フライングWindows API待機関数

Windows APIのタイムアウト指定待機関数では、指定期間よりも僅かに早くタイムアウト発生する。この振る舞いは仕様通り(by design)とのこと。

• WaitForSingleObject, WaitForSingleObjectEx
• WaitForMultipleObjects, WaitForMultipleObjectsEx
• MsgWaitForMultipleObjects, MsgWaitForMultipleObjectsEx
• etc.

Windows OSのデフォルトタイマ割込間隔は 64 [Hz]＝15.625 [msec] となっているため、平均的に数ミリ秒だけ早くタイムアウトが発生しうる。

Wait Functions and Time-out Intervals
The accuracy of the specified time-out interval depends on the resolution of the system clock. The system clock "ticks" at a constant rate. If the time-out interval is less than the resolution of the system clock, the wait may time out in less than the specified length of time. If the time-out interval is greater than one tick but less than two, the wait can be anywhere between one and two ticks, and so on.

https://docs.microsoft.com/windows/win32/sync/wait-functions

関連URL

• (docx) Timers, Timer Resolution, and Development of Efficient Code
• http://www.windowstimestamp.com/
• https://github.com/yohhoy/yamc/pull/25