gcj internals documentation

[Boehm, Hans]

> From: Paul Biggar
> On 04 Oct 2006 09:14:38 -0600, Tom Tromey <tromey@redhat.com> wrote:
> >
> > The compiler turns  'synchronized' into calls  to 
> _Jv_MonitorEnter and 
> > _Jv_MonitorExit.  It also does the obvious transformation 
> here for the 
> > monitor-related bytecode instructions.
> 
> It looks like synchronization removal can simply be done by 
> removing these function calls in cases where the object 
> doesnt escape. Does this sound right?
> 
> 
> > Paul> Is the synchronization model accurate to Java1.4? 
> Will it change 
> > Paul> when the ecj compiler is put in, and we model Java 1.5?
> >
> > The spec for synchronization hasn't really changed over the years.
> > (The memory model has a bit, I suppose.)  We're ok up to 1.4.
> 
In 1.5, synchronization operations on objects that do not escape the
thread can be removed.  Locks have memory visibility implications only
when a lock is released by one thread and then acquired by another.  I
believe that was not technically true in 1.4 and earlier, so this
transformation technically isn't valid there.  However, the pre-1.5
memory model had enough problems that I don't think anyone really cares
about it.

Hans