Visual Studio Hacks

Debug a Failing Application #42

Chapter 5, Debugging

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Windows Forms JIT Debugging

When you first try JIT debugging with a Windows Forms application, it

probably won’t work. By default, Windows Forms will display a dialog that

gives you the ability to see the details of the exception, continue, or quit, but

not the ability to attach a debugger to the process. To enable JIT debugging

with Windows Forms, you will need to add a configuration setting either to

the app.config of your application or, if you want to enable JIT debugging

for all Windows Forms applications, to the machine.config. To enable JIT

debugging, you need to add the following element inside the

<config-

uration>

element:

<system.windows.forms jitDebugging="true" />

This will enable JIT debugging either for the application (if you added it to

the app.config) or for all Windows Forms applications on your machine (if

you added it to the machine.config).

If your application does not already have an app.config, you

will need to create one by right-clicking on the project,

selecting Add New Item, and then selecting the application

configuration file from the list of files.

If you want to modify the machine.config file to enable JIT debugging for all

Windows Forms applications, the file can be found in the following direc-

tory:

%SystemRoot%\Microsoft.NET\Framework\v1.1.4322\machine.config

The machine.config file actually already has this element—it simply needs to

be uncommented.

JIT Settings

A number of settings, in both Visual Studio and the registry, allow you to

control how JIT debugging works. The first way that you can configure JIT

debugging is through the Tool

➝ Options window. Under the Debugging

folder is an item for JIT debugging, which is shown in Figure 5-32.

On this screen, you can disable JIT debugging for any of the various pro-

gram types. Disabling JIT debugging here overrides any settings in your con-

figuration files. When an exception is thrown, you will see a dialog stating

that JIT debugging is disabled.

A number of registry settings can also be used to configure JIT debugging

and the .NET framework. Both keys are located at:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework

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Chapter 5, Debugging

#42 Debug a Failing Application

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The first key is called DbgManagedDebugger and specifies what application

should be launched when an exception is detected. The default value for

this is vs7jit.exe, which launches the standard Visual Studio .NET JIT

debugger dialog that was shown in Figure 5-30. The second key is

DbgJITDebugLaunchSetting, which specifies what should be done when an

unhandled exception is caught. Table 5-1 shows the possible values for

this key.

Using the settings available in Visual Studio and the registry, you will be

able to configure JIT debugging to your specific needs.

Figure 5-32. Just-in-Time Debugging settings

Table 5-1. DbgJITDebugLaunchSetting key values

Value Behavior

0 Will prompt you with a dialog giving you two options:

OK

Terminates the application

Cancel

Calls the application specified in

DbgManagedDebugger

1 Disables JIT debugging and passes control back to the application and the default

error handler.

2 Control is immediately passed to the application specified in

DbgManagedDebugger. This is the default behavior.