Bug 131630 – monotonicallyIncreasingTime() should only initialize its static timebaseInfo once

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Mark Lam]

The current initialization of the static field is not thread safe.

[Mark Lam]

<rdar://problem/16413527>

[Mark Lam]

Created attachment 229302 [details]
the patch

[Filip Pizlo]

Comment on attachment 229302 [details]
the patch

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".

[Mark Lam]

Thanks.  Patch has been updated as suggested.  Landed in r167263: <http://trac.webkit.org/r167263>.