[Windows] time.sleep() should use CREATE_WAITABLE_TIMER_HIGH_RESOLUTION #89592

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1. vstinner commented on Oct 11, 2021

   

   vstinner

   on Oct 11, 2021

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   In bpo-21302, the Windows implementation of time.sleep() was modified to use a waitable timer:

   New changeset 58f8adf by Victor Stinner in branch 'main':
   bpo-21302: time.sleep() uses waitable timer on Windows (GH-28483)
   58f8adf

   It now calls the functions:

   • CreateWaitableTimerW()
   • SetWaitableTimer()
   • WaitForMultipleObjects()

   While SetWaitableTimer() has a resolution of 100 ns, the timer has a resolution of 15.6 ms in practice.

   We could use the undocumented CREATE_WAITABLE_TIMER_HIGH_RESOLUTION flag with CreateWaitableTimerEx(). See: https://bugs.python.org/issue21302#msg403550

   See also:

   • https://randomascii.wordpress.com/2013/07/08/windows-timer-resolution-megawatts-wasted/
   • https://vstinner.readthedocs.io/windows.html#time
2. vstinner

   added

   3.11only security fixesonly security fixes

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   type-featureA feature request or enhancementA feature request or enhancement

   OS-windows

   on Oct 11, 2021
3. vstinner commented on Oct 11, 2021

   

   vstinner

   on Oct 11, 2021

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   See also: https://groups.google.com/a/chromium.org/g/scheduler-dev/c/0GlSPYreJeY
4. vstinner commented on Oct 11, 2021

   

   vstinner

   on Oct 11, 2021

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   The Go programming language called timeBeginPeriod(1) to get more accurate timers. With the following change, it can now use a high resolution timer (CREATE_WAITABLE_TIMER_HIGH_RESOLUTION) to sleep:
   https://go-review.googlesource.com/c/go/+/248699/

   🚀React with 🚀1Reacted by iglak
5. vstinner commented on Oct 11, 2021

   

   vstinner

   on Oct 11, 2021

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   See also bpo-19007: "precise time.time() under Windows 8: use GetSystemTimePreciseAsFileTime".
6. eryksun commented on Oct 11, 2021

   

   eryksun

   on Oct 11, 2021

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   It's up to the core devs whether or not Python should try to use a high-resolution timer, which is currently undocumented in the Windows API and implemented only in recent releases of Windows 10 and 11. But if this does get supported, the code should fall back on creating a normal timer if CREATE_WAITABLE_TIMER_HIGH_RESOLUTION makes the call fail. For example:

       #ifndef CREATE_WAITABLE_TIMER_HIGH_RESOLUTION
       #define CREATE_WAITABLE_TIMER_HIGH_RESOLUTION 0x00000002
       #endif

       LARGE_INTEGER relative_timeout;
       // No need to check for integer overflow, both types are signed
       assert(sizeof(relative_timeout) == sizeof(timeout_100ns));
       // SetWaitableTimerEx(): a negative due time is relative
       relative_timeout.QuadPart = -timeout_100ns;
       DWORD flags = CREATE_WAITABLE_TIMER_HIGH_RESOLUTION;
   
   create_timer:
   

           HANDLE timer = CreateWaitableTimerExW(NULL, NULL, flags, TIMER_ALL_ACCESS);
           if (timer == NULL)
           {
               if (flags && GetLastError() == ERROR_INVALID_PARAMETER) {
                   // CREATE_WAITABLE_TIMER_HIGH_RESOLUTION is not supported.
                   flags = 0;
                   goto create_timer;
               }
               PyErr_SetFromWindowsErr(0);
               return -1;
           }
   
           if (!SetWaitableTimerEx(timer, &relative_timeout,
                 0,          // no period; the timer is signaled once
                 NULL, NULL, // no completion routine
                 NULL,       // no wake context; do not resume from suspend
                 0))         // no tolerable delay for timer coalescing
           {
               PyErr_SetFromWindowsErr(0);
               goto error;
           }
7. Livius90 commented on Oct 23, 2021

   

   Livius90mannequin

   on Oct 23, 2021

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   A similar solution was introduced in VirtualBox some months ago. Soon, i could get back my Windows 10 developing PC and i can try this things.

   https://www.virtualbox.org/browser/vbox/trunk/src/VBox/Runtime/r3/win/timer-win.cpp#L312
8. corona10 commented on Oct 24, 2021

   

   corona10

   on Oct 24, 2021

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   AS-IS:
   average: 0.015609736680984497

   TO-BE:
   average: 2.7387380599975585e-05

   Impressive result :)
9. corona10 commented on Nov 16, 2021

   

   corona10

   on Nov 16, 2021

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   New changeset 55868f1 by Dong-hee Na in branch 'main':
   bpo-45429: Support CREATE_WAITABLE_TIMER_HIGH_RESOLUTION if possible (GH-29203)
   55868f1
10. ambv commented on Nov 18, 2021

    

    ambv

    on Nov 18, 2021

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    New changeset fc4474e by Dong-hee Na in branch 'main':
    bpo-45429: Merge whatsnew about time.sleep (GH-29589)
    fc4474e
11. corona10

    closed this as completedon Nov 18, 2021
12. ezio-melotti

    transferred this issue fromon Apr 10, 2022
13. Livius90 commented on Nov 12, 2022

    

    Livius90

    on Nov 12, 2022

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    some test-run:
    #65501 (comment)