CLR Profilers and Windows Store apps

Last month Microsoft published a white paper about profiling Windows Store apps. The paper is very detailed and provides rich information how to build CLR profiler for Windows Store apps. I was very curious to read it because at the time when we released JustTrace Q3 2012 there was no documentation. After all, I was curious to know whether JustTrace is compliant with the guidelines Microsoft provided. It turns out it is. Almost.

At time of writing JustTrace profiler uses a few Win32 functions that are not officially supported for Windows Store apps. The only reason for this is the support for Windows XP. Typical example is CreateEvent which is not supported for Windows Store apps but is supported since Windows XP. Rather one should use CreateEventEx which is supported since Windows Vista.

One option is to drop the support for Windows XP. I am a bit reluctant though. At least such decision should be carefully thought and must be supported by actual data for our customers using Window XP. Another option is to accept the burden to develop and maintain two source code bases – one for Windows XP and another for Windows Vista and higher. Whatever decision we are going to make, it will be thoroughly thought out.

Let’s have a look at the paper. There is one very interesting detail about memory profiling.

The garbage collector and managed heap are not fundamentally different in a Windows Store app as compared to a desktop app.  However, there are some subtle differences that profiler authors need to be aware of.

It continues even more interesting.

When doing memory profiling, your Profiler DLL typically creates a separate thread from which to call ForceGC. This is nothing new.  But what might be surprising is that the act of doing a garbage collection inside a Windows Store app may transform your thread into a managed thread (for example, a Profiling API ThreadID will be created for that thread)

Very subtle indeed. For a detailed explanation, you can read the paper. Fortunately JustTrace is not affected by this change.

In conclusion, I think the paper is very good. It is a mandatory reading for anyone interested in building CLR profiler for Windows Store apps. I would encourage you to see CLR profiler implementation as well.

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