Bug 153042 – Windows system timer resolution needlessly cranked up when nextFireTime is in the past

• Status: NEW
• Component: Platform

[John N. Lehner]

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.

[Brent Fulgham]

Nice catch! We'll try to allocate some time to this soon.