Attaching on Startup

Here’s a neat trick I stumbled onto that can make life a lot easier – in our development workstations, certainly, and even in a pinch on staging and testing machines:

How many times have you wished you could attach to a process immediately when it launchs? If we’re running a simple EXE, we can launch it from the debugger directly, but if we’re trying to debug a Windows Service, a scheduled task or a sub-process that is launched automatically, it isn’t that simple. We can try press CTRL-ALT-P as quickly as possible, but that will almost always miss the very beginning. We can add a call to System.Diagnostics.Debugger.Launch() to out Application_Startup() function, but that’s polluting production code with debugging statements, and isn’t really something we can send over to a staging or QA machine.

I was all set to write a tool to monitor new processes being launched and latch onto them when I discovered that there’s no need, and Windows provides me with this facility automatically!

All we need to do is create a new registry key under HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Image File ExecutionOptions and name it after the EXE we want to attach to.

Under this key, we create two values: A DWORD named PauseOnStartup with a value of 1, and a string named Debugger, with a value of vsjitdebugger.exe. Here’s a sample .REG file

Now, when MyApplication.exe launches, it will automatically launch the familiar “Choose the debugger to use” dialog, and we can point it to our solution of choice.