Re: [NEW TASK PROPOSAL] onceonly

[Alexey N. Solofnenko]

Hello Peter,
 It seems like a work-around of another serious issue - <ant>&Co should 
not be used at all when there is a chance that some tasks will be 
executed twice or more times. There are now other mechanisms that work 
better - <import> and <macrodef>.

- Alexey.
Peter Reilly wrote:
For my site antlib, I am currently using a task <onceonly>
which may be usefull to have as a std ant task (or ant-contrib task).
The idea is that the task will only be run  once, even if
called multiple times (via ant, antcall, subant - indirectly
via import).
For example:
<project default="caller">
 <onceonly>
    <echo>Initializing Project</echo>
    <!-- some complicated list of initializing tasks -->
 </onceonly>
 <target name="caller">
     <echo>In call</echo>
     <antcall target="callee"/>
</target>
<target name="callee">
   <echo>In callee</echo>
 </target>
<project>
Peter
------------------------------------------------------------------------
package net.sf.antextra;
import java.util.Set;
import java.util.HashSet;
import java.util.Collections;
import org.apache.tools.ant.taskdefs.Sequential;
/**
* Ant task to run a sequence of tasks only
* once.
* Usefull for setting up stuff in files that may
* be called a number of times (via ant or import
* for example).
*/
public class OnceOnly extends Sequential {
   private static Set locations = new HashSet();
   /**
    * Execute the list of nested tasks by calling
    * super.execute() if this location has not been
    * seen before.
    */
   public void execute() {
       String location = getLocation().toString();
       synchronized(locations) {
           if (locations.contains(location)) {
               return; // Do nothing, action already done
           }
           locations.add(location);
       }
       super.execute();
   }
}
 

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