mozglue/misc/TimeStamp_darwin.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 //
   8 // Implement TimeStamp::Now() with mach_absolute_time
   9 //
  10 // The "tick" unit for mach_absolute_time is defined using mach_timebase_info()
  11 // which gives a conversion ratio to nanoseconds. For more information see
  12 // Apple's QA1398.
  13 //
  14 // This code is inspired by Chromium's time_mac.cc. The biggest
  15 // differences are that we explicitly initialize using
  16 // TimeStamp::Initialize() instead of lazily in Now() and that
  17 // we store the time value in ticks and convert when needed instead
  18 // of storing the time value in nanoseconds.
  19
  20 #include <mach/mach_time.h>
  21 #include <sys/time.h>
  22 #include <sys/sysctl.h>
  23 #include <time.h>
  24 #include <unistd.h>
  25
  26 #include "mozilla/TimeStamp.h"
  27 #include "mozilla/Uptime.h"
  28
  29 // Estimate of the smallest duration of time we can measure.
  30 static uint64_t sResolution;
  31 static uint64_t sResolutionSigDigs;
  32
  33 static const uint64_t kNsPerMs = 1000000;
  34 static const uint64_t kUsPerSec = 1000000;
  35 static const double kNsPerMsd = 1000000.0;
  36 static const double kNsPerSecd = 1000000000.0;
  37
  38 static bool gInitialized = false;
  39 static double sNsPerTick;
  40
  41 static uint64_t ClockTime() {
  42   // mach_absolute_time is it when it comes to ticks on the Mac.  Other calls
  43   // with less precision (such as TickCount) just call through to
  44   // mach_absolute_time.
  45   //
  46   // At the time of writing mach_absolute_time returns the number of nanoseconds
  47   // since boot. This won't overflow 64bits for 500+ years so we aren't going
  48   // to worry about that possiblity
  49   return mach_absolute_time();
  50 }
  51
  52 static uint64_t ClockResolutionNs() {
  53   uint64_t start = ClockTime();
  54   uint64_t end = ClockTime();
  55   uint64_t minres = (end - start);
  56
  57   // 10 total trials is arbitrary: what we're trying to avoid by
  58   // looping is getting unlucky and being interrupted by a context
  59   // switch or signal, or being bitten by paging/cache effects
  60   for (int i = 0; i < 9; ++i) {
  61     start = ClockTime();
  62     end = ClockTime();
  63
  64     uint64_t candidate = (start - end);
  65     if (candidate < minres) {
  66       minres = candidate;
  67     }
  68   }
  69
  70   if (0 == minres) {
  71     // measurable resolution is either incredibly low, ~1ns, or very
  72     // high.  fall back on NSPR's resolution assumption
  73     minres = 1 * kNsPerMs;
  74   }
  75
  76   return minres;
  77 }
  78
  79 namespace mozilla {
  80
  81 double BaseTimeDurationPlatformUtils::ToSeconds(int64_t aTicks) {
  82   MOZ_ASSERT(gInitialized, "calling TimeDuration too early");
  83   return (aTicks * sNsPerTick) / kNsPerSecd;
  84 }
  85
  86 double BaseTimeDurationPlatformUtils::ToSecondsSigDigits(int64_t aTicks) {
  87   MOZ_ASSERT(gInitialized, "calling TimeDuration too early");
  88   // don't report a value < mResolution ...
  89   int64_t valueSigDigs = sResolution * (aTicks / sResolution);
  90   // and chop off insignificant digits
  91   valueSigDigs = sResolutionSigDigs * (valueSigDigs / sResolutionSigDigs);
  92   return (valueSigDigs * sNsPerTick) / kNsPerSecd;
  93 }
  94
  95 int64_t BaseTimeDurationPlatformUtils::TicksFromMilliseconds(
  96     double aMilliseconds) {
  97   MOZ_ASSERT(gInitialized, "calling TimeDuration too early");
  98   double result = (aMilliseconds * kNsPerMsd) / sNsPerTick;
  99   if (result > double(INT64_MAX)) {
 100     return INT64_MAX;
 101   } else if (result < double(INT64_MIN)) {
 102     return INT64_MIN;
 103   }
 104
 105   return result;
 106 }
 107
 108 int64_t BaseTimeDurationPlatformUtils::ResolutionInTicks() {
 109   MOZ_ASSERT(gInitialized, "calling TimeDuration too early");
 110   return static_cast<int64_t>(sResolution);
 111 }
 112
 113 void TimeStamp::Startup() {
 114   if (gInitialized) {
 115     return;
 116   }
 117
 118   mach_timebase_info_data_t timebaseInfo;
 119   // Apple's QA1398 suggests that the output from mach_timebase_info
 120   // will not change while a program is running, so it should be safe
 121   // to cache the result.
 122   kern_return_t kr = mach_timebase_info(&timebaseInfo);
 123   if (kr != KERN_SUCCESS) {
 124     MOZ_RELEASE_ASSERT(false, "mach_timebase_info failed");
 125   }
 126
 127   sNsPerTick = double(timebaseInfo.numer) / timebaseInfo.denom;
 128
 129   sResolution = ClockResolutionNs();
 130
 131   // find the number of significant digits in sResolution, for the
 132   // sake of ToSecondsSigDigits()
 133   for (sResolutionSigDigs = 1; !(sResolutionSigDigs == sResolution ||
 134                                  10 * sResolutionSigDigs > sResolution);
 135        sResolutionSigDigs *= 10)
 136     ;
 137
 138   gInitialized = true;
 139 }
 140
 141 void TimeStamp::Shutdown() {}
 142
 143 TimeStamp TimeStamp::Now(bool aHighResolution) {
 144   return TimeStamp(ClockTime());
 145 }
 146
 147 uint64_t TimeStamp::RawMachAbsoluteTimeNanoseconds() const {
 148   return static_cast<uint64_t>(double(mValue) * sNsPerTick);
 149 }
 150
 151 // Computes and returns the process uptime in microseconds.
 152 // Returns 0 if an error was encountered.
 153 uint64_t TimeStamp::ComputeProcessUptime() {
 154   struct timeval tv;
 155   int rv = gettimeofday(&tv, nullptr);
 156
 157   if (rv == -1) {
 158     return 0;
 159   }
 160
 161   int mib[] = {
 162       CTL_KERN,
 163       KERN_PROC,
 164       KERN_PROC_PID,
 165       getpid(),
 166   };
 167   u_int mibLen = sizeof(mib) / sizeof(mib[0]);
 168
 169   struct kinfo_proc proc;
 170   size_t bufferSize = sizeof(proc);
 171   rv = sysctl(mib, mibLen, &proc, &bufferSize, nullptr, 0);
 172
 173   if (rv == -1) {
 174     return 0;
 175   }
 176
 177   uint64_t startTime =
 178       ((uint64_t)proc.kp_proc.p_un.__p_starttime.tv_sec * kUsPerSec) +
 179       proc.kp_proc.p_un.__p_starttime.tv_usec;
 180   uint64_t now = (tv.tv_sec * kUsPerSec) + tv.tv_usec;
 181
 182   if (startTime > now) {
 183     return 0;
 184   }
 185
 186   return now - startTime;
 187 }
 188
 189 }  // namespace mozilla