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

[David Holmes]

Hi Rob,

A couple of minor things ...

Process.waitFor:

+         long startTime = System.nanoTime();
+         long rem = unit.toNanos(timeout) - (System.nanoTime() - 
startTime);

should just be

+         long startTime = System.nanoTime();
+         long rem = unit.toNanos(timeout);

The second reading of nanoTime is not generally useful. Under ideal 
conditions "no time" will have passed and you waste more time asking for 
the updated time. Someone may argue that you could get preempted after 
the first call to nanoTime and so we need to re-check; but you could get 
preempted at any time: after the first nanoTime, after the second, after 
the calculation of rem, etc. This is a game of "chase your tail" that 
you can not win. These timeouts are only rough hints. Also you don't do 
this double-read in UnixProcess.waitFor

And a style-nit:  if(rem > 0), while(rem>0) - should have a space before 
the (

---

UNIXProcess.java.linux

  221         if (timeout <= 0) return false;
  222
  223                 long timeoutAsNanos = unit.toNanos(timeout);
  224                 long startTime = System.nanoTime();

Wrong indentation.

---

UNIXProcess.java.solaris

  167         if (timeout <= 0) return false;
  168
  169                 long timeoutAsNanos = unit.toNanos(timeout);

Wrong indentation.

---

The test programs look okay. Time-based testing is always a potential 
problem so we will just have to see how these go in practice.

David
-----

On 24/06/2012 10:57 PM, Rob McKenna wrote:
> Hi folks,
>
> 5th, and hopefully final review has been posted to:
>
> http://cr.openjdk.java.net/~robm/4244896/webrev.05/
> <http://cr.openjdk.java.net/%7Erobm/4244896/webrev.05/>
>
> Let me know if there are any comments or concerns, and thanks a lot for
> the help so far.
>
> -Rob
>
> On 01/06/12 01:41, David Holmes wrote:
>> Hi Rob,
>>
>> This looks good to me. I'm glad to see that destroyForcibly mandates
>> that Process instances from ProcessBuilder.start and Runtime.exec must
>> do a forcible destroy. That addresses my concern about documenting the
>> actual implementations.
>>
>> Two minor comments:
>>
>> Process.java:
>>
>> 236 * {@link ProcessBuilder#start} and {@link Runtime#exec} are of
>> type that
>>
>> "are of type" -> "are of a type ..."
>>
>> ProcessKillTest.sh:
>>
>> BIT_FLAG is now unused.
>>
>> Thanks,
>> David
>>
>>
>> On 1/06/2012 1:05 AM, Rob McKenna wrote:
>>> Latest version including work on the spec language:
>>>
>>> http://cr.openjdk.java.net/~robm/4244896/webrev.04/
>>> <http://cr.openjdk.java.net/%7Erobm/4244896/webrev.03/>
>>>
>>> -Rob
>>>
>>> On 10/05/12 19:56, Rob McKenna wrote:
>>>> Hi folks,
>>>>
>>>> The latest version is at:
>>>>
>>>> http://cr.openjdk.java.net/~robm/4244896/webrev.03/
>>>> <http://cr.openjdk.java.net/%7Erobm/4244896/webrev.03/>
>>>>
>>>> Feedback greatly appreciated.
>>>>
>>>> -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.
>>>>>
>>>>>
>>>>>
>>>>>
>
>