mozglue/misc/TimeStamp_posix.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 POSIX clocks.
   9 //
  10 // The "tick" unit for POSIX clocks is simply a nanosecond, as this is
  11 // the smallest unit of time representable by struct timespec.  That
  12 // doesn't mean that a nanosecond is the resolution of TimeDurations
  13 // obtained with this API; see TimeDuration::Resolution;
  14 //
  15
  16 #include <sys/syscall.h>
  17 #include <time.h>
  18 #include <unistd.h>
  19 #include <string.h>
  20
  21 #if defined(__DragonFly__) || defined(__FreeBSD__) || defined(__NetBSD__) || \
  22     defined(__OpenBSD__)
  23 #  include <sys/param.h>
  24 #  include <sys/sysctl.h>
  25 #endif
  26
  27 #if defined(__DragonFly__) || defined(__FreeBSD__)
  28 #  include <sys/user.h>
  29 #endif
  30
  31 #if defined(__NetBSD__)
  32 #  undef KERN_PROC
  33 #  define KERN_PROC KERN_PROC2
  34 #  define KINFO_PROC struct kinfo_proc2
  35 #else
  36 #  define KINFO_PROC struct kinfo_proc
  37 #endif
  38
  39 #if defined(__DragonFly__)
  40 #  define KP_START_SEC kp_start.tv_sec
  41 #  define KP_START_USEC kp_start.tv_usec
  42 #elif defined(__FreeBSD__)
  43 #  define KP_START_SEC ki_start.tv_sec
  44 #  define KP_START_USEC ki_start.tv_usec
  45 #else
  46 #  define KP_START_SEC p_ustart_sec
  47 #  define KP_START_USEC p_ustart_usec
  48 #endif
  49
  50 #include "mozilla/Sprintf.h"
  51 #include "mozilla/TimeStamp.h"
  52
  53 #if !defined(__wasi__)
  54 #  include <pthread.h>
  55 #endif
  56
  57 // Estimate of the smallest duration of time we can measure.
  58 static uint64_t sResolution;
  59 static uint64_t sResolutionSigDigs;
  60
  61 #if !defined(__wasi__)
  62 static const uint16_t kNsPerUs = 1000;
  63 #endif
  64
  65 static const uint64_t kNsPerMs = 1000000;
  66 static const uint64_t kNsPerSec = 1000000000;
  67 static const double kNsPerMsd = 1000000.0;
  68 static const double kNsPerSecd = 1000000000.0;
  69
  70 static uint64_t TimespecToNs(const struct timespec& aTs) {
  71   uint64_t baseNs = uint64_t(aTs.tv_sec) * kNsPerSec;
  72   return baseNs + uint64_t(aTs.tv_nsec);
  73 }
  74
  75 static uint64_t ClockTimeNs() {
  76   struct timespec ts;
  77   // this can't fail: we know &ts is valid, and TimeStamp::Startup()
  78   // checks that CLOCK_MONOTONIC is supported (and aborts if not)
  79   clock_gettime(CLOCK_MONOTONIC, &ts);
  80
  81   // tv_sec is defined to be relative to an arbitrary point in time,
  82   // but it would be madness for that point in time to be earlier than
  83   // the Epoch.  So we can safely assume that even if time_t is 32
  84   // bits, tv_sec won't overflow while the browser is open.  Revisit
  85   // this argument if we're still building with 32-bit time_t around
  86   // the year 2037.
  87   return TimespecToNs(ts);
  88 }
  89
  90 static uint64_t ClockResolutionNs() {
  91   // NB: why not rely on clock_getres()?  Two reasons: (i) it might
  92   // lie, and (ii) it might return an "ideal" resolution that while
  93   // theoretically true, could never be measured in practice.  Since
  94   // clock_gettime() likely involves a system call on your platform,
  95   // the "actual" timing resolution shouldn't be lower than syscall
  96   // overhead.
