Issue #22117: Add a new Python timestamp format _PyTime_t to pytime.h

In practice, _PyTime_t is a number of nanoseconds. Its C type is a 64-bit
signed number. It's integer value is in the range [-2^63; 2^63-1]. In seconds,
the range is around [-292 years; +292 years]. In term of Epoch timestamp
(1970-01-01), it can store a date between 1677-09-21 and 2262-04-11.

The API has a resolution of 1 nanosecond and use integer number. With a
resolution on 1 nanosecond, 64-bit IEEE 754 floating point numbers loose
precision after 194 days. It's not the case with this API. The drawback is
overflow for values outside [-2^63; 2^63-1], but these values are unlikely for
most Python modules, except of the datetime module.

New functions:

- _PyTime_GetMonotonicClock()
- _PyTime_FromObject()
- _PyTime_AsMilliseconds()
- _PyTime_AsTimeval()

This change uses these new functions in time.sleep() to avoid rounding issues.

The new API will be extended step by step, and the old API will be removed step
by step. Currently, some code is duplicated just to be able to move
incrementally, instead of pushing a large change at once.

1 files changed, 310 insertions, 1 deletions

diff --git a/Python/pytime.c b/Python/pytime.c
index 578569d..52bd958 100644
--- a/Python/pytime.c
+++ b/Python/pytime.c
@@ -7,11 +7,21 @@
 #include <mach/mach_time.h>   /* mach_absolute_time(), mach_timebase_info() */
 #endif
 
+/* To millisecond (10^-3) */
 #define SEC_TO_MS 1000
+
+/* To microseconds (10^-6) */
 #define MS_TO_US 1000
+#define SEC_TO_US (SEC_TO_MS * MS_TO_US)
+
+/* To nanoseconds (10^-9) */
 #define US_TO_NS 1000
+#define MS_TO_NS (MS_TO_US * US_TO_NS)
+#define SEC_TO_NS (SEC_TO_MS * MS_TO_NS)
 
-#define SEC_TO_US (SEC_TO_MS * MS_TO_US)
+#ifdef MS_WINDOWS
+static OSVERSIONINFOEX winver;
+#endif
 
 static int
 pygettimeofday(_PyTime_timeval *tp, _Py_clock_info_t *info, int raise)
@@ -390,10 +400,305 @@ _PyTime_AddDouble(_PyTime_timeval *tv, double interval, _PyTime_round_t round)
     tv->tv_usec %= SEC_TO_US;
 }
 
