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

[John Sheu 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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johnsheu wrote:

Taking the parameter by-value is directly nonconforming, as the standard calls for the parameter to be taken by-const-ref.  This is a change that we cannot do without an amendment to the standard.

As @jwakely points out, taking the parameter by-const-ref and then making a copy internally, in addition to having the observable behavior of different timeout handling, also has a user-observable additional copy.

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