  97
  98   uint64_t start = ClockTimeNs();
  99   uint64_t end = ClockTimeNs();
 100   uint64_t minres = (end - start);
 101
 102   // 10 total trials is arbitrary: what we're trying to avoid by
 103   // looping is getting unlucky and being interrupted by a context
 104   // switch or signal, or being bitten by paging/cache effects
 105   for (int i = 0; i < 9; ++i) {
 106     start = ClockTimeNs();
 107     end = ClockTimeNs();
 108
 109     uint64_t candidate = (start - end);
 110     if (candidate < minres) {
 111       minres = candidate;
 112     }
 113   }
 114
 115   if (0 == minres) {
 116     // measurable resolution is either incredibly low, ~1ns, or very
 117     // high.  fall back on clock_getres()
 118     struct timespec ts;
 119     if (0 == clock_getres(CLOCK_MONOTONIC, &ts)) {
 120       minres = TimespecToNs(ts);
 121     }
 122   }
 123
 124   if (0 == minres) {
 125     // clock_getres probably failed.  fall back on NSPR's resolution
 126     // assumption
 127     minres = 1 * kNsPerMs;
 128   }
 129
 130   return minres;
 131 }
 132
 133 namespace mozilla {
 134
 135 double BaseTimeDurationPlatformUtils::ToSeconds(int64_t aTicks) {
 136   return double(aTicks) / kNsPerSecd;
 137 }
 138
 139 double BaseTimeDurationPlatformUtils::ToSecondsSigDigits(int64_t aTicks) {
 140   // don't report a value < mResolution ...
 141   int64_t valueSigDigs = sResolution * (aTicks / sResolution);
 142   // and chop off insignificant digits
 143   valueSigDigs = sResolutionSigDigs * (valueSigDigs / sResolutionSigDigs);
 144   return double(valueSigDigs) / kNsPerSecd;
 145 }
 146
 147 int64_t BaseTimeDurationPlatformUtils::TicksFromMilliseconds(
 148     double aMilliseconds) {
 149   double result = aMilliseconds * kNsPerMsd;
 150   if (result > double(INT64_MAX)) {
 151     return INT64_MAX;
 152   }
 153   if (result < INT64_MIN) {
 154     return INT64_MIN;
 155   }
 156
 157   return result;
 158 }
 159
 160 int64_t BaseTimeDurationPlatformUtils::ResolutionInTicks() {
 161   return static_cast<int64_t>(sResolution);
 162 }
 163
 164 static bool gInitialized = false;
 165
 166 void TimeStamp::Startup() {
 167   if (gInitialized) {
 168     return;
 169   }
 170
 171   struct timespec dummy;
 172   if (clock_gettime(CLOCK_MONOTONIC, &dummy) != 0) {
 173     MOZ_CRASH("CLOCK_MONOTONIC is absent!");
 174   }
 175
 176   sResolution = ClockResolutionNs();
 177
 178   // find the number of significant digits in sResolution, for the
 179   // sake of ToSecondsSigDigits()
 180   for (sResolutionSigDigs = 1; !(sResolutionSigDigs == sResolution ||
 181                                  10 * sResolutionSigDigs > sResolution);
 182        sResolutionSigDigs *= 10)
 183     ;
 184
 185   gInitialized = true;
 186 }
 187
 188 void TimeStamp::Shutdown() {}
 189
 190 TimeStamp TimeStamp::Now(bool aHighResolution) {
 191   return TimeStamp(ClockTimeNs());
 192 }
 193
 194 #if defined(XP_LINUX) || defined(ANDROID)
 195
 196 // Calculates the amount of jiffies that have elapsed since boot and up to the
 197 // starttime value of a specific process as found in its /proc/*/stat file.
 198 // Returns 0 if an error occurred.
