mozglue/misc/TimeStamp_darwin.cpp
author Gerald Squelart <gsquelart@mozilla.com>
Thu, 04 Jul 2019 04:38:16 +0000
changeset 481213 8fed7bc35767fdfab4bac0908ae9b21c08f49e1f
parent 448947 6f3709b3878117466168c40affa7bca0b60cf75b
child 503197 4b979a591152d7315776d09b294312e938fa6faa
permissions -rw-r--r--
Bug 1559000 - mozglue's AutoProfilerLabel doesn't need to know about ProfilingStack - r=mstange `ProfilingStack*` happens to be the information that the current Gecko Profiler entry function wants to forward to the exit function, but AutoProfilerLabel does not really need to know about that. Changing it to `void*`, so that we can later use different entry/exit functions that use different context types. Differential Revision: https://phabricator.services.mozilla.com/D34806

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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::NowFuzzy(TimeStampValue(false, ClockTime()));
}

TimeStamp TimeStamp::NowUnfuzzed(bool aHighResolution) {
  return TimeStamp(TimeStampValue(false, 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