/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

//

// Implement TimeStamp::Now() with POSIX clocks.

//

// The "tick" unit for POSIX clocks is simply a nanosecond, as this is

// the smallest unit of time representable by struct timespec.  That

// doesn't mean that a nanosecond is the resolution of TimeDurations

// obtained with this API; see TimeDuration::Resolution;

//

#include <sys/syscall.h>

#include <time.h>

#include <unistd.h>

#include <string.h>

#if defined(__DragonFly__) || defined(__FreeBSD__) \

    || defined(__NetBSD__) || defined(__OpenBSD__)

#include <sys/param.h>

#include <sys/sysctl.h>

#endif

#if defined(__DragonFly__) || defined(__FreeBSD__)

#include <sys/user.h>

#endif

#if defined(__NetBSD__)

#undef KERN_PROC

#define KERN_PROC KERN_PROC2

#define KINFO_PROC struct kinfo_proc2

#else

#define KINFO_PROC struct kinfo_proc

#endif

#if defined(__DragonFly__)

#define KP_START_SEC kp_start.tv_sec

#define KP_START_USEC kp_start.tv_usec

#elif defined(__FreeBSD__)

#define KP_START_SEC ki_start.tv_sec

#define KP_START_USEC ki_start.tv_usec

#else

#define KP_START_SEC p_ustart_sec

#define KP_START_USEC p_ustart_usec

#endif

#include "mozilla/Sprintf.h"

#include "mozilla/TimeStamp.h"

#include <pthread.h>

// Estimate of the smallest duration of time we can measure.

static uint64_t sResolution;

static uint64_t sResolutionSigDigs;

static const uint16_t kNsPerUs   =       1000;

static const uint64_t kNsPerMs   =    1000000;

static const uint64_t kNsPerSec  = 1000000000;

static const double kNsPerMsd    =    1000000.0;

static const double kNsPerSecd   = 1000000000.0;

static uint64_t

TimespecToNs(const struct timespec& aTs)

{

  uint64_t baseNs = uint64_t(aTs.tv_sec) * kNsPerSec;

  return baseNs + uint64_t(aTs.tv_nsec);

}

static uint64_t

ClockTimeNs()

{

  struct timespec ts;

  // this can't fail: we know &ts is valid, and TimeStamp::Startup()

  // checks that CLOCK_MONOTONIC is supported (and aborts if not)

  clock_gettime(CLOCK_MONOTONIC, &ts);

  // tv_sec is defined to be relative to an arbitrary point in time,

  // but it would be madness for that point in time to be earlier than

  // the Epoch.  So we can safely assume that even if time_t is 32

  // bits, tv_sec won't overflow while the browser is open.  Revisit

  // this argument if we're still building with 32-bit time_t around

  // the year 2037.

  return TimespecToNs(ts);

}

static uint64_t

ClockResolutionNs()

{

  // NB: why not rely on clock_getres()?  Two reasons: (i) it might

  // lie, and (ii) it might return an "ideal" resolution that while

  // theoretically true, could never be measured in practice.  Since

  // clock_gettime() likely involves a system call on your platform,

  // the "actual" timing resolution shouldn't be lower than syscall

  // overhead.

  uint64_t start = ClockTimeNs();

  uint64_t end = ClockTimeNs();

  uint64_t minres = (end - start);

  // 10 total trials is arbitrary: what we're trying to avoid by

  // looping is getting unlucky and being interrupted by a context

  // switch or signal, or being bitten by paging/cache effects

  for (int i = 0; i < 9; ++i) {

    start = ClockTimeNs();

    end = ClockTimeNs();

    uint64_t candidate = (start - end);

    if (candidate < minres) {

      minres = candidate;

    }

  }

  if (0 == minres) {

    // measurable resolution is either incredibly low, ~1ns, or very

    // high.  fall back on clock_getres()

    struct timespec ts;

    if (0 == clock_getres(CLOCK_MONOTONIC, &ts)) {

      minres = TimespecToNs(ts);

    }

  }

  if (0 == minres) {

    // clock_getres probably failed.  fall back on NSPR's resolution

    // assumption

    minres = 1 * kNsPerMs;

  }

  return minres;

}

namespace mozilla {

double

BaseTimeDurationPlatformUtils::ToSeconds(int64_t aTicks)

{

  return double(aTicks) / kNsPerSecd;

}

double

BaseTimeDurationPlatformUtils::ToSecondsSigDigits(int64_t aTicks)

{

  // don't report a value < mResolution ...

  int64_t valueSigDigs = sResolution * (aTicks / sResolution);

  // and chop off insignificant digits

  valueSigDigs = sResolutionSigDigs * (valueSigDigs / sResolutionSigDigs);

  return double(valueSigDigs) / kNsPerSecd;

}

int64_t

BaseTimeDurationPlatformUtils::TicksFromMilliseconds(double aMilliseconds)

{

  double result = aMilliseconds * kNsPerMsd;

  if (result > INT64_MAX) {

    return INT64_MAX;

  }

  if (result < INT64_MIN) {

    return INT64_MIN;

  }

  return result;

}

int64_t

BaseTimeDurationPlatformUtils::ResolutionInTicks()

