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Re: [libvirt] [PATCH 1/2] Java bindings for domain events



On Tue, 2008-11-18 at 16:51 +0000, Daniel P. Berrange wrote:
> On Tue, Nov 18, 2008 at 11:06:10AM -0500, David Lively wrote:
> > The attached patch (against libvirt-java) implements Java bindings for
> > libvirt domain events.  This version provides a libvirt EventImpl
> > running in its own Java Thread, and provides per-Connect synchronization
> > that makes using the bindings thread-safe.  (Note the Domain, Network,
> > StoragePool, and StorageVol methods also synchronize on their Connect
> > object, as required by libvirt.  I have similar changes for
> > NodeDevice.java that need to be made when that code is checked in.)
> 
> I don't particularly like the event loop code because it is adding a huge 
> pile of non-portable JNI code that won't work on Windows, which lacks
> pipe() and poll(). Java already provides a portable pure Java API for 
> building a poll() like event loop in form of NIO.
> 
>   http://www.xhaus.com/alan/python/jynio/select.html

Yeah, Daniel V and I had briefly considered this, and rejected it on the
basis of "it's complicated" and (more importantly) some negative
feedback I hear from our Java folks on the java.nio Select mechanism.

But I agree the java.nio Select mechanism should greatly decrease the
amount of JNI code in the Java EventImpl.  I need to look over the docs
again, but I think it's "just" a matter of implementing a
SelectableChannel on top of a fd.  (That JNI code will presumably be
very different in Win32 and Unix, but it should be a relatively small
amount of JNI code in comparison to my current impl.)

So I'll look over the java.nio Select documentation and start thinking
about a more portable approach ... (and also talk more with our Java
folks about their Select gripes).

Dave

> The addition of the 'synchronized' annotatioons is something we need 
> regardless of the rest of the patch, since our API contract dictates
> that only a single thread is allowed to use a single virConnectPtr
> at once.
> 
> > This version of the patch also implements and uses an enum class
> > (DomainEvent.Type), as suggested by Tóth István.
> > 
> > IMPORTANT: THIS PATCH WILL BREAK THINGS UNLESS THE NEXT [PATCH 2/2] IS
> > APPLIED TO libvirt FIRST.  Also, libvirt must be compiled WITH_PTHREADS
> > for Java events to work.
> 
> Daniel



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