<ivy:cachepath> is SLOW, how to avoid doing it every build and improve ivy cachepath performance?

Question

Compile times are slowed by 4s resolving dependant libs for my javac step every build on this line:

    <target name="compile" depends="bootstrap">
        <ivy:cachepath pathid="classpath"/> <!-- SLOW -->

I want to essentially CACHE the results of ivy:cachepath so I don't have to do it every build. I want ${classpath} to exist in less than 0.2 seconds

Context: This is a vanilla ant build.xml which bootstraps ivy, uses an ivy.xml file that lists standard maven dependencies, then calls javac with those libs in a class path)

    <property name="ivy.install.version" value="2.4.0"/>
    <property name="ivy.jar.dir" value="${basedir}/ivy"/>
    <property name="ivy.jar.file" value="${ivy.jar.dir}/ivy.jar"/>
    <property name="build.dir" value="build"/>
    <property name="src.dir" value="src"/>
    <target name="bootstrap" description="--> install ivy">
        <path id="ivy.lib.path">
            <fileset dir="${ivy.jar.dir}" includes="*.jar"/>
        </path>
        <taskdef resource="org/apache/ivy/ant/antlib.xml" uri="antlib:org.apache.ivy.ant" classpathref="ivy.lib.path"/>
    </target>

    <!-- Download any missing libs -->
    <target name="install" depends="bootstrap">
        <!-- install ivy.jar -->
        <mkdir dir="${ivy.jar.dir}"/>
        <echo message="installing ivy..."/>
        <get src="https://repo1.maven.org/maven2/org/apache/ivy/ivy/${ivy.install.version}/ivy-${ivy.install.version}.jar" dest="${ivy.jar.file}" usetimestamp="true"/>
        <!-- Downloads all the libraries from maven central via ivy.xml and saves them to classpath-->
        <ivy:settings file="ivysettings.xml"/>
        <ivy:resolve/>
        <ivy:retrieve sync="true"
                      type="jar,bundle"/>
        <ivy:cachepath pathid="classpath"/>
    </target>

  <target name="clean" depends="bootstrap">
        <delete dir="${build_dir}"/>
        <delete dir="./lib"/>
        <delete dir="./bin"/>
        <ivy:cleancache/>
  </target>


    <!-- Compile -->
    <target name="compile" depends="bootstrap">
        <ivy:cachepath pathid="classpath"/>
        <ivy:settings file="ivysettings.xml"/>
        <mkdir dir="${build_dir}"/>
        <javac encoding="ISO-8859-1"
               includeantruntime="false"
               srcdir="${src_dir}"
               destdir="${build_dir}"
               classpathref="classpath"
               debug="on">
            <!--<withKotlin/> &lt;!&ndash; If this is undefined, run "Build" target first. &ndash;&gt;-->
        </javac>
        <!--<kotlinc src="${src_dir}/TestSuite/TestSuite.java" output="${build_dir}/${jar_name}.jar"/>-->

        <delete file="${dist_dir}/${jar_name}.jar"/>

        <pathconvert property="classpath.name" pathsep=" ">
            <path refid="classpath" />
            <mapper>
                <chainedmapper>
                    <flattenmapper />
                    <globmapper from="*.jar" to="../lib/*.jar" />
                </chainedmapper>
            </mapper>
        </pathconvert>

        <echo message="classpath.name : ${classpath.name} " />
        <jar destfile="bin/${jar_name}.jar" basedir="build" includes="**/*.class lib/*">
            <manifest>
                <attribute name="Main-Class" value="${main-class}"/>
                <attribute name="Class-Path" value="${classpath.name}"/>
            </manifest>
        </jar>
    </target>

Answer 1

This is probably a stupid way to do it, but I just brute forced a solution by writing classpath to disk and cut build times in half:

Write via:

    <pathconvert property="classpath">
        <path refid="classpath" />
    </pathconvert>
    <propertyfile file="my.properties" comment="My properties">
        <entry key="classpath" value="${classpath}"/>
    </propertyfile>

Read via:

    <loadproperties srcFile="my.properties"/>

Use via:

    <javac classpath="${classpath}" ... >

It may have been even faster with the <echo file= task