+/****************** NEW _PyTime_t API **********************/
+
+static void
+_PyTime_overflow(void)
+{
+    PyErr_SetString(PyExc_OverflowError,
+                    "timestamp too large to convert to C _PyTime_t");
+}
+
+#if !defined(MS_WINDOWS) && !defined(__APPLE__)
+static int
+_PyTime_FromTimespec(_PyTime_t *tp, struct timespec *ts)
+{
+    _PyTime_t t;
+    t = (_PyTime_t)ts->tv_sec * SEC_TO_NS;
+    if (t / SEC_TO_NS != ts->tv_sec) {
+        _PyTime_overflow();
+        return -1;
+    }
+
+    t += ts->tv_nsec;
+
+    *tp = t;
+    return 0;
+}
+#endif
+
+int
+_PyTime_FromObject(_PyTime_t *t, PyObject *obj, _PyTime_round_t round)
+{
+    if (PyFloat_Check(obj)) {
+        double d, err;
+
+        /* convert to a number of nanoseconds */
+        d = PyFloat_AsDouble(obj);
+        d *= 1e9;
+
+        /* FIXME: use sign */
+        if (round == _PyTime_ROUND_UP)
+            d = ceil(d);
+        else
+            d = floor(d);
+
+        *t = (_PyTime_t)d;
+        err = d - (double)*t;
+        if (fabs(err) >= 1.0) {
+            _PyTime_overflow();
+            return -1;
+        }
+        return 0;
+    }
+    else {
+#ifdef HAVE_LONG_LONG
+        PY_LONG_LONG sec;
+        sec = PyLong_AsLongLong(obj);
+        assert(sizeof(PY_LONG_LONG) <= sizeof(_PyTime_t));
+#else
+        long sec;
+        sec = PyLong_AsLong(obj);
+        assert(sizeof(PY_LONG_LONG) <= sizeof(_PyTime_t));
+#endif
+        if (sec == -1 && PyErr_Occurred()) {
+            if (PyErr_ExceptionMatches(PyExc_OverflowError))
+                _PyTime_overflow();
+            return -1;
+        }
+        *t = sec * SEC_TO_NS;
+        if (*t / SEC_TO_NS != sec) {
+            _PyTime_overflow();
+            return -1;
+        }
+        return 0;
+    }
+}
+
+static _PyTime_t
+_PyTime_Multiply(_PyTime_t t, unsigned int multiply, _PyTime_round_t round)
+{
+    _PyTime_t k;
+    if (multiply < SEC_TO_NS) {
+        k = SEC_TO_NS / multiply;
+        if (round == _PyTime_ROUND_UP)
+            return (t + k - 1) / k;
+        else
+            return t / k;
+    }
+    else {
+        k = multiply / SEC_TO_NS;
+        return t * k;
+    }
+}
+
+_PyTime_t
+_PyTime_AsMilliseconds(_PyTime_t t, _PyTime_round_t round)
+{
+    return _PyTime_Multiply(t, 1000, round);
+}
+
+int
+_PyTime_AsTimeval(_PyTime_t t, struct timeval *tv, _PyTime_round_t round)
+{
+    _PyTime_t secs, ns;
+
+    secs = t / SEC_TO_NS;
+    ns = t % SEC_TO_NS;
+
+#ifdef MS_WINDOWS
+    /* On Windows, timeval.tv_sec is a long (32 bit),
+       whereas time_t can be 64-bit. */
+    assert(sizeof(tv->tv_sec) == sizeof(long));
+#if SIZEOF_TIME_T > SIZEOF_LONG
+    if (secs > LONG_MAX) {
+        _PyTime_overflow();
+        return -1;
+    }
+#endif
+    tv->tv_sec = (long)secs;
+#else
+    /* On OpenBSD 5.4, timeval.tv_sec is a long.
+       Example: long is 64-bit, whereas time_t is 32-bit. */
+    tv->tv_sec = secs;
+    if ((_PyTime_t)tv->tv_sec != secs) {
+        _PyTime_overflow();
+        return -1;
+    }
+#endif
+
+    if (round == _PyTime_ROUND_UP)
+        tv->tv_usec = (int)((ns + US_TO_NS - 1) / US_TO_NS);
+    else
+        tv->tv_usec = (int)(ns / US_TO_NS);
+    return 0;
+}
+
+static int
+pymonotonic_new(_PyTime_t *tp, _Py_clock_info_t *info, int raise)
+{
+#ifdef Py_DEBUG
+    static int last_set = 0;
+    static _PyTime_t last = 0;
+#endif
+#if defined(MS_WINDOWS)
+    static ULONGLONG (*GetTickCount64) (void) = NULL;
+    static ULONGLONG (CALLBACK *Py_GetTickCount64)(void);
+    static int has_gettickcount64 = -1;
+    ULONGLONG result;
+
+    assert(info == NULL || raise);
+
+    if (has_gettickcount64 == -1) {
+        /* GetTickCount64() was added to Windows Vista */
+        has_gettickcount64 = (winver.dwMajorVersion >= 6);
+        if (has_gettickcount64) {
+            HINSTANCE hKernel32;
+            hKernel32 = GetModuleHandleW(L"KERNEL32");
+            *(FARPROC*)&Py_GetTickCount64 = GetProcAddress(hKernel32,
+                                                           "GetTickCount64");
