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tclWinTime.c

/*
 * tclWinTime.c --
 *
 *    Contains Windows specific versions of Tcl functions that obtain time
 *    values from the operating system.
 *
 * Copyright 1995-1998 by Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclWinTime.c,v 1.33 2005/11/04 00:06:51 dkf Exp $
 */

#include "tclInt.h"

#define SECSPERDAY      (60L * 60L * 24L)
#define SECSPERYEAR     (SECSPERDAY * 365L)
#define SECSPER4YEAR    (SECSPERYEAR * 4L + SECSPERDAY)

/*
 * Number of samples over which to estimate the performance counter.
 */

#define SAMPLES         64

/*
 * The following arrays contain the day of year for the last day of each
 * month, where index 1 is January.
 */

static int normalDays[] = {
    -1, 30, 58, 89, 119, 150, 180, 211, 242, 272, 303, 333, 364
};

static int leapDays[] = {
    -1, 30, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365
};

typedef struct ThreadSpecificData {
    char tzName[64];          /* Time zone name */
    struct tm tm;       /* time information */
} ThreadSpecificData;
static Tcl_ThreadDataKey dataKey;

/*
 * Data for managing high-resolution timers.
 */

typedef struct TimeInfo {
    CRITICAL_SECTION cs;      /* Mutex guarding this structure. */
    int initialized;          /* Flag == 1 if this structure is
                         * initialized. */
    int perfCounterAvailable; /* Flag == 1 if the hardware has a performance
                         * counter. */
    HANDLE calibrationThread; /* Handle to the thread that keeps the virtual
                         * clock calibrated. */
    HANDLE readyEvent;        /* System event used to trigger the requesting
                         * thread when the clock calibration procedure
                         * is initialized for the first time. */
    HANDLE exitEvent;         /* Event to signal out of an exit handler to
                         * tell the calibration loop to terminate. */
    LARGE_INTEGER nominalFreq;      /* Nominal frequency of the system performance
                         * counter, that is, the value returned from
                         * QueryPerformanceFrequency. */

    /*
     * The following values are used for calculating virtual time. Virtual
     * time is always equal to:
     *    lastFileTime + (current perf counter - lastCounter)
     *                        * 10000000 / curCounterFreq
     * and lastFileTime and lastCounter are updated any time that virtual time
     * is returned to a caller.
     */

    ULARGE_INTEGER fileTimeLastCall;
    LARGE_INTEGER perfCounterLastCall;
    LARGE_INTEGER curCounterFreq;

    /*
     * Data used in developing the estimate of performance counter frequency
     */

    Tcl_WideUInt fileTimeSample[SAMPLES];
                        /* Last 64 samples of system time. */
    Tcl_WideInt perfCounterSample[SAMPLES];
                        /* Last 64 samples of performance counter. */
    int sampleNo;       /* Current sample number. */
} TimeInfo;

static TimeInfo timeInfo = {
    { NULL },
    0,
    0,
    (HANDLE) NULL,
    (HANDLE) NULL,
    (HANDLE) NULL,
#ifdef HAVE_CAST_TO_UNION
    (LARGE_INTEGER) (Tcl_WideInt) 0,
    (ULARGE_INTEGER) (DWORDLONG) 0,
    (LARGE_INTEGER) (Tcl_WideInt) 0,
    (LARGE_INTEGER) (Tcl_WideInt) 0,
#else
    0,
    0,
    0,
    0,
#endif
    { 0 },
    { 0 },
    0
};

/*
 * Declarations for functions defined later in this file.
 */

static struct tm *      ComputeGMT(const time_t *tp);
static void       StopCalibration(ClientData clientData);
static DWORD WINAPI     CalibrationThread(LPVOID arg);
static void             UpdateTimeEachSecond(void);
static void       ResetCounterSamples(Tcl_WideUInt fileTime,
                      Tcl_WideInt perfCounter, Tcl_WideInt perfFreq);
static Tcl_WideInt      AccumulateSample(Tcl_WideInt perfCounter,
                      Tcl_WideUInt fileTime);
static void       NativeScaleTime(Tcl_Time* timebuf,
                      ClientData clientData);
static void       NativeGetTime(Tcl_Time* timebuf,
                      ClientData clientData);

/*
 * TIP #233 (Virtualized Time): Data for the time hooks, if any.
 */

Tcl_GetTimeProc *tclGetTimeProcPtr = NativeGetTime;
Tcl_ScaleTimeProc *tclScaleTimeProcPtr = NativeScaleTime;
ClientData tclTimeClientData = NULL;

