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 #ifdef CLOCK_MONOTONIC_COARSE
  62 static bool sSupportsMonotonicCoarseClock = false;
  63 #endif
  64
  65 #if !defined(__wasi__)
  66 static const uint16_t kNsPerUs = 1000;
  67 #endif
  68
  69 static const uint64_t kNsPerMs = 1000000;
  70 static const uint64_t kNsPerSec = 1000000000;
  71 static const double kNsPerMsd = 1000000.0;
  72 static const double kNsPerSecd = 1000000000.0;
  73
  74 static uint64_t TimespecToNs(const struct timespec& aTs) {
  75   uint64_t baseNs = uint64_t(aTs.tv_sec) * kNsPerSec;
  76   return baseNs + uint64_t(aTs.tv_nsec);
  77 }
  78
  79 static uint64_t ClockTimeNs(const clockid_t aClockId = CLOCK_MONOTONIC) {
  80   struct timespec ts;
  81 #ifdef CLOCK_MONOTONIC_COARSE
  82   MOZ_RELEASE_ASSERT(
  83       aClockId == CLOCK_MONOTONIC ||
  84       (sSupportsMonotonicCoarseClock && aClockId == CLOCK_MONOTONIC_COARSE));
  85 #else
  86   MOZ_RELEASE_ASSERT(aClockId == CLOCK_MONOTONIC);
  87 #endif
  88   // this can't fail: we know &ts is valid, and TimeStamp::Startup()
  89   // checks that CLOCK_MONOTONIC / CLOCK_MONOTONIC_COARSE are
  90   // supported (and aborts if the former is not).
  91   clock_gettime(aClockId, &ts);
  92
  93   // tv_sec is defined to be relative to an arbitrary point in time,
  94   // but it would be madness for that point in time to be earlier than
  95   // the Epoch.  So we can safely assume that even if time_t is 32
  96   // bits, tv_sec won't overflow while the browser is open.  Revisit
  97   // this argument if we're still building with 32-bit time_t around
  98   // the year 2037.
  99   return TimespecToNs(ts);
 100 }
 101
 102 static uint64_t ClockResolutionNs() {
 103   // NB: why not rely on clock_getres()?  Two reasons: (i) it might
 104   // lie, and (ii) it might return an "ideal" resolution that while
 105   // theoretically true, could never be measured in practice.  Since
 106   // clock_gettime() likely involves a system call on your platform,
 107   // the "actual" timing resolution shouldn't be lower than syscall
 108   // overhead.
 109
 110   uint64_t start = ClockTimeNs();
 111   uint64_t end = ClockTimeNs();
 112   uint64_t minres = (end - start);
 113
 114   // 10 total trials is arbitrary: what we're trying to avoid by
 115   // looping is getting unlucky and being interrupted by a context
 116   // switch or signal, or being bitten by paging/cache effects
 117   for (int i = 0; i < 9; ++i) {
 118     start = ClockTimeNs();
 119     end = ClockTimeNs();
 120
 121     uint64_t candidate = (start - end);
 122     if (candidate < minres) {
 123       minres = candidate;
 124     }
 125   }
 126
 127   if (0 == minres) {
 128     // measurable resolution is either incredibly low, ~1ns, or very
 129     // high.  fall back on clock_getres()
 130     struct timespec ts;
 131     if (0 == clock_getres(CLOCK_MONOTONIC, &ts)) {
 132       minres = TimespecToNs(ts);
 133     }
 134   }
 135
 136   if (0 == minres) {
 137     // clock_getres probably failed.  fall back on NSPR's resolution
 138     // assumption
 139     minres = 1 * kNsPerMs;
 140   }
 141
 142   return minres;
 143 }
 144
 145 namespace mozilla {
 146
 147 double BaseTimeDurationPlatformUtils::ToSeconds(int64_t aTicks) {
 148   return double(aTicks) / kNsPerSecd;
 149 }
 150
 151 double BaseTimeDurationPlatformUtils::ToSecondsSigDigits(int64_t aTicks) {
 152   // don't report a value < mResolution ...
