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__) \
  22     || defined(__NetBSD__) || 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 #include <pthread.h>
  53
  54 // Estimate of the smallest duration of time we can measure.
  55 static uint64_t sResolution;
  56 static uint64_t sResolutionSigDigs;
  57
  58 static const uint16_t kNsPerUs   =       1000;
  59 static const uint64_t kNsPerMs   =    1000000;
  60 static const uint64_t kNsPerSec  = 1000000000;
  61 static const double kNsPerMsd    =    1000000.0;
  62 static const double kNsPerSecd   = 1000000000.0;
  63
  64 static uint64_t
  65 TimespecToNs(const struct timespec& aTs)
  66 {
  67   uint64_t baseNs = uint64_t(aTs.tv_sec) * kNsPerSec;
  68   return baseNs + uint64_t(aTs.tv_nsec);
  69 }
  70
  71 static uint64_t
  72 ClockTimeNs()
  73 {
  74   struct timespec ts;
  75   // this can't fail: we know &ts is valid, and TimeStamp::Startup()
  76   // checks that CLOCK_MONOTONIC is supported (and aborts if not)
  77   clock_gettime(CLOCK_MONOTONIC, &ts);
  78
  79   // tv_sec is defined to be relative to an arbitrary point in time,
  80   // but it would be madness for that point in time to be earlier than
  81   // the Epoch.  So we can safely assume that even if time_t is 32
  82   // bits, tv_sec won't overflow while the browser is open.  Revisit
  83   // this argument if we're still building with 32-bit time_t around
  84   // the year 2037.
  85   return TimespecToNs(ts);
  86 }
  87
  88 static uint64_t
  89 ClockResolutionNs()
  90 {
  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
 136 BaseTimeDurationPlatformUtils::ToSeconds(int64_t aTicks)
 137 {
 138   return double(aTicks) / kNsPerSecd;
 139 }
 140
 141 double
 142 BaseTimeDurationPlatformUtils::ToSecondsSigDigits(int64_t aTicks)
 143 {
 144   // don't report a value < mResolution ...
 145   int64_t valueSigDigs = sResolution * (aTicks / sResolution);
 146   // and chop off insignificant digits
 147   valueSigDigs = sResolutionSigDigs * (valueSigDigs / sResolutionSigDigs);
 148   return double(valueSigDigs) / kNsPerSecd;
 149 }
 150
 151 int64_t
 152 BaseTimeDurationPlatformUtils::TicksFromMilliseconds(double aMilliseconds)
 153 {
 154   double result = aMilliseconds * kNsPerMsd;
 155   if (result > INT64_MAX) {
 156     return INT64_MAX;
 157   }
 158   if (result < INT64_MIN) {
 159     return INT64_MIN;
 160   }
 161
 162   return result;
 163 }
 164
 165 int64_t
 166 BaseTimeDurationPlatformUtils::ResolutionInTicks()
 167 {
 168   return static_cast<int64_t>(sResolution);
 169 }
 170
 171 static bool gInitialized = false;
 172
 173 void
 174 TimeStamp::Startup()
 175 {
 176   if (gInitialized) {
 177     return;
 178   }
 179
 180   struct timespec dummy;
 181   if (clock_gettime(CLOCK_MONOTONIC, &dummy) != 0) {
 182     MOZ_CRASH("CLOCK_MONOTONIC is absent!");
 183   }
 184
 185   sResolution = ClockResolutionNs();
 186
 187   // find the number of significant digits in sResolution, for the
 188   // sake of ToSecondsSigDigits()
 189   for (sResolutionSigDigs = 1;
 190        !(sResolutionSigDigs == sResolution ||
 191          10 * sResolutionSigDigs > sResolution);
 192        sResolutionSigDigs *= 10);
 193
 194   gInitialized = true;
 195 }
 196
 197 void
 198 TimeStamp::Shutdown()
 199 {
 200 }
 201
 202 TimeStamp
 203 TimeStamp::Now(bool aHighResolution)
 204 {
 205   return TimeStamp::NowFuzzy(TimeStampValue(false, ClockTimeNs()));
 206 }
 207
 208 TimeStamp
 209 TimeStamp::NowUnfuzzed(bool aHighResolution)
 210 {
 211   return TimeStamp(TimeStampValue(false, ClockTimeNs()));
 212 }
 213
 214 #if defined(XP_LINUX) || defined(ANDROID)
 215
 216 // Calculates the amount of jiffies that have elapsed since boot and up to the
 217 // starttime value of a specific process as found in its /proc/*/stat file.
 218 // Returns 0 if an error occurred.
 219
 220 static uint64_t
 221 JiffiesSinceBoot(const char* aFile)
 222 {
 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*
 266 ComputeProcessUptimeThread(void* aTime)
 267 {
 268   uint64_t* uptime = static_cast<uint64_t*>(aTime);
 269   long hz = sysconf(_SC_CLK_TCK);
 270
 271   *uptime = 0;
 272
 273   if (!hz) {
 274     return nullptr;
 275   }
 276
 277   char threadStat[40];
 278   SprintfLiteral(threadStat, "/proc/self/task/%d/stat", (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
 295 TimeStamp::ComputeProcessUptime()
 296 {
 297   uint64_t uptime = 0;
 298   pthread_t uptime_pthread;
 299
 300   if (pthread_create(&uptime_pthread, nullptr, ComputeProcessUptimeThread, &uptime)) {
 301     MOZ_CRASH("Failed to create process uptime thread.");
 302     return 0;
 303   }
 304
 305   pthread_join(uptime_pthread, NULL);
 306
 307   return uptime / kNsPerUs;
 308 }
 309
 310 #elif defined(__DragonFly__) || defined(__FreeBSD__) \
 311       || defined(__NetBSD__) || defined(__OpenBSD__)
 312
 313 // Computes and returns the process uptime in us on various BSD flavors.
 314 // Returns 0 if an error was encountered.
 315
 316 uint64_t
 317 TimeStamp::ComputeProcessUptime()
 318 {
 319   struct timespec ts;
 320   int rv = clock_gettime(CLOCK_REALTIME, &ts);
 321
 322   if (rv == -1) {
 323     return 0;
 324   }
 325
 326   int mib[] = {
 327     CTL_KERN,
 328     KERN_PROC,
 329     KERN_PROC_PID,
 330     getpid(),
 331 #if defined(__NetBSD__) || defined(__OpenBSD__)
 332     sizeof(KINFO_PROC),
 333     1,
 334 #endif
 335   };
 336   u_int mibLen = sizeof(mib) / sizeof(mib[0]);
 337
 338   KINFO_PROC proc;
 339   size_t bufferSize = sizeof(proc);
 340   rv = sysctl(mib, mibLen, &proc, &bufferSize, nullptr, 0);
 341
 342   if (rv == -1) {
 343     return 0;
 344   }
 345
 346   uint64_t startTime = ((uint64_t)proc.KP_START_SEC * kNsPerSec) +
 347     (proc.KP_START_USEC * kNsPerUs);
 348   uint64_t now = ((uint64_t)ts.tv_sec * kNsPerSec) + ts.tv_nsec;
 349
 350   if (startTime > now) {
 351     return 0;
 352   }
 353
 354   return (now - startTime) / kNsPerUs;
 355 }
 356
 357 #else
 358
 359 uint64_t
 360 TimeStamp::ComputeProcessUptime()
 361 {
 362   return 0;
 363 }
 364
 365 #endif
 366
 367 } // namespace mozilla