[Vm-dev] How does Time>millisecondClockValue get a resolution of 1 millisecond?

[Eliot Miranda]

On Wed, Aug 8, 2012 at 2:50 PM, Eliot Miranda <eliot.miranda at gmail.com>wrote:

> Hi Louis,
>
> On Wed, Aug 8, 2012 at 1:12 PM, Louis LaBrunda <Lou at keystone-software.com>wrote:
>
>>
>> Hi VM Guys,
>>
>> How does Squeak's Time>millisecondClockValue get a resolution of 1
>> millisecond?  It is primitive: 135.  I thought it was based upon an OS
>> function that kept a millisecond clock from when the OS was booted like in
>> my case for Windows GetTickCount.  The resolution of the GetTickCount
>> function is limited to the resolution of the system timer, which is
>> typically in the range of 10 milliseconds to 16 milliseconds.
>>
>> On my machine with VA Smalltalk the resolution seems to be about 15
>> milliseconds.  Yet, in Squeak it is 1 millisecond.  So it would seem the
>> Squeak VM is using something else.
>>
>
> Well, things are different across platforms, and different between the Cog
> and the Interpreter VMs.  But on WIndows millisecond time is derived from
> timeGetTime, which answers milliseconds since Windows booted.  The
> different between Cog and the Interpreter is that the Interpreter accesses
> timeGetTime directly to answer milliseconds, whereas Cog updates the time
> in a background thread every 1 or two milliseconds, and answers the saved
> value.  So you may see the effective resolution in Cog be only 2
> milliseconds, not 1.
>

Oh, and importantly, the VM ups the resolution of timeGetTime() via
timeBeginPeriod to 1 millisecond if possible.


>
> HTH
> Eliot
>
>
>>
>> Lou
>> -----------------------------------------------------------
>> Louis LaBrunda
>> Keystone Software Corp.
>> SkypeMe callto://PhotonDemon
>> mailto:Lou at Keystone-Software.com http://www.Keystone-Software.com
>>
>>
>
>
> --
> best,
> Eliot
>
>


-- 
best,
Eliot
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