Interpreter change

Andreas Raab andreas.raab at
Mon Apr 17 21:04:08 UTC 2006

Hi John -

The rational of this change is to ensure that when you force an 
interrupt check that we query for i/o events as well since the effect of 
the interrupt change might be related to i/o. The case in question was 
sockets: Without that change, ioProcessEvents would only be called every 
200ms if the VM is in a busy loop which limits latency to 200ms in a 
case like this:

   socket connectTo: addr port: port.
   [socket isConnected] whileFalse.

(this is a bit unrealistic example but there are many realistic ones)

In order to overcome the latency issue we need to both, signal the VM 
that something has happened (we do this via forceInterruptCheck) but we 
also need to make sure we look at ioProcessEvents ASAP, which is why the 
nextPollTick is being reset. This brings the latency down to 
(effectively) nothing as illustrated in the Croquet VM tests.

Note that these changes will likely have *dramatic* positive impacts for 
systems running on servers under heavy computational load. Many of the 
oddities reported on Unix systems can likely be traced to this very problem.

   - Andreas

John M McIntosh wrote:
> This is a bit uclear, all this is doing is forcing a call to 
> ioProcessEvents()
> This assumes ioProcessEvents() is doing something interesting that you 
> want it to do...
> which is?
> Hint on the mac all it does is check to see if the screen bits should be 
> flush (every 20ms) , and snatch any pending UI events  (every 16ms).
> Nothing else. So what else should it be doing?
> On 17-Apr-06, at 10:33 AM, Ian Piumarta wrote:
>> Please integrate immediately, unless the same change already reached 
>> the Squeak VMM by way of the Croquet VMM.
>> 'From Croquet1.0beta of 11 April 2006 [latest update: #0] on 17 April 
>> 2006 at 10:29:39 am'!
>> "Change Set:        Socket-latencyFix-ikp
>> Date:            14 April 2006
>> Author:            Ian Piumarta
>> Reset nextPollTick to zero in forceInterruptCheck so that asynchronous 
>> external i/o can obtain an immediate ioProcessEvents."!
>> !Interpreter methodsFor: 'processes' stamp: 'ikp 4/14/2006 16:30'!
>> forceInterruptCheck
>>     "force an interrupt check ASAP"
>>     interruptCheckCounter := -1000.
>>     nextPollTick := 0! !
> -- 
> ===========================================================================
> John M. McIntosh <johnmci at> 1-800-477-2659
> Corporate Smalltalk Consulting Ltd.
> ===========================================================================

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