 153   int64_t valueSigDigs = sResolution * (aTicks / sResolution);
 154   // and chop off insignificant digits
 155   valueSigDigs = sResolutionSigDigs * (valueSigDigs / sResolutionSigDigs);
 156   return double(valueSigDigs) / kNsPerSecd;
 157 }
 158
 159 int64_t BaseTimeDurationPlatformUtils::TicksFromMilliseconds(
 160     double aMilliseconds) {
 161   double result = aMilliseconds * kNsPerMsd;
 162   if (result > double(INT64_MAX)) {
 163     return INT64_MAX;
 164   }
 165   if (result < INT64_MIN) {
 166     return INT64_MIN;
 167   }
 168
 169   return result;
 170 }
 171
 172 int64_t BaseTimeDurationPlatformUtils::ResolutionInTicks() {
 173   return static_cast<int64_t>(sResolution);
 174 }
 175
 176 static bool gInitialized = false;
 177
 178 void TimeStamp::Startup() {
 179   if (gInitialized) {
 180     return;
 181   }
 182
 183   struct timespec dummy;
 184   if (clock_gettime(CLOCK_MONOTONIC, &dummy) != 0) {
 185     MOZ_CRASH("CLOCK_MONOTONIC is absent!");
 186   }
 187
 188 #ifdef CLOCK_MONOTONIC_COARSE
 189   if (clock_gettime(CLOCK_MONOTONIC_COARSE, &dummy) == 0) {
 190     sSupportsMonotonicCoarseClock = true;
 191   }
 192 #endif
 193
 194   sResolution = ClockResolutionNs();
 195
 196   // find the number of significant digits in sResolution, for the
 197   // sake of ToSecondsSigDigits()
 198   for (sResolutionSigDigs = 1; !(sResolutionSigDigs == sResolution ||
 199                                  10 * sResolutionSigDigs > sResolution);
 200        sResolutionSigDigs *= 10)
 201     ;
 202
 203   gInitialized = true;
 204 }
 205
 206 void TimeStamp::Shutdown() {}
 207
 208 TimeStamp TimeStamp::Now(bool aHighResolution) {
 209 #ifdef CLOCK_MONOTONIC_COARSE
 210   if (!aHighResolution && sSupportsMonotonicCoarseClock) {
 211     return TimeStamp(ClockTimeNs(CLOCK_MONOTONIC_COARSE));
 212   }
 213 #endif
 214   return TimeStamp(ClockTimeNs(CLOCK_MONOTONIC));
 215 }
 216
 217 #if defined(XP_LINUX) || defined(ANDROID)
 218
 219 // Calculates the amount of jiffies that have elapsed since boot and up to the
 220 // starttime value of a specific process as found in its /proc/*/stat file.
 221 // Returns 0 if an error occurred.
 222
 223 static uint64_t JiffiesSinceBoot(const char* aFile) {
 224   char stat[512];
 225
 226   FILE* f = fopen(aFile, "r");
 227   if (!f) {
 228     return 0;
 229   }
 230
 231   int n = fread(&stat, 1, sizeof(stat) - 1, f);
 232
 233   fclose(f);
 234
 235   if (n <= 0) {
 236     return 0;
 237   }
 238
 239   stat[n] = 0;
 240
 241   long long unsigned startTime = 0;  // instead of uint64_t to keep GCC quiet
 242   char* s = strrchr(stat, ')');
 243
 244   if (!s) {
 245     return 0;
 246   }
 247
 248   int rv = sscanf(s + 2,
 249                   "%*c %*d %*d %*d %*d %*d %*u %*u %*u %*u "
 250                   "%*u %*u %*u %*d %*d %*d %*d %*d %*d %llu",
 251                   &startTime);
 252
 253   if (rv != 1 || !startTime) {
 254     return 0;
 255   }
 256
 257   return startTime;
 258 }
 259
 260 // Computes the interval that has elapsed between the thread creation and the
 261 // process creation by comparing the starttime fields in the respective
 262 // /proc/*/stat files. The resulting value will be a good approximation of the
 263 // process uptime. This value will be stored at the address pointed by aTime;
 264 // if an error occurred 0 will be stored instead.
