Time.cpp

/* -*- 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/. */

/* PR time code. */

#include "vm/Time.h"

#include "mozilla/DebugOnly.h"
#include "mozilla/MathAlgorithms.h"

#ifdef SOLARIS
#  define _REENTRANT 1
#endif
#include <algorithm>
#include <string.h>
#include <time.h>

#include "jstypes.h"

#ifdef XP_WIN
#  include <windef.h>
#  include <winbase.h>
#  include <crtdbg.h>   /* for _CrtSetReportMode */
#  include <mmsystem.h> /* for timeBegin/EndPeriod */
#  include <stdlib.h>   /* for _set_invalid_parameter_handler */
#endif

#ifdef XP_UNIX

#  ifdef _SVID_GETTOD /* Defined only on Solaris, see Solaris <sys/types.h> */
extern int gettimeofday(struct timeval* tv);
#  endif

#  include <sys/time.h>

#endif /* XP_UNIX */

using mozilla::DebugOnly;

// Forward declare the function
static int64_t PRMJ_NowImpl();

int64_t PRMJ_Now() {
  if (mozilla::TimeStamp::GetFuzzyfoxEnabled()) {
    return mozilla::TimeStamp::NowFuzzyTime();
  }

  // We check the FuzzyFox clock in case it was recently disabled, to prevent
  // time from going backwards.
  return std::max(PRMJ_NowImpl(), mozilla::TimeStamp::NowFuzzyTime());
}

#if defined(XP_UNIX)
static int64_t PRMJ_NowImpl() {
  struct timeval tv;

#  ifdef _SVID_GETTOD /* Defined only on Solaris, see Solaris <sys/types.h> */
  gettimeofday(&tv);
#  else
  gettimeofday(&tv, 0);
#  endif /* _SVID_GETTOD */

  return int64_t(tv.tv_sec) * PRMJ_USEC_PER_SEC + int64_t(tv.tv_usec);
}

#else

// Returns the number of microseconds since the Unix epoch.
static double FileTimeToUnixMicroseconds(const FILETIME& ft) {
  // Get the time in 100ns intervals.
  int64_t t = (int64_t(ft.dwHighDateTime) << 32) | int64_t(ft.dwLowDateTime);

  // The Windows epoch is around 1600. The Unix epoch is around 1970.
  // Subtract the difference.
  static const int64_t TimeToEpochIn100ns = 0x19DB1DED53E8000;
  t -= TimeToEpochIn100ns;

  // Divide by 10 to convert to microseconds.
  return double(t) * 0.1;
}

struct CalibrationData {
  double freq;         /* The performance counter frequency */
  double offset;       /* The low res 'epoch' */
  double timer_offset; /* The high res 'epoch' */

  bool calibrated;

  CRITICAL_SECTION data_lock;
};

static CalibrationData calibration = {0};

static void NowCalibrate() {
  MOZ_ASSERT(calibration.freq > 0);

  // By wrapping a timeBegin/EndPeriod pair of calls around this loop,
  // the loop seems to take much less time (1 ms vs 15ms) on Vista.
  timeBeginPeriod(1);
  FILETIME ft, ftStart;
  GetSystemTimeAsFileTime(&ftStart);
  do {
    GetSystemTimeAsFileTime(&ft);
  } while (memcmp(&ftStart, &ft, sizeof(ft)) == 0);
  timeEndPeriod(1);

  LARGE_INTEGER now;
  QueryPerformanceCounter(&now);

  calibration.offset = FileTimeToUnixMicroseconds(ft);
  calibration.timer_offset = double(now.QuadPart);
  calibration.calibrated = true;
}

static const unsigned DataLockSpinCount = 4096;

static void(WINAPI* pGetSystemTimePreciseAsFileTime)(LPFILETIME) = nullptr;

void PRMJ_NowInit() {
  memset(&calibration, 0, sizeof(calibration));

  // According to the documentation, QueryPerformanceFrequency will never
  // return false or return a non-zero frequency on systems that run
  // Windows XP or later. Also, the frequency is fixed so we only have to
  // query it once.
  LARGE_INTEGER liFreq;
  DebugOnly<BOOL> res = QueryPerformanceFrequency(&liFreq);
  MOZ_ASSERT(res);
  calibration.freq = double(liFreq.QuadPart);
  MOZ_ASSERT(calibration.freq > 0.0);

  InitializeCriticalSectionAndSpinCount(&calibration.data_lock,
                                        DataLockSpinCount);

  // Windows 8 has a new API function we can use.
  if (HMODULE h = GetModuleHandle("kernel32.dll")) {
    pGetSystemTimePreciseAsFileTime = (void(WINAPI*)(LPFILETIME))GetProcAddress(
        h, "GetSystemTimePreciseAsFileTime");
  }
}

void PRMJ_NowShutdown() { DeleteCriticalSection(&calibration.data_lock); }

#  define MUTEX_LOCK(m) EnterCriticalSection(m)
#  define MUTEX_UNLOCK(m) LeaveCriticalSection(m)
#  define MUTEX_SETSPINCOUNT(m, c) SetCriticalSectionSpinCount((m), (c))

