vs2012 debugger hangs while i want to expand some collection variable

Question

I'm debugging a project using VS2012 ultimate, but encountered this problem very often now. usually it happens when i want to expand a collection type value(e.g, List<>, Dictionary<> and so on) to watch its value. It just failed to show the value and then hangs forever, the error message is like "Function evaluation disabled because a previous function evaluation timed out. You must continue execution to reenable function evaluation." the only thing i could do is to restart the debugger. can anybody give some help?

Answer 1

When you expand a value in the debugger to see its members, the debugger does somethings called a "func-eval" behind the scenes, which basically means it 'wakes up' one of the the threads in the debuggee and runs some code in it in order to display its result. This is usually either executing a property's getter or an object's .ToString() method.

Sometimes, the evaluation can take too long (often because a property getter gets stuck waiting on some lock that is held by another thread, in which case, you could keep waiting forever and it'll never return, because all threads except the thread that's doing the func-eval are paused by the debugger). In these cases, after a short while the debugger will decide to 'give up' and display the message you've encountered. You don't have to restart your app to try evaluating properties again - you can simply do another Step Over (F10).

As a more permanent solution, you can do one of two things:

1. Go into Tools->Options->Debugging->General and disable "Enable property evaluation and other implicit function calls". This will make the debugger's display a lot less useful as you will only be able to view fields, but it guarantees you will never get stuck and receive the timeout message.
2. Try to figure out which property in which object is the one that keeps timing-out. This can be a bit tricky, by try paying attention to which objects you are viewing when this happens - the timeout will usually occur just after you scroll down to the offending property. Once you know which property is at fault, either change it into a method, or put [DebuggerBrowsable(DebuggerBrowsableState.Never)] above it to prevent the debugger from displaying it.