review request: 4244896: (process) Provide System.getPid(), System.killProcess(String pid)

[David Holmes]

Hi Rob,

On 20/04/2012 11:33 AM, Rob McKenna wrote:
> I've uploaded another webrev to:
>
> http://cr.openjdk.java.net/~robm/4244896/webrev.02/
> <http://cr.openjdk.java.net/%7Erobm/4244896/webrev.02/>

I'll take a look as soon as I have a chance but will be OOTO the rest of 
today.

> I plan to spend some time over the coming day or two beefing up the test
> for waitFor (right now its really geared towards destroyForcibly) so I
> won't guarantee its 100% quite yet. That said, I would like feedback on
> a couple of points before I proceed:
>
> 1) Alan suggested the use of System.nanoTime() so I altered
> waitFor(long) to allow for a TimeUnit parameter. UnixProcess objects can
> use Object.wait(long, int) but unfortunately WaitForMultipleObjects (on
> Windows) only works to millisecond precision.

Object.wait (like Thread.sleep) doesn't honour the nanosecond argument 
so there is no point trying to use it.

David
-----

> 2) As Alan noted, there is really no need for isAlive() if people are
> happy with the idea of waitFor(long, TimeUnit). I'd appreciate any
> feedback on this aspect of the fix.
>
> -Rob
>
> On 19/04/12 12:05, Alan Bateman wrote:
>> On 19/04/2012 01:05, David Holmes wrote:
>>> On 18/04/2012 11:44 PM, Jason Mehrens wrote:
>>>>
>>>> Rob,
>>>>
>>>> It looks like waitFor is calling Object.wait(long) without owning
>>>> this objects monitor. If I pass Long.MAX_VALUE to waitFor, shouldn't
>>>> waitFor return if the early if the process ends?
>>>
>>> Also waitFor doesn't call wait() under the guard of a looping
>>> predicate so it will suffer from lost signals and potentially
>>> spurious wakeups. I also don't see anything calling notify[All] to
>>> indicate the process has now terminated. It would appear that
>>> wait(timeout) is being used as a sleep mechanism and that is wrong on
>>> a number of levels.
>> I assume waitFor(timout) will require 3 distinct implementations, one
>> for Solaris/Linux/Mac, another for Windows, and a default
>> implementations for Process implementations that exist outside of the
>> JDK.
>>
>> It's likely the Solaris/Linux/Mac implementation will involve two
>> threads, one to block in waitpid and the other to interrupt it via a
>> signal if the timeout elapses before the child terminates. The Windows
>> implementation should be trivial because it can be a timed wait.
>>
>> I assume the default implementation (which is what is being discussed
>> here) will need to loop calling exitValue until the timeout elapses or
>> the child terminates. Not very efficient but at least it won't be used
>> when when creating Processes via Runtime.exec or ProcessBuilder.
>>
>> I think the question we need to consider is whether waitFor(timeout)
>> is really needed. If it's something that it pushed out for another day
>> then it brings up the question as to whether to include isAlive now or
>> not (as waitFor without timeout gives us an isAlive equivalent too).
>>
>> -Alan.
>>
>>
>>
>>