Wait condition_variable_any for steady_clock by AlexGuteniev · Pull Request #4755 · microsoft/STL (original) (raw)

Fixes #4723

Turned out that:

• WinAPI SleepConditionVariableSRW times out using a steady clock that is not precisely synchronized with steady_clock implemented based on QueryPerformanceCounter
• Fixing it with GetTickCount64() check doesn't help, as GetTickCount64() is also not precisely synchronized with QueryPerformanceCounter

The fix is to check exactly steady_clock in condition_variable_any.

This is done in a header, rather than in .cpp for these reasons:

• The header implementation of steady_clock::now() is nontrivial, and resides in a non-core header, and we don't have a good core header to extract it into
• Other call sites of the internal condition variable wait function check against the clock on their own already

That's why GetTickCount64() was removed from internal wait function.

To avoid destabilizing behavior for already compiled code, I kept GetTickCount64() on that code path (it might improve over raw SleepConditionVariableSRW a bit).

I've inlined _Wait_for_ms_count as to me it appeared clearer this way after these changes.