/*
 *----------------------------------------------------------------------
 *
 * TclpGetSeconds --
 *
 *    This procedure returns the number of seconds from the epoch. On most
 *    Unix systems the epoch is Midnight Jan 1, 1970 GMT.
 *
 * Results:
 *    Number of seconds from the epoch.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

unsigned long
TclpGetSeconds(void)
{
    Tcl_Time t;

    (*tclGetTimeProcPtr) (&t, tclTimeClientData);    /* Tcl_GetTime inlined. */
    return t.sec;
}

/*
 *----------------------------------------------------------------------
 *
 * TclpGetClicks --
 *
 *    This procedure returns a value that represents the highest resolution
 *    clock available on the system. There are no guarantees on what the
 *    resolution will be. In Tcl we will call this value a "click". The
 *    start time is also system dependant.
 *
 * Results:
 *    Number of clicks from some start time.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

unsigned long
TclpGetClicks(void)
{
    /*
     * Use the Tcl_GetTime abstraction to get the time in microseconds, as
     * nearly as we can, and return it.
     */

    Tcl_Time now;       /* Current Tcl time */
    unsigned long retval;     /* Value to return */

    (*tclGetTimeProcPtr) (&now, tclTimeClientData);   /* Tcl_GetTime inlined */

    retval = (now.sec * 1000000) + now.usec;
    return retval;

}

/*
 *----------------------------------------------------------------------
 *
 * TclpGetTimeZone --
 *
 *    Determines the current timezone. The method varies wildly between
 *    different Platform implementations, so its hidden in this function.
 *
 * Results:
 *    Minutes west of GMT.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

int
TclpGetTimeZone(
    unsigned long currentTime)
{
    int timeZone;

    tzset();
    timeZone = timezone / 60;

    return timeZone;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetTime --
 *
 *    Gets the current system time in seconds and microseconds since the
 *    beginning of the epoch: 00:00 UCT, January 1, 1970.
 *
 * Results:
 *    Returns the current time in timePtr.
 *
 * Side effects:
 *    On the first call, initializes a set of static variables to keep track
 *    of the base value of the performance counter, the corresponding wall
 *    clock (obtained through ftime) and the frequency of the performance
 *    counter. Also spins a thread whose function is to wake up periodically
 *    and monitor these values, adjusting them as necessary to correct for
 *    drift in the performance counter's oscillator.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_GetTime(
    Tcl_Time *timePtr)        /* Location to store time information. */
{
    (*tclGetTimeProcPtr) (timePtr, tclTimeClientData);
}

/*
 *----------------------------------------------------------------------
 *
 * NativeScaleTime --
 *
 *    TIP #233: Scale from virtual time to the real-time. For native scaling
 *    the relationship is 1:1 and nothing has to be done.
 *
 * Results:
 *    Scales the time in timePtr.
 *
 * Side effects:
 *    See above.
 *
 *----------------------------------------------------------------------
 */

static void
NativeScaleTime(
    Tcl_Time *timePtr,
    ClientData clientData)
{
    /*
     * Native scale is 1:1. Nothing is done.
     */
}

/*
 *----------------------------------------------------------------------
 *
 * NativeGetTime --
 *
 *    TIP #233: Gets the current system time in seconds and microseconds
 *    since the beginning of the epoch: 00:00 UCT, January 1, 1970.
 *
 * Results:
 *    Returns the current time in timePtr.
 *
 * Side effects:
 *    On the first call, initializes a set of static variables to keep track
 *    of the base value of the performance counter, the corresponding wall
 *    clock (obtained through ftime) and the frequency of the performance
 *    counter. Also spins a thread whose function is to wake up periodically
 *    and monitor these values, adjusting them as necessary to correct for
 *    drift in the performance counter's oscillator.
 *
 *----------------------------------------------------------------------
 */

static void
NativeGetTime(
    Tcl_Time *timePtr,
    ClientData clientData)
{
    struct timeb t;
    int useFtime = 1;         /* Flag == TRUE if we need to fall back on
                         * ftime rather than using the perf counter. */

    /*
     * Initialize static storage on the first trip through.
     *
     * Note: Outer check for 'initialized' is a performance win since it
     * avoids an extra mutex lock in the common case.
     */

    if (!timeInfo.initialized) {
      TclpInitLock();
      if (!timeInfo.initialized) {
          timeInfo.perfCounterAvailable =
                QueryPerformanceFrequency(&timeInfo.nominalFreq);

