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3085 :: Need example of awaitAny()

• cdunn2001 (orginal) [2017-08-01T22:30:56+02:00] view original

  awaitAny() takes openarray[FlowVarBase]. It rejects seq[FlowVar[T]]. But the caret operator expects FlowVar[T]. So how can I use awaitAny() and then get the data from the actual FlowVar[T]? Could someone point me to a simple example?

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• cdunn2001 (orginal) [2017-08-02T00:12:15+02:00] view original

  I ended up doing this:

  proc foo() =
    var nsubs = len(settings.file_list)
    var responsesB = newSeq[FlowVarBase](nsubs)
    var responsesT = newSeq[FlowVar[string]](nsubs)
    for i in 0..<nsubs:
      let fn = settings.file_list[i]
      let fv: FlowVar[string] = spawn myfunc(fn)
      responsesT[i] = fv
      responsesB[i] = fv
    while nsubs > 0:
      let i = awaitAny(responsesB)
      let fv: FlowVar[string] = responsesT[i]
      let fn_rtn = ^fv
      nsubs.dec
  Run

  Is that dumb? At least it compiles.

  Second problem: When myfunc immediately returns, awaitAny() just waits forever. I think there is a race condition. If I add a delay into myfunc(), this works.

  So awaitAny() seems useless. Am I using it wrong? I'm going to try callbacks instead. But then should a add a final "sync()" after all callbacks are created?

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