How can I load a package and keep the debugger working?

Question

I'm using TJvPluginManager in the JVCL to create and load BPL-based plugins for my program. Problem is, one of the plugins isn't loading properly, and I can't debug it. Every time I try to trace into the loading sequence, it gets as far as the LoadLibrary API call, and then the debugger seems to forget what it's there for. It completely loses the ability to associate program code with source lines, give meaningful data in a call stack, or display local variables. It will still stop at breakpoints, but it breaks to the CPU window, with all the inline source code stripped out.

This happens on Delphi 2007 and 2009, and it's driving me nuts. Does anyone know how to load a plugin without it breaking the debugger? Does anyone even know why it's breaking it in the first place?

NOTE: I'm not looking for alternative methods of debugging. I know all about tracing and logging and all the rest. What I want is to understand what's going wrong and how to fix it. Surely I'm not the only person who's ever used TJvPluginManager?

Answer 1

Not quite the answer to your question: Have you tried to debug the package project, by setting the host application and putting a breakpoint into the package's startup code?

Answer 2

I've found Ray Kanopka's (Raize) CodeSite to be invaluable for debugging in situations where the integrated debugger is acting up. Thinking about the things I want to monitor using CodeSite actually helps me focus on what's important - it enforces good habits.

Answer 3

Another alternative to Codesite is Overseer which is part of the nexus project, but stands alone so does not require you to use their framework. Codesite is by far the better option, but in a pinch Overseer would work just as well.

Answer 4

I found that using packages for plugins can be problematic and many years ago switched to a completely COM based implementation for plugins and never had any problems. The other advantage to COM based plugins, they don't require Delphi to write, do not need to be recompiled when the main app switches to a new version of the compiler (my plugins compiled with Delphi 5 still run fine against the main application compiled in Delphi 2009!) and they are easier to write test applications to assist in debugging.

The only side effect I notice, is that shared code ends up in both executables and the plugins require registration into the registry.

Answer 5

Hmmmm... This is a stupid question, but I have to ask: the initialization function have the EXACT declaration syntax like the other plugins that work ?(from your question, I deducted you made some others that work)

Answer 6

Check your dependencies. Make sure each unit is compiled into one package only. Whenever a package needs to reference a unit from another package, use the requires clause to do so. Watch for compiler warnings about implicitly linked units.