I have a few comments, but first I wanted to raise the point that I'm not sure why we're having this argument about maximally sharded Precompiles at all. For one thing, it's already implemented, and optional, via "-XshardPrecompile". I can't think of any reason to muck with this, or why it would have any relevance to sharded linking. Can we just table that part for now, or is there something I'm missing?
Okay, so now on to sharded linking itself. Here's what I love: - Love the overall goals: do more work in parallel and eliminate serialization overhead. - Love the idea of simulated sharding because it enforces consistency. - Love that the linkers all run in the same order. Here's what I don't love: - I'm not sure why development mode wouldn't run a sharded link first. Wouldn't it make sense if development mode works just like production compile, it just runs a single "development mode" permutation shard link before running the final link? - I dislike the whole transition period followed by having to forcibly update all linkers, unless there's a really compelling reason to do so. Maybe I'm missing some use cases, but I don't see what problems result from having some linkers run early and others run late. As Lex noted, all the linkers are largely independent of each other and mostly won't step on each other's toes. - It seems unnecessary to have to annotate Artifacts to say which ones are transferable, because I thought we already mandated that all Artifacts have to be transferable. I have in mind a different proposal that I believe addresses the same goals, but in a less-disruptive fashion. Please feel free to poke holes in it: 1) Linker was made an abstract class specifically so that it could be extended later. I propose simply adding a new method "linkSharded()" with the same semantics as "link()". Linkers that don't override this method would simply do nothing on the shards and possibly lose out on the opportunity to shard work. Linkers that can effectively do some work on shards would override this method to do so. (We might also have a "relinkSharded()" for development mode.) 2) Instead of trying to do automatic thinning, we just let the linkers themselves do the thinning. For example, one of the most serialization-expensive things we do is serialize/deserialze symbolMaps. To avoid this, we update SymbolMapsLinker to do most of its work during sharding, and update IFrameLinker (et al) to remove the CompilationResult during the sharded link so it never gets sent across to the final link. The pros to this idea are (I think) that you don't break anyone... instead you opt-in to the optimization. If you don't do anything, it should still work, but maybe slower than it could. The cons are... well maybe it's too simplistic and I'm missing some of the corner cases, or ways this could break down. Thoughts? Scott -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