          /*
           * Some hardware abstraction layers use the CPU clock in place of
           * the real-time clock as a performance counter reference. This
           * results in:
           *    - inconsistent results among the processors on
           *      multi-processor systems.
           *    - unpredictable changes in performance counter frequency on
           *      "gearshift" processors such as Transmeta and SpeedStep.
           *
           * There seems to be no way to test whether the performance
           * counter is reliable, but a useful heuristic is that if its
           * frequency is 1.193182 MHz or 3.579545 MHz, it's derived from a
           * colorburst crystal and is therefore the RTC rather than the
           * TSC.
           *
           * A sloppier but serviceable heuristic is that the RTC crystal is
           * normally less than 15 MHz while the TSC crystal is virtually
           * assured to be greater than 100 MHz. Since Win98SE appears to
           * fiddle with the definition of the perf counter frequency
           * (perhaps in an attempt to calibrate the clock?), we use the
           * latter rule rather than an exact match.
           *
           * We also assume (perhaps questionably) that the vendors have
           * gotten their act together on Win64, so bypass all this rubbish
           * on that platform.
           */

#if !defined(_WIN64)
          if (timeInfo.perfCounterAvailable
                /*
                 * The following lines would do an exact match on crystal
                 * frequency:
                 * && timeInfo.nominalFreq.QuadPart != (Tcl_WideInt)1193182
                 * && timeInfo.nominalFreq.QuadPart != (Tcl_WideInt)3579545
                 */
                && timeInfo.nominalFreq.QuadPart > (Tcl_WideInt) 15000000){
            /*
             * As an exception, if every logical processor on the system
             * is on the same chip, we use the performance counter anyway,
             * presuming that everyone's TSC is locked to the same
             * oscillator.
             */

            SYSTEM_INFO systemInfo;
            unsigned int regs[4];

            GetSystemInfo(&systemInfo);
            if (TclWinCPUID(0, regs) == TCL_OK
                  && regs[1] == 0x756e6547      /* "Genu" */
                  && regs[3] == 0x49656e69      /* "ineI" */
                  && regs[2] == 0x6c65746e      /* "ntel" */
                  && TclWinCPUID(1, regs) == TCL_OK
                  && ((regs[0]&0x00000F00) == 0x00000F00 /* Pentium 4 */
                  || ((regs[0] & 0x00F00000)    /* Extended family */
                  && (regs[3] & 0x10000000)))   /* Hyperthread */
                  && (((regs[1]&0x00FF0000) >> 16)/* CPU count */
                      == systemInfo.dwNumberOfProcessors)) {
                timeInfo.perfCounterAvailable = TRUE;
            } else {
                timeInfo.perfCounterAvailable = FALSE;
            }
          }
#endif /* above code is Win32 only */

          /*
           * If the performance counter is available, start a thread to
           * calibrate it.
           */

          if (timeInfo.perfCounterAvailable) {
            DWORD id;

            InitializeCriticalSection(&timeInfo.cs);
            timeInfo.readyEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
            timeInfo.exitEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
            timeInfo.calibrationThread = CreateThread(NULL, 256,
                  CalibrationThread, (LPVOID) NULL, 0, &id);
            SetThreadPriority(timeInfo.calibrationThread,
                  THREAD_PRIORITY_HIGHEST);

            /*
             * Wait for the thread just launched to start running, and
             * create an exit handler that kills it so that it doesn't
             * outlive unloading tclXX.dll
             */

            WaitForSingleObject(timeInfo.readyEvent, INFINITE);
            CloseHandle(timeInfo.readyEvent);
            Tcl_CreateExitHandler(StopCalibration, (ClientData) NULL);
          }
          timeInfo.initialized = TRUE;
      }
      TclpInitUnlock();
    }

    if (timeInfo.perfCounterAvailable && timeInfo.curCounterFreq.QuadPart!=0) {
      /*
       * Query the performance counter and use it to calculate the current
       * time.
       */

      LARGE_INTEGER curCounter;
                        /* Current performance counter. */
      Tcl_WideInt curFileTime;/* Current estimated time, expressed as 100-ns
                         * ticks since the Windows epoch. */
      static LARGE_INTEGER posixEpoch;
                        /* Posix epoch expressed as 100-ns ticks since
                         * the windows epoch. */
      Tcl_WideInt usecSincePosixEpoch;
                        /* Current microseconds since Posix epoch. */

      posixEpoch.LowPart = 0xD53E8000;
      posixEpoch.HighPart = 0x019DB1DE;

      EnterCriticalSection(&timeInfo.cs);

      QueryPerformanceCounter(&curCounter);

