Increase internal Windows timer rates

[Flova]

By default windows timing is only accurate to about ~15ms. Things like time.monotonic() tick with only that rate even if the datatype would allow for higher prescision. This is a common issue for things like Games as well, so newer windows versions offer ways to boost the scheduler rate. Fyi this does not only concern ROS timers, even if they might be affected by it.

In the past this has lead to a number of issues, that have been fixed mostly in a symptomatic manner. Some of them include:

• Timer related tests experience more jitter on windows #513 (this one even describes a low res tick step pattern, which is a result of this issue)
• Timer tests fail sporadically #267
• 👩‍🌾 Regression on TestExecutor.test_create_task_coroutine_wake_from_another_thread #1562
• Fix windows regression: Increase clock accuracy #1564 (additional flaky test noticed during the fix of 👩‍🌾 Regression on TestExecutor.test_create_task_coroutine_wake_from_another_thread #1562)

The following PR includes a bit of off-topic discussion, including some simple experiments, regarding this isuue: #1563

As originally suggested by (@traversaro) possible fix could include something like this during the start/stop of rclpy:

WindowsSchedulerBooster()
{
#if defined(_WIN32)
    // Only affects Windows systems.
    TIMECAPS tm; // Stores system timer capabilities.
    // Get the minimum timer resolution supported by the system.
    timeGetDevCaps(&tm, sizeof(TIMECAPS));
    // Set the system timer resolution to the minimum value for higher precision.
    timeBeginPeriod(tm.wPeriodMin);
#endif
}

~WindowsSchedulerBooster()
{
#if defined(_WIN32)
    // Only affects Windows systems.
    TIMECAPS tm; // Stores system timer capabilities.
    // Get the minimum timer resolution supported by the system.
    timeGetDevCaps(&tm, sizeof(TIMECAPS));
    // Restore the system timer resolution to the default value.
    timeEndPeriod(tm.wPeriodMin);
#endif
}

Here is a blog post that talks about timer accuracy in windows: https://www.siliceum.com/en/blog/post/windows-high-resolution-timers/

[mjcarroll]

I think this would be an interesting experiment. Do you think you could open a PR?

[Flova]

Here is another application that has logic like this: https://github.com/instamatic-dev/instamatic/blob/main/src/instamatic/utils/high_precision_timers.py

[Flova]

I did a quick and dirty test using only python and the ctypes module and the suggested code works (or my python port of it), constistently improving a the timer in a small python test node I build:

Without boosting:

import rclpy
import time
from rclpy.node import Node

rclpy.init(args=None)

n = Node("test")

t1 = time.perf_counter()

counter = 0

def cb():
    global counter
    counter+=1
    if counter == 100:
        print("Mean Interval", (time.perf_counter() - t1)/100)
        rclpy.shutdown()

n.create_timer(0.01, cb)
rclpy.spin(n)

Result:

Mean Interval 0.015458337000018219

With boosted sheduler:

import sys
import ctypes
from ctypes import wintypes

import rclpy
import time
from rclpy.node import Node


_winmm = ctypes.WinDLL('winmm')

# UINT timeBeginPeriod(UINT uPeriod);
_winmm.timeBeginPeriod.argtypes = (wintypes.UINT,)
_winmm.timeBeginPeriod.restype  = wintypes.UINT

# UINT timeEndPeriod(UINT uPeriod);
_winmm.timeEndPeriod.argtypes  = (wintypes.UINT,)
_winmm.timeEndPeriod.restype   = wintypes.UINT

# MMRESULT timeGetDevCaps(LPTIMECAPS ptc, UINT cbtc);
class TIMECAPS(ctypes.Structure):
    _fields_ = [('wPeriodMin', wintypes.UINT),
                ('wPeriodMax', wintypes.UINT)]

_winmm.timeGetDevCaps.argtypes = (ctypes.POINTER(TIMECAPS), wintypes.UINT)
_winmm.timeGetDevCaps.restype  = wintypes.UINT   # MMRESULT

def _get_min_timer_resolution() -> int:
    """Return the smallest period (in milliseconds) the system can support."""
    caps = TIMECAPS()
    res = _winmm.timeGetDevCaps(ctypes.byref(caps), ctypes.sizeof(caps))
    if res != 0:                     # non‑zero = MMSYSERR error
        raise RuntimeError(f'timeGetDevCaps failed, error {res}')
    return caps.wPeriodMin

period = _get_min_timer_resolution()
err = _winmm.timeBeginPeriod(period)

rclpy.init(args=None)

n = Node("test")

t1 = time.perf_counter()

counter = 0

def cb():
    global counter
    counter+=1
    if counter == 100:
        print("Mean Interval", (time.perf_counter() - t1)/100)
        rclpy.shutdown()

n.create_timer(0.01, cb)
rclpy.spin(n)

_winmm.timeEndPeriod(period)

Result:

Mean Interval 0.010003618999980972

[Flova]

Where would be the best place to add this? Or should we do this in a fully ROS independent manner and make a seperate PyPi package that does this if it is imported by the process?