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

[Alan Bateman]

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.