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[runtime] Add some debugging aid to xamarin_release_managed_ref. #15767

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Merged
rolfbjarne merged 1 commit into from
Aug 26, 2022
Merged

[runtime] Add some debugging aid to xamarin_release_managed_ref. #15767

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25 changes: 25 additions & 0 deletions runtime/runtime.m
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Original file line number Diff line number Diff line change
Expand Up @@ -1861,6 +1861,27 @@ -(void) xamarinSetFlags: (enum XamarinGCHandleFlags) flags;
}
#endif

// It's fairly frequent (due to various types of coding errors) to have the
// call to '[self release]' in xamarin_release_managed_ref crash. These
// crashes are typically very hard to diagnose, because it can be hard to
// figure out which object caused the crash. So here we store the native
// object in a static variable, so that it can be read using lldb from a core
// dump. The variable is declared as volatile so that the compiler doesn't
// optimize away anything (we want both writes in
// xamarin_release_managed_ref), and it's attributed with 'unused' because
// otherwise the compiler complains that the variable is never read.
//
// Admittedly the variable should also be thread-local, but that's not
// supported on all platforms we build for (in particular it requires min
// iOS 10), and it's also slower than a straight forward write to a static
// variable. Also while xamarin_release_managed_ref can be called on
// multiple threads, the vast majority of the calls occur on the main
// thread, so let's keep the variable global for now and if it turns out
// to be a problem we can make it thread-local later.
extern "C" {
volatile id xamarin_handle_to_be_released __attribute__((unused));
}

void
xamarin_release_managed_ref (id self, bool user_type)
{
Expand Down Expand Up @@ -1946,7 +1967,11 @@ -(void) xamarinSetFlags: (enum XamarinGCHandleFlags) flags;
xamarin_framework_peer_waypoint_safe ();
}

xamarin_handle_to_be_released = self;

[self release];

xamarin_handle_to_be_released = NULL;
}

/*
Expand Down