Future plans for AppCDS?

[Mike Hearn]

Hi there,

I'm wondering if there are any plans to extend AppCDS in future to include
serializing the code cache to disk?

I ask because I have a (not very complicated) desktop JavaFX app. It starts
in about three seconds, which isn't terrible, but I'd like it to be faster.

Unfortunately I am frequently frustrated in this goal.  Some testing shows
that one step of the initialisation sequence takes about a second normally.
If I put it in a loop to let it fully compile, that drops to more like a
quarter of a second.

Likewise, my app loads a series of items to display them on the screen. The
first one can take a solid 700-800 msec. The rest are more like 10% of that.

I tried parallelising some of the things done during startup, but it made
no difference. My theory is that the compile threads are taking up the
spare cores that could be doing startup tasks (it's a bit hard to profile
this though as the whole sequence only lasts a few seconds).

AppCDS already knows how to serialise lots of HotSpot state to disk for
unchanging JARs. If it could store compiled method code as well, then I
could probably shave a second or two off app startup.

I do understand that this situation is a bit rare for Java developers and
that due to extra disk IO etc, loading compiled code from disk might not
always be faster. But for devices that have an SSD it probably can be,
especially if HotSpot were to do the same trick Microsoft does and lay out
compiled methods on disk in the order they will be used.