ant error Unable to rename old file to temporary file

Question

I'm using ant 1.8.0 and java 1.6.0.17 and I'm running into a strange problem.

In my build.xml, I have a simple task that compiles the code

<javac destdir="${dir.build.classes}" debug="on">
    <classpath refid="classpath"/>
    <src path="${dir.src.java}"/>
</javac>

In the "classpath" is a jar, call it library.jar

In a later task, I need to add a few classes to library.jar, which I do like this

<jar destfile="library.jar" update="true" duplicate="fail">
    <fileset dir="${dir.build.classes}">
        <include name="some/class/files"/>
    </fileset>
</jar>

This will fail with the error Unable to rename old file (library.jar) to temporary file

I stuck in a call to handle.exe before and after the javac call, and I can confirm that the java process running ant grabs a file handle to library.jar during the javac call, and it doesn't give it up. This causes my later attempt to update the jar to fail.

Why would ant keep a handle to the jar in a classpath open even after the javac task is complete?

Answer 1

So I found the answer, after some experimentation. By adding fork="true" to my javac task, the file handle is closed at the end of the task. This allows my jar modification to succeed later in the build.

It's unfortunate though, because I have to remember to add this to every upstream javac task.