If you are not familiar with the new IntelliTrace feature in Visual Studio Team System 2010 than you might want to first check out either my or John Robbins’ introductions to this feature as a general overview of IntelliTrace would be helpful before digging into this article.
What is an iTrace file?
In my introduction article linked above I talked a little about how IntelliTrace captures the current state of the debugger at multiple points during a program’s execution and, when F5 debugging, allows you to debug back in time to previous debug states in your program. This in and of itself is a very handy feature, but in this day and age it’s often hard to have a bug with an easy and consistent repro that you can debug on a local dev box.
The solution to this lack of a local repro is that not only does IntelliTrace enhance your local debugging experience, but it also saves all the collected debugger data points into a trace log file (.itrace extension) that can then be opened and debugged using Visual Studio later and on a different machine. The analogy for this scenario is that of a black box in an airplane in that iTrace files provide a “voice from the grave” from crashed programs that allow for a developer to debug in and around the point of failure after the fact.
Integration with Microsoft Test and Lab Manager
One of the big new testing features being added in Visual Studio Team System 2010 is the Microsoft Test and Lab Manager (more info on MTLM on their blog site here). MTLM is a standalone tool that focuses on the tester role by providing a TFS-integrated UI for managing test cases and lab environments without the overhead of a full Visual Studio installation. Since one of the key focuses of IntelliTrace is to try to eliminate the “no repro” disconnect between developers and testers we knew that we needed to get IntelliTrace integrated with MTLM. This integration is accomplished via a combination of TFS and iTrace files. I’ll detail the scenario more in a future blog post, but at a basic level at anytime during a test run a tester using MTLM can choose to file a bug on a specific test step failure and when that bug is filed an iTrace file of all the recent debugging events and exceptions is automatically collected and attached to the bug. Then, when the developer opens up the bug in Visual Studio, they can just click the iTrace file linked in the bug and be debugging into the exact execution path in which the tester was seeing the failure.
iTrace files collected during debugging
Whenever you are running a normal F5 debugging session from the Visual Studio IDE with IntelliTrace turned on you are collected an iTrace file in the background. Now in this scenario you can pretty easily be using IntelliTrace features like browsing back in debug history without ever noticing that this file exists, especially since to keep your system from getting clogged with iTrace files we clean these files out when Visual Studio is shut down. So if you ran into something interesting while debugging from the IDE with IntelliTrace you will need to copy the iTrace file out from its saved location to keep it from being cleaned up. Just look under the following file path to see the iTrace files that have been collected during the current VS session: C:\Users\All Users\Microsoft Visual Studio\10.0\TraceDebugging. With both the IDE scenario and the MTLM scenario iTrace files will be truncated at a specific size (currently set to 100MB by default) to keep from filling up your hard drive. This truncation value will discard older events from the log and can be changed from Tools->Options->IntelliTrace->Advanced.
Collecting iTrace files from the command line
If you want to collect iTrace debugging files without having Visual Studio up and running we’ve provided the IntelliTrace.exe command line tool. IntelliTrace.exe will get its own blog entry sometime in the future but if you want to try figuring out how to get it running just try starting with the /? command for help. Intellitrace.exe is located in your Visual Studio install at “Team Tools\TraceDebugger Tools.”
Working with iTrace files in Visual Studio
(Note: All screenshots are from my current working build and will look a little different from Beta 2 builds)
Regardless of if you collected your iTrace file via MTLM, Visual Studio or IntelliTrace.exe when you first open it up in Visual Studio you will end up with a document that looks somewhat like the below.
Note that at this point we’ve just opened up the document summarizing the debugging session. No debugging session has been started and the time to open up the document should be pretty minimal. At the top of the document you will see a chart showing all the threads that were running during the life of this debugging session. Below that there are a series of lists containing more information about Threads, Exceptions, Test Events, System Information and Modules for the debugging session. Currently, the Exceptions list is expanded out and showing all the exceptions that were encountered during the debugging run. The exception that is currently selected in this list is represented in the thread timeline by a vertical red bar. This bar helps you match up exactly where in your program’s execution an exception was being thrown. In addition to supplying the thread, HResult and message of the exception we will list out the stack of each thrown exception in the textbox below the exceptions list.
The threads list provides a table view of the threads active during your debugging session. The actively selected thread will be highlighted in the thread chart above, and vice-versa.
The system information section contains a set of information about the computer that this iTrace file was collected on. It seems pretty basic, but this info has already come in useful several times for me during my development work. In particular knowing the OS, the number of processers and the CLR version have been useful to me when investigating bugs that QA has provided me with iTrace files for.
I don’t have a picture of this right now, as I’m going to be speaking more about this when I cover MTLM integration in greater depth. When you collected an iTrace file via MTLM (since this file was not collected via MTLM the section is grayed out) the test data section will contain info on all the test steps that were logged via MTLM during the execution of the tests.
As expected, this control lists out the modules that were loaded during debugging.
On all of these controls there is a search box above the list. If you are looking for a specific module or exception just start typing into one of those boxes to narrow down the results being shown in the list.
Starting a debug session from an iTrace file
Up until now we’ve been dealing with the information that you can glean from the summary page of an iTrace file. But while it can be quite informative the real point of the summary page is to allow the user to jump into debugging close to some point of interest. Lots of information can be collected during a debugging session and if you were to just jump into debugging an iTrace file blindly it could take a while to get to the correct location to start diagnosing a failure.
From an iTrace summary page you can jump into debugging from a thread, from an exception or from a test event (with a caveat that I’ll mention later for test events). For threads you can double click on a thread in the thread chart, double click on a thread in the threads list or click the “Start Debugging” button. Any of these options will start up the debugger and jump you to the last event that we collected on that thread. We chose the last event as in many cases an iTrace log captured a failure or crash so starting at the end point makes more sense than starting at the beginning of the log when all was running smoothly. For exceptions, you can either double click the exception in the list, or click the “Start Debugging” button below the exception list. Starting debugging on an exception will start the debug session exactly on the exception event selected (see picture below). Note that starting the session is a slightly slow process and it might take a bit for the debugger to get up and running. Test data function much the same as exception with the only difference being that since test events are not represented in our debugging UI debugging context will actually be set to the event in time nearest the selected test event.
This entry is mainly focused on the iTrace file and summary page so I’ll cover more about the IntelliTrace UI during debugging later. But as for now, you can look at the picture above and see that debugging has been started and our context has been set to the exception that I clicked in the summary page by looking at the source location and the autos window.
Coming up next I’ll be talking more about the various controls that you can use to move around in IntelliTrace debugging data and what data we will be showing in the Visual Studio UI.