RFR [6853696] (ref) ReferenceQueue.remove(timeout) may return null even if timeout has not expired

[Ivan Gerasimov]

On 25.02.2014 6:52, David Holmes wrote:
> On 25/02/2014 1:34 AM, Ivan Gerasimov wrote:
>> Thank you Roger for looking at the fix!
>>
>> On 24.02.2014 18:37, roger riggs wrote:
>>> Hi Ivan,
>>>
>>> The code is correct as written but there might be some creep in the
>>> end time due to the sampling of System.nanoTime.
>>>
>>> I would be inclined to calculate the final time of the timeout once
>>> and then compare simply with the current nanotime.
>>>
>>> long end = (timeout == 0) ? Long.MAX_VALUE : (System.nanoTime() +
>>> timeout * 1000000);
>>>
>> I don't think it is always correct.
>> According to the documentation, "The value returned represents
>> nanoseconds since some fixed but *arbitrary* origin time".
>> http://download.java.net/jdk8/docs/api/java/lang/System.html#nanoTime--
>>
>> Thus, Long.MAX_VALUE may just happen to represent some valid time in the
>> near future, and we'll achieve wrong result.
>
> Correct. Simplest thing is to calculate end ignoring whether timeout 
> is zero, and only check "now < end" if timeout != 0.

David, as Martin said before, 'now < end' may hold true even if now is 
after end (now is negative).
In my version of the code, I operate on the difference (after - before), 
thus avoiding the possible overflow.

Sincerely yours,
Ivan

>
> David
>
>> Sincerely yours,
>> Ivan
>>
>>> Then the test in the loop can be:
>>>
>>>   if (System.nanoTime() > end) {
>>>      return null;
>>>   }
>>>
>>> Roger (Not a Reviewer)
>>>
>>> On 2/24/2014 12:59 AM, Ivan Gerasimov wrote:
>>>> Hello!
>>>>
>>>> ReferenceQueue.remove(timeout) may return too early, i.e. before the
>>>> specified timeout has elapsed.
>>>>
>>>> Would you please review the fix?
>>>> The change also includes a regression test, which can be used to
>>>> demonstrate the issue.
>>>>
>>>> BUGURL: https://bugs.openjdk.java.net/browse/JDK-6853696
>>>> WEBREV: http://cr.openjdk.java.net/~igerasim/6853696/0/webrev/
>>>>
>>>> Sincerely yours,
>>>> Ivan
>>>
>>>
>>
>
>