pythongh-63207: Use GetSystemTimePreciseAsFileTime() in time.time()

vstinner · Mar 14, 2024 · 85790f4 · 85790f4
1 parent b54d7c8
commit 85790f4
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Showing 3 changed files with 25 additions and 15 deletions.
diff --git a/Doc/whatsnew/3.13.rst b/Doc/whatsnew/3.13.rst
@@ -560,6 +560,12 @@ time
   instead of the ``GetTickCount64()`` clock which has a resolution of 15.6 ms.
   (Contributed by Victor Stinner in :gh:`88494`.)
 
+* On Windows, :func:`time.time()` now uses the
+  ``GetSystemTimePreciseAsFileTime()`` clock to have a resolution better
+  than 1 us, instead of the ``GetSystemTimeAsFileTime()`` clock which has a
+  resolution of 15.6 ms.
+  (Contributed by Victor Stinner in :gh:`63207`.)
+
 
 tkinter
 -------

diff --git a/Misc/NEWS.d/next/Library/2024-03-14-17-21-25.gh-issue-63207.LV16SL.rst b/Misc/NEWS.d/next/Library/2024-03-14-17-21-25.gh-issue-63207.LV16SL.rst
@@ -0,0 +1,4 @@
+On Windows, :func:`time.time()` now uses the
+``GetSystemTimePreciseAsFileTime()`` clock to have a resolution better than 1
+us, instead of the ``GetSystemTimeAsFileTime()`` clock which has a resolution
+of 15.6 ms. Patch by Victor Stinner.
diff --git a/Python/pytime.c b/Python/pytime.c
@@ -895,7 +895,7 @@ py_get_system_clock(PyTime_t *tp, _Py_clock_info_t *info, int raise_exc)
     FILETIME system_time;
     ULARGE_INTEGER large;
 
-    GetSystemTimeAsFileTime(&system_time);
+    GetSystemTimePreciseAsFileTime(&system_time);
     large.u.LowPart = system_time.dwLowDateTime;
     large.u.HighPart = system_time.dwHighDateTime;
     /* 11,644,473,600,000,000,000: number of nanoseconds between
@@ -904,18 +904,17 @@ py_get_system_clock(PyTime_t *tp, _Py_clock_info_t *info, int raise_exc)
     PyTime_t ns = large.QuadPart * 100 - 11644473600000000000;
     *tp = ns;
     if (info) {
-        DWORD timeAdjustment, timeIncrement;
-        BOOL isTimeAdjustmentDisabled, ok;
+        // GetSystemTimePreciseAsFileTime() is implemented using
+        // QueryPerformanceCounter() internally.
+        if (py_qpc_base.denom == 0) {
+            if (py_win_perf_counter_frequency(&py_qpc_base, raise_exc) < 0) {
+                return -1;
+            }
+        }
 
-        info->implementation = "GetSystemTimeAsFileTime()";
+        info->implementation = "GetSystemTimePreciseAsFileTime()";
         info->monotonic = 0;
-        ok = GetSystemTimeAdjustment(&timeAdjustment, &timeIncrement,
-                                     &isTimeAdjustmentDisabled);
-        if (!ok) {
-            PyErr_SetFromWindowsErr(0);
-            return -1;
-        }
-        info->resolution = timeIncrement * 1e-7;
+        info->resolution = _PyTimeFraction_Resolution(&py_qpc_base);
         info->adjustable = 1;
     }
 
@@ -1057,22 +1056,23 @@ py_win_perf_counter_frequency(_PyTimeFraction *base, int raise_exc)
 }
 
 
+static _PyTimeFraction py_qpc_base = {0, 0};
+
 // N.B. If raise_exc=0, this may be called without the GIL.
 static int
 py_get_win_perf_counter(PyTime_t *tp, _Py_clock_info_t *info, int raise_exc)
 {
     assert(info == NULL || raise_exc);
 
-    static _PyTimeFraction base = {0, 0};
-    if (base.denom == 0) {
-        if (py_win_perf_counter_frequency(&base, raise_exc) < 0) {
+    if (py_qpc_base.denom == 0) {
+        if (py_win_perf_counter_frequency(&py_qpc_base, raise_exc) < 0) {
             return -1;
         }
     }
 
     if (info) {
         info->implementation = "QueryPerformanceCounter()";
-        info->resolution = _PyTimeFraction_Resolution(&base);
+        info->resolution = _PyTimeFraction_Resolution(&py_qpc_base);
         info->monotonic = 1;
         info->adjustable = 0;
     }