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

[Paul Sandoz]

Hi Rob,

I dunno if the following has been pointed out before. It's hard to track review comments.


The implementation of Process.waitFor normalizes the end time and duration remaining time to nano seconds.  However, the Thread.sleep method expects a duration in units of milliseconds.

You could use:

  http://docs.oracle.com/javase/7/docs/api/java/lang/Thread.html#sleep(long, int)

Or just round things up to the nearest millisecond:

  Thread.sleep(Math.min(TimeUnit.NANOSECONDS.toMillis(rem) + 1, 100));

That would be more consistent and wait for less time over that of the requested duration.


For the following code:

 227         long rem = end - now;
 228         while (!hasExited && (rem > 0)) {
 229             wait(TimeUnit.NANOSECONDS.toMillis(rem));
 230             rem = end - System.nanoTime();
 231         }

Can the above go into a spin loop once the duration is less than 1 millisecond for the rest of that duration? If so you may want to round it up to the nearest millisecond.

Paul.

On May 10, 2012, at 8:56 PM, 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.
>> 
>> 
>> 
>>