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Operator `or` causes a future to be completed more than once #8982

k0zmo opened this issue Sep 16, 2018 · 0 comments


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commented Sep 16, 2018

Following code:

import asyncdispatch

proc failingAwaitable(p: int) {.async.} =
    await sleepAsync(500)
    if p > 0:
        raise newException(Exception, "exception")

proc main() {.async.} =
    let fut = failingAwaitable(1)
        await fut or sleepAsync(100)
        if fut.finished:
            echo "finished"
            echo "timeout"
        echo "failed"

asyncCheck main()

uses operator or defined in here. When one of the future fails (like in above test case) the result future is complete twice - once using complete() and once using fail(). I propose following implementation of operator or:

proc `or`*[T, Y](fut1: Future[T], fut2: Future[Y]): Future[void] =
    ## Returns a future which will complete once either ``fut1`` or ``fut2``
    ## complete.
    var retFuture = newFuture[void]("asyncdispatch.`or`")
    proc cb[X](fut: Future[X]) =
      if not retFuture.finished:
        if fut.failed:
        else: retFuture.complete()
    fut1.callback = cb[T]
    fut2.callback = cb[Y]
    return retFuture

@dom96 dom96 closed this in #9632 Nov 9, 2018

dom96 added a commit that referenced this issue Nov 9, 2018

complete future only once in `or` (fixes #8982) (#9632)
* complete future only once in `or`

Analogous to `and`.
Credits to @k0zmo for proposing the solution.

* add test
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