bpo-31415: Add _PyTime_GetPerfCounter() and use it for -X importtime (#3936)

* Add _PyTime_GetPerfCounter()
* Use _PyTime_GetPerfCounter() for -X importtime

Include/pytime.h

@@ -192,6 +192,22 @@ PyAPI_FUNC(int) _PyTime_localtime(time_t t, struct tm *tm);
    Return 0 on success, raise an exception and return -1 on error. */
 PyAPI_FUNC(int) _PyTime_gmtime(time_t t, struct tm *tm);
 
+#ifdef MS_WINDOWS
+PyAPI_FUNC(int) _PyTime_GetWinPerfCounterWithInfo(
+    _PyTime_t *t,
+    _Py_clock_info_t *info);
+#endif
+
+/* Get the performance counter: clock with the highest available resolution to
+   measure a short duration. */
+PyAPI_FUNC(_PyTime_t) _PyTime_GetPerfCounter(void);
+
+/* Similar to _PyTime_GetPerfCounter(),
+   but get also clock info if info is non-NULL. */
+PyAPI_FUNC(int) _PyTime_GetPerfCounterWithInfo(
+    _PyTime_t *t,
+    _Py_clock_info_t *info);
+
 #ifdef __cplusplus
 }
 #endif

Modules/timemodule.c

@@ -60,6 +60,13 @@ Fractions of a second may be present if the system clock provides them.");
 #endif
 #endif
 
+static PyObject*
+_PyFloat_FromPyTime(_PyTime_t t)
+{
+    double d = _PyTime_AsSecondsDouble(t);
+    return PyFloat_FromDouble(d);
+}
+
 static PyObject *
 floatclock(_Py_clock_info_t *info)
 {
@@ -81,47 +88,19 @@ floatclock(_Py_clock_info_t *info)
 }
 #endif /* HAVE_CLOCK */
 
-#ifdef MS_WINDOWS
-#define WIN32_PERF_COUNTER
-/* Win32 has better clock replacement; we have our own version, due to Mark
-   Hammond and Tim Peters */
-static PyObject*
-win_perf_counter(_Py_clock_info_t *info)
-{
-    static LONGLONG cpu_frequency = 0;
-    static LONGLONG ctrStart;
-    LARGE_INTEGER now;
-    double diff;
-
-    if (cpu_frequency == 0) {
-        LARGE_INTEGER freq;
-        QueryPerformanceCounter(&now);
-        ctrStart = now.QuadPart;
-        if (!QueryPerformanceFrequency(&freq) || freq.QuadPart == 0) {
-            PyErr_SetFromWindowsErr(0);
-            return NULL;
-        }
-        cpu_frequency = freq.QuadPart;
-    }
-    QueryPerformanceCounter(&now);
-    diff = (double)(now.QuadPart - ctrStart);
-    if (info) {
-        info->implementation = "QueryPerformanceCounter()";
-        info->resolution = 1.0 / (double)cpu_frequency;
-        info->monotonic = 1;
-        info->adjustable = 0;
-    }
-    return PyFloat_FromDouble(diff / (double)cpu_frequency);
-}
-#endif   /* MS_WINDOWS */
-
-#if defined(WIN32_PERF_COUNTER) || defined(HAVE_CLOCK)
+#if defined(MS_WINDOWS) || defined(HAVE_CLOCK)
 #define PYCLOCK
 static PyObject*
 pyclock(_Py_clock_info_t *info)
 {
-#ifdef WIN32_PERF_COUNTER
-    return win_perf_counter(info);
+#ifdef MS_WINDOWS
+    /* Win32 has better clock replacement; we have our own version, due to Mark
+       Hammond and Tim Peters */
+    _PyTime_t t;
+    if (_PyTime_GetWinPerfCounterWithInfo(&t, info) < 0) {
+        return NULL;
+    }
+    return _PyFloat_FromPyTime(t);
 #else
     return floatclock(info);
 #endif
@@ -939,13 +918,11 @@ static PyObject *
 pymonotonic(_Py_clock_info_t *info)
 {
     _PyTime_t t;
-    double d;
     if (_PyTime_GetMonotonicClockWithInfo(&t, info) < 0) {
         assert(info != NULL);
         return NULL;
     }
-    d = _PyTime_AsSecondsDouble(t);
-    return PyFloat_FromDouble(d);
+    return _PyFloat_FromPyTime(t);
 }
 
 static PyObject *
@@ -962,11 +939,11 @@ Monotonic clock, cannot go backward.");
 static PyObject*
 perf_counter(_Py_clock_info_t *info)
 {
-#ifdef WIN32_PERF_COUNTER
-    return win_perf_counter(info);
-#else
-    return pymonotonic(info);
-#endif
+    _PyTime_t t;
+    if (_PyTime_GetPerfCounterWithInfo(&t, info) < 0) {
+        return NULL;
+    }
+    return _PyFloat_FromPyTime(t);
 }
 
 static PyObject *
@@ -1448,13 +1425,11 @@ static PyObject*
 floattime(_Py_clock_info_t *info)
 {
     _PyTime_t t;
-    double d;
     if (_PyTime_GetSystemClockWithInfo(&t, info) < 0) {
         assert(info != NULL);
         return NULL;
     }
-    d = _PyTime_AsSecondsDouble(t);
-    return PyFloat_FromDouble(d);
+    return _PyFloat_FromPyTime(t);
 }
 
