[concurrency-interest] Future.isCompletedNormally Future.isCompletedAbnormally

Joe Bowbeer joe.bowbeer at gmail.com
Sat Mar 7 18:32:58 EST 2015


More comments and suggestions

1. I think "isCompletedAbnormally" is confusing in relation to the existing
method isCancelled.  Is cancellation an abnormal completion?  I think this
is debatable and therefore a point of confusion.  I think these names are
clearer:

hasFailed()
hasCompletedWithException()

2. hasCompletedNormally instead of isCompletedNormally?

3. Would a non-blocking sibling of get() be a more basic building block for
these methods? For example:

getOptional() returns an Optional that is present if f.isDone, empty if
!f.isDone, and otherwise throws the usual exceptions?  (Except it does
*not* throw InterruptedException?)

--Joe

On Sat, Mar 7, 2015 at 2:27 PM, Luke Sandberg <lukeisandberg at gmail.com>
wrote:

> I think these would be pretty useful (isCancelled() is pretty useful), I
> would also be interested in efficient methods to get the failure cause of a
> future (without paying the cost of an ExecutionException).  A lot of time
> the executionexception contains no useful information (if a library is
> dereferencing a users future), and so i end up discarding the EE or
> replacing it with something more useful.
>
> On Thu, Mar 5, 2015 at 11:58 AM, Martin Buchholz <martinrb at google.com>
> wrote:
>
>> Perhaps Doug can explain why isCompletedNormally and
>> isCompletedAbnormally landed in ForkJoinTask but no other Future
>> implementation.
>>
>> On Thu, Mar 5, 2015 at 11:07 AM, thurstonn <thurston at nomagicsoftware.com>
>> wrote:
>>
>>>
>>> > All of the is* methods would (obviously) have the same happens-before
>>> > semantics.
>>>
>>> But that's deliberate - isDone() can't have any specified memory
>>> consistency
>>> rules, since
>>> the following **doesn't** hold:
>>>  isDone == true iff isCompletedNormally() == true
>>>
>>>
>> I don't see why that's true.  I expect the action in the thread that
>> makes the future done (setting result or exceptional value) happens-before
>> actions isDone returning true
>>
>>
>>> The usefulness of isCompletedNormally() would lie exactly in this, e,g,
>>>
>>> if (f.isCompletedNormally())
>>>    do something  //all done
>>> else if (waitedlongenough())
>>>    f.cancel()
>>>    schedule a backup/replacement execution
>>>
>>>
>> I don't think eliding the try/catch block is good motivation.
>>
>>
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>
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