 265
 266 static void* ComputeProcessUptimeThread(void* aTime) {
 267   uint64_t* uptime = static_cast<uint64_t*>(aTime);
 268   long hz = sysconf(_SC_CLK_TCK);
 269
 270   *uptime = 0;
 271
 272   if (!hz) {
 273     return nullptr;
 274   }
 275
 276   char threadStat[40];
 277   SprintfLiteral(threadStat, "/proc/self/task/%d/stat",
 278                  (pid_t)syscall(__NR_gettid));
 279
 280   uint64_t threadJiffies = JiffiesSinceBoot(threadStat);
 281   uint64_t selfJiffies = JiffiesSinceBoot("/proc/self/stat");
 282
 283   if (!threadJiffies || !selfJiffies) {
 284     return nullptr;
 285   }
 286
 287   *uptime = ((threadJiffies - selfJiffies) * kNsPerSec) / hz;
 288   return nullptr;
 289 }
 290
 291 // Computes and returns the process uptime in us on Linux & its derivatives.
 292 // Returns 0 if an error was encountered.
 293
 294 uint64_t TimeStamp::ComputeProcessUptime() {
 295   uint64_t uptime = 0;
 296   pthread_t uptime_pthread;
 297
 298   if (pthread_create(&uptime_pthread, nullptr, ComputeProcessUptimeThread,
 299                      &uptime)) {
 300     MOZ_CRASH("Failed to create process uptime thread.");
 301     return 0;
 302   }
 303
 304   pthread_join(uptime_pthread, NULL);
 305
 306   return uptime / kNsPerUs;
 307 }
 308
 309 #elif defined(__DragonFly__) || defined(__FreeBSD__) || defined(__NetBSD__) || \
 310     defined(__OpenBSD__)
 311
 312 // Computes and returns the process uptime in us on various BSD flavors.
 313 // Returns 0 if an error was encountered.
 314
 315 uint64_t TimeStamp::ComputeProcessUptime() {
 316   struct timespec ts;
 317   int rv = clock_gettime(CLOCK_REALTIME, &ts);
 318
 319   if (rv == -1) {
 320     return 0;
 321   }
 322
 323   int mib[] = {
 324     CTL_KERN,
 325     KERN_PROC,
 326     KERN_PROC_PID,
 327     getpid(),
 328 #  if defined(__NetBSD__) || defined(__OpenBSD__)
 329     sizeof(KINFO_PROC),
 330     1,
 331 #  endif
 332   };
 333   u_int mibLen = sizeof(mib) / sizeof(mib[0]);
 334
 335   KINFO_PROC proc;
 336   size_t bufferSize = sizeof(proc);
 337   rv = sysctl(mib, mibLen, &proc, &bufferSize, nullptr, 0);
 338
 339   if (rv == -1) {
 340     return 0;
 341   }
 342
 343   uint64_t startTime = ((uint64_t)proc.KP_START_SEC * kNsPerSec) +
 344                        (proc.KP_START_USEC * kNsPerUs);
 345   uint64_t now = ((uint64_t)ts.tv_sec * kNsPerSec) + ts.tv_nsec;
 346
 347   if (startTime > now) {
 348     return 0;
 349   }
 350
 351   return (now - startTime) / kNsPerUs;
 352 }
 353
 354 #else
 355
 356 uint64_t TimeStamp::ComputeProcessUptime() { return 0; }
 357
 358 #endif
 359
 360 }  // namespace mozilla