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chap02 ex1 better implement #31

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chap02 ex1 better implement #31

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14 changes: 3 additions & 11 deletions src/main/scala/org/learningconcurrency/exercises/ch2/ex1.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -7,23 +7,15 @@ import org.learningconcurrency.ch2.thread
object Ex1 extends App {

def parallel[A, B](a: =>A, b: =>B): (A, B) = {
var aVal: A = null.asInstanceOf[A]
var bVal: B = null.asInstanceOf[B]

val t1 = thread {
aVal = a
log(aVal.toString())
a
}

val t2 = thread {
bVal = b
log(bVal.toString())
b
}

t1.join()
t2.join()

(aVal, bVal)
(a, b)
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@amoszhou Commeny from @ryblovAV is correct - the expression a is by name (not lazy), and it will be executed twice now. The first time in parallel in the thread statement, and the second time when returning from the method. This effectively removes parallelism, and if the a or b are side-effecting, will execute the side-effect twice.

If you want nicer code, you could do this:

lazy evaluatedA = a
lazy evaluatedB = b

val t1 = thread {
  evaluatedA
}
...
(evaluatedA, evaluatedB)

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yes, thank you

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You are welcome, just don't forget to add lazy vals and push again to sync the pull request if you made any changes.

}

}