 

Python/import.c

@@ -1695,7 +1695,7 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
 
         if (ximporttime) {
             import_level++;
-            t1 = _PyTime_GetMonotonicClock();
+            t1 = _PyTime_GetPerfCounter();
             accumulated = 0;
         }
 
@@ -1711,7 +1711,7 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
                                            mod != NULL);
 
         if (ximporttime) {
-            _PyTime_t cum = _PyTime_GetMonotonicClock() - t1;
+            _PyTime_t cum = _PyTime_GetPerfCounter() - t1;
 
             import_level--;
             fprintf(stderr, "import time: %9ld | %10ld | %*s%s\n",

Python/pytime.c

@@ -285,8 +285,8 @@ _PyTime_FromTimeval(_PyTime_t *tp, struct timeval *tv, int raise)
 #endif
 
 static int
-_PyTime_FromFloatObject(_PyTime_t *t, double value, _PyTime_round_t round,
-                        long unit_to_ns)
+_PyTime_FromDouble(_PyTime_t *t, double value, _PyTime_round_t round,
+                   long unit_to_ns)
 {
     /* volatile avoids optimization changing how numbers are rounded */
     volatile double d;
@@ -315,7 +315,7 @@ _PyTime_FromObject(_PyTime_t *t, PyObject *obj, _PyTime_round_t round,
             PyErr_SetString(PyExc_ValueError, "Invalid value NaN (not a number)");
             return -1;
         }
-        return _PyTime_FromFloatObject(t, d, round, unit_to_ns);
+        return _PyTime_FromDouble(t, d, round, unit_to_ns);
     }
     else {
         long long sec;
@@ -779,19 +779,80 @@ _PyTime_GetMonotonicClockWithInfo(_PyTime_t *tp, _Py_clock_info_t *info)
     return pymonotonic(tp, info, 1);
 }
 
+
+#ifdef MS_WINDOWS
 int
-_PyTime_Init(void)
+_PyTime_GetWinPerfCounterWithInfo(_PyTime_t *t, _Py_clock_info_t *info)
+{
+    static LONGLONG cpu_frequency = 0;
+    static LONGLONG ctrStart;
+    LARGE_INTEGER now;
+    double diff;
+
+    if (cpu_frequency == 0) {
+        LARGE_INTEGER freq;
+        QueryPerformanceCounter(&now);
+        ctrStart = now.QuadPart;
+        if (!QueryPerformanceFrequency(&freq) || freq.QuadPart == 0) {
+            PyErr_SetFromWindowsErr(0);
+            return -1;
+        }
+        cpu_frequency = freq.QuadPart;
+    }
+    QueryPerformanceCounter(&now);
+    diff = (double)(now.QuadPart - ctrStart);
+    if (info) {
+        info->implementation = "QueryPerformanceCounter()";
+        info->resolution = 1.0 / (double)cpu_frequency;
+        info->monotonic = 1;
+        info->adjustable = 0;
+    }
+
+    diff = diff / (double)cpu_frequency;
+    return _PyTime_FromDouble(t, diff, _PyTime_ROUND_FLOOR, SEC_TO_NS);
+}
+#endif
+
+
+int
+_PyTime_GetPerfCounterWithInfo(_PyTime_t *t, _Py_clock_info_t *info)
+{
+#ifdef MS_WINDOWS
+    return _PyTime_GetWinPerfCounterWithInfo(t, info);
+#else
+    return _PyTime_GetMonotonicClockWithInfo(t, info);
+#endif
+}
+
+
+_PyTime_t
+_PyTime_GetPerfCounter(void)
 {
     _PyTime_t t;
+    if (_PyTime_GetPerfCounterWithInfo(&t, NULL) < 0) {
+        /* should not happen, _PyTime_Init() checked the clock at startup */
+        Py_UNREACHABLE();
+    }
+    return t;
+}
 
-    /* ensure that the system clock works */
-    if (_PyTime_GetSystemClockWithInfo(&t, NULL) < 0)
-        return -1;
 
-    /* ensure that the operating system provides a monotonic clock */
-    if (_PyTime_GetMonotonicClockWithInfo(&t, NULL) < 0)
+int
+_PyTime_Init(void)
+{
+    /* check that the 3 most important clocks are working properly
+       to not have to check for exceptions at runtime. If a clock works once,
+       it cannot fail in next calls. */
+    _PyTime_t t;
+    if (_PyTime_GetSystemClockWithInfo(&t, NULL) < 0) {
         return -1;
-
+    }
+    if (_PyTime_GetMonotonicClockWithInfo(&t, NULL) < 0) {
+        return -1;
+    }
+    if (_PyTime_GetPerfCounterWithInfo(&t, NULL) < 0) {
+        return -1;
+    }
     return 0;
 }