      /*
       * If it appears to be more than 1.1 seconds since the last trip
       * through the calibration loop, the performance counter may have
       * jumped forward. (See MSDN Knowledge Base article Q274323 for a
       * description of the hardware problem that makes this test
       * necessary.) If the counter jumps, we don't want to use it directly.
       * Instead, we must return system time. Eventually, the calibration
       * loop should recover.
       */

      if (curCounter.QuadPart - timeInfo.perfCounterLastCall.QuadPart <
            11 * timeInfo.curCounterFreq.QuadPart / 10) {
          curFileTime = timeInfo.fileTimeLastCall.QuadPart +
             ((curCounter.QuadPart - timeInfo.perfCounterLastCall.QuadPart)
                * 10000000 / timeInfo.curCounterFreq.QuadPart);
          timeInfo.fileTimeLastCall.QuadPart = curFileTime;
          timeInfo.perfCounterLastCall.QuadPart = curCounter.QuadPart;
          usecSincePosixEpoch = (curFileTime - posixEpoch.QuadPart) / 10;
          timePtr->sec = (long) (usecSincePosixEpoch / 1000000);
          timePtr->usec = (unsigned long) (usecSincePosixEpoch % 1000000);
          useFtime = 0;
      }

      LeaveCriticalSection(&timeInfo.cs);
    }

    if (useFtime) {
      /*
       * High resolution timer is not available. Just use ftime.
       */

      ftime(&t);
      timePtr->sec = (long)t.time;
      timePtr->usec = t.millitm * 1000;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * StopCalibration --
 *
 *    Turns off the calibration thread in preparation for exiting the
 *    process.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Sets the 'exitEvent' event in the 'timeInfo' structure to ask the
 *    thread in question to exit, and waits for it to do so.
 *
 *----------------------------------------------------------------------
 */

static void
StopCalibration(
    ClientData unused)        /* Client data is unused */
{
    SetEvent(timeInfo.exitEvent);

    /*
     * If Tcl_Finalize was called from DllMain, the calibration thread is in a
     * paused state so we need to timeout and continue.
     */

    WaitForSingleObject(timeInfo.calibrationThread, 100);
    CloseHandle(timeInfo.exitEvent);
    CloseHandle(timeInfo.calibrationThread);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpGetTZName --
 *
 *    Gets the current timezone string.
 *
 * Results:
 *    Returns a pointer to a static string, or NULL on failure.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

char *
TclpGetTZName(
    int dst)
{
    int len;
    char *zone, *p;
    TIME_ZONE_INFORMATION tz;
    Tcl_Encoding encoding;
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    char *name = tsdPtr->tzName;

    /*
     * tzset() under Borland doesn't seem to set up tzname[] at all.
     * tzset() under MSVC has the following weird observed behavior:
     *       First time we call "clock format [clock seconds] -format %Z -gmt 1"
     *       we get "GMT", but on all subsequent calls we get the current time
     *       ezone string, even though env(TZ) is GMT and the variable _timezone
     *       is 0.
     */

    name[0] = '\0';

    zone = getenv("TZ");
    if (zone != NULL) {
      /*
       * TZ is of form "NST-4:30NDT", where "NST" would be the name of the
       * standard time zone for this area, "-4:30" is the offset from GMT in
       * hours, and "NDT is the name of the daylight savings time zone in
       * this area. The offset and DST strings are optional.
       */

      len = strlen(zone);
      if (len > 3) {
          len = 3;
      }
      if (dst != 0) {
          /*
           * Skip the offset string and get the DST string.
           */

          p = zone + len;
          p += strspn(p, "+-:0123456789");
          if (*p != '\0') {
            zone = p;
            len = strlen(zone);
            if (len > 3) {
                len = 3;
            }
          }
      }
      Tcl_ExternalToUtf(NULL, NULL, zone, len, 0, NULL, name,
            sizeof(tsdPtr->tzName), NULL, NULL, NULL);
    }
    if (name[0] == '\0') {
      if (GetTimeZoneInformation(&tz) == TIME_ZONE_ID_UNKNOWN) {
          /*
           * MSDN: On NT this is returned if DST is not used in the current
           * TZ
           */

          dst = 0;
      }
      encoding = Tcl_GetEncoding(NULL, "unicode");
      Tcl_ExternalToUtf(NULL, encoding,
            (char *) ((dst) ? tz.DaylightName : tz.StandardName), -1,
            0, NULL, name, sizeof(tsdPtr->tzName), NULL, NULL, NULL);
      Tcl_FreeEncoding(encoding);
    }
    return name;
}

/*
 *----------------------------------------------------------------------
 *
 * TclpGetDate --
 *
 *    This function converts between seconds and struct tm. If useGMT is
 *    true, then the returned date will be in Greenwich Mean Time (GMT).
 *    Otherwise, it will be in the local time zone.
 *
 * Results:
 *    Returns a static tm structure.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

struct tm *
TclpGetDate(
    CONST time_t *t,
    int useGMT)
{
    struct tm *tmPtr;
    time_t time;

    if (!useGMT) {
      tzset();

