The [NSURL URLByAppendingPathComponent:] will try and check if a file:///
url is point to a directory or not, and in that process it will read metadata
about the file, which strangely enough makes macOS create a new thread.
Just after calling URLByAppendingPathComponent: we will call setenv to set
MONO_REGISTRY_PATH to the calculated path.
At the same time (sometimes _exactly_ at the same time) the new thread will
read the current environment variables.
Since getenv/setenv isn't thread-safe (!!!), there's a race condition here
that may once in a while cause a crash (bug #37794).
So instead of calling URLByAppendingPathComponent: we call
URLByAppendingPathComponent:isDirectory:, thus telling the API
if the resulting path is a directory or not, which means it doesn't
have to check (and won't create any new threads).
So with this change Xamarin.Mac apps are effectively single-threaded
until we're done setting environment variables.
https://bugzilla.xamarin.com/show_bug.cgi?id=37794
* [XM] Dynamically look up NSExtensionMain to unbreak pre-10.10 XM apps
- So having a simple reference to NSExtensionMain is enough for /usr/lib/libextension.dylib to get added as a reference to libxammac.dylib
- If you have a reference to /usr/lib/libextension.dylib then any XM app (including our tests) bomb out on startup. This is suboptimal.
- So dlopen/dysm our way to victory.
* Fix spacing
Chris Hamons
Rolf Bjarne Kvinge