--- Tom Tromey <[EMAIL PROTECTED]> wrote: > * Fragmentation. I think there are too many free JVMs.
Amen to that. I hate to say it, since my own favorite VM is one of the ones keeping that space big. But a "state of the art" optimizing compiler stops being "state of the art" when the art progresses without hte optimizing compiler getting upgraded too. > It ought to be possible, > though difficult, to write a configurable core VM that can be reused > by other projects. The idea here is, have a reusable reference > implementation, and reduce writing a VM to writing an execution > engine (and perhaps a GC). This idea sounds really cool in the abstract. I have difficulty understanding what it would really mean in the specifics, though. I'd like to take off on a tangent here. At one point I had the naive idea that I could make Jikes RVM able to play nicely with GCJ. What really quashed the idea was the issue of garbage collection -- GCC is not designed to pass type information down to the lower levels of the compiler, so GCJ doesn't build a "gc map", which you need in order to be use any GC other than a Boehm-style conservative non-copying collector. In other words, GCJ is restricted to using a garbage collection that looks for any bit patterns in the data that might be pointers, and it has to assume that all of them are pointers. If I am mis-stating the problem, I would appreciate someone publicly correcting me. Further, I've heard (have not looked at it myself, nor am I competent to do so) that it would be an enormous amount of work to retrofit GCC so that GCJ could build GC maps. Still, though, I would very very much like to have Jikes RVM able to link with stuff made by an ahead-of-time compiler like GCJ. So, GC compatibility is a serious issue here. For instance, if I pass any reference to an object from Jikes RVM's code into GCJ's code, right now I would have to assume that that object is forever afterwards immovable. Perhaps there's some way that we could have the two types of GC talk to each other, and stay in their own separate spaces? Jikes RVM would have to pin down any object it passed into GCJ land, but then perhaps it could tell the GCJ garbage collector something like "I have pinned down the object at this address for your sake. Please tell me once you no longer have any references to it." GCJ's garbage collector would have a much easier job, since it could just go ahead and use its conservative "examine every piece of data" algorithm on the Jikes RVM heap and stack as well as on its own. Does this make sense, or am I off the wall here? Criticisms welcomed. --Steve Augart Jikes RVM: A free, open source, Virtual Machine http://jikesrvm.sf.net __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