      /*
       * If we are in the valid range, let the C run-time library handle it.
       * Otherwise we need to fake it. Note that this algorithm ignores
       * daylight savings time before the epoch.
       */

      /*
       * Hm, Borland's localtime manages to return NULL under certain
       * circumstances (e.g. wintime.test, test 1.2). Nobody tests for this,
       * since 'localtime' isn't supposed to do this, possibly leading to
       * crashes.
       *
       * Patch: We only call this function if we are at least one day into
       * the epoch, else we handle it ourselves (like we do for times < 0).
       * H. Giese, June 2003
       */

#ifdef __BORLANDC__
#define LOCALTIME_VALIDITY_BOUNDARY SECSPERDAY
#else
#define LOCALTIME_VALIDITY_BOUNDARY 0
#endif

      if (*t >= LOCALTIME_VALIDITY_BOUNDARY) {
          return TclpLocaltime(t);
      }

      time = *t - timezone;

      /*
       * If we aren't near to overflowing the long, just add the bias and
       * use the normal calculation. Otherwise we will need to adjust the
       * result at the end.
       */

      if (*t < (LONG_MAX - 2*SECSPERDAY) && *t > (LONG_MIN + 2*SECSPERDAY)) {
          tmPtr = ComputeGMT(&time);
      } else {
          tmPtr = ComputeGMT(t);

          tzset();

          /*
           * Add the bias directly to the tm structure to avoid overflow.
           * Propagate seconds overflow into minutes, hours and days.
           */

          time = tmPtr->tm_sec - timezone;
          tmPtr->tm_sec = (int)(time % 60);
          if (tmPtr->tm_sec < 0) {
            tmPtr->tm_sec += 60;
            time -= 60;
          }

          time = tmPtr->tm_min + time/60;
          tmPtr->tm_min = (int)(time % 60);
          if (tmPtr->tm_min < 0) {
            tmPtr->tm_min += 60;
            time -= 60;
          }

          time = tmPtr->tm_hour + time/60;
          tmPtr->tm_hour = (int)(time % 24);
          if (tmPtr->tm_hour < 0) {
            tmPtr->tm_hour += 24;
            time -= 24;
          }

          time /= 24;
          tmPtr->tm_mday += (int)time;
          tmPtr->tm_yday += (int)time;
          tmPtr->tm_wday = (tmPtr->tm_wday + (int)time) % 7;
      }
    } else {
      tmPtr = ComputeGMT(t);
    }
    return tmPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * ComputeGMT --
 *
 *    This function computes GMT given the number of seconds since the epoch
 *    (midnight Jan 1 1970).
 *
 * Results:
 *    Returns a (per thread) statically allocated struct tm.
 *
 * Side effects:
 *    Updates the values of the static struct tm.
 *
 *----------------------------------------------------------------------
 */

static struct tm *
ComputeGMT(
    const time_t *tp)
{
    struct tm *tmPtr;
    long tmp, rem;
    int isLeap;
    int *days;
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    tmPtr = &tsdPtr->tm;

    /*
     * Compute the 4 year span containing the specified time.
     */

    tmp = (long)(*tp / SECSPER4YEAR);
    rem = (long)(*tp % SECSPER4YEAR);

    /*
     * Correct for weird mod semantics so the remainder is always positive.
     */

    if (rem < 0) {
      tmp--;
      rem += SECSPER4YEAR;
    }

    /*
     * Compute the year after 1900 by taking the 4 year span and adjusting for
     * the remainder. This works because 2000 is a leap year, and 1900/2100
     * are out of the range.
     */

    tmp = (tmp * 4) + 70;
    isLeap = 0;
    if (rem >= SECSPERYEAR) {               /* 1971, etc. */
      tmp++;
      rem -= SECSPERYEAR;
      if (rem >= SECSPERYEAR) {             /* 1972, etc. */
          tmp++;
          rem -= SECSPERYEAR;
          if (rem >= SECSPERYEAR + SECSPERDAY) { /* 1973, etc. */
            tmp++;
            rem -= SECSPERYEAR + SECSPERDAY;
          } else {
            isLeap = 1;
          }
      }
    }
    tmPtr->tm_year = tmp;

    /*
     * Compute the day of year and leave the seconds in the current day in the
     * remainder.
     */

    tmPtr->tm_yday = rem / SECSPERDAY;
    rem %= SECSPERDAY;

    /*
     * Compute the time of day.
     */

    tmPtr->tm_hour = rem / 3600;
    rem %= 3600;
    tmPtr->tm_min = rem / 60;
    tmPtr->tm_sec = rem % 60;

