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   gInitialized = true;
 203 }
 204
 205 void TimeStamp::Shutdown() {}
 206
 207 TimeStamp TimeStamp::Now(bool aHighResolution) {
 208 #ifdef CLOCK_MONOTONIC_COARSE
 209   if (!aHighResolution && sSupportsMonotonicCoarseClock) {
 210     return TimeStamp(ClockTimeNs(CLOCK_MONOTONIC_COARSE));
 211   }
 212 #endif
 213   return TimeStamp(ClockTimeNs(CLOCK_MONOTONIC));
 214 }
 215
 216 #if defined(XP_LINUX) || defined(ANDROID)
 217
 218 // Calculates the amount of jiffies that have elapsed since boot and up to the
 219 // starttime value of a specific process as found in its /proc/*/stat file.
 220 // Returns 0 if an error occurred.
 221
 222 static uint64_t JiffiesSinceBoot(const char* aFile) {
 223   char stat[512];
 224
 225   FILE* f = fopen(aFile, "r");
 226   if (!f) {
 227     return 0;
 228   }
 229
 230   int n = fread(&stat, 1, sizeof(stat) - 1, f);
 231
 232   fclose(f);
 233
 234   if (n <= 0) {
 235     return 0;
 236   }
 237
 238   stat[n] = 0;
 239
 240   long long unsigned startTime = 0;  // instead of uint64_t to keep GCC quiet
 241   char* s = strrchr(stat, ')');
 242
 243   if (!s) {
 244     return 0;
 245   }
 246
 247   int rv = sscanf(s + 2,
 248                   "%*c %*d %*d %*d %*d %*d %*u %*u %*u %*u "
 249                   "%*u %*u %*u %*d %*d %*d %*d %*d %*d %llu",
 250                   &startTime);
 251
 252   if (rv != 1 || !startTime) {
 253     return 0;
 254   }
 255
 256   return startTime;
 257 }
 258
 259 // Computes the interval that has elapsed between the thread creation and the
 260 // process creation by comparing the starttime fields in the respective
 261 // /proc/*/stat files. The resulting value will be a good approximation of the
 262 // process uptime. This value will be stored at the address pointed by aTime;
 263 // if an error occurred 0 will be stored instead.
 264
 265 static void* ComputeProcessUptimeThread(void* aTime) {
 266   uint64_t* uptime = static_cast<uint64_t*>(aTime);
 267   long hz = sysconf(_SC_CLK_TCK);
 268
 269   *uptime = 0;
 270
 271   if (!hz) {
 272     return nullptr;
 273   }
 274
 275   char threadStat[40];
 276   SprintfLiteral(threadStat, "/proc/self/task/%d/stat",
 277                  (pid_t)syscall(__NR_gettid));
 278
 279   uint64_t threadJiffies = JiffiesSinceBoot(threadStat);
 280   uint64_t selfJiffies = JiffiesSinceBoot("/proc/self/stat");
 281
 282   if (!threadJiffies || !selfJiffies) {
 283     return nullptr;
 284   }
 285
 286   *uptime = ((threadJiffies - selfJiffies) * kNsPerSec) / hz;
 287   return nullptr;
 288 }
 289
 290 // Computes and returns the process uptime in us on Linux & its derivatives.
 291 // Returns 0 if an error was encountered.
 292
 293 uint64_t TimeStamp::ComputeProcessUptime() {
 294   uint64_t uptime = 0;
 295   pthread_t uptime_pthread;
 296
 297   if (pthread_create(&uptime_pthread, nullptr, ComputeProcessUptimeThread,
 298                      &uptime)) {
 299     MOZ_CRASH("Failed to create process uptime thread.");
 300     return 0;
 301   }
 302
 303   pthread_join(uptime_pthread, NULL);
 304
 305   return uptime / kNsPerUs;
 306 }
 307
 308 #elif defined(__DragonFly__) || defined(__FreeBSD__) || defined(__NetBSD__) || \
 309     defined(__OpenBSD__)
 310
 311 // Computes and returns the process uptime in us on various BSD flavors.
 312 // Returns 0 if an error was encountered.
 313
 314 uint64_t TimeStamp::ComputeProcessUptime() {
 315   struct timespec ts;
 316   int rv = clock_gettime(CLOCK_REALTIME, &ts);
 317
 318   if (rv == -1) {
 319     return 0;
 320   }
 321
 322   int mib[] = {
 323       // clang-format off
 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       // clang-format on
 333   };
 334   u_int mibLen = sizeof(mib) / sizeof(mib[0]);
 335
 336   KINFO_PROC proc;
 337   size_t bufferSize = sizeof(proc);
 338   rv = sysctl(mib, mibLen, &proc, &bufferSize, nullptr, 0);
 339
 340   if (rv == -1) {
 341     return 0;
 342   }
 343
 344   uint64_t startTime = ((uint64_t)proc.KP_START_SEC * kNsPerSec) +
 345                        (proc.KP_START_USEC * kNsPerUs);
 346   uint64_t now = ((uint64_t)ts.tv_sec * kNsPerSec) + ts.tv_nsec;
 347
 348   if (startTime > now) {
 349     return 0;
 350   }
 351
 352   return (now - startTime) / kNsPerUs;
 353 }
 354
 355 #else
 356
 357 uint64_t TimeStamp::ComputeProcessUptime() { return 0; }
 358
 359 #endif
 360
 361 }  // namespace mozilla