xpcom/ds/TimeStamp_posix.cpp

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim:set ts=2 sw=2 sts=2 et cindent: */
   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
  20 #if defined(__DragonFly__) || defined(__FreeBSD__) \
  21     || defined(__NetBSD__) || defined(__OpenBSD__)
  22 #include <sys/param.h>
  23 #include <sys/sysctl.h>
  24 #endif
  25
  26 #if defined(__DragonFly__) || defined(__FreeBSD__)
  27 #include <sys/user.h>
  28 #endif
  29
  30 #if defined(__NetBSD__)
  31 #undef KERN_PROC
  32 #define KERN_PROC KERN_PROC2
  33 #define KINFO_PROC struct kinfo_proc2
  34 #else
  35 #define KINFO_PROC struct kinfo_proc
  36 #endif
  37
  38 #if defined(__DragonFly__)
  39 #define KP_START_SEC kp_start.tv_sec
  40 #define KP_START_USEC kp_start.tv_usec
  41 #elif defined(__FreeBSD__)
  42 #define KP_START_SEC ki_start.tv_sec
  43 #define KP_START_USEC ki_start.tv_usec
  44 #else
  45 #define KP_START_SEC p_ustart_sec
  46 #define KP_START_USEC p_ustart_usec
  47 #endif
  48
  49 #include "mozilla/TimeStamp.h"
  50 #include "nsCRT.h"
  51 #include "prprf.h"
  52 #include "prthread.h"
  53 #include "nsDebug.h"
  54
  55 // Estimate of the smallest duration of time we can measure.
  56 static uint64_t sResolution;
  57 static uint64_t sResolutionSigDigs;
  58
  59 static const uint16_t kNsPerUs   =       1000;
  60 static const uint64_t kNsPerMs   =    1000000;
  61 static const uint64_t kNsPerSec  = 1000000000;
  62 static const double kNsPerMsd    =    1000000.0;
  63 static const double kNsPerSecd   = 1000000000.0;
  64
  65 static uint64_t
  66 TimespecToNs(const struct timespec& aTs)
  67 {
  68   uint64_t baseNs = uint64_t(aTs.tv_sec) * kNsPerSec;
  69   return baseNs + uint64_t(aTs.tv_nsec);
  70 }
  71
  72 static uint64_t
  73 ClockTimeNs()
  74 {
  75   struct timespec ts;
  76   // this can't fail: we know &ts is valid, and TimeStamp::Startup()
  77   // checks that CLOCK_MONOTONIC is supported (and aborts if not)
  78   clock_gettime(CLOCK_MONOTONIC, &ts);
  79
  80   // tv_sec is defined to be relative to an arbitrary point in time,
  81   // but it would be madness for that point in time to be earlier than
  82   // the Epoch.  So we can safely assume that even if time_t is 32
  83   // bits, tv_sec won't overflow while the browser is open.  Revisit
  84   // this argument if we're still building with 32-bit time_t around
  85   // the year 2037.
  86   return TimespecToNs(ts);
  87 }
  88
  89 static uint64_t
  90 ClockResolutionNs()
  91 {
  92   // NB: why not rely on clock_getres()?  Two reasons: (i) it might
  93   // lie, and (ii) it might return an "ideal" resolution that while
  94   // theoretically true, could never be measured in practice.  Since
  95   // clock_gettime() likely involves a system call on your platform,
  96   // the "actual" timing resolution shouldn't be lower than syscall
  97   // overhead.
  98
  99   uint64_t start = ClockTimeNs();
 100   uint64_t end = ClockTimeNs();
 101   uint64_t minres = (end - start);
 102
 103   // 10 total trials is arbitrary: what we're trying to avoid by
 104   // looping is getting unlucky and being interrupted by a context
 105   // switch or signal, or being bitten by paging/cache effects
 106   for (int i = 0; i < 9; ++i) {
 107     start = ClockTimeNs();
 108     end = ClockTimeNs();
 109
 110     uint64_t candidate = (start - end);
 111     if (candidate < minres) {
 112       minres = candidate;
 113     }
 114   }
 115
 116   if (0 == minres) {
 117     // measurable resolution is either incredibly low, ~1ns, or very
 118     // high.  fall back on clock_getres()
 119     struct timespec ts;
 120     if (0 == clock_getres(CLOCK_MONOTONIC, &ts)) {
 121       minres = TimespecToNs(ts);
 122     }
 123   }
 124
 125   if (0 == minres) {
 126     // clock_getres probably failed.  fall back on NSPR's resolution
 127     // assumption
 128     minres = 1 * kNsPerMs;
 129   }
 130
 131   return minres;
 132 }
 133
 134 namespace mozilla {
 135
 136 double
 137 BaseTimeDurationPlatformUtils::ToSeconds(int64_t aTicks)
 138 {
 139   return double(aTicks) / kNsPerSecd;
 140 }
 141
 142 double
 143 BaseTimeDurationPlatformUtils::ToSecondsSigDigits(int64_t aTicks)
 144 {
 145   // don't report a value < mResolution ...
