[Vm-dev] We need help from VM experts. Re: Freeze after Morph& nbsp; & nbsp; & nbsp; & nbsp; Activity

[Eliot Miranda]

Hi David,

On Mon, Mar 6, 2017 at 5:50 PM, David T. Lewis <lewis at mail.msen.com> wrote:

>
> In the VM, the millisecond clock wraps within the 32 bit integer range:
>
>   #define MillisecondClockMask 0x1FFFFFFF
>
> In the Cuis image, Delay class>>handleTimerEvent does this:
>
>   nextTick := nextTick min: SmallInteger maxVal.
>
> On a 64-bit Spur image, SmallInteger maxVal is 16rFFFFFFFFFFFFFFF, but on
> a 32-bit image it is 16r3FFFFFFF.
>
> Could that be it?
>
> I don't really know how to test in Squeak. As you say, Squeak is now
> using the microsecond clock in #handleTimerEvent. I do not see anything
> in primitiveSignalAtMilliseconds that would behave any differently on
> a 64 bit versus 32 bit image or VM, but I do not know how to test to
> be sure.
>

I bet that the following code from primitiveSignalAtMilliseconds ends up
wrapping when given
    Delay primSignal: s atMilliseconds: Time primMillisecondClock - 10.

deltaMsecs := msecs - (self ioMSecs bitAnd: MillisecondClockMask).
deltaMsecs < 0 ifTrue:
[deltaMsecs := deltaMsecs + MillisecondClockMask + 1].
nextWakeupUsecs := self ioUTCMicroseconds + (deltaMsecs * 1000).

and I bet you'll find that the VM will wake up in about 6 days and 5 hours
;-)


I suppose we could fix this, but I'm *much* happier to simply not use
primitiveSignalAtMilliseconds and stay with the simpler and wrapping-immune
primitiveSignalAtUTCMicroseconds


> Dave
>
>
> On Mon, Mar 06, 2017 at 11:06:22AM -0300, Juan Vuletich wrote:
> >
> > I finally understood what was happening. The problem with is primitive
> 136:
> >
> > primSignal: aSemaphore atMilliseconds: aSmallInteger
> >     "Signal the semaphore when the millisecond clock reaches the value
> > of the second argument. Fail if the first argument is neither a
> > Semaphore nor nil. Essential. See Object documentation whatIsAPrimitive."
> > <primitive: 136>
> >     ^self primitiveFailed
> >
> > If the requested tick is already in the past, all the VMs except for
> > Spur-64 will signal the semaphore anyway. Spur-64 won't. Taking care of
> > this in the Cuis image was easy enough.
> >
> > Squeak seems not to be affected because it uses a newer primitive, that
> > takes the large integer microsecond ticker, that might have the older
> > behavior (signaling anyway). I'm not really sure, and maybe someone
> > could check the primitive behavior and the corresponding assumptions in
> > Squeak.
> >
> > Older Squeak images are not affected, as they are all 32-bit. So maybe
> > there's no action required. In any case, making the behavior consistent
> > across VMs and in both primitives would be nice.
> >
> > Cheers,
> >
> > On 3/3/2017 3:55 PM, Juan Vuletich wrote:
> > >
> > >
> > >
> > >Hi Folks,
> > >
> > >Today, I was able to get closer to the origin of the problem. The
> > >problem is when Morphic tries to do a Delay (inter-cycle-pause) of 1
> > >or two milliseconds. (Usually they are quite larger, and the problem
> > >does not appear). With the 64-bit VM, sometimes very short delays hang
> > >the complete system. I don't know why, but this:
> > >
> > >waitDelay _ Delay forMilliseconds: 50.
> > >[ true ] whileTrue: [
> > >    1000 atRandom print.
> > >    waitDelay setDelay: 1; wait ].
> > >
> > >is enough to hang Cuis in a short time. When trying to reproduce the
> > >problem in Squeak I had mixed results. It doesn't seem to hang there,
> > >but if I let this run for a couple of minutes and then try to halt
> > >with alt-. , then the hang occurs, and Squeak becomes irresponsibe. As
> > >a workaround, in Cuis in the inter cycle pause, I'm avoiding very
> > >short delays.
> > >
> > >I'm not sure if the bug is in the VM, in  the image, or both, but it
> > >is still there, and it also affects Squeak. I haven't tried it, but
> > >Pharo might also have the problem (if not, it can show a possible
> > >solution).
> > >
> > >BTW, Bert, I guess Squeak never does short delays in #interCyclePause:
> ...
> > >
> > >Thanks,
> > >
> > >On 2/6/2017 12:28 PM, Bert Freudenberg wrote:
> > >>
> > >>
> > >>
> > >>Yes, I tried with Spur64. Have not seen it freeze yet on Mac in
> > >>Squeak, but we possibly have not replicated the test well enough yet.
> > >>
> > >>It *did* freeze in Cuis Spur64 on Mac too.
> > >>
> > >>- Bert -
> > >>
> > >>On Mon, Feb 6, 2017 at 2:08 PM, Juan Vuletich <juanvuletich at zoho.com
> > >><mailto:juanvuletich at zoho.com>> wrote:
> > >>
> > >>
> > >>    Were you usig Spur64? On Debian it does not freeze with CogV3 or
> > >>    Spur32. Only with Spur64.
> > >>
> > >>    Thanks,
> > >>    Juan
> > >>
> > >>    Sent using Zoho Mail <https://www.zoho.com/mail/>
> > >>
> > >>
> > >>        ---- On Mon, 06 Feb 2017 09:19:48 -0300 *bert at freudenbergs.de
> > >>        <mailto:bert at freudenbergs.de> * wrote ----
> > >>
> > >>        On Mon, Feb 6, 2017 at 3:15 AM, David T. Lewis
> > >>        <lewis at mail.msen.com <mailto:lewis at mail.msen.com>> wrote:
> > >>
> > >>            It would be interesting to try reproducing this in a
> > >>            Squeak image, but I
> > >>            have not quite figured out how to make the Tokenish
> > >>            example work in Squeak.
> > >>
> > >>
> > >>        See attachment. Did not freeze on Mac with 10 Tokenish jumping.
> > >>        - Bert -
> > >>
> > >>
> > >>
> > >
> > >
> > >--
> > >Juan Vuletich
> > >www.cuis-smalltalk.org
> > >https://github.com/Cuis-Smalltalk/Cuis-Smalltalk-Dev
> > >@JuanVuletich
> >
> >
> > --
> > Juan Vuletich
> > www.cuis-smalltalk.org
> > https://github.com/Cuis-Smalltalk/Cuis-Smalltalk-Dev
> > @JuanVuletich
> >
>
>


-- 
_,,,^..^,,,_
best, Eliot
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.squeakfoundation.org/pipermail/vm-dev/attachments/20170309/b85a6436/attachment.html>