// Please see bug 363258 for why the win32 timing code is so complex.
static int64_t PRMJ_NowImpl() {
  if (pGetSystemTimePreciseAsFileTime) {
    // Windows 8 has a new API function that does all the work.
    FILETIME ft;
    pGetSystemTimePreciseAsFileTime(&ft);
    return int64_t(FileTimeToUnixMicroseconds(ft));
  }

  bool calibrated = false;
  bool needsCalibration = !calibration.calibrated;
  double cachedOffset = 0.0;
  while (true) {
    if (needsCalibration) {
      MUTEX_LOCK(&calibration.data_lock);

      // Recalibrate only if no one else did before us.
      if (calibration.offset == cachedOffset) {
        // Since calibration can take a while, make any other
        // threads immediately wait.
        MUTEX_SETSPINCOUNT(&calibration.data_lock, 0);

        NowCalibrate();

        calibrated = true;

        // Restore spin count.
        MUTEX_SETSPINCOUNT(&calibration.data_lock, DataLockSpinCount);
      }

      MUTEX_UNLOCK(&calibration.data_lock);
    }

    // Calculate a low resolution time.
    FILETIME ft;
    GetSystemTimeAsFileTime(&ft);
    double lowresTime = FileTimeToUnixMicroseconds(ft);

    // Grab high resolution time.
    LARGE_INTEGER now;
    QueryPerformanceCounter(&now);
    double highresTimerValue = double(now.QuadPart);

    MUTEX_LOCK(&calibration.data_lock);
    double highresTime = calibration.offset +
                         PRMJ_USEC_PER_SEC *
                             (highresTimerValue - calibration.timer_offset) /
                             calibration.freq;
    cachedOffset = calibration.offset;
    MUTEX_UNLOCK(&calibration.data_lock);

    // Assume the NT kernel ticks every 15.6 ms. Unfortunately there's no
    // good way to determine this (NtQueryTimerResolution is an undocumented
    // API), but 15.6 ms seems to be the max possible value. Hardcoding 15.6
    // means we'll recalibrate if the highres and lowres timers diverge by
    // more than 30 ms.
    static const double KernelTickInMicroseconds = 15625.25;

    // Check for clock skew.
    double diff = lowresTime - highresTime;

    // For some reason that I have not determined, the skew can be
    // up to twice a kernel tick. This does not seem to happen by
    // itself, but I have only seen it triggered by another program
    // doing some kind of file I/O. The symptoms are a negative diff
    // followed by an equally large positive diff.
    if (mozilla::Abs(diff) <= 2 * KernelTickInMicroseconds) {
      // No detectable clock skew.
      return int64_t(highresTime);
    }

    if (calibrated) {
      // If we already calibrated once this instance, and the
      // clock is still skewed, then either the processor(s) are
      // wildly changing clockspeed or the system is so busy that
      // we get switched out for long periods of time. In either
      // case, it would be infeasible to make use of high
      // resolution results for anything, so let's resort to old
      // behavior for this call. It's possible that in the
      // future, the user will want the high resolution timer, so
      // we don't disable it entirely.
      return int64_t(lowresTime);
    }

    // It is possible that when we recalibrate, we will return a
    // value less than what we have returned before; this is
    // unavoidable. We cannot tell the different between a
    // faulty QueryPerformanceCounter implementation and user
    // changes to the operating system time. Since we must
    // respect user changes to the operating system time, we
    // cannot maintain the invariant that Date.now() never
    // decreases; the old implementation has this behavior as
    // well.
    needsCalibration = true;
  }
}
#endif

#if !JS_HAS_INTL_API || MOZ_SYSTEM_ICU
#  ifdef XP_WIN
static void PRMJ_InvalidParameterHandler(const wchar_t* expression,
                                         const wchar_t* function,
                                         const wchar_t* file, unsigned int line,
                                         uintptr_t pReserved) {
  /* empty */
}
#  endif

/* Format a time value into a buffer. Same semantics as strftime() */
size_t PRMJ_FormatTime(char* buf, size_t buflen, const char* fmt,
                       const PRMJTime* prtm, int timeZoneYear,
                       int offsetInSeconds) {
  size_t result = 0;
#  if defined(XP_UNIX) || defined(XP_WIN)
  struct tm a;
#    ifdef XP_WIN
  _invalid_parameter_handler oldHandler;
#      ifndef __MINGW32__
  int oldReportMode;
#      endif  // __MINGW32__
#    endif    // XP_WIN

  memset(&a, 0, sizeof(struct tm));

  a.tm_sec = prtm->tm_sec;
  a.tm_min = prtm->tm_min;
  a.tm_hour = prtm->tm_hour;
  a.tm_mday = prtm->tm_mday;
  a.tm_mon = prtm->tm_mon;
  a.tm_wday = prtm->tm_wday;

