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annotate 2-Io/day3-concurrency.io @ 90:c27c87cd0f08

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Add most of the Day 2 exercises for Haskell
author IBBoard <dev@ibboard.co.uk>
date Sun, 16 Jun 2019 21:09:33 +0100
parents 03782444978f
children
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1 # Concurrency and coroutines don't appear to need any special syntax beyond "yield"
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2 # and a slight tweak to how you invoke the method/send the message
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3
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4 vizzini := Object clone
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5 vizzini talk := method(
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6 "Fezzik, are there rocks ahead?" println
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7 yield
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8 "No more rhymes now, I mean it." println
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9 yield
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10 )
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11
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12 fezzik := Object clone
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13 fezzik rhyme := method(
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14 yield
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15 "If there are, we'll all be dead." println
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16 yield
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17 "Anoybody want a peanut?" println
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18 )
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19
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20 # The magic happens here - call it with "@@" and it gets kicked off in a thread
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21 vizzini @@talk; fezzik @@rhyme
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22 # And further magic with classes/functions we never knew existed before,
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23 # which holds the thread open until the threads are done
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24 # (Initially this looked like two lines of Coroutine output joined together in print!)
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25 #Coroutine currentCoroutine pause
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26 # It's not clear WHY they're yielding to each other. Nothing in the code appears to
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27 # create a relationship, and in other languages then the threads would run at
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28 # arbitrary slices and (semi-randomly) intersperse their output without the yields.
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29 # But Io.
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30 # Oh, and apparently we can't use it when we want to do other things afterwards,
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31 # because we get "Scheduler: nothing left to resume so we are exiting". So
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32 # it isn't the same as "join" in other languages to wait for threads to finish/merge
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33
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34 # Apparently "asyny messages" (@@) makes something an actor
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35 slower := Object clone
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36 slower start := method(wait(2); writeln("2s delay"))
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37 faster := Object clone
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38 faster start := method(wait(1); writeln("1s delay"))
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39 # Even though slower starts first, they should be threaded so faster should print first
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40 slower @@start; faster @@start; wait(3)
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41
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42
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43 # Futures use a single "@" and are more sensible. They return a placeholder straight away
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44 # but let you carry on with other things, then block when you call them until the value
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45 # is *actually* available
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46 slow_method := method(wait(3); return "Some slow value")
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47 "Calling slow method" println
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48 value := @slow_method
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49 "Now we do other stuff…" println
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50 "And a bit more" println
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51 "And now we try to print the value…" println
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52 value println
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53 "That should have paused, but not due to the outer code" println
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54 "Wut?" println
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55 "Now everything prints twice!" println
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56 "What is going on?" println
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57 "It's as if Io created a second thread for no discernable reason!" println
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58 "But it isn't anything to do with our slower/faster threads, because everything before printing 'value' is fine" println