The previous hack wasn't thread-safe: read-only access would
access the reference counter multiple times at the same time,
which therefore would have to be thread-local to ever work.
The current solution just disables the calls to lock/unlock
for copyconstructed objects, which works if the copyconstructed
object isn't used anymore after the original is destructed.
This is the case then the copy construction only happens
upon passing a temporary to a function, which is the case.
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