[libcxx-commits] [libcxx] [libc++] Save duration/timeout locally for condition_variable waits (PR #148330)

[Nikolas Klauser via libcxx-commits]

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@@ -188,9 +188,10 @@ public:
   _LIBCPP_HIDE_FROM_ABI cv_status wait_until(_Lock& __lock, const chrono::time_point<_Clock, _Duration>& __t) {
     shared_ptr<mutex> __mut = __mut_;
     unique_lock<mutex> __lk(*__mut);
+    const chrono::time_point<_Clock, _Duration> __t_local = __t;
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philnik777 wrote:

> > > What do you mean by "observable" here? The specification is for the call to `wait_until()` to take the timeout by-const-ref, so taking it by-value would be nonconforming.
> > 
> > Why? How do you observe the difference? "non-conforming" means that you somehow don't follow the standard. https://eel.is/c++draft/intro.abstract#1 gives us explicit permission to change things as long as they are not observable by users (aka the as-if rule).
> 
> Again, which proposed change are you referring to?  The change to the specification to `wait_until()` to take the parameter by-value, or the change that internally makes a copy and leaves the external specification unchanged?

As I quoted: taking the parameter by value

https://github.com/llvm/llvm-project/pull/148330