Ant calling targets several times - ant

Question

I set up a simple Ant script to understand why my dependency targets are being called several times when I specified several targets to execute (in Eclipse):
<project name="test">
<macrodef name="mkjar" description="Build a jar from 'tgt'">
<attribute name="tgt" />
<sequential>
<echo message="mkjar #{tgt}" level="info" />
</sequential>
</macrodef>
<target name="Common">
<mkjar tgt="Common" />
</target>
<target name="Net" depends="Common">
<mkjar tgt="Net" />
</target>
<target name="DB" depends="Common">
<mkjar tgt="DB" />
</target>
<target name="FooBar" depends="Common,DB">
<mkjar tgt="FooBar" />
</target>
<target name="FooBar2" depends="Common,Net,DB">
<mkjar tgt="FooBar2" />
</target>
</project>
Output:
Buildfile: buildtest.xml
Common:
[echo] mkjar Common
Net:
[echo] mkjar Net
DB:
[echo] mkjar DB
FooBar2:
[echo] mkjar FooBar2
Common:
[echo] mkjar Common
DB:
[echo] mkjar DB
FooBar:
[echo] mkjar FooBar
BUILD SUCCESSFUL
Total time: 283 milliseconds
Why is Ant going twice into targets Common and DB? I thought macrodef would be executed inside the same Ant flow and project scope. I tried uglier things with antcall
<target name="mkjar" unless="jar-${tgt}">
<property name="jar-${tgt}" value="true" />
...
</target>
But it's not better (it's even creating several jar-<tgt> properties!).

Answer 1

I thought macrodef would be executed inside the same Ant flow and project scope
It does. When you invoke ant FooBar2 FooBar, both targets are executed in the same Ant project. But in this case, Ant does not "track" that a dependency target has already executed when it is also a dependency for the second target.
A dependency target is invoked only once when it is in the same chain of dependencies of only one target, for example:
<target name="A"/>
<target name="B" depends="A"/>
<target name="C" depends="B"/>
<target name="D" depends="C,B,A"/>
When running ant D, the following chain of targets is run: A --> B --> C --> D.
See https://ant.apache.org/manual/targets.html for more info.
One way to solve the issue here is to add a condition on the target to skip running it when a property is set:
<target name="Common" unless="common.already.executed">
<mkjar tgt="Common" />
<property name="common.already.executed" value="true" />
</target>