RFR 9: 8077350 Process API Updates Implementation Review

Roger Riggs Roger.Riggs at Oracle.com
Thu May 14 13:44:52 UTC 2015

Hi Peter,

On 5/14/15 8:19 AM, Peter Levart wrote:
> Hi Roger,
> The new API using Optional(s) looks fine. In particular for the 
> ProcessHandle returning methods. They now either return 
> Stream<ProcessHandle> or Optional<ProcessHandle>.
> At some point in the development of this API, the implementation 
> introduced the AsyncExecutor to execute synchronous continuations of 
> the onExit() returned CompletableFuture(s). What was the main 
> motivation for this given that:
> - previously, ForkJoinPoll.commonPool() was used instead that by 
> default possesses some similar characteristics (Innocuous threads when 
> SecurityManager is active)
The AsyncExecutor also uses InnocuousThreads.

> - this AsyncExecutor is only effective for 1st "wave" of synchronous 
> continuations. Asynchronous continuations and synchronous 
> continuations following them will still use ForkJoinPoll.commonPool()
Unfortunately, the common ForkJoinPool assumes that tasks queued to it 
complete relatively
quickly and free the thread.  It does not grow the number of threads and 
is not appropriate
for tasks that block for indefinite periods as might be need to wait for 
a Process to exit.

> Would an alternative be to define two overloaded onExit() methods in 
> the style of CompletableFuture itself?
>     CompletableFuture<ProcessHandle> onExit();
>     CompletableFuture<ProcessHandle> onExit(Executor executor);
> ...and give the user a chance to supply it's own Executor if the 
> default ForkJoinPoll.commonPool() does not fit?
It is only one more method in PH and Process but that function is 
available from CompletableFuture
though perhaps not as conveniently.
The onExit method returns a CompletableFuture that has the entire 
complement of
synchronous and async methods available to it.  The application can control
where subsequent computations are performed.

That convenience method could be added later when the use case and 
frequency is clearer.
> Is there expectation that ForkJoinPoll.commonPool() will not fit in 
> the common case?
I don't have a sense of how onExit would be used or how often it would 
be used.
The common FJP seems like a good start for computations to be performed
after the Process has exited.  I'd wait and see what needs can be 
hopefully within the JDK 9 timeframe.

Thanks, Roger

> Regards, Peter
> On 05/13/2015 04:16 PM, Roger Riggs wrote:
>> Hi,
>> Are there any comments about the use of java.util.Optional in the 
>> ProcessHandle API?
>> Or a review of the changes?
>> Thanks, Roger
>> On 5/11/2015 11:49 AM, Roger Riggs wrote:
>>> Please review clarifications and updates to the proposed Precess API.
>>> A few loose ends in the ProcessHandle API were identified.
>>> 1) The ProcessHandle.parent() method currently returns null if the 
>>> parent cannot
>>> be determined and the ProcessHandle.of(PID) method returns null if 
>>> the PID does not exist.
>>> It has been suggested to return an Optional<ProcessHandle> to make
>>> these methods more flexible and allow a fluent style and work better 
>>> with streams.
>>> 2) The behavior of Processhandle.destroy and destroyForcibly are 
>>> different
>>> than Process.destroy and destroyForcibly.  Those functions always 
>>> succeed because
>>> they are children of the spawning process.
>>> In contrast, ProcessHandle.destroy and destroyForcible are requests to
>>> destroy the process and may not succeed due to operating system 
>>> restrictions such
>>> as the process not being a child or not having enough privilege.
>>> The description of the methods needs to be clarified that it is a 
>>> request to destroy
>>> and it may not succeed, In that case the destroy and destroyForcibly 
>>> methods
>>> should indicate that the request was not successful.  In particular, 
>>> the caller
>>> may not want to wait for the process to terminate (its not going to).
>>> The proposed update is to return an Optional<ProcessHandle> .
>>> It can be streamed and can take advantage of the conditional 
>>> operations on the Optional.
>>> 3) Using Optional is also attractive for the return values of the 
>>> information
>>> about a ProcessHandles, since not all values are available from 
>>> every OS.
>>> The returns values of Info.command, arguments, startInstant, 
>>> totalDuration, and user
>>> are proposed to be updated to return Optional<x>.
>>> It allows for more compact code and fewer explicit checks for null.
>>> Please review and comment:
>>> Webrev:
>>> http://cr.openjdk.java.net/~rriggs/webrev-ph/
>>> javadoc:
>>> http://cr.openjdk.java.net/~rriggs/ph-apidraft/
>>> Diffs of the spec/javadoc from previous draft:
>>> http://cr.openjdk.java.net/~rriggs/ph-diffs-2015-05-11/overview-summary.html 
>>> Thanks, Roger

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