mirror of
https://github.com/mozilla/gecko-dev.git
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196 lines
5.2 KiB
C++
196 lines
5.2 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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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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//
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// Implement TimeStamp::Now() with mach_absolute_time
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//
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// The "tick" unit for mach_absolute_time is defined using mach_timebase_info() which
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// gives a conversion ratio to nanoseconds. For more information see Apple's QA1398.
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//
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// This code is inspired by Chromium's time_mac.cc. The biggest
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// differences are that we explicitly initialize using
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// TimeStamp::Initialize() instead of lazily in Now() and that
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// we store the time value in ticks and convert when needed instead
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// of storing the time value in nanoseconds.
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#include <mach/mach_time.h>
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#include <sys/time.h>
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#include <sys/sysctl.h>
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#include <time.h>
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#include "mozilla/TimeStamp.h"
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#include "nsDebug.h"
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// Estimate of the smallest duration of time we can measure.
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static uint64_t sResolution;
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static uint64_t sResolutionSigDigs;
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static const uint64_t kNsPerMs = 1000000;
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static const uint64_t kUsPerSec = 1000000;
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static const uint64_t 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 bool gInitialized = false;
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static double sNsPerTick;
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static uint64_t
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ClockTime()
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{
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// mach_absolute_time is it when it comes to ticks on the Mac. Other calls
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// with less precision (such as TickCount) just call through to
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// mach_absolute_time.
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//
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// At the time of writing mach_absolute_time returns the number of nanoseconds
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// since boot. This won't overflow 64bits for 500+ years so we aren't going
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// to worry about that possiblity
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return mach_absolute_time();
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}
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static uint64_t
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ClockResolutionNs()
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{
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uint64_t start = ClockTime();
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uint64_t end = ClockTime();
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uint64_t 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 = ClockTime();
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end = ClockTime();
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uint64_t 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 NSPR's resolution 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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NS_ABORT_IF_FALSE(gInitialized, "calling TimeDuration too early");
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return (mValue * sNsPerTick) / 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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NS_ABORT_IF_FALSE(gInitialized, "calling TimeDuration too early");
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// don't report a value < mResolution ...
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int64_t 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 (valueSigDigs * sNsPerTick) / 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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NS_ABORT_IF_FALSE(gInitialized, "calling TimeDuration too early");
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return TimeDuration::FromTicks(int64_t((aMilliseconds * kNsPerMsd) / sNsPerTick));
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}
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TimeDuration
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TimeDuration::Resolution()
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{
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NS_ABORT_IF_FALSE(gInitialized, "calling TimeDuration too early");
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return TimeDuration::FromTicks(int64_t(sResolution));
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}
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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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mach_timebase_info_data_t timebaseInfo;
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// Apple's QA1398 suggests that the output from mach_timebase_info
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// will not change while a program is running, so it should be safe
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// to cache the result.
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kern_return_t kr = mach_timebase_info(&timebaseInfo);
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if (kr != KERN_SUCCESS)
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NS_RUNTIMEABORT("mach_timebase_info failed");
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sNsPerTick = double(timebaseInfo.numer) / timebaseInfo.denom;
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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(bool aHighResolution)
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{
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return TimeStamp(ClockTime());
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}
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// Computes and returns the process uptime in microseconds.
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// Returns 0 if an error was encountered.
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uint64_t
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TimeStamp::ComputeProcessUptime()
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{
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struct timeval tv;
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int rv = gettimeofday(&tv, nullptr);
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if (rv == -1) {
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return 0;
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}
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int mib[] = {
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CTL_KERN,
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KERN_PROC,
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KERN_PROC_PID,
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getpid(),
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};
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u_int mibLen = sizeof(mib) / sizeof(mib[0]);
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struct kinfo_proc proc;
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size_t bufferSize = sizeof(proc);
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rv = sysctl(mib, mibLen, &proc, &bufferSize, nullptr, 0);
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if (rv == -1)
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return 0;
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uint64_t startTime =
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((uint64_t)proc.kp_proc.p_un.__p_starttime.tv_sec * kUsPerSec) +
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proc.kp_proc.p_un.__p_starttime.tv_usec;
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uint64_t now = (tv.tv_sec * kUsPerSec) + tv.tv_usec;
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if (startTime > now)
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return 0;
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return now - startTime;
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}
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} // namespace mozilla
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