Fix of flaky timedwait on Windows #115
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The Windows implementation of `lf_timed_wait` calculates between the timepoint to wait until and the current physical time. In some seldom cases, the current physical time could already be larger then the specified timepoint. This will lead to a negative delay to `SleepConditionVariableCS`. While the documentation does not specify this precisely, experimentation showed that negative delays are interpreted as infinite delays and hence the program would block forever. This fix makes to changes. First, it checks for negative delays and returns without waiting if the delay is less or equal to zero. Second, the number of milliseconds tow wait for is rounded up in order to prevent unnecessary busy waiting when the call to `SleepConditionVariableCS` returns early.
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Thank you Christian! |
Co-authored-by: Peter Donovan <[email protected]>
edwardalee
approved these changes
Oct 7, 2022
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Great catch about the negative time interval! This looks like a good solution to me, but rounding up does mean that time precision below one ms will be impossible on Windows machines. E.g., any deadline below 1 ms is likely to be violated. But this probably true anyway on any non-RTOS because of the OS jiffy interval (or whatever it is called in Windows).
lhstrh
changed the title
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The Windows implementation of
lf_timed_waitcalculates the difference between the timepoint to wait until and the current physical time. In some seldom cases, the current physical time could already be larger then the specified timepoint. This will lead to a negative delay passed toSleepConditionVariableCS. While the documentation does not specify this precisely, experimentation showed that negative delays are interpreted as infinite delays and hence the program would block forever.This fix makes two changes. First, it checks for negative delays and returns without waiting if the delay is less or equal to zero. Second, the number of milliseconds to wait for is rounded up in order to prevent unnecessary busy waiting when the call to
SleepConditionVariableCSreturns early.