RFR(S): 8230126: delay_to_keep_mmu can delay shutdown

[Kim Barrett]

> On Aug 27, 2019, at 7:06 PM, sangheon.kim at oracle.com wrote:
> 
> Hi Kim,
> 
> On 8/27/19 12:22 PM, Kim Barrett wrote:
>> […]
>> CR:
>> https://bugs.openjdk.java.net/browse/JDK-8230126
>> 
>> Webrev:
>> http://cr.openjdk.java.net/~kbarrett/8230126/open.00/
> Couldn't always use 'ms'?
> I think 'os::elapsedTime() * 1000' seems simpler instead of 'ms -> sec -> ms' conversion and may remove ceil() call.

The only ms -> sec conversion is the prediction in mmu_delay_end, and
that's necessary because we have a prediction value provided in ms and
the tracker wants sec.  Having the delay_end return a ms value would
add another sec -> ms conversion (using when_ms rather than when_sec;
remember that both take arguments in secs, and there was a bug in the
old code wrto that).

In delay_to_keep_mmu, there's necessarily going to be a sec -> ms
conversion somewhere because os::elapsedTime() returns secs and we
need to compute a ms value based on it, for Monitor::wait.

The use of ceil doesn't go away if the sec -> ms conversion is moved.
The floating point time value is a minimum delay; conversion of a
positive value to a jlong will truncate, which is the wrong rounding
direction.