Summary: __register_frame and the corresponding _Unwind_Find_FDE use a
global mutex for frame registration and unwinding. This can lead to very
poor performance on machines with high core counts. This patch organizes
the frames in a b-tree with read-optimized synchronization instead,
which
The __register_frame/__deregister_frame functions are used to register
unwinding frames from JITed code in a sorted list. That list itself
is protected by object_mutex, which leads to terrible performance
in multi-threaded code and is somewhat expensive even if single-threaded.
There was already
