source: downloads/tcl8.5.2/win/tclWinTime.c @ 68

/*
 * 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:
 */