[concurrency-interest] Proper workaround for FutureTask.set()/get() race (CR 7132378)

Kirk Pepperdine kirk at kodewerk.com
Mon Apr 23 13:31:41 EDT 2012


define failure for putIfAbsent???


On 2012-04-23, at 7:10 PM, David M. Lloyd wrote:

> I disagree.  May times using set() on an object like this is the point of coordination.  Would you throw an exception if putIfAbsent() failed?
> 
> On 04/23/2012 11:37 AM, Nathan Reynolds wrote:
>> Consider throwing an exception instead of returning false. The exception
>> will force the caller to deal with the already set condition. Returning
>> false is a bug waiting to happen.
>> 
>> Calling set() twice usually indicates a larger bug in the caller code.
>> Why would the algorithm call it twice? Is there a race between 2 threads
>> in the caller code? Is one part of the caller code not aware of what the
>> other part of code did?
>> 
>> I raise this concern because FindBugs flags issues if the caller doesn't
>> deal with the result of the java.io.File and java.util.concurrent.Lock
>> APIs. For many that don't use FindBugs, they will have a lot of bugs.
>> 
>> Nathan Reynolds
>> <http://psr.us.oracle.com/wiki/index.php/User:Nathan_Reynolds> |
>> Consulting Member of Technical Staff | 602.333.9091
>> Oracle PSR Engineering <http://psr.us.oracle.com/> | Server Technology
>> 
>> On 4/21/2012 1:33 PM, Joe Bowbeer wrote:
>>> On Sat, Apr 21, 2012 at 12:08 PM, Aleksey Shipilev wrote:
>>> 
>>>    Yes. SettableFuture-like class is something missing from concurrent
>>>    classes I'm redoing over and over again in most of the projects.
>>>    Implementing it directly on top of AQS might provide some benefits
>>>    comparing to extending from FutureTask? Oh wait, it smells like
>>>    another
>>>    API enhancement proposal? :)
>>> 
>>> 
>>> Alex,
>>> 
>>> Bill Pugh once suggested a separate concurrency abstraction: an
>>> externally settable FutureValue<V>, which supports the following methods:
>>> 
>>> V get() - Waits if necessary for the value to be set, and then returns
>>> the value.
>>> boolean isDone() - Returns true if the value is set
>>> boolean set(V v) - Sets the value if it was not already set.
>>> Returns true if the value was set by this call, false if it
>>> was set by another call.
>>> 
>>> Having set(v) return a boolean seems like a good idea. What do you think?
>>> 
>>> To this I would also add the other Future methods such as cancel(),
>>> plus setException(). In other words, I envision FutureValue as a
>>> Future with two additional methods: boolean set(v) and boolean
>>> setException(e).
>>> 
>>> Are there any other Future enhancements that you think are sorely
>>> needed in j.u.c.?
>>> 
>>> --Joe
>>> 
>>> 
>>> 
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>> 
>> 
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> 
> 
> -- 
> - DML
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