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

[David Holmes]

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

> 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
>>
>>
>