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 TimeDuration::ToSeconds() const
 138 {
 139   return double(mValue) / kNsPerSecd;
 140 }
 141
 142 double
 143 TimeDuration::ToSecondsSigDigits() const
 144 {
 145   // don't report a value < mResolution ...
 146   int64_t valueSigDigs = sResolution * (mValue / sResolution);
 147   // and chop off insignificant digits
 148   valueSigDigs = sResolutionSigDigs * (valueSigDigs / sResolutionSigDigs);
 149   return double(valueSigDigs) / kNsPerSecd;
 150 }
 151
 152 TimeDuration
 153 TimeDuration::FromMilliseconds(double aMilliseconds)
 154 {
 155   return TimeDuration::FromTicks(aMilliseconds * kNsPerMsd);
 156 }
 157
 158 TimeDuration
 159 TimeDuration::Resolution()
 160 {
 161   return TimeDuration::FromTicks(int64_t(sResolution));
 162 }
 163
 164 static bool gInitialized = false;
 165
 166 nsresult
 167 TimeStamp::Startup()
 168 {
 169   if (gInitialized) {
 170     return NS_OK;
 171   }
 172
 173   struct timespec dummy;
 174   if (clock_gettime(CLOCK_MONOTONIC, &dummy) != 0) {
 175     NS_RUNTIMEABORT("CLOCK_MONOTONIC is absent!");
 176   }
 177
 178   sResolution = ClockResolutionNs();
 179
 180   // find the number of significant digits in sResolution, for the
 181   // sake of ToSecondsSigDigits()
 182   for (sResolutionSigDigs = 1;
 183        !(sResolutionSigDigs == sResolution ||
 184          10 * sResolutionSigDigs > sResolution);
 185        sResolutionSigDigs *= 10);
 186
 187   gInitialized = true;
 188
 189   return NS_OK;
 190 }
 191
 192 void
 193 TimeStamp::Shutdown()
 194 {
 195 }
 196
 197 TimeStamp
 198 TimeStamp::Now(bool aHighResolution)
 199 {
 200   return TimeStamp(ClockTimeNs());
 201 }
 202
 203 #if defined(LINUX) || defined(ANDROID)
 204
 205 // Calculates the amount of jiffies that have elapsed since boot and up to the
 206 // starttime value of a specific process as found in its /proc/*/stat file.
 207 // Returns 0 if an error occurred.
 208
 209 static uint64_t
 210 JiffiesSinceBoot(const char* aFile)
 211 {
 212   char stat[512];
 213
 214   FILE* f = fopen(aFile, "r");
 215   if (!f) {
 216     return 0;
 217   }
 218
 219   int n = fread(&stat, 1, sizeof(stat) - 1, f);
 220
 221   fclose(f);
 222
 223   if (n <= 0) {
 224     return 0;
 225   }
 226
 227   stat[n] = 0;
 228
 229   long long unsigned startTime = 0; // instead of uint64_t to keep GCC quiet
 230   char* s = strrchr(stat, ')');
 231
 232   if (!s) {
 233     return 0;
 234   }
 235
 236   int rv = sscanf(s + 2,
 237                   "%*c %*d %*d %*d %*d %*d %*u %*u %*u %*u "
 238                   "%*u %*u %*u %*d %*d %*d %*d %*d %*d %llu",
 239                   &startTime);
 240
 241   if (rv != 1 || !startTime) {
 242     return 0;
 243   }
 244
 245   return startTime;
 246 }
 247
 248 // Computes the interval that has elapsed between the thread creation and the
 249 // process creation by comparing the starttime fields in the respective
 250 // /proc/*/stat files. The resulting value will be a good approximation of the
 251 // process uptime. This value will be stored at the address pointed by aTime;
 252 // if an error occurred 0 will be stored instead.
 253
 254 static void
 255 ComputeProcessUptimeThread(void* aTime)
 256 {
 257   uint64_t* uptime = static_cast<uint64_t*>(aTime);
 258   long hz = sysconf(_SC_CLK_TCK);
 259
 260   *uptime = 0;
 261
 262   if (!hz) {
 263     return;
 264   }
 265
 266   char threadStat[40];
 267   sprintf(threadStat, "/proc/self/task/%d/stat", (pid_t)syscall(__NR_gettid));
 268
 269   uint64_t threadJiffies = JiffiesSinceBoot(threadStat);
 270   uint64_t selfJiffies = JiffiesSinceBoot("/proc/self/stat");
 271
 272   if (!threadJiffies || !selfJiffies) {
 273     return;
 274   }
 275
 276   *uptime = ((threadJiffies - selfJiffies) * kNsPerSec) / hz;
 277 }
 278
 279 // Computes and returns the process uptime in us on Linux & its derivatives.
 280 // Returns 0 if an error was encountered.
 281
 282 uint64_t
 283 TimeStamp::ComputeProcessUptime()
 284 {
 285   uint64_t uptime = 0;
 286   PRThread* thread = PR_CreateThread(PR_USER_THREAD,
 287                                      ComputeProcessUptimeThread,
 288                                      &uptime,
 289                                      PR_PRIORITY_NORMAL,
 290                                      PR_GLOBAL_THREAD,
 291                                      PR_JOINABLE_THREAD,
 292                                      0);
 293
 294   PR_JoinThread(thread);
 295
 296   return uptime / kNsPerUs;
 297 }
 298
 299 #elif defined(__DragonFly__) || defined(__FreeBSD__) \
 300       || defined(__NetBSD__) || defined(__OpenBSD__)
 301
 302 // Computes and returns the process uptime in us on various BSD flavors.
 303 // Returns 0 if an error was encountered.
 304
 305 uint64_t
 306 TimeStamp::ComputeProcessUptime()
 307 {
 308   struct timespec ts;
 309   int rv = clock_gettime(CLOCK_REALTIME, &ts);
 310
 311   if (rv == -1) {
 312     return 0;
 313   }
 314
 315   int mib[] = {
 316     CTL_KERN,
 317     KERN_PROC,
 318     KERN_PROC_PID,
 319     getpid(),
 320 #if defined(__NetBSD__) || defined(__OpenBSD__)
 321     sizeof(KINFO_PROC),
 322     1,
 323 #endif
 324   };
 325   u_int mibLen = sizeof(mib) / sizeof(mib[0]);
 326
 327   KINFO_PROC proc;
 328   size_t bufferSize = sizeof(proc);
 329   rv = sysctl(mib, mibLen, &proc, &bufferSize, nullptr, 0);
 330
 331   if (rv == -1) {
 332     return 0;
 333   }
 334
 335   uint64_t startTime = ((uint64_t)proc.KP_START_SEC * kNsPerSec) +
 336     (proc.KP_START_USEC * kNsPerUs);
 337   uint64_t now = ((uint64_t)ts.tv_sec * kNsPerSec) + ts.tv_nsec;
 338
 339   if (startTime > now) {
 340     return 0;
 341   }
 342
 343   return (now - startTime) / kNsPerUs;
 344 }
 345
 346 #else
 347
 348 uint64_t
 349 TimeStamp::ComputeProcessUptime()
 350 {
 351   return 0;
 352 }
 353
 354 #endif
 355
 356 } // namespace mozilla