[Webkit-unassigned] [Bug 157924] REGRESSION (r188642): All pages are blank when printing a webpage in iOS Safari

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=157924

--- Comment #5 from Andy Estes <aestes at apple.com> ---
(In reply to comment #4)
> There are two issues I think:
> 
> 1) The functional style would have you let WTF::Condition do the time math
> for you.  Instead of having a wait loop, do:
> 
> m_condition.waitFor(m_lock, timeout, [&] () -> bool { loop body });

Unfortunately this would just move the overflow into Condition::absoluteFromRelative(), where have these two lines:

    Clock::duration myRelativeTimeout =
        std::chrono::duration_cast<Clock::duration>(relativeTimeout);

    return Clock::now() + myRelativeTimeout;

libc++ represents both nanoseconds and milliseconds using the same type (long long), so the duration_cast will overflow trying to convert the largest long long into an even larger number of nanosecond ticks. Now we're right back where we started, subtracting from Clock::now() instead of adding.

> 
> 2) The style that I've been settling on is to just use doubles for time. 
> Maybe when I have time to mess around I'll propose that we do this.  I've
> encountered so many bugs due to std::chrono having overflows where our old
> double-based time code would have recovered like a champ.  In fact, one of
> those overflows was in GCC's version of libstdc++!  It would cause some uses
> of std::condition_variable to freak out on Linux but not anywhere else.
> 
> In this case, we could just go back to using a double timeout. 
> waitForSeconds(+Inf) should correctly cause our code to recognize that you
> want to timeout forever.
> 
> I'm also fine with Geoff's proposed solution.

Yeah, this is basically what I proposed doing in Radar, although now Geoff made me realize that my patch has a totally unnecessary subtraction in it!

Thanks for the feedback, Geoff and Phil.

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