Use a monotonic clock to compute timeouts

Python/pytime.c

--- a/Python/pytime.c	Sun Aug 31 14:47:56 2014 +0200
+++ b/Python/pytime.c	Sun Aug 31 15:02:13 2014 +0200
@@ -3,6 +3,14 @@
 #include <windows.h>
 #endif
 
+#if defined(__APPLE__)
+#include <mach/mach_time.h>   /* mach_absolute_time(), mach_timebase_info() */
+#endif
+
+#ifdef MS_WINDOWS
+static OSVERSIONINFOEX winver;
+#endif
+
 static int
 pygettimeofday(_PyTime_timeval *tp, _Py_clock_info_t *info, int raise)
 {
@@ -112,6 +120,152 @@ int
     return pygettimeofday(tp, info, 1);
 }
 
+static int
+pymonotonic(_PyTime_timeval *tp, _Py_clock_info_t *info, int raise)
+{
+#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->tv_sec = result / 1000;
+    tp->tv_usec = (result % 1000) * 1000;
+
+    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;
+    }
+    return 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();
+
+    /* nanoseconds => microseconds */
+    time /= 1000;
+    /* apply timebase factor */
+    time *= timebase.numer;
+    time /= timebase.denom;
+    tp->tv_sec = time / (1000 * 1000);
+    tp->tv_usec = time % (1000 * 1000);
+
+    if (info) {
+        info->implementation = "mach_absolute_time()";
+        info->resolution = (double)timebase.numer / timebase.denom * 1e-9;
+        info->monotonic = 1;
+        info->adjustable = 0;
+    }
+    return 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;
+        }
+        tp->tv_sec = 0;
+        tp->tv_usec = 0;
+        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;
+    }
+    tp->tv_sec = ts.tv_sec;
+    tp->tv_usec = ts.tv_nsec / 1000;
+    return 0;
+#endif
+}
+
+void
+_PyTime_monotonic(_PyTime_timeval *tp)
+{
+    if (pymonotonic(tp, NULL, 0) < 0) {
+        /* cannot happen, _PyTime_Init() checks that pymonotonic() works */
+        assert(0);
+        tp->tv_sec = 0;
+        tp->tv_usec = 0;
+    }
+}
+
+int
+_PyTime_monotonic_info(_PyTime_timeval *tp, _Py_clock_info_t *info)
+{
+    return pymonotonic(tp, info, 1);
+}
+
 static void
 error_time_t_overflow(void)
 {
@@ -248,8 +402,21 @@ int
 _PyTime_Init(void)
 {
     _PyTime_timeval tv;
+
+#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)
         return -1;
+
+    /* ensure that the operating system provides a monotonic clock */
+    if (_PyTime_monotonic_info(&tv, NULL) < 0)
+        return -1;
     return 0;
 }