[Webkit-unassigned] [Bug 153042] New: Windows system timer resolution needlessly cranked up when nextFireTime is in the past

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=153042

            Bug ID: 153042
           Summary: Windows system timer resolution needlessly cranked up
                    when nextFireTime is in the past
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: PC
                OS: Windows 7
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Platform
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: jnlehner at yahoo.com

In http://trac.webkit.org/browser/trunk/Source/WebCore/platform/win/MainThreadSharedTimerWin.cpp

if MainThreadSharedTimer::setFireInterval() is called with an interval of 0, as will happen when ThreadTimers::updateSharedTimer() executes

m_sharedTimer->setFireInterval(std::max(nextFireTime - currentMonotonicTime, 0.0));

with nextFireTime in the past, then the following executes:

138    if (Settings::shouldUseHighResolutionTimers()) {
139            if (interval < highResolutionThresholdMsec) {
140                if (!highResTimerActive) {
141                    highResTimerActive = true;
142                    timeBeginPeriod(timerResolution);
143                }

highResolutionThresholdMsec is 16, so 0 < 16 and we call timeBeginPeriod(1) which stays in effect ~1/3 of a second.  This increases power consumption needlessly.

We should only increase the system timer resolution if we're going to actually proceed to the CreateTimerQueueTimer() call; if we're going to PostMessage() immediately no resolution increase is necessary.

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