How do I speed up the gwt compiler

Question

We re starting to make heavier use of GWT in our projects  and the performance of the GWT compiler is becoming increasingly annoying    We re going to start altering our working practices to mitigate the problem  including a greater emphasis on the hosted-mode browser  which defers the need to run the GWT compiler until a later time  but that brings its own risks  particularly that of not catching issues with real browsers until much later than we d like   Ideally  we d like to make the GWT compiler itself quicker - a minute to compile a fairly small application is taking the piss  However  we are using the compile if a fairly naive fashion  so I m hoping we can make some quick and easy gains   We re currently invoking com google gwt dev Compiler as a java application from ant Ant target  with 256m max heap and lots of stack space  The compiler is launched by Ant using fork true and the latest Java 6 JRE  to try and take advantage of Java6 s improved performance  We pass our main controller class to the compiler along with the application classpath  and off it goes   What else can we do to get some extra speed  Can we give it more information so it spends less time doing discovery of what to do   I know we can tell it to only compile for one browser  but we need to do multi-browser testing  so that s not really practical   All suggestions welcome at this point

User · Answer

You can add one option to your build for production:

-localWorkers 8 – Where 8 is the number of concurrent threads that calculate permutations. All you have to do is to adjust this number to the number that is more convenient to you. See GWT compilation performance (thanks to Dennis Ich comment).

If you are compiling to the testing environment, you can also use:

-draftCompile which enables faster, but less-optimized compilations

-optimize 0 which does not optimize your code (9 is the max optimization value)

Another thing that more than doubled the build and hosted mode performance was the use of an SSD disk (now hostedmode works like a charm). It's not an cheap solution, but depending on how much you use GWT and the cost of your time, it may worth it!

Hope this helps you!

User · Answer

For GWT 2 x I just discovered that if you use    lt set-property name  user agent  value  ie6   gt   lt extend-property values  ie8 gecko1 8  name  user agent   gt    You can even specify more than one permutation

User · Answer

If you run the GWT compiler with the -localWorkers flag  the compiler will compile multiple permutations in parallel     This lets you use all the cores of a multi-core machine  for example -localWorkers 2 will tell the compiler to do compile two permutations in parallel  You won t get order of magnitudes differences  not everything in the compiler is parallelizable  but it is still a noticable speedup if you are compiling multiple permutations   If you re willing to use the trunk version of GWT  you ll be able to use hosted mode for any browser  out of process hosted mode   which alleviates most of the current issues with hosted mode   That seems to be where the GWT is going - always develop with hosted mode  since compiles aren t likely to get magnitudes faster

User · Answer

Split your application into multiple modules or entry points and re-compile then only when needed  Analyse your application using the trunk version - which provides the Story of your compile  This may or may not be relevant to the 1 6 compiler but it can indicate what s going on

User · Answer

Here is a list of user agent values you can set it to    Adding this here because I keep ending up here when I search for what I should set to make it only produce a permutation for chrome  Answer is   lt set-property name  user agent  value  safari   gt

User · Answer

In the newer versions of GWT  starting either 2 3 or 2 4  i believe   you can also add   lt collapse-all-properties   gt    to your gwt xml for development purposes  That will tell the GWT compiler to create a single permutation which covers all locales and browsers   Therefore  you can still test in all browsers and languages  but are still only compiling a single permutation

User · Answer

Let s start with the uncomfortable truth  GWT compiler performance is really lousy  You can use some hacks here and there  but you re not going to get significantly better performance   A nice performance hack you can do is to compile for only specific browsers  by inserting the following line in your gwt xml    lt define-property name  user agent  values  ie6 gecko gecko1 8  gt  lt  define-property gt    or in gwt 2 x syntax  and for one browser only    lt set-property name  user agent  value  gecko1 8   gt    This  for example  will compile your application for IE and FF only  If you know you are using only a specific browser for testing  you can use this little hack   Another option  if you are using several locales  and again using only one for testing  you can comment them all out so that GWT will use the default locale  this shaves off some additional overhead from compile time   Bottom line  you re not going to get order-of-magnitude increase in compiler performance  but taking several relaxations  you can shave off a few minutes here and there

User · Answer

Although this entry is quite old and most of you probably already know  I think it s worth mention that GWT 2 x includes a new compile flag which speeds up compiles by skipping optimizations  You definitely shouldn t deploy JavaScript compiled that way  but it can be a time saver during non-production continuous builds    Just include the flag  -draftCompile to your GWT compiler line

User · Answer

The GWT compiler is doing a lot of code analysis so it is going to be difficult to speed it up   This session from Google IO 2008 will give you a good idea of what GWT is doing and why it does take so long   My recommendation is for development use Hosted Mode as much as possible and then only compile when you want to do your testing   This does sound like the solution you ve come to already  but basically that s why Hosted Mode is there  well  that and debugging    You can speed up the GWT compile but only compiling for some browsers  rather than 5 kinds which GWT does by default   If you want to use Hosted Mode make sure you compile for at least two browsers  if you compile for a single browser then the browser detection code is optimised away and then Hosted Mode doesn t work any more   An easy way to configure compiling for fewer browsers is to create a second module which inherits from your main module    lt module rename-to  myproject  gt     lt inherits name  com mycompany MyProject   gt     lt  -- Compile for IE and Chrome -- gt     lt  -- If you compile for only one browser  the browser detection javascript        is optimised away and then Hosted Mode doesn t work -- gt     lt set-property name  user agent  value  ie6 safari   gt   lt  module gt    If the rename-to attribute is set the same then the output files will be same as if you did a full compile

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