[webkit-reviews] review granted: [Bug 131630] monotonicallyIncreasingTime() should only initialize its static timebaseInfo once : [Attachment 229302] the patch

[bugzilla-daemon at webkit.org]

Filip Pizlo <fpizlo at apple.com> has granted Mark Lam <mark.lam at apple.com>'s
request for review:
Bug 131630: monotonicallyIncreasingTime() should only initialize its static
timebaseInfo once
https://bugs.webkit.org/show_bug.cgi?id=131630

Attachment 229302: the patch
https://bugs.webkit.org/attachment.cgi?id=229302&action=review

------- Additional Comments from Filip Pizlo <fpizlo at apple.com>
View in context: https://bugs.webkit.org/attachment.cgi?id=229302&action=review


> Source/WTF/wtf/CurrentTime.cpp:278
>      // Based on listing #2 from Apple QA 1398.
>      static mach_timebase_info_data_t timebaseInfo;
> -    if (!timebaseInfo.denom) {
> +    static std::once_flag initializeTimerOnceFlag;
> +    std::call_once(initializeTimerOnceFlag, [] {

You should change the comment to say that it fixes the race condition in that
listing.  Say something like "Based on listing #2 from Apple QA 1398, but
modified to be thread-safe".