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From "Robin Chaddock" <robin.chadd...@iplay.com>
Subject Re: AW: extended parallelism
Date Wed, 19 Dec 2007 14:42:00 GMT
The target "depends" attribute already gives all the information you need to be able to determine
which targets can be executed in parallel?

As I mentioned earlier the only road-block at the moment to a totally transparent mechanism
for supporting parallel execution is the dubious implicit dependencies that the documentation
for the "depends" attribute makes reference to. (and the great many build scripts in the wild
that rely upon it :( )


  ----- Original Message ----- 
  From: Chuck Holzwarth 
  To: Ant Users List 
  Sent: Wednesday, December 19, 2007 2:33 PM
  Subject: Re: AW: extended parallelism


  The problem with giving a command line option is that ant is effectively a set of rules.
The rules form a tree and the dependencies give a list of targets that are to be executed
before the current target. There would have to be some intelligence in the build file that
would show ant which tartets could be completed in parallel. For example, if you are using
ant to compile C programs, the obj files that the executable requires must be completed before
the linkage stage. There are areas where parallel processes can be leveraged, but ant will
not be able to determine those places. In my experience, even the programmers who have written
the code have difficulty identifying those places.

  In my case, there are times where parallem processing could be helpful. I retrieve the latest
copy of all files from the repository for builds, I retrieve the CM log information, I create
the release boiler plate file using information in a property file that is loaded at startup.
These could all be executed in parallel. One part of the build that could not be executed
in parallel is creation of the zip file that includes only the HTML files that changed since
the previous release. These files are copied from the complete release zip files and can't
be attempted until the zip files with the complete set of files is available.

  Jan.Materne@rzf.fin-nrw.de wrote: > It may be better to stay away from a grammar that
gives the 
  > rules and use something like:
  > 
  >   
  >  

  > 
   ... 
  >  
  >  


  You could provide another executor ;)
  In my approach I dont want the user to change the buildfile. Just set
  the property on command line.
     ant -Dant.executor.class=ParallelExecutor ...

  > How do you propose to handle potential fatal/non fatal 
  > errors? 

  The implementation collects thrown BuildExceptions from the target.
  A target will be started, if no dependend target has failed. 
  Why not try to build the jar only because the test fails? If there is a
  dependency you should 
  describe that dependency using the depends-attribute.



  >If target a exits due to an error, should there be an 
  > option to kill a or allow it to complete (similar to 
  > failonerror="yes/no")? If both a and (b,c) must succeed for 
  > d, should a be killed if b or c fails? 

  If you want to have that, use 
    
  If there is no dependency - why stop the build?


  > It was not difficult, but error handling was always the issue.

  My biggest problem is spreading all the logs. In a single thread you
  have output like
    target-1
    target-1
    target-2
    target-2
  When parallelizing that you could earn
    target-2
    target-1
    target-2
    target-1

  I thought about using a logger per thread
      Logger log = Logger.getLogger( targetName + "." + threadNumber );


  Jan

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  Thank you,
  Chuck Holzwarth
  (804) 403-3478 (home)
  (540) 335-3171 (cell)
         
  ---------------------------------
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