[Vm-dev] [ANN] ARM Stack VMs available

[J. Vuletich (mail lists)]

Hi Folks,

The Squeak process scheduler usually preempts a process only by  
another one of higher priority. And when the scheduler is ready to go  
back at the lower priority, it will always resume the same process  
that was last suspended. The only way for two or more processes of the  
same priority to share the processor is when the running process calls  
#wait or #yield.

This means that using shared state from several processes at the same  
priority (without using any locking mechanism, such as Semaphores,  
Monitors or critical sections) is safe, as long as the processes do  
#wait or #yield only when that shared state is in a consistent state.

It looks like this ARM VM is somehow not following this convention. If  
this was the case, the problems Ken sees are to be expected.

HTH,
Juan Vuletich

Quoting Douglas McPherson <djm1329 at san.rr.com>:

> Hi Ken,
>
>> On Nov 11, 2014, at 16:28, Ken Dickey <Ken.Dickey at whidbey.com> wrote:
>>
>>
>> On Sun, 9 Nov 2014 20:56:47 -0800
>> Douglas McPherson <djm1329 at san.rr.com> wrote:
>>
>> KenD>>
>>>> The stkspurlinuxhtARM VM, however, complains:
>>>> This interpreter (vers. 6521) cannot read image file (vers. 6505).
>>>>
>>>> I presume some conversion is required to get the image into SPUR format?
>>>>
>>> Yes, the Spur VMs require a new image format. There are recent  
>>> Squeak trunk images in the spur format on Eliot’s site. I’ll let  
>>> Eliot and others comment about how a Cuis image might be converted.
>>
>> I tried out the Squeak SPUR image from the Cog site and everything  
>> Squeak seems fine.
>>
>>
>> There is a timing bug with Cuis redraw that shows up on both the  
>> stklinuxhtARM vm and the one you sent me earlier.
>>
>> Basically, I am using DisplayObject>>slideFrom:to:nSteps:delay: to  
>> do some animation.  When multiple timer events fire during an  
>> animation it sometimes appears that the x,y redraw origin is used  
>> from the currently drawing morph's position, not 0,0.  I.e. part of  
>> the redisplay is offset.  [Display redraw via menu corrects the  
>> display].
>>
>> This _only_ happens on the Samsung ARM Chromebook, never on Intel CPUs.
>>
>
> Thanks for reporting this. I’ll try to look into it. There are  
> definitely ARM-specific changes to support certain atomic  
> operations, so there may be something not quite right with these.
>
> Can you suggest a method for reproducing this in Squeak? I  
> repeatedly sent morphs to the trash (with appropriate preference set  
> to enable the animation) but didn’t see an issue. I suspect I’m not  
> driving it hard enough.
>
>> My life is really, really busy right now, so I have never had time  
>> to dig into this.  I can redraw the display, so a workaround exists.
>>
>> [One possible resource.  The Apache Portable Runtime,  
>> http://apr.apache.org/ , implements compareAndSwap and various  
>> other atomic operations across various OSs.]
>>
>
> Thanks for the reference. It may be useful. I also found a library  
> called Mintomic  
> (http://preshing.com/20130505/introducing-mintomic-a-small-portable-lock-free-api/) which may  
> help.
>
>> I am happy to do quick tests, but must apologize for lack of time  
>> to dig into this.
>>
>
> No problems, and thanks again for reporting it.
>
>
>> FYI,
>> -KenD