[Issue 19956] Subclassing Thread with synchronized (this) may deadlock

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19956

--- Comment #2 from FeepingCreature <default_357-line at yahoo.de> ---
Sure, but even being protected would not have helped here.

Maybe `Thread` should be `final`?

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