Debugging and common mistakes

Debugging and common mistakes

When debugging asynchronous code, the Call Stack window shows only the current thread. Visual Studio 2026 has two special windows (https://learn.microsoft.com/visualstudio/debugger/using-the-tasks-window):

• Debug → Windows → Tasks (available after stopping at a breakpoint)—a table of tasks with the columns ID, Status (Scheduled, Active, Blocked, Awaiting, Deadlocked), Start Time, Duration, Location, and Task (Fig. 5.10);
• Debug → Windows → Parallel Stacks in Tasks mode—a graph of asynchronous call stacks: you can see which method is waiting at which await (Fig. 5.11) (https://learn.microsoft.com/visualstudio/debugger/using-the-parallel-stacks-window).

Figure 5.10. The Tasks window during debugging

Figure 5.11. The Parallel Stacks window in Tasks mode

The mistakes made most often when writing asynchronous code are listed in Table 5.3.

Table 5.3. Common mistakes in asynchronous programming

Problem	Cause	Fix
the window is "Not Responding" during an operation	long synchronous work in a handler	await an asynchronous method or await Task.Run(…)
the window freezes forever	.Result or .Wait() on the UI thread (deadlock)	an async handler and await
InvalidOperationException: Cross-thread operation not valid	accessing a control inside Task.Run or after ConfigureAwait(false)	return the result from the task, IProgress<T>, InvokeAsync
the operation was started twice	the button was not disabled during the operation (reentrancy)	Enabled = false, restored in finally
an exception was not caught, and the application exited	async void outside an event handler, a forgotten await (CS4014)	return Task, wait with await, try/catch in the handler
the Cancel button does not stop the operation	the token was not passed to calls or is not checked in the loop	pass the token on, ThrowIfCancellationRequested
the progress indicator jumps or slows down the interface	Report is called thousands of times per second	report less often: every file, every percent