Differences Between Running an Executable with Visual Studio Debugger VS Without Debugger

Differences between running an executable with Visual Studio debugger vs without debugger

Windows Heap behaves differently if process is started under the debugger. To disable this behavior (in order to find a problem while debugging) add _NO_DEBUG_HEAP=1 to environment (like in this question).

Alternatively you can attach to process early in program execution. Heap will not enter the debug mode then. Add DebugBreak() line somewhere in the beginning of the execution, run with Ctrl+F5, and start debugging when asked to.

is there a difference between running an executable and debugging it in Visual Studio?

Yes! Running a program directly form the debugger the debug heap is in use. Assuming it isn't compiled in debug mode.
And the memory layout changes when the debugger is loaded into the process address space. So some weird things may happen.

If you have such strange effects it is sometimes better to attach the debugger to the running process.

What's the difference between running a debug app hosted in Visual Studio and running it directly?

The one thing that's different when running the Release build without a debugger is that the JIT optimizer is enabled. The code runs faster. Which has a strong correlation with your problem, threading problems are timing sensitive. Count yourself lucky (I'm sure you don't) that this goes wrong while your code is still running on your dev machine, the really nasty threading problems are the ones mess up your program once a week on your customer's machines.

Making this problem debuggable is still the most important way to tackle it. Other than Tools + Attach to Process, another way to get the debugger started is by using System.Diagnostics.Debugger.Launch() in your code. You'll get a dialog that lets you choose the debugger.

Another way that doesn't require attaching the debugger is to switch VS to the Release build. Use Tools + Options, Debugging, General and untick "Suppress JIT optimization on module load". Pressing F5 now runs your program with the optimizer enabled and the debugger pre-attached. Still not quite a slamdunk since having the debugger attached in itself causes timing differences.

Another common approach to tackle difficult concurrency bugs is to add logging to your code. Write a line whenever it acquired a lock. With luck, you'll quickly find the deadlock reason. If you're not so lucky, the logging alters the thread timing enough to make the deadlock disappear. There have been plenty of programs shipped with logging left enabled because that was the only way to keep them running.

A code review is yet another approach, especially when done by somebody else. And last but not least, consider whether threading is really the optimal solution in your app. The nagging "did I really solve it?" feeling never goes away, proving that threaded code is free of defects is close to impossible.

Difference between Run Code and Run without Debugging in VS Code

Ctrl + Alt + N (Run Code) is a shortcut provided by the "Code Runner" extension you installed while Ctrl + F5 (Run Without Debugging) is a shortcut provided by VS Code by default. Both shortcuts run the code without debugging and they have the same function.

Different behavior of WPF Application: IDE debugging vs directly running the executable

I answer myself.

few days ago, i modify Class Name IdleTimeFinder to NativeMethods.
IdleTimeFinder's role is just check the time that the user does not use PC.

after roll back all of code operate normally.

What is the difference between Start Debugging and Attach to Process

"Start Debugging" launches a new instance of the executable with the debugger attached right from the beginning, so the overhead of all the needed debugger calls is incurred from launch, whereas "Attach to Process" attaches to a already running process, so until then your process was running without any additional overhead caused by debugging.

VStudio - Debug Mode vs. Release Mode and Start without Debugging

These features are completely orthogonal.

The choice of build does(By default, you can change these settings separately and create new build targets):

• The debug build generates debug informations, has IL optimizations disabled and the DEBUG conditional symbol defined
• The release build doesn't generate debug informations, has IL optimizations enabled and the DEBUG symbol is not defined

Run vs Run without Debugger determines if the debugger gets attached on the started process. By default starting with debugger also disables JIT optimizations.

Difference between Visual Studio launching an executable and launching it yourself?

So the question is: How can attaching a debugger to a C# process affect its behavior?!

In all kinds of ways. It affects JIT optimizations, garbage collection, timing (think race conditions), anything which explicitly tries to detect whether it's running in the debugger, and potentially the order and timing of type initialization.

If you can now reproduce it, I would start adding logging and see where that leads you - once you've worked out what the problem actually is, you may well find it's obvious why the debugger changes things.

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