    /*
     * Compute the month and day of month.
     */

    days = (isLeap) ? leapDays : normalDays;
    for (tmp = 1; days[tmp] < tmPtr->tm_yday; tmp++) {
      /* empty body */
    }
    tmPtr->tm_mon = --tmp;
    tmPtr->tm_mday = tmPtr->tm_yday - days[tmp];

    /*
     * Compute day of week.  Epoch started on a Thursday.
     */

    tmPtr->tm_wday = (long)(*tp / SECSPERDAY) + 4;
    if ((*tp % SECSPERDAY) < 0) {
      tmPtr->tm_wday--;
    }
    tmPtr->tm_wday %= 7;
    if (tmPtr->tm_wday < 0) {
      tmPtr->tm_wday += 7;
    }

    return tmPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * CalibrationThread --
 *
 *    Thread that manages calibration of the hi-resolution time derived from
 *    the performance counter, to keep it synchronized with the system
 *    clock.
 *
 * Parameters:
 *    arg - Client data from the CreateThread call. This parameter points to
 *          the static TimeInfo structure.
 *
 * Return value:
 *    None. This thread embeds an infinite loop.
 *
 * Side effects:
 *    At an interval of 1s, this thread performs virtual time discipline.
 *
 * Note: When this thread is entered, TclpInitLock has been called to
 * safeguard the static storage. There is therefore no synchronization in the
 * body of this procedure.
 *
 *----------------------------------------------------------------------
 */

static DWORD WINAPI
CalibrationThread(
    LPVOID arg)
{
    FILETIME curFileTime;
    DWORD waitResult;

    /*
     * Get initial system time and performance counter.
     */

    GetSystemTimeAsFileTime(&curFileTime);
    QueryPerformanceCounter(&timeInfo.perfCounterLastCall);
    QueryPerformanceFrequency(&timeInfo.curCounterFreq);
    timeInfo.fileTimeLastCall.LowPart = curFileTime.dwLowDateTime;
    timeInfo.fileTimeLastCall.HighPart = curFileTime.dwHighDateTime;

    ResetCounterSamples(timeInfo.fileTimeLastCall.QuadPart,
          timeInfo.perfCounterLastCall.QuadPart,
          timeInfo.curCounterFreq.QuadPart);

    /*
     * Wake up the calling thread. When it wakes up, it will release the
     * initialization lock.
     */

    SetEvent(timeInfo.readyEvent);

    /*
     * Run the calibration once a second.
     */

    while (timeInfo.perfCounterAvailable) {
      /*
       * If the exitEvent is set, break out of the loop.
       */

      waitResult = WaitForSingleObjectEx(timeInfo.exitEvent, 1000, FALSE);
      if (waitResult == WAIT_OBJECT_0) {
          break;
      }
      UpdateTimeEachSecond();
    }

    /* lint */
    return (DWORD) 0;
}

/*
 *----------------------------------------------------------------------
 *
 * UpdateTimeEachSecond --
 *
 *    Callback from the waitable timer in the clock calibration thread that
 *    updates system time.
 *
 * Parameters:
 *    info - Pointer to the static TimeInfo structure
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Performs virtual time calibration discipline.
 *
 *----------------------------------------------------------------------
 */

static void
UpdateTimeEachSecond(void)
{
    LARGE_INTEGER curPerfCounter;
                        /* Current value returned from
                         * QueryPerformanceCounter. */
    FILETIME curSysTime;      /* Current system time. */
    LARGE_INTEGER curFileTime;      /* File time at the time this callback was
                         * scheduled. */
    Tcl_WideInt estFreq;      /* Estimated perf counter frequency. */
    Tcl_WideInt vt0;          /* Tcl time right now. */
    Tcl_WideInt vt1;          /* Tcl time one second from now. */
    Tcl_WideInt tdiff;        /* Difference between system clock and Tcl
                         * time. */
    Tcl_WideInt driftFreq;    /* Frequency needed to drift virtual time into
                         * step over 1 second. */

    /*
     * Sample performance counter and system time.
     */

    QueryPerformanceCounter(&curPerfCounter);
    GetSystemTimeAsFileTime(&curSysTime);
    curFileTime.LowPart = curSysTime.dwLowDateTime;
    curFileTime.HighPart = curSysTime.dwHighDateTime;

    EnterCriticalSection(&timeInfo.cs);

    /*
     * We devide by timeInfo.curCounterFreq.QuadPart in several places. That
     * value should always be positive on a correctly functioning system. But
     * it is good to be defensive about such matters. So if something goes
     * wrong and the value does goes to zero, we clear the
     * timeInfo.perfCounterAvailable in order to cause the calibration thread
     * to shut itself down, then return without additional processing.
     */

    if (timeInfo.curCounterFreq.QuadPart == 0){
      LeaveCriticalSection(&timeInfo.cs);
      timeInfo.perfCounterAvailable = 0;
      return;
    }

