зеркало из https://github.com/mozilla/pjs.git
209 строки
6.0 KiB
C++
209 строки
6.0 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim:set ts=2 sw=2 sts=2 et cindent: */
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/* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is Mozilla code.
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*
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* The Initial Developer of the Original Code is the Mozilla Corporation.
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* Portions created by the Initial Developer are Copyright (C) 2009
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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* Chris Jones <jones.chris.g@gmail.com>
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either the GNU General Public License Version 2 or later (the "GPL"), or
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* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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//
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// Implement TimeStamp::Now() with POSIX clocks.
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//
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// The "tick" unit for POSIX clocks is simply a nanosecond, as this is
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// the smallest unit of time representable by struct timespec. That
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// doesn't mean that a nanosecond is the resolution of TimeDurations
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// obtained with this API; see TimeDuration::Resolution;
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//
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#include <time.h>
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#include "mozilla/TimeStamp.h"
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// Estimate of the smallest duration of time we can measure.
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static PRUint64 sResolution;
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static PRUint64 sResolutionSigDigs;
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static const PRUint16 kNsPerUs = 1000;
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static const PRUint64 kNsPerMs = 1000000;
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static const PRUint64 kNsPerSec = 1000000000;
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static const double kNsPerMsd = 1000000.0;
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static const double kNsPerSecd = 1000000000.0;
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static PRUint64
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TimespecToNs(const struct timespec& ts)
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{
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PRUint64 baseNs = PRUint64(ts.tv_sec) * kNsPerSec;
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return baseNs + PRUint64(ts.tv_nsec);
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}
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static PRUint64
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ClockTimeNs()
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{
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struct timespec ts;
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// this can't fail: we know &ts is valid, and TimeStamp::Init()
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// checks that CLOCK_MONOTONIC is supported (and aborts if not)
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clock_gettime(CLOCK_MONOTONIC, &ts);
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// tv_sec is defined to be relative to an arbitrary point in time,
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// but it would be madness for that point in time to be earlier than
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// the Epoch. So we can safely assume that even if time_t is 32
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// bits, tv_sec won't overflow while the browser is open. Revisit
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// this argument if we're still building with 32-bit time_t around
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// the year 2037.
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return TimespecToNs(ts);
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}
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static PRUint64
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ClockResolutionNs()
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{
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// NB: why not rely on clock_getres()? Two reasons: (i) it might
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// lie, and (ii) it might return an "ideal" resolution that while
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// theoretically true, could never be measured in practice. Since
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// clock_gettime() likely involves a system call on your platform,
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// the "actual" timing resolution shouldn't be lower than syscall
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// overhead.
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PRUint64 start = ClockTimeNs();
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PRUint64 end = ClockTimeNs();
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PRUint64 minres = (end - start);
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// 10 total trials is arbitrary: what we're trying to avoid by
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// looping is getting unlucky and being interrupted by a context
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// switch or signal, or being bitten by paging/cache effects
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for (int i = 0; i < 9; ++i) {
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start = ClockTimeNs();
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end = ClockTimeNs();
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PRUint64 candidate = (start - end);
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if (candidate < minres)
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minres = candidate;
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}
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if (0 == minres) {
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// measurable resolution is either incredibly low, ~1ns, or very
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// high. fall back on clock_getres()
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struct timespec ts;
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if (0 == clock_getres(CLOCK_MONOTONIC, &ts)) {
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minres = TimespecToNs(ts);
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}
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}
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if (0 == minres) {
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// clock_getres probably failed. fall back on NSPR's resolution
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// assumption
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minres = 1 * kNsPerMs;
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}
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return minres;
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}
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namespace mozilla {
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double
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TimeDuration::ToSeconds() const
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{
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return double(mValue) / kNsPerSecd;
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}
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double
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TimeDuration::ToSecondsSigDigits() const
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{
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// don't report a value < mResolution ...
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PRInt64 valueSigDigs = sResolution * (mValue / sResolution);
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// and chop off insignificant digits
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valueSigDigs = sResolutionSigDigs * (valueSigDigs / sResolutionSigDigs);
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return double(valueSigDigs) / kNsPerSecd;
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}
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TimeDuration
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TimeDuration::FromMilliseconds(double aMilliseconds)
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{
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return TimeDuration::FromTicks(aMilliseconds * kNsPerMsd);
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}
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TimeDuration
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TimeDuration::Resolution()
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{
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return TimeDuration::FromTicks(PRInt64(sResolution));
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}
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struct TimeStampInitialization
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{
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TimeStampInitialization() {
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TimeStamp::Startup();
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}
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~TimeStampInitialization() {
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TimeStamp::Shutdown();
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}
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};
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static TimeStampInitialization initOnce;
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static bool gInitialized = false;
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nsresult
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TimeStamp::Startup()
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{
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if (gInitialized)
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return NS_OK;
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struct timespec dummy;
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if (0 != clock_gettime(CLOCK_MONOTONIC, &dummy))
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NS_RUNTIMEABORT("CLOCK_MONOTONIC is absent!");
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sResolution = ClockResolutionNs();
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// find the number of significant digits in sResolution, for the
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// sake of ToSecondsSigDigits()
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for (sResolutionSigDigs = 1;
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!(sResolutionSigDigs == sResolution
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|| 10*sResolutionSigDigs > sResolution);
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sResolutionSigDigs *= 10);
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gInitialized = true;
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return NS_OK;
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}
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void
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TimeStamp::Shutdown()
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{
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}
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TimeStamp
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TimeStamp::Now()
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{
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return TimeStamp(ClockTimeNs());
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}
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}
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