  /*
   * On systems where |struct tm| has members tm_gmtoff and tm_zone, we
   * must fill in those values, or else strftime will return wrong results
   * (e.g., bug 511726, bug 554338).
   */
#    if defined(HAVE_LOCALTIME_R) && defined(HAVE_TM_ZONE_TM_GMTOFF)
  char emptyTimeZoneId[] = "";
  {
    /*
     * Fill out |td| to the time represented by |prtm|, leaving the
     * timezone fields zeroed out. localtime_r will then fill in the
     * timezone fields for that local time according to the system's
     * timezone parameters. Use |timeZoneYear| for the year to ensure the
     * time zone name matches the time zone offset used by the caller.
     */
    struct tm td;
    memset(&td, 0, sizeof(td));
    td.tm_sec = prtm->tm_sec;
    td.tm_min = prtm->tm_min;
    td.tm_hour = prtm->tm_hour;
    td.tm_mday = prtm->tm_mday;
    td.tm_mon = prtm->tm_mon;
    td.tm_wday = prtm->tm_wday;
    td.tm_year = timeZoneYear - 1900;
    td.tm_yday = prtm->tm_yday;
    td.tm_isdst = prtm->tm_isdst;

    time_t t = mktime(&td);

    // If either mktime or localtime_r failed, fill in the fallback time
    // zone offset |offsetInSeconds| and set the time zone identifier to
    // the empty string.
    if (t != static_cast<time_t>(-1) && localtime_r(&t, &td)) {
      a.tm_gmtoff = td.tm_gmtoff;
      a.tm_zone = td.tm_zone;
    } else {
      a.tm_gmtoff = offsetInSeconds;
      a.tm_zone = emptyTimeZoneId;
    }
  }
#    endif

  /*
   * Years before 1900 and after 9999 cause strftime() to abort on Windows.
   * To avoid that we replace it with FAKE_YEAR_BASE + year % 100 and then
   * replace matching substrings in the strftime() result with the real year.
   * Note that FAKE_YEAR_BASE should be a multiple of 100 to make 2-digit
   * year formats (%y) work correctly (since we won't find the fake year
   * in that case).
   */
  constexpr int FAKE_YEAR_BASE = 9900;
  int fake_tm_year = 0;
  if (prtm->tm_year < 1900 || prtm->tm_year > 9999) {
    fake_tm_year = FAKE_YEAR_BASE + prtm->tm_year % 100;
    a.tm_year = fake_tm_year - 1900;
  } else {
    a.tm_year = prtm->tm_year - 1900;
  }
  a.tm_yday = prtm->tm_yday;
  a.tm_isdst = prtm->tm_isdst;

  /*
   * Even with the above, SunOS 4 seems to detonate if tm_zone and tm_gmtoff
   * are null.  This doesn't quite work, though - the timezone is off by
   * tzoff + dst.  (And mktime seems to return -1 for the exact dst
   * changeover time.)
   */

#    ifdef XP_WIN
  oldHandler = _set_invalid_parameter_handler(PRMJ_InvalidParameterHandler);
#      ifndef __MINGW32__
  /*
   * MinGW doesn't have _CrtSetReportMode and defines it to be a no-op.
   * We ifdef it off to avoid warnings about unused variables
   */
  oldReportMode = _CrtSetReportMode(_CRT_ASSERT, 0);
#      endif  // __MINGW32__
#    endif    // XP_WIN

  result = strftime(buf, buflen, fmt, &a);

#    ifdef XP_WIN
  _set_invalid_parameter_handler(oldHandler);
#      ifndef __MINGW32__
  _CrtSetReportMode(_CRT_ASSERT, oldReportMode);
#      endif  // __MINGW32__
#    endif    // XP_WIN

  if (fake_tm_year && result) {
    char real_year[16];
    char fake_year[16];
    size_t real_year_len;
    size_t fake_year_len;
    char* p;

    sprintf(real_year, "%d", prtm->tm_year);
    real_year_len = strlen(real_year);
    sprintf(fake_year, "%d", fake_tm_year);
    fake_year_len = strlen(fake_year);

    /* Replace the fake year in the result with the real year. */
    for (p = buf; (p = strstr(p, fake_year)); p += real_year_len) {
      size_t new_result = result + real_year_len - fake_year_len;
      if (new_result >= buflen) {
        return 0;
      }
      memmove(p + real_year_len, p + fake_year_len, strlen(p + fake_year_len));
      memcpy(p, real_year, real_year_len);
      result = new_result;
      *(buf + result) = '\0';
    }
  }
#  endif
  return result;
}
#endif /* !JS_HAS_INTL_API || MOZ_SYSTEM_ICU */