    /*
     * Several things may have gone wrong here that have to be checked for.
     *  (1) The performance counter may have jumped.
     *  (2) The system clock may have been reset.
     *
     * In either case, we'll need to reinitialize the circular buffer with
     * samples relative to the current system time and the NOMINAL performance
     * frequency (not the actual, because the actual has probably run slow in
     * the first case). Our estimated frequency will be the nominal frequency.
     *
     * Store the current sample into the circular buffer of samples, and
     * estimate the performance counter frequency.
     */

    estFreq = AccumulateSample(curPerfCounter.QuadPart,
          (Tcl_WideUInt) curFileTime.QuadPart);

    /*
     * We want to adjust things so that time appears to be continuous.
     * Virtual file time, right now, is
     *
     * vt0 = 10000000 * (curPerfCounter - perfCounterLastCall)
     *           / curCounterFreq
     *           + fileTimeLastCall
     *
     * Ideally, we would like to drift the clock into place over a period of 2
     * sec, so that virtual time 2 sec from now will be
     *
     * vt1 = 20000000 + curFileTime
     *
     * The frequency that we need to use to drift the counter back into place
     * is estFreq * 20000000 / (vt1 - vt0)
     */

    vt0 = 10000000 * (curPerfCounter.QuadPart
            - timeInfo.perfCounterLastCall.QuadPart)
          / timeInfo.curCounterFreq.QuadPart
          + timeInfo.fileTimeLastCall.QuadPart;
    vt1 = 20000000 + curFileTime.QuadPart;

    /*
     * If we've gotten more than a second away from system time, then drifting
     * the clock is going to be pretty hopeless. Just let it jump. Otherwise,
     * compute the drift frequency and fill in everything.
     */

    tdiff = vt0 - curFileTime.QuadPart;
    if (tdiff > 10000000 || tdiff < -10000000) {
      timeInfo.fileTimeLastCall.QuadPart = curFileTime.QuadPart;
      timeInfo.curCounterFreq.QuadPart = estFreq;
    } else {
      driftFreq = estFreq * 20000000 / (vt1 - vt0);

      if (driftFreq > 1003*estFreq/1000) {
          driftFreq = 1003*estFreq/1000;
      } else if (driftFreq < 997*estFreq/1000) {
          driftFreq = 997*estFreq/1000;
      }

      timeInfo.fileTimeLastCall.QuadPart = vt0;
      timeInfo.curCounterFreq.QuadPart = driftFreq;
    }

    timeInfo.perfCounterLastCall.QuadPart = curPerfCounter.QuadPart;

    LeaveCriticalSection(&timeInfo.cs);
}

/*
 *----------------------------------------------------------------------
 *
 * ResetCounterSamples --
 *
 *    Fills the sample arrays in 'timeInfo' with dummy values that will
 *    yield the current performance counter and frequency.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The array of samples is filled in so that it appears that there are
 *    SAMPLES samples at one-second intervals, separated by precisely the
 *    given frequency.
 *
 *----------------------------------------------------------------------
 */

static void
ResetCounterSamples(
    Tcl_WideUInt fileTime,    /* Current file time */
    Tcl_WideInt perfCounter,  /* Current performance counter */
    Tcl_WideInt perfFreq)     /* Target performance frequency */
{
    int i;
    for (i=SAMPLES-1 ; i>=0 ; --i) {
      timeInfo.perfCounterSample[i] = perfCounter;
      timeInfo.fileTimeSample[i] = fileTime;
      perfCounter -= perfFreq;
      fileTime -= 10000000;
    }
    timeInfo.sampleNo = 0;
}

/*
 *----------------------------------------------------------------------
 *
 * AccumulateSample --
 *
 *    Updates the circular buffer of performance counter and system time
 *    samples with a new data point.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    The new data point replaces the oldest point in the circular buffer,
 *    and the descriptive statistics are updated to accumulate the new
 *    point.
 *
 * Several things may have gone wrong here that have to be checked for.
 *  (1) The performance counter may have jumped.
 *  (2) The system clock may have been reset.
 *
 * In either case, we'll need to reinitialize the circular buffer with samples
 * relative to the current system time and the NOMINAL performance frequency
 * (not the actual, because the actual has probably run slow in the first
 * case).
 */

static Tcl_WideInt
AccumulateSample(
    Tcl_WideInt perfCounter,
    Tcl_WideUInt fileTime)
{
    Tcl_WideUInt workFTSample;      /* File time sample being removed from or
                         * added to the circular buffer. */
    Tcl_WideInt workPCSample; /* Performance counter sample being removed
                         * from or added to the circular buffer. */
    Tcl_WideUInt lastFTSample;      /* Last file time sample recorded */
    Tcl_WideInt lastPCSample; /* Last performance counter sample recorded */
    Tcl_WideInt FTdiff;       /* Difference between last FT and current */
    Tcl_WideInt PCdiff;       /* Difference between last PC and current */
    Tcl_WideInt estFreq;      /* Estimated performance counter frequency */

