Hi Peter,
If delegating to another Process and not needing to return the CF<subtype>
then the overridden implementation might be:
public CompletableFuture<Process> onExit() {
return delegate.onExit();
}
The .thenApply(ph -> this) would be needed only for the return value to
be CF<subtype>.
The explanation can get lengthy if the best-practice options are described
and mentioning toHandle() reintroduces the possibility of UOE.
* @implNote
* The default implementation of this method employs a thread from
* {@link java.util.concurrent.ForkJoinPool#commonPool() common pool}
* to {@link #waitFor() wait} for process exit, which might consume a lot
* of memory for thread stacks if large number of processes are waited for
* concurrently.<p>
* External implementations are advised to override this method and provide
* more efficient implementation, for example, if the implementation also
* provides {@link #toHandle()} method, it can simply do the following:
* <pre>{@code
* public CompletableFuture<Process> onExit() {
* return delegate.onExit();
* }
* }</pre>
* ...which in case of implementation of the delegate is used.
A more general class level note about delegating each of the methods of the
underlying process might be sufficient but might be overlooked.
Thanks, Roger
On 3/13/2015 3:35 AM, Peter Levart wrote:
Hi Roger,
Now that the method has a non-throwing default implementation, what do
you think of the following implementation note for Process.onExit():
* @implNote
* The default implementation of this method employs a thread from
* {@link java.util.concurrent.ForkJoinPool#commonPool() common pool}
* to {@link #waitFor() wait} for process exit, which might consume a lot
* of memory for thread stacks if large number of processes are waited for
* concurrently.<p>
* External implementations are advised to override this method and provide
* more efficient implementation, for example, if the implementation also
* provides {@link #toHandle()} method, it can simply do the following:
* <pre>{@code
* public CompletableFuture<Process> onExit() {
* return toHandle().onExit().thenApply(ph -> this);
* }
* }</pre>
* ...which in case of internal implementation of ProcessHandle
* ({@link java.lang.ProcessHandle#of(long)}}), employs a more efficient
* mechanism for waiting on process exit.
Regards, Peter
On 03/12/2015 11:33 PM, Peter Levart wrote:
On 03/12/2015 09:41 PM, Roger Riggs wrote:
Hi Peter,
Introducing a public Process subtype would not be a binary
compatible change;
the return type of ProcessBuilder.start can not be narrowed.
As you surmised, a different start method would be needed on
ProcessBuilder.
Since ProcessBuilder is the preferred mechanism to created
processes, I would
leave Runtime.exec alone to avoid a proliferation of similar methods.
If ProcessHandle were an interface, Process would still have the
conflict over the
return type of onExit() since CompletableFuture<Process> is not type
compatible
with CF<ProcessHandle>. So not quite the winning combination to
enable polymorphism.
Roger
That's right. The delegation approach with unrelated Process /
ProcessHandle seems to be the most clean from API perspective.
Regards, Peter
On 3/12/2015 10:38 AM, Peter Levart wrote:
On 03/12/2015 02:39 PM, Roger Riggs wrote:
Hi,
Just a thought, it might be useful to introduce a public subtype
of Process that is
returned from ProcessBuilder for which the guarantees about
behavior could be
tighter (no UOEs). It would also provide a place to document the
behaviors
now spread across ProcessBuilder and Process.
$.02, Roger
That was my thinking too today. A Process2 or XProcess? If
ProcessHandle was an interface this subtype could implement it
(back to square one). I think it could be an interface if Process2
was not publicly extendable (package-protected constructor) as it
would not represent part of extensible API.
Does that mean that we would need additional methods
ProcessBuilder.start2() / Runtime.exec2() too?
Peter