 146   int64_t valueSigDigs = sResolution * (aTicks / sResolution);
 147   // and chop off insignificant digits
 148   valueSigDigs = sResolutionSigDigs * (valueSigDigs / sResolutionSigDigs);
 149   return double(valueSigDigs) / kNsPerSecd;
 150 }
 151
 152 int64_t
 153 BaseTimeDurationPlatformUtils::TicksFromMilliseconds(double aMilliseconds)
 154 {
 155   double result = aMilliseconds * kNsPerMsd;
 156   if (result > INT64_MAX) {
 157     return INT64_MAX;
 158   } else 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 nsresult
 174 TimeStamp::Startup()
 175 {
 176   if (gInitialized) {
 177     return NS_OK;
 178   }
 179
 180   struct timespec dummy;
 181   if (clock_gettime(CLOCK_MONOTONIC, &dummy) != 0) {
 182     NS_RUNTIMEABORT("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   return NS_OK;
 197 }
 198
 199 void
 200 TimeStamp::Shutdown()
 201 {
 202 }
 203
 204 TimeStamp
 205 TimeStamp::Now(bool aHighResolution)
 206 {
 207   return TimeStamp(ClockTimeNs());
 208 }
 209
 210 #if defined(LINUX) || defined(ANDROID)
 211
 212 // Calculates the amount of jiffies that have elapsed since boot and up to the
 213 // starttime value of a specific process as found in its /proc/*/stat file.
 214 // Returns 0 if an error occurred.
 215
 216 static uint64_t
 217 JiffiesSinceBoot(const char* aFile)
 218 {
 219   char stat[512];
 220
 221   FILE* f = fopen(aFile, "r");
 222   if (!f) {
 223     return 0;
 224   }
 225
 226   int n = fread(&stat, 1, sizeof(stat) - 1, f);
 227
 228   fclose(f);
 229
 230   if (n <= 0) {
 231     return 0;
 232   }
 233
 234   stat[n] = 0;
 235
 236   long long unsigned startTime = 0; // instead of uint64_t to keep GCC quiet
 237   char* s = strrchr(stat, ')');
 238
 239   if (!s) {
 240     return 0;
 241   }
 242
 243   int rv = sscanf(s + 2,
 244                   "%*c %*d %*d %*d %*d %*d %*u %*u %*u %*u "
 245                   "%*u %*u %*u %*d %*d %*d %*d %*d %*d %llu",
 246                   &startTime);
 247
 248   if (rv != 1 || !startTime) {
 249     return 0;
 250   }
 251
 252   return startTime;
 253 }
 254
 255 // Computes the interval that has elapsed between the thread creation and the
 256 // process creation by comparing the starttime fields in the respective
 257 // /proc/*/stat files. The resulting value will be a good approximation of the
 258 // process uptime. This value will be stored at the address pointed by aTime;
 259 // if an error occurred 0 will be stored instead.
 260
 261 static void
 262 ComputeProcessUptimeThread(void* aTime)
 263 {
 264   uint64_t* uptime = static_cast<uint64_t*>(aTime);
 265   long hz = sysconf(_SC_CLK_TCK);
 266
 267   *uptime = 0;
 268
 269   if (!hz) {
 270     return;
 271   }
 272
 273   char threadStat[40];
 274   sprintf(threadStat, "/proc/self/task/%d/stat", (pid_t)syscall(__NR_gettid));
 275
 276   uint64_t threadJiffies = JiffiesSinceBoot(threadStat);
 277   uint64_t selfJiffies = JiffiesSinceBoot("/proc/self/stat");
 278
 279   if (!threadJiffies || !selfJiffies) {
 280     return;
 281   }
 282
 283   *uptime = ((threadJiffies - selfJiffies) * kNsPerSec) / hz;
 284 }
 285
 286 // Computes and returns the process uptime in us on Linux & its derivatives.
 287 // Returns 0 if an error was encountered.
 288
 289 uint64_t
 290 TimeStamp::ComputeProcessUptime()
 291 {
 292   uint64_t uptime = 0;
 293   PRThread* thread = PR_CreateThread(PR_USER_THREAD,
 294                                      ComputeProcessUptimeThread,
 295                                      &uptime,
 296                                      PR_PRIORITY_NORMAL,
 297                                      PR_GLOBAL_THREAD,
 298                                      PR_JOINABLE_THREAD,
 299                                      0);
 300
 301   PR_JoinThread(thread);
 302
 303   return uptime / kNsPerUs;
 304 }
 305
 306 #elif defined(__DragonFly__) || defined(__FreeBSD__) \
 307       || defined(__NetBSD__) || defined(__OpenBSD__)
 308
 309 // Computes and returns the process uptime in us on various BSD flavors.
 310 // Returns 0 if an error was encountered.
 311
 312 uint64_t
 313 TimeStamp::ComputeProcessUptime()
 314 {
 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     CTL_KERN,
 324     KERN_PROC,
 325     KERN_PROC_PID,
 326     getpid(),
 327 #if defined(__NetBSD__) || defined(__OpenBSD__)
 328     sizeof(KINFO_PROC),
 329     1,
 330 #endif
 331   };
 332   u_int mibLen = sizeof(mib) / sizeof(mib[0]);
 333
 334   KINFO_PROC proc;
 335   size_t bufferSize = sizeof(proc);
 336   rv = sysctl(mib, mibLen, &proc, &bufferSize, nullptr, 0);
 337
 338   if (rv == -1) {
 339     return 0;
 340   }
 341
 342   uint64_t startTime = ((uint64_t)proc.KP_START_SEC * kNsPerSec) +
 343     (proc.KP_START_USEC * kNsPerUs);
 344   uint64_t now = ((uint64_t)ts.tv_sec * kNsPerSec) + ts.tv_nsec;
 345
 346   if (startTime > now) {
 347     return 0;
 348   }
 349
 350   return (now - startTime) / kNsPerUs;
 351 }
 352
 353 #else
 354
 355 uint64_t
 356 TimeStamp::ComputeProcessUptime()
 357 {
 358   return 0;
 359 }
 360
 361 #endif
 362
 363 } // namespace mozilla