    /*
     * Test for jumps and reset the samples if we have one.
     */

    if (timeInfo.sampleNo == 0) {
      lastPCSample =
            timeInfo.perfCounterSample[timeInfo.sampleNo + SAMPLES - 1];
      lastFTSample =
            timeInfo.fileTimeSample[timeInfo.sampleNo + SAMPLES - 1];
    } else {
      lastPCSample = timeInfo.perfCounterSample[timeInfo.sampleNo - 1];
      lastFTSample = timeInfo.fileTimeSample[timeInfo.sampleNo - 1];
    }

    PCdiff = perfCounter - lastPCSample;
    FTdiff = fileTime - lastFTSample;
    if (PCdiff < timeInfo.nominalFreq.QuadPart * 9 / 10
          || PCdiff > timeInfo.nominalFreq.QuadPart * 11 / 10
          || FTdiff < 9000000 || FTdiff > 11000000) {
      ResetCounterSamples(fileTime, perfCounter,
            timeInfo.nominalFreq.QuadPart);
      return timeInfo.nominalFreq.QuadPart;
    } else {
      /*
       * Estimate the frequency.
       */

      workPCSample = timeInfo.perfCounterSample[timeInfo.sampleNo];
      workFTSample = timeInfo.fileTimeSample[timeInfo.sampleNo];
      estFreq = 10000000 * (perfCounter - workPCSample)
            / (fileTime - workFTSample);
      timeInfo.perfCounterSample[timeInfo.sampleNo] = perfCounter;
      timeInfo.fileTimeSample[timeInfo.sampleNo] = (Tcl_WideInt) fileTime;

      /*
       * Advance the sample number.
       */

      if (++timeInfo.sampleNo >= SAMPLES) {
          timeInfo.sampleNo = 0;
      }

      return estFreq;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TclpGmtime --
 *
 *    Wrapper around the 'gmtime' library function to make it thread safe.
 *
 * Results:
 *    Returns a pointer to a 'struct tm' in thread-specific data.
 *
 * Side effects:
 *    Invokes gmtime or gmtime_r as appropriate.
 *
 *----------------------------------------------------------------------
 */

struct tm *
TclpGmtime(
    CONST time_t *timePtr)    /* Pointer to the number of seconds since the
                         * local system's epoch */
{
    /*
     * The MS implementation of gmtime is thread safe because it returns the
     * time in a block of thread-local storage, and Windows does not provide a
     * Posix gmtime_r function.
     */

    return gmtime(timePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpLocaltime --
 *
 *    Wrapper around the 'localtime' library function to make it thread
 *    safe.
 *
 * Results:
 *    Returns a pointer to a 'struct tm' in thread-specific data.
 *
 * Side effects:
 *    Invokes localtime or localtime_r as appropriate.
 *
 *----------------------------------------------------------------------
 */

struct tm *
TclpLocaltime(
    CONST time_t *timePtr)    /* Pointer to the number of seconds since the
                         * local system's epoch */

{
    /*
     * The MS implementation of localtime is thread safe because it returns
     * the time in a block of thread-local storage, and Windows does not
     * provide a Posix localtime_r function.
     */

    return localtime(timePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_SetTimeProc --
 *
 *    TIP #233 (Virtualized Time): Registers two handlers for the
 *    virtualization of Tcl's access to time information.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Remembers the handlers, alters core behaviour.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_SetTimeProc(
    Tcl_GetTimeProc *getProc,
    Tcl_ScaleTimeProc *scaleProc,
    ClientData clientData)
{
    tclGetTimeProcPtr = getProc;
    tclScaleTimeProcPtr = scaleProc;
    tclTimeClientData = clientData;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_QueryTimeProc --
 *
 *    TIP #233 (Virtualized Time): Query which time handlers are registered.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_QueryTimeProc(
    Tcl_GetTimeProc **getProc,
    Tcl_ScaleTimeProc **scaleProc,
    ClientData *clientData)
{
    if (getProc) {
      *getProc = tclGetTimeProcPtr;
    }
    if (scaleProc) {
      *scaleProc = tclScaleTimeProcPtr;
    }
    if (clientData) {
      *clientData = tclTimeClientData;
    }
}

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */

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