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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
//
// Implement TimeStamp::Now() with mach_absolute_time
//
// The "tick" unit for mach_absolute_time is defined using mach_timebase_info() which
// gives a conversion ratio to nanoseconds. For more information see Apple's QA1398.
//
// This code is inspired by Chromium's time_mac.cc. The biggest
// differences are that we explicitly initialize using
// TimeStamp::Initialize() instead of lazily in Now() and that
// we store the time value in ticks and convert when needed instead
// of storing the time value in nanoseconds.
#include <mach/mach_time.h>
#include <sys/time.h>
#include <sys/sysctl.h>
#include <time.h>
#include <unistd.h>
#include "mozilla/TimeStamp.h"
// Estimate of the smallest duration of time we can measure.
static uint64_t sResolution;
static uint64_t sResolutionSigDigs;
static const uint64_t kNsPerMs = 1000000;
static const uint64_t kUsPerSec = 1000000;
static const double kNsPerMsd = 1000000.0;
static const double kNsPerSecd = 1000000000.0;
static bool gInitialized = false;
static double sNsPerTick;
static uint64_t
ClockTime()
{
// mach_absolute_time is it when it comes to ticks on the Mac. Other calls
// with less precision (such as TickCount) just call through to
// mach_absolute_time.
//
// At the time of writing mach_absolute_time returns the number of nanoseconds
// since boot. This won't overflow 64bits for 500+ years so we aren't going
// to worry about that possiblity
return mach_absolute_time();
}
static uint64_t
ClockResolutionNs()
{
uint64_t start = ClockTime();
uint64_t end = ClockTime();
uint64_t minres = (end - start);
// 10 total trials is arbitrary: what we're trying to avoid by
// looping is getting unlucky and being interrupted by a context
// switch or signal, or being bitten by paging/cache effects
for (int i = 0; i < 9; ++i) {
start = ClockTime();
end = ClockTime();
uint64_t candidate = (start - end);
if (candidate < minres) {
minres = candidate;
}
}
if (0 == minres) {
// measurable resolution is either incredibly low, ~1ns, or very
// high. fall back on NSPR's resolution assumption
minres = 1 * kNsPerMs;
}
return minres;
}
namespace mozilla {
double
BaseTimeDurationPlatformUtils::ToSeconds(int64_t aTicks)
{
MOZ_ASSERT(gInitialized, "calling TimeDuration too early");
return (aTicks * sNsPerTick) / kNsPerSecd;
}
double
BaseTimeDurationPlatformUtils::ToSecondsSigDigits(int64_t aTicks)
{
MOZ_ASSERT(gInitialized, "calling TimeDuration too early");
// don't report a value < mResolution ...
int64_t valueSigDigs = sResolution * (aTicks / sResolution);
// and chop off insignificant digits
valueSigDigs = sResolutionSigDigs * (valueSigDigs / sResolutionSigDigs);
return (valueSigDigs * sNsPerTick) / kNsPerSecd;
}
int64_t
BaseTimeDurationPlatformUtils::TicksFromMilliseconds(double aMilliseconds)
{
MOZ_ASSERT(gInitialized, "calling TimeDuration too early");
double result = (aMilliseconds * kNsPerMsd) / sNsPerTick;
if (result > INT64_MAX) {
return INT64_MAX;
} else if (result < INT64_MIN) {
return INT64_MIN;
}
return result;
}
int64_t
BaseTimeDurationPlatformUtils::ResolutionInTicks()
{
MOZ_ASSERT(gInitialized, "calling TimeDuration too early");
return static_cast<int64_t>(sResolution);
}
void
TimeStamp::Startup()
{
if (gInitialized) {
return;
}
mach_timebase_info_data_t timebaseInfo;
// Apple's QA1398 suggests that the output from mach_timebase_info
// will not change while a program is running, so it should be safe
// to cache the result.
kern_return_t kr = mach_timebase_info(&timebaseInfo);
if (kr != KERN_SUCCESS) {
MOZ_RELEASE_ASSERT(false, "mach_timebase_info failed");
}
sNsPerTick = double(timebaseInfo.numer) / timebaseInfo.denom;
sResolution = ClockResolutionNs();
// find the number of significant digits in sResolution, for the
// sake of ToSecondsSigDigits()
for (sResolutionSigDigs = 1;
!(sResolutionSigDigs == sResolution ||
10 * sResolutionSigDigs > sResolution);
sResolutionSigDigs *= 10);
gInitialized = true;
return;
}
void
TimeStamp::Shutdown()
{
}
TimeStamp
TimeStamp::Now(bool aHighResolution)
{
return TimeStamp(ClockTime());
}
// Computes and returns the process uptime in microseconds.
// Returns 0 if an error was encountered.
uint64_t
TimeStamp::ComputeProcessUptime()
{
struct timeval tv;
int rv = gettimeofday(&tv, nullptr);
if (rv == -1) {
return 0;
}
int mib[] = {
CTL_KERN,
KERN_PROC,
KERN_PROC_PID,
getpid(),
};
u_int mibLen = sizeof(mib) / sizeof(mib[0]);
struct kinfo_proc proc;
size_t bufferSize = sizeof(proc);
rv = sysctl(mib, mibLen, &proc, &bufferSize, nullptr, 0);
if (rv == -1) {
return 0;
}
uint64_t startTime =
((uint64_t)proc.kp_proc.p_un.__p_starttime.tv_sec * kUsPerSec) +
proc.kp_proc.p_un.__p_starttime.tv_usec;
uint64_t now = (tv.tv_sec * kUsPerSec) + tv.tv_usec;
if (startTime > now) {
return 0;
}
return now - startTime;
}
} // namespace mozilla
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