<T>, isOptional?: typeof optional) => {

					if (_done) {
						throw illegalState('service accessor is only valid during the invocation of its target method');
					}

					const result = this._getOrCreateServiceInstance(id, _trace);
					if (!result && isOptional !== optional) {
						throw new Error(`[invokeFunction] unknown service '${id}'`);
					}
					return result;
				}

	private _getOrCreateServiceInstance<T>(id: ServiceIdentifier<T>, _trace: Trace): T {
		let thing = this._getServiceInstanceOrDescriptor(id);
		if (thing instanceof SyncDescriptor) {
			return this._createAndCacheServiceInstance(id, thing, _trace.branch(id, true));
		} else {
			_trace.branch(id, false);
			return thing;
		}
	}