{

  return static_cast<int64_t>(sResolution);

}

static bool gInitialized = false;

void

TimeStamp::Startup()

{

  if (gInitialized) {

    return;

  }

  struct timespec dummy;

  if (clock_gettime(CLOCK_MONOTONIC, &dummy) != 0) {

    MOZ_CRASH("CLOCK_MONOTONIC is absent!");

  }

  sResolution = ClockResolutionNs();

  // find the number of significant digits in sResolution, for the

  // sake of ToSecondsSigDigits()

  for (sResolutionSigDigs = 1;

       !(sResolutionSigDigs == sResolution ||

         10 * sResolutionSigDigs > sResolution);

       sResolutionSigDigs *= 10);

  gInitialized = true;

}

void

TimeStamp::Shutdown()

{

}

TimeStamp

TimeStamp::Now(bool aHighResolution)

{

  return TimeStamp(ClockTimeNs());

}

#if defined(XP_LINUX) || defined(ANDROID)

// Calculates the amount of jiffies that have elapsed since boot and up to the

// starttime value of a specific process as found in its /proc/*/stat file.

// Returns 0 if an error occurred.

static uint64_t

JiffiesSinceBoot(const char* aFile)

{

  char stat[512];

  FILE* f = fopen(aFile, "r");

  if (!f) {

    return 0;

  }

  int n = fread(&stat, 1, sizeof(stat) - 1, f);

  fclose(f);

  if (n <= 0) {

    return 0;

  }

  stat[n] = 0;

  long long unsigned startTime = 0; // instead of uint64_t to keep GCC quiet

  char* s = strrchr(stat, ')');

  if (!s) {

    return 0;

  }

  int rv = sscanf(s + 2,

                  "%*c %*d %*d %*d %*d %*d %*u %*u %*u %*u "

                  "%*u %*u %*u %*d %*d %*d %*d %*d %*d %llu",

                  &startTime);

  if (rv != 1 || !startTime) {

    return 0;

  }

  return startTime;

}

// Computes the interval that has elapsed between the thread creation and the

// process creation by comparing the starttime fields in the respective

// /proc/*/stat files. The resulting value will be a good approximation of the

// process uptime. This value will be stored at the address pointed by aTime;

// if an error occurred 0 will be stored instead.

static void*

ComputeProcessUptimeThread(void* aTime)

{

  uint64_t* uptime = static_cast<uint64_t*>(aTime);

  long hz = sysconf(_SC_CLK_TCK);

  *uptime = 0;

  if (!hz) {

    return nullptr;

  }

  char threadStat[40];

  SprintfLiteral(threadStat, "/proc/self/task/%d/stat", (pid_t)syscall(__NR_gettid));

  uint64_t threadJiffies = JiffiesSinceBoot(threadStat);

  uint64_t selfJiffies = JiffiesSinceBoot("/proc/self/stat");

  if (!threadJiffies || !selfJiffies) {

    return nullptr;

  }

  *uptime = ((threadJiffies - selfJiffies) * kNsPerSec) / hz;

  return nullptr;

}

// Computes and returns the process uptime in us on Linux & its derivatives.

// Returns 0 if an error was encountered.

uint64_t

TimeStamp::ComputeProcessUptime()

{

  uint64_t uptime = 0;

  pthread_t uptime_pthread;

  if (pthread_create(&uptime_pthread, nullptr, ComputeProcessUptimeThread, &uptime)) {

    MOZ_CRASH("Failed to create process uptime thread.");

    return 0;

  }

  pthread_join(uptime_pthread, NULL);

  return uptime / kNsPerUs;

}

#elif defined(__DragonFly__) || defined(__FreeBSD__) \

      || defined(__NetBSD__) || defined(__OpenBSD__)

// Computes and returns the process uptime in us on various BSD flavors.

// Returns 0 if an error was encountered.

uint64_t

TimeStamp::ComputeProcessUptime()

{

  struct timespec ts;

  int rv = clock_gettime(CLOCK_REALTIME, &ts);

  if (rv == -1) {

    return 0;

  }

  int mib[] = {

    CTL_KERN,

    KERN_PROC,

    KERN_PROC_PID,

    getpid(),

#if defined(__NetBSD__) || defined(__OpenBSD__)

    sizeof(KINFO_PROC),

    1,

#endif

  };

  u_int mibLen = sizeof(mib) / sizeof(mib[0]);

  KINFO_PROC proc;

  size_t bufferSize = sizeof(proc);

  rv = sysctl(mib, mibLen, &proc, &bufferSize, nullptr, 0);

  if (rv == -1) {

    return 0;

  }

  uint64_t startTime = ((uint64_t)proc.KP_START_SEC * kNsPerSec) +

    (proc.KP_START_USEC * kNsPerUs);

  uint64_t now = ((uint64_t)ts.tv_sec * kNsPerSec) + ts.tv_nsec;

  if (startTime > now) {

    return 0;

  }

  return (now - startTime) / kNsPerUs;

}

#else

uint64_t

TimeStamp::ComputeProcessUptime()

{

  return 0;

}

#endif

} // namespace mozilla