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<p class=MsoNormal>Hi all,<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I consider myself a Twisted “newbie”, so this
might seem like a simple couple of questions, hope you’ll indulge me.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>When I first began experimenting with deferreds I was breaking
up tasks into sequences of steps something like this:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>d = Deferred()<o:p></o:p></p>
<p class=MsoNormal>d.succeed(True)<o:p></o:p></p>
<p class=MsoNormal>d.addCallback(step1)<o:p></o:p></p>
<p class=MsoNormal>d.addCallback(step2)<o:p></o:p></p>
<p class=MsoNormal>d.addCallback(step3)<o:p></o:p></p>
<p class=MsoNormal>etc.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>When this runs I was under the mistaken impression that at
the end of each callback (step1, step2, step3, etc) the deferred would yield
back to the main loop (reactor) and allow other deferreds to run. Now I know
that the callback functions run sequentially one after another with no break.
So my first question is this: what is the advantage of this over just combining
the callback functions into one big function?, something like this:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>d = Deferred()<o:p></o:p></p>
<p class=MsoNormal>d.succeed(True)<o:p></o:p></p>
<p class=MsoNormal>d.addCallback(OneBigStep)<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>If step1(), step2() and step3() take a fair bit of time to
complete, doesn’t this effectively block the reactor loop for the entire
exection of all the steps?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>My second question is related to this; what is a recommended
way to create the cooperative state machine I’m thinking of using
deferreds? For example if I create something like this:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>d1 = Deferred()<o:p></o:p></p>
<p class=MsoNormal>d1.succeed(True)<o:p></o:p></p>
<p class=MsoNormal>d1.addCallback(d1_step1)<o:p></o:p></p>
<p class=MsoNormal>d1.addCallback(d1_step2)<o:p></o:p></p>
<p class=MsoNormal>d1.addCallback(d1_step3)<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>d2 = Deferred()<o:p></o:p></p>
<p class=MsoNormal>d2.succeed(True)<o:p></o:p></p>
<p class=MsoNormal>d2.addCallback(d2_step1)<o:p></o:p></p>
<p class=MsoNormal>d2.addCallback(d2_step2)<o:p></o:p></p>
<p class=MsoNormal>d2.addCallback(d2_step3)<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>How do I get the execution of this to be this:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>1)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>d1_step1<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>2)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>d2_step1<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>3)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>d1_step2<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>4)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>d2_step2<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>5)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>d1_step3<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>6)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>d2_step3<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I want to have the state machines I create cooperatively ‘multi-task’,
yielding control back to the main loop at each state transition.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Thanks in advance for any help, guidance or references you
can provide. I really enjoy Twisted, I’m still working on getting the ‘Zen’
of it.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Doug<o:p></o:p></p>
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