<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Thu, Aug 7, 2014 at 8:43 PM, Ben Coman <span dir="ltr"><<a href="mailto:btc@openinworld.com" target="_blank">btc@openinworld.com</a>></span> wrote:<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
I am looking at dealing with multiple in-image threads and am wondering about what operations are atomic. The current understanding is that...<br>
(myvar == nil) ifTrue: [ myvar := 1. myvar2 := #something ]<br>
is atomic, but I see some indication in comments (sorry lost my reference) that...<br>
myvar ifNil: [ myvar:=1 ]<br>
might not be - but maybe those comments were historical. What is the current status and likely future guarantees for Squeak/Pharo/Cuis/other? </blockquote><div><br></div><div>On Squeak-derived systems the two operations that are not atomic are message sends and backward branches; these are where the VM checks for external events and your process might be preempted by one with a higher priority. #ifTrue: and #ifNil: are atomic because the bytecode compiler inlines them (#ifTrue: has always been inlined, but I don't think #ifNil: always was). #== is atomic because the VM implements it without a send. This is all if code runs normally. If run through the debugger you might be interrupted at any operation because the simulation is implemented in terms of Smalltalk code with tons of sends. One should not rely on these implementation details and instead use semaphores or (very rarely) #valueUnpreemptively.</div>
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