On Sun, Mar 13, 2016 at 1:47 AM, Aliaksei Syrel <alex.syrel@gmail.com> wrote:
Hi

At some point I got a feeling that actual Delay time is longer than expected. It is especially visible on small delays less than 100ms (otherwise difference is < 1%).

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Documentation says that Delay waits approximately for��specified��amount of time. However, according to experimental data an actual difference is always positive with the value around 1.5-2 seconds. It is actually strange where such a constant difference, independent from delay length, comes from.
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To conclude, if you want to wait more precisely you need to create delays with duration 1.5 seconds less than expected. Also it would be interesting to test on different hardwares to make sure that difference stays constant (around 1.5-2s)

I used the following script to gather data and save in .csv file

Tested on:
Pharo: #50636
Spur-VM: #463
OS: Mac OS Yosemite
CPU: Intel Core i7 2.39 GHz


Nice analysis.�� I've previously wondered about such an effect from resumptionTime being calculated by the high priority thread in #handleTimerEvent: and thus delayed by switching threads, rather than being calculated as-soon-as-possible by the low priority process when #schedule: is called. �� I can't remember my line of reasoning, but doing it the low priority process seemed to open the potential for nasty race conditions, so I left it as I found it.�� Perhaps we should take a time snapshot in the #schedule: and pass that through to #handleTimerEvent: similar to scheduledDelay.�� Would you like to try that?

btw, I have some cleanup of DelayScheduler almost complete that I had meant to get into Pharo 5 earlier, but now I think best to wait for early Pharo 6.

cheers -ben��