When might a CodeBuffer be moved?

[Gary Benson]

The only place I explicitly create one is in Shark, I think.  Shark
compiles the method into it, then passes it to ciEnv::register_method
along with everything else.  After that, as I understand it, the code
is relocated into a more permanent area, and the original CodeBuffer
gets freed automagically when the frame it's in exits (it's a
StackObj, right?)

Cheers,
Gary

Tom Rodriguez wrote:
> You wouldn't want to just build a CodeBuffer and keep it around.
> Normally we use BufferBlobs for any piece of code that we want to
> generate but which doesn't need to be relocatable.  The interpreter
> for instance is constructed this way as are a lot of helper snippers
> of various kinds.  You wouldn't want to just build a CodeBuffer and
> keep it around.  The preferred way would be the make a BufferBlob
> and then build a CodeBuffer on top of it to use for code generation.
> You'd just drop the CodeBuffer onces you were done with code
> generation and build a new one if you needed it.
>
> tom
>
> On Jun 11, 2009, at 2:18 AM, Gary Benson wrote:
> > Oh, that's excellent news.  Now to figure out if I can use it! ;)
> >
> > Cheers,
> > Gary
> >
> > Tom Rodriguez wrote:
> > > CodeBlobs are never moved automatically by anything.
> > > CodeBuffers have support for resizing the code generation buffer
> > > by moving the instructions from one CodeBlob to a new larger one
> > > but you have to ask for that using
> > > maybe_expand_to_ensure_remaining.  nmethod can be reclaimed by
> > > the sweeper once they are no longer referenced as a result of
> > > being made not entrant or zombie.
> > >
> > > tom
> > >
> > > On Jun 10, 2009, at 6:55 AM, Gary Benson wrote:
> > > > Hi all,
> > > >
> > > > I know CodeBuffers aren't moved by the garbage collector, but
> > > > can they move at all?  I remember someone (Steve Goldman?)
> > > > telling me about a code compactor once, but can't remember the
> > > > details.  Can a code buffer move at any safepoint?
> > > >
> > > > Cheers,
> > > > Gary
> > > >
> > > > -- 
> > > > http://gbenson.net/