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<p class="MsoNormal">Hi Eliot, all,</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I'm back to my original question what is the *<b>desirable</b>* semantics of #resume and #suspend for Squeak:</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">We’ve discussed #suspend and you’ve implemented the very elegant backing of the blocked process before the send wait.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Now we have this unexpected #resume behavior plainly letting a process continue regardless of whether it’s being blocked.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve checked VW and VA:</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">VW’s #suspend removes the process from the conditional variable’s list and #resume fails an attempt to resume a blocked process. The examples below behave as expected.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">VA on the other hand treat blocked processes equally as suspended processes which seems to me as if they ignored/redefined the idea of conditional variables; i.e. suspending a blocked process is a no-op and resuming a blocked process simply
removes it from the semaphore and puts it in the runnable list.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">It seems to me Squeak sits inconsistently somewhere in-between. From #resume and #suspend comments being identical to VW’s I guess VW’s behavior was the original intention.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">best,</p>
<p class="MsoNormal">~~~</p>
<p class="MsoNormal">^[^ Jaromir</p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="border:none;padding:0in"><b>From: </b><a href="mailto:mail@jaromir.net">Jaromir Matas</a><br>
<b>Sent: </b>Thursday, January 13, 2022 19:29<br>
<b>To: </b><a href="mailto:vm-dev@lists.squeakfoundation.org">vm-dev@lists.squeakfoundation.org</a>;
<a href="mailto:eliot.miranda@gmail.com">Eliot Miranda</a><br>
<b>Subject: </b>Unexpected #resume behavior</p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hi Eliot, all,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I'm baffled by this example:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">p := [Semaphore new wait] fork.<o:p></o:p></p>
<p class="MsoNormal">Processor yield.<o:p></o:p></p>
<p class="MsoNormal">p resume explore<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I expected to get an error but the process just gets out of the semaphore and finishes happily.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">#resume comment says:<o:p></o:p></p>
<p class="MsoNormal"> Primitive. Allow the process that the receiver represents to continue. Put
<o:p></o:p></p>
<p class="MsoNormal"> the receiver in line to become the activeProcess. *Fail if the receiver is
<o:p></o:p></p>
<p class="MsoNormal"> already waiting in a queue (in a Semaphore or ProcessScheduler)*. Fail if<o:p></o:p></p>
<p class="MsoNormal"> the receiver's suspendedContext is not a context.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The following works as expected - p sits at the semaphore:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">p := [Semaphore new wait] fork.<o:p></o:p></p>
<p class="MsoNormal">Processor yield.<o:p></o:p></p>
<p class="MsoNormal">p explore<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This works as well (with the new VM) - p backs up and sits before the wait:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">p := [Semaphore new wait] fork.<o:p></o:p></p>
<p class="MsoNormal">Processor yield.<o:p></o:p></p>
<p class="MsoNormal">p suspend.<o:p></o:p></p>
<p class="MsoNormal">p explore<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">And this works too indeed - p sits at the semaphore again after suspend.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">p := [Semaphore new wait] fork.<o:p></o:p></p>
<p class="MsoNormal">Processor yield.<o:p></o:p></p>
<p class="MsoNormal">p suspend.<o:p></o:p></p>
<p class="MsoNormal">p resume explore<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Is this a bug? Or is the comment just outdated? <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I've been trying to figure out possible ways how to prevent resuming a process being terminated (other than setting its suspendedContext to nil) and this unexpected behavior gave me a real hard time :)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Many thanks for your help.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Best regards,<o:p></o:p></p>
<p class="MsoNormal">Jaromir<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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