 199
 200 static uint64_t JiffiesSinceBoot(const char* aFile) {
 201   char stat[512];
 202
 203   FILE* f = fopen(aFile, "r");
 204   if (!f) {
 205     return 0;
 206   }
 207
 208   int n = fread(&stat, 1, sizeof(stat) - 1, f);
 209
 210   fclose(f);
 211
 212   if (n <= 0) {
 213     return 0;
 214   }
 215
 216   stat[n] = 0;
 217
 218   long long unsigned startTime = 0;  // instead of uint64_t to keep GCC quiet
 219   char* s = strrchr(stat, ')');
 220
 221   if (!s) {
 222     return 0;
 223   }
 224
 225   int rv = sscanf(s + 2,
 226                   "%*c %*d %*d %*d %*d %*d %*u %*u %*u %*u "
 227                   "%*u %*u %*u %*d %*d %*d %*d %*d %*d %llu",
 228                   &startTime);
 229
 230   if (rv != 1 || !startTime) {
 231     return 0;
 232   }
 233
 234   return startTime;
 235 }
 236
 237 // Computes the interval that has elapsed between the thread creation and the
 238 // process creation by comparing the starttime fields in the respective
 239 // /proc/*/stat files. The resulting value will be a good approximation of the
 240 // process uptime. This value will be stored at the address pointed by aTime;
 241 // if an error occurred 0 will be stored instead.
 242
 243 static void* ComputeProcessUptimeThread(void* aTime) {
 244   uint64_t* uptime = static_cast<uint64_t*>(aTime);
 245   long hz = sysconf(_SC_CLK_TCK);
 246
 247   *uptime = 0;
 248
 249   if (!hz) {
 250     return nullptr;
 251   }
 252
 253   char threadStat[40];
 254   SprintfLiteral(threadStat, "/proc/self/task/%d/stat",
 255                  (pid_t)syscall(__NR_gettid));
 256
 257   uint64_t threadJiffies = JiffiesSinceBoot(threadStat);
 258   uint64_t selfJiffies = JiffiesSinceBoot("/proc/self/stat");
 259
 260   if (!threadJiffies || !selfJiffies) {
 261     return nullptr;
 262   }
 263
 264   *uptime = ((threadJiffies - selfJiffies) * kNsPerSec) / hz;
 265   return nullptr;
 266 }
 267
 268 // Computes and returns the process uptime in us on Linux & its derivatives.
 269 // Returns 0 if an error was encountered.
 270
 271 uint64_t TimeStamp::ComputeProcessUptime() {
 272   uint64_t uptime = 0;
 273   pthread_t uptime_pthread;
 274
 275   if (pthread_create(&uptime_pthread, nullptr, ComputeProcessUptimeThread,
 276                      &uptime)) {
 277     MOZ_CRASH("Failed to create process uptime thread.");
 278     return 0;
 279   }
 280
 281   pthread_join(uptime_pthread, NULL);
 282
 283   return uptime / kNsPerUs;
 284 }
 285
 286 #elif defined(__DragonFly__) || defined(__FreeBSD__) || defined(__NetBSD__) || \
 287     defined(__OpenBSD__)
 288
 289 // Computes and returns the process uptime in us on various BSD flavors.
 290 // Returns 0 if an error was encountered.
 291
 292 uint64_t TimeStamp::ComputeProcessUptime() {
 293   struct timespec ts;
 294   int rv = clock_gettime(CLOCK_REALTIME, &ts);
 295
 296   if (rv == -1) {
 297     return 0;
 298   }
 299
 300   int mib[] = {
 301     CTL_KERN,
 302     KERN_PROC,
 303     KERN_PROC_PID,
 304     getpid(),
 305 #  if defined(__NetBSD__) || defined(__OpenBSD__)
 306     sizeof(KINFO_PROC),
 307     1,
 308 #  endif
 309   };
 310   u_int mibLen = sizeof(mib) / sizeof(mib[0]);
 311
 312   KINFO_PROC proc;
 313   size_t bufferSize = sizeof(proc);
 314   rv = sysctl(mib, mibLen, &proc, &bufferSize, nullptr, 0);
 315
 316   if (rv == -1) {
 317     return 0;
 318   }
 319
 320   uint64_t startTime = ((uint64_t)proc.KP_START_SEC * kNsPerSec) +
 321                        (proc.KP_START_USEC * kNsPerUs);
 322   uint64_t now = ((uint64_t)ts.tv_sec * kNsPerSec) + ts.tv_nsec;
 323
 324   if (startTime > now) {
 325     return 0;
 326   }
 327
 328   return (now - startTime) / kNsPerUs;
 329 }
 330
 331 #else
 332
 333 uint64_t TimeStamp::ComputeProcessUptime() { return 0; }
 334
 335 #endif
 336
 337 }  // namespace mozilla