Short answer is "yes", but there are a few issues you need to take into
account. You need to deal with:
1) Changed classes/jars. Need to be able to detect when you have a
new copy of a jar or a classfile
2) Instrumented code. If you are in a situation where code is
getting instrumented (JVMTI, Apps using BCEL, etc) you need to make sure
not to cache the intrsumented code if it is at all dependent on runtime
parameters or environmental parameters
3) Custom Classloaders. Hard to know what they will load and from where.
4) Security concerns. Can someone get at the JITed code on disk? (In
general this is probably not too big a deal, since given disk access
someone could hack any of your images. You just want to make sure
people recognize distributing cached images is not really as safe as
distributing Java)
If you're just looking to make startup fast, you can cache purely on a
per class level where you simply ignore the first three problems and
just cache classname, MD5 hash and native code. Then as a class is
being loaded verify the MD5 hash and pull the image from disk is that
you need to make sure to have no optimizations that take into account
anything else or have some kind of dependency tree for them. E.g. If
class A uses class B, and we inline a number of the methods where classA
calls into classB, then cache these to disk. Then if class B changes,
class A needs to know that it needs to be rebuilt as well (although this
may not be too hard since you probably need to cache that info as well.
. .).
If you want to cache to allow long running optimizations to be preserved
it's a bit trickier because you need to deal with issues 1-3 above.
--Will
Michael Haupt wrote:
Hi,
On 9/21/05, will pugh <[EMAIL PROTECTED]> wrote:
2) The FastJIT needs to be Fast! Otherwise, you run the risk of
people not wanting to use it for IDEs and Apps because the startup time
is too slow.
couldn't startup time be increased by caching native code versions of
methods somewhere on the hard disk and loading instead of compiling
them every time the VM is started up?
Sorry for being off-topic,
Michael