+            assert(Py_GetTickCount64 != NULL);
+        }
+    }
+
+    if (has_gettickcount64) {
+        result = Py_GetTickCount64();
+    }
+    else {
+        static DWORD last_ticks = 0;
+        static DWORD n_overflow = 0;
+        DWORD ticks;
+
+        ticks = GetTickCount();
+        if (ticks < last_ticks)
+            n_overflow++;
+        last_ticks = ticks;
+
+        result = (ULONGLONG)n_overflow << 32;
+        result += ticks;
+    }
+
+    *tp = result * MS_TO_NS;
+    if (*tp / MS_TO_NS != result) {
+        if (raise) {
+            _PyTime_overflow();
+            return -1;
+        }
+        /* Hello, time traveler! */
+        assert(0);
+    }
+
+    if (info) {
+        DWORD timeAdjustment, timeIncrement;
+        BOOL isTimeAdjustmentDisabled, ok;
+        if (has_gettickcount64)
+            info->implementation = "GetTickCount64()";
+        else
+            info->implementation = "GetTickCount()";
+        info->monotonic = 1;
+        ok = GetSystemTimeAdjustment(&timeAdjustment, &timeIncrement,
+                                     &isTimeAdjustmentDisabled);
+        if (!ok) {
+            PyErr_SetFromWindowsErr(0);
+            return -1;
+        }
+        info->resolution = timeIncrement * 1e-7;
+        info->adjustable = 0;
+    }
+
+#elif defined(__APPLE__)
+    static mach_timebase_info_data_t timebase;
+    uint64_t time;
+
+    if (timebase.denom == 0) {
+        /* According to the Technical Q&A QA1398, mach_timebase_info() cannot
+           fail: https://developer.apple.com/library/mac/#qa/qa1398/ */
+        (void)mach_timebase_info(&timebase);
+    }
+
+    time = mach_absolute_time();
+
+    /* apply timebase factor */
+    time *= timebase.numer;
+    time /= timebase.denom;
+
+    *tp = time;
+
+    if (info) {
+        info->implementation = "mach_absolute_time()";
+        info->resolution = (double)timebase.numer / timebase.denom * 1e-9;
+        info->monotonic = 1;
+        info->adjustable = 0;
+    }
+
+#else
+    struct timespec ts;
+#ifdef CLOCK_HIGHRES
+    const clockid_t clk_id = CLOCK_HIGHRES;
+    const char *implementation = "clock_gettime(CLOCK_HIGHRES)";
+#else
+    const clockid_t clk_id = CLOCK_MONOTONIC;
+    const char *implementation = "clock_gettime(CLOCK_MONOTONIC)";
+#endif
+
+    assert(info == NULL || raise);
+
+    if (clock_gettime(clk_id, &ts) != 0) {
+        if (raise) {
+            PyErr_SetFromErrno(PyExc_OSError);
+            return -1;
+        }
+        return -1;
+    }
+
+    if (info) {
+        struct timespec res;
+        info->monotonic = 1;
+        info->implementation = implementation;
+        info->adjustable = 0;
+        if (clock_getres(clk_id, &res) != 0) {
+            PyErr_SetFromErrno(PyExc_OSError);
+            return -1;
+        }
+        info->resolution = res.tv_sec + res.tv_nsec * 1e-9;
+    }
+    if (_PyTime_FromTimespec(tp, &ts) < 0)
+        return -1;
+#endif
+#ifdef Py_DEBUG
+    /* monotonic clock cannot go backward */
+    assert(!last_set || last <= *tp);
+    last = *tp;
+    last_set = 1;
+#endif
+    return 0;
+}
+
+_PyTime_t
+_PyTime_GetMonotonicClock(void)
+{
+    _PyTime_t t;
+    if (pymonotonic_new(&t, NULL, 0) < 0) {
+        /* cannot happen, _PyTime_Init() checks that pymonotonic_new() works */
+        assert(0);
+        t = 0;
+    }
+    return t;
+}
+
 int
 _PyTime_Init(void)
 {
     _PyTime_timeval tv;
+    _PyTime_t t;
+
+#ifdef MS_WINDOWS
+    winver.dwOSVersionInfoSize = sizeof(winver);
+    if (!GetVersionEx((OSVERSIONINFO*)&winver)) {
+        PyErr_SetFromWindowsErr(0);
+        return -1;
+    }
+#endif
 
     /* ensure that the system clock works */
     if (_PyTime_gettimeofday_info(&tv, NULL) < 0)
@@ -402,5 +707,9 @@ _PyTime_Init(void)
     /* ensure that the operating system provides a monotonic clock */
     if (_PyTime_monotonic_info(&tv, NULL) < 0)
         return -1;
+
+    /* ensure that the operating system provides a monotonic clock */
+    if (pymonotonic_new(&t, NULL, 1) < 0)
+        return -1;
     return 0;
 }