Re: Building Dependent targets

[Steve Loughran <st...@apache.org>]

query wrote:
> Earlier I was using some other build tool to build my project. Here if a target is built and if the same target is used to build some other target, it compares the timestamp and will not build the dependent targets again.

Ant doesnt compare the timestamps on targets, but it looks at the 
timestamp of artifacts consumed and created by tasks. e.g  <javac> does 
work only if there is java source to compile, but the <javac> task is 
called on every build.

> As I started working on ANT, I found it very useful and intersting. 

But in ANT, while building each target, it will try to build all the 
dependent targets that many times as it occurs in different targets.

As a result it is increasing project\'s build time.Is there any task to 
ensure that the dependent targets once built will not&nbsp; be built 
again ????

Every target in a build file should run once. if the same targets run 
again and again in a single build, your are using <ant> when you dont 
need to. Every task in a target should do its own dependency rules, 
though some <javadoc> dont. You can use <uptodate> to determine if 
targets need skipping


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Re: Building Dependent targets

[Matt Benson <gu...@yahoo.com>]

--- Steve Loughran <st...@apache.org> wrote:

> query wrote:
> > Earlier I was using some other build tool to build
> my project. Here if a target is built and if the
> same target is used to build some other target, it
> compares the timestamp and will not build the
> dependent targets again.
> 
> Ant doesnt compare the timestamps on targets, but it
> looks at the 
> timestamp of artifacts consumed and created by
> tasks. e.g  <javac> does 
> work only if there is java source to compile, but
> the <javac> task is 
> called on every build.

Note that this behavior can only be expected on a
per-task basis.  Some tasks, especially optional or
third-party tasks, may not perform any or the expected
dependency analysis.

> 
> > As I started working on ANT, I found it very
> useful and intersting. 
> 
> But in ANT, while building each target, it will try
> to build all the 
> dependent targets that many times as it occurs in
> different targets.
> 
> As a result it is increasing project\'s build
> time.Is there any task to 
> ensure that the dependent targets once built will
> not&nbsp; be built 
> again ????
> 
> Every target in a build file should run once. if the
> same targets run 
> again and again in a single build, your are using
> <ant> when you dont 
> need to. Every task in a target should do its own
> dependency rules, 
> though some <javadoc> dont. You can use <uptodate>
> to determine if 
> targets need skipping
> 

The other case in which you would re-run targets is if
you have several targets, all of which depend on some
initializing or similar target, e.g.:

target name="foo" depends="init"
target name="bar" depends="init"

'ant foo bar' will run init, foo, init, bar .  There
are a few workarounds here:

 - The old standard IMHO was to set a property in the
init target and name this property in init's unless
attribute:

<target name="init" unless="init.complete">
  ...
  <property name="init.complete" value="any value" />
</target>

 - Another approach is to make another target that
calls both the other targets:

target name="foobar" depends="foo,bar"

'ant foobar' will then execute init, foo, bar. 
Obviously this could get messy depending on how many
"first-class" targets you may have.

 - More recently Ant was augmented with the notion of
a Project Executor.  An implementation is provided
OOTB that will "pretend" there is a target described
like target "foobar" above.  It is called the single
check executor and you can invoke it thus:

ant
-Dant.executor.class=org.apache.tools.ant.helper.SingleCheckExecutor
foo bar

The Executor will run targets init, foo, bar by virtue
of its having used a single dependency check to
generate the call graph for all called targets.

Finally, If you are using the <ant> and/or <antcall>
tasks (which I personally discourage, but there you
are) you can call multiple targets by specifying
nested <target> elements in these tasks.  This will
make your <ant>/<antcall> invocation (1) use a
SingleCheckExecutor (unless, in theory, some top-level
custom executor was configured otherwise for
subprojects) and (2) use less time and resources
because you're only running one subproject instead of
n (where n = number of targets called).

HTH,
Matt

> 
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