CLR V4: Load your profiler without using the registry

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One of the new features in CLR V4 is the ability to load your profiler without needing to register it first.  In V2, we would look at the following environment variables:

COR_ENABLE_PROFILING=1

COR_PROFILER={CLSID of profiler}

and look up the CLSID from COR_PROFILER in the registry to find the full path to your profiler's DLL.  Just like with any COM server DLL, we look for your profiler's CLSID under HKEY_CLASSES_ROOT, which merges the classes from HKLM and HKCU.

We mostly follow the same algorithm in V4, so you can continue registering your profiler if you wish.  However, in V4 we look for one more environment variable first:

COR_PROFILER_PATH=full path to your profiler's DLL

If that environment variable is present, we skip the registry look up altogether, and just use the path from COR_PROFILER_PATH to load your DLL.  A couple things to note about this:

  • COR_PROFILER_PATH is purely optional.  If you don't specify COR_PROFILER_PATH, we use the old procedure of looking up your profiler's CLSID in the registry to find its path
  • If you specify COR_PROFILER_PATH and register your profiler, then COR_PROFILER_PATH always wins.  Even if COR_PROFILER_PATH points to an invalid path, we will still use COR_PROFILER_PATH, and just fail to load your profiler.
  • COR_PROFILER is always required.  If you specify COR_PROFILER_PATH, we skip the registry look up; however, we still need to know your profiler's CLSID, so we can pass it to your class factory's CreateInstance call.