=============== Summary ===============

Change Set:        fix-busyWait-precision
Date:            28 March 2022
Author:            Christoph Thiede

Fixes #busyWait for durations < 1 milliSecond. Since the original proposal (Chronology-Core-ct.67), the implementation had been moved from Duration to Delay (Chronology-Core-mt.71). However, Delay has only milliseconds precision, causing shorter durations to be handled as a delayDuration of 0 milliSeconds and leading to this erroneous output:

    [1 microSeconds busyWait] bench '6,240,000 per second. 160 nanoseconds per run. 0.67973 % GC time.'

Moves #busyWait implementation back to Duration and invokes it from Delay. Not sure whether we need the latter hook, though.

=============== Diff ===============

Delay>>busyWait {delaying} · ct 3/28/2022 22:36 (changed)
busyWait
-     "BEWARE! This method is more precise than #wait, but it sacrifices many CPU cycles for that precision. Also note that the GC runs more often. Also note that only processes with a higher priority can run while waiting.
-     
-     The following lists the precision (in milliseconds) of #wait on a Microsoft Surface Pro 6, Windows 10 21H1, OSVM 202104182333:
-         100 -> 100
-         50 -> 51.1 ... 102.2%
-         10 -> 11.6 ... 105.5% ... maybe use #busyWait
-         5 -> 5.93 ... 118.6% ... use #busyWait but check process priorities
-         1 -> 1.41 ... 141.0% ... use #busyWait but check process priorities
-     
-     As of July 2021, the shortest delay that we can guarantee on all platforms is still 1 millisecond as the value of #utcMicrosecondClock might not change any faster than that. For more information, see http://lists.squeakfoundation.org/pipermail/squeak-dev/2021-July/215928.html"
-     
-     "[5 milliSeconds busyWait] bench"
+     "BEWARE! This method is more precise than #wait, but it sacrifices many CPU cycles for that precision. Also note that the GC runs more often. Also note that only processes with a higher priority can run while waiting. See more detailed commentary in Duration >> #busyWait."

-     | proceedTime |
-     proceedTime := Time utcMicrosecondClock + (delayDuration "milliseconds" * 1000).
-     [Time utcMicrosecondClock >= proceedTime] whileFalse.
+     ^ self delayDuration microSeconds busyWait

Duration>>busyWait {squeak protocol} · ct 3/28/2022 22:39 (changed)
busyWait
-     "BEWARE! This method is more precise than #wait, but it sacrifices many CPU cycles for that precision. Also note that only processes with a higher priority can run while waiting. See more detailed commentary in Delay >> #busyWait."
+     "BEWARE! This method is more precise than #wait, but it sacrifices many CPU cycles for that precision. Also note that the GC runs more often. Also note that only processes with a higher priority can run while waiting.
+     
+     The following lists the precision (in milliseconds) of #wait on a Microsoft Surface Pro 6, Windows 10 21H1, OSVM 202104182333:
+         100 -> 100
+         50 -> 51.1 ... 102.2%
+         10 -> 11.6 ... 105.5% ... maybe use #busyWait
+         5 -> 5.93 ... 118.6% ... use #busyWait but check process priorities
+         1 -> 1.41 ... 141.0% ... use #busyWait but check process priorities
+     
+     As of July 2021, the shortest delay that we can guarantee on all platforms is still 1 millisecond as the value of #utcMicrosecondClock might not change any faster than that. For more information, see http://lists.squeakfoundation.org/pipermail/squeak-dev/2021-July/215928.html"
+     
+     "[5 milliSeconds busyWait] bench"

-     ^ self asDelay busyWait
+     | proceedTime |
+     proceedTime := Time utcMicrosecondClock + self asMicroSeconds.
+     [Time utcMicrosecondClock >= proceedTime] whileFalse.

["fix-busyWait-precision.1.cs"]

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