[Issue 11216] Make synchronized statement `nothrow`

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=11216

--- Comment #11 from FeepingCreature <default_357-line at yahoo.de> ---
Istm a possible approach would be:

 * Define SimpleMonitor : Monitor with nothrow

 * change DMD to use nothrow when locking SimpleMonitors

 * subclass druntime's Mutex with SimpleMutex : Mutex, SimpleMonitor

 * use SimpleMutex as the mutex implementation for class monitors

Then synchronized(this) should be nothrow without breaking existing code that
depends on Mutex/Monitor. It would only break if you were assigning to
_monitor, and that's easily fixed by using a separate member.

I don't know how to implement this on the DMD side though.

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