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