gwt multiple modules without redundant code

Question

I'm trying to find a way to rid redundant compilation and js from a client's GWT code. Problem is that they have a multiple EntryPoint site and a massive model that gets compiled for every module. We're talking about 30 GWT modules and entry points each compiling the entire model package of the app separately. It takes about 15 minutes on my 8 core monster just to GWT compile this beast. And yes, compilation is parallellized and uses all cores (can hardly move my mouse in Ubuntu :) )

To change the architecture to a single module is not really an option I think. Is there no way to have inherits be shared between modules? The modules aren't necessarily that big all of them, but the problem is again that all inherits are compiled redundantly for each module. This of course has negative effects for the end user as well since every page basically has to load the entire model-js again and again.

According to

http://www.gwtproject.org/doc/latest/DevGuideOrganizingProjects.html#DevGuideModuleXml

the suggestion still seems to be to just make one great monolithic module. Isn't there any better way?

Any tips highly appreciated!

Answer 1

As it is said in the GWT Documentation you refer to, GWT mechanism to face the problem of avoiding redundant code is merging all modules in just a a super-gwt-module which includes all sub-modules you have in your applications.

I suppose you are producing a module for a different page or feature at your website, so using a unique module, as I say, implies that you will need a mechanism to run the appropriate application-code per page, based on the url or something.

You can take advantage of using code-splitting, so your modules will be EntryPoints instead of RunAsyncCallbacks, and each module will be compiled in one js fragment which will be loaded asynchronously.

Note that you will include the same javascript fragment in all pages, and this will load other fragments depending on the page.

The advantages of this solution are many:

• You only have one compilation process. It could take a long time, but for sure it will take much less than compiling all modules individually because redundant code will be compiled once.
• You can maintain different .gwt.xml, one to continue developing the individual modules with its own EntryPoint, and another without EntryPoint which will be inherited by your super-module.
• Once compiled, the first fragment loaded (shared by all apps) would be very small, and it will be cached just once, so all apps would load very fast.
• Many of the code shared by the modules (gwt-core, jre, etc), could go to the first fragment and would be shared by all the modules, decreasing the final downloaded size of each app.
• This is an out-of-the-box solution, gwt compiler makes a good job splitting the code, merging shared code to intermediate modules, and adding the methods to load fragments asynchronously when demanded.
• Java ecosystem facilitates modular apps (dependencies, maven, etc).

Otherwise, if you continue wanting individual modules, the way to compile all of them is what you are actually doing: executing gwt compiler once per module (and permutation). You can improve your compilation time, though, having a continuous integration cluster like Jenkins and running jobs in parallel, or using more brute force (memory, cpu, ...).

Answer 2

As you probably know GWT compiles each module into one big JavaScript file and optimizes everything based on all available information about everything in the whole module. This is why you need to compile everything for each module.

One solution might be to do create one big module, but use code splitting similar to the module structure. Than you don't get one very large monolithic JavaScript file, but 'modules' are loaded as needed.

Did you try compiling with less localworkers, instead of using all possible available cores? I've had the best results with localworker set to 4 (even on a 6-core machine).