debug: fetch the rest of the callstack lazily

fixes #25605

src/vs/workbench/parts/debug/common/debugModel.ts

@@ -379,7 +379,7 @@ export class Thread implements IThread {
 	constructor(public process: IProcess, public name: string, public threadId: number) {
 		this.fetchPromise = null;
 		this.stoppedDetails = null;
-		this.callStack = null;
+		this.callStack = [];
 		this.stopped = false;
 	}
 
@@ -389,7 +389,7 @@ export class Thread implements IThread {
 
 	public clearCallStack(): void {
 		this.fetchPromise = null;
-		this.callStack = null;
+		this.callStack = [];
 	}
 
 	public getCallStack(): IStackFrame[] {
@@ -779,8 +779,8 @@ export class Model implements IModel {
 		}
 	}
 
-	public fetchCallStack(thread: Thread): TPromise<void> {
-		return thread.fetchCallStack().then(() => {
+	public fetchCallStack(thread: IThread): TPromise<void> {
+		return (<Thread>thread).fetchCallStack().then(() => {
 			this._onDidChangeCallStack.fire();
 		});
 	}

src/vs/workbench/parts/debug/electron-browser/debugService.ts

@@ -7,6 +7,7 @@ import * as nls from 'vs/nls';
 import * as lifecycle from 'vs/base/common/lifecycle';
 import Event, { Emitter } from 'vs/base/common/event';
 import * as paths from 'vs/base/common/paths';
+import { RunOnceScheduler } from 'vs/base/common/async';
 import * as strings from 'vs/base/common/strings';
 import { generateUuid } from 'vs/base/common/uuid';
 import uri from 'vs/base/common/uri';
@@ -79,6 +80,7 @@ export class DebugService implements debug.IDebugService {
 	private debugType: IContextKey<string>;
 	private debugState: IContextKey<string>;
 	private breakpointsToSendOnResourceSaved: Set<string>;
+	private callStackScheduler: RunOnceScheduler;
 
 	constructor(
 		@IStorageService private storageService: IStorageService,
@@ -117,6 +119,17 @@ export class DebugService implements debug.IDebugService {
 			this.loadExceptionBreakpoints(), this.loadWatchExpressions());
 		this.toDispose.push(this.model);
 		this.viewModel = new ViewModel(this.storageService.get(DEBUG_SELECTED_CONFIG_NAME_KEY, StorageScope.WORKSPACE, null));
+		this.callStackScheduler = new RunOnceScheduler(() => {
+			const focusedThread = this.viewModel.focusedThread;
+			if (focusedThread) {
+				const callStack = focusedThread.getCallStack();
+				// Some adapters might not respect the number levels in StackTraceRequest and might
+				// return more stackFrames than requested. For those do not send an additional stackTrace request.
+				if (callStack.length <= 1) {
+					this.model.fetchCallStack(focusedThread).done(undefined, errors.onUnexpectedError);
+				}
+			}
+		}, 420);
 
 		this.registerListeners(lifecycleService);
 	}
@@ -295,11 +308,7 @@ export class DebugService implements debug.IDebugService {
 					// Second retrieves the rest of the call stack. For performance reasons #25605
 					this.model.fetchCallStack(thread).then(() => {
 						const callStack = thread.getCallStack();
-						// Some adapters might not respect the number levels in StackTraceRequest and might
-						// return more stackFrames than requested. For those do not send an additional stackTrace request.
-						if (callStack.length <= 1) {
-							this.model.fetchCallStack(thread).done(undefined, errors.onUnexpectedError);
-						}
+						this.callStackScheduler.schedule();
 						if (callStack.length > 0 && !this.viewModel.focusedStackFrame) {
 							// focus first stack frame from top that has source location if no other stack frame is focussed
 							const stackFrameToFocus = first(callStack, sf => sf.source && sf.source.available, callStack[0]);

src/vs/workbench/parts/debug/electron-browser/debugViewer.ts

@@ -370,7 +370,7 @@ export class CallStackDataSource implements IDataSource {
 		if (thread.stoppedDetails && thread.stoppedDetails.framesErrorMessage) {
 			return callStack.concat([thread.stoppedDetails.framesErrorMessage]);
 		}
-		if (thread.stoppedDetails && thread.stoppedDetails.totalFrames > callStack.length) {
+		if (thread.stoppedDetails && thread.stoppedDetails.totalFrames > callStack.length && callStack.length > 1) {
 			return callStack.concat([new ThreadAndProcessIds(thread.process.getId(), thread.threadId)]);
 		}