RFR 9: 8064932: test java/lang/ProcessBuilder/Basic.java: waitFor didn't take long enough

[Martin Buchholz]

Hi Roger,

I keep staring at the code in UNIXProcess.java and am having trouble
imagining how waitFor could possibly return early - that loop can only
terminate when elapsed time as measured by System.nanoTime exceeds
timeoutAsNanos.  It's true that we might have truncation when
converting to millis, but then the wait should get called a second
time with arg 1 (which is suboptimal, yes - we should improve waitFor
(and very sadly, we should also improve Object.wait)).

Is there a way for me to repro this test failure?  The JDK tries hard
to provide monotonic nanoTime().

On Fri, Nov 14, 2014 at 2:15 PM, roger riggs <roger.riggs at oracle.com> wrote:
> Hi Martin,
>
> The artifact is by-product of using System.nanoTime to measure the duration
> in UNIXProcess and the conversion to milliseconds to call Object.wait():
>
> The low order bits of nanoseconds are truncated in the conversion.
>
>         long timeoutAsNanos = unit.toNanos(timeout);
>         long startTime = System.nanoTime();
>         long rem = timeoutAsNanos;
>
>         while (!hasExited && (rem > 0)) {
>             wait(Math.max(TimeUnit.NANOSECONDS.toMillis(rem), 1));
>             rem = timeoutAsNanos - (System.nanoTime() - startTime);
>         }
>
> The issue may be further complicated by the test logic also doing the
> timing in nanoSeconds when the best Object.wait can do is milliseconds.
>
> If System.nanoTime is to be used, perhaps it should be modulo milliseconds.
>
> Roger
>
>
>
> On 11/14/2014 2:57 PM, Martin Buchholz wrote:
>>
>> This sort of change may be a necessary concession to reality, but
>> before we go there ... as I said in a previous review, this test may
>> demonstrate a real bug in the jdk implementation.  Is this
>> system-dependent?  Is it easy to reproduce?  Can we fix the JDK?
>>
>> On Fri, Nov 14, 2014 at 11:48 AM, roger riggs <roger.riggs at oracle.com>
>> wrote:
>>>
>>> Please review this test change to make the wait time in
>>> ProcessBuilder/Basic
>>> a bit more lenient.
>>>
>>> Webrev:
>>> http://cr.openjdk.java.net/~rriggs/webrev-basic-notenough-8064932/
>>>
>>> Issue:
>>>     8064932: java/lang/ProcessBuilder/Basic.java: waitFor didn't take
>>> long
>>> enough
>>>
>>> Thanks, Roger
>>>
>