Asynchronous operation of FileTree files?

Is there a way I can easily make the processing of FileTree files in a smart way in gradle tasks? I basically need to wait for the execution of all files, much like what you can do with GPars, but how do I do this gradle with FileTree?

task compressJs(dependsOn: [copyJsToBuild]) << {
    println 'Minifying JS'

    fileTree {
        from 'build/js'
        include开发者_如何学运维 '**/*.js'
    }.visit { element ->
        if (element.file.isFile()) {
            println "Minifying ${element.relativePath}"
            ant.java(jar: "lib/yuicompressor-2.4.6.jar", fork: true) {
                arg(value: "build/js/${element.relativePath}")
                arg(value: "-o")
                arg(value: "build/js/${element.relativePath}")
            }
        }
    }
}

It would be lovely if I could do something like .visit{}.async(wait:true), but my googling turned up nothing. Is there a way I can easily make this multi-threaded? The processing of one element has no effect on the processing of any other element.

---

Before thinking about going multi-threaded, I'd try the following:

• Run everything in the same JVM. Forking a new JVM for each input file is very inefficient.
• Make the compressJs task incremental so that it only executes if some input file has changed since the previous run.
• Run the minifier directly rather than via Ant (saves creation of a new class loader for each input file; not sure if it matters).

If this still leaves you unhappy with the performance, and you can't use a more performant minifier, you can still try to go multi-threaded. Gradle won't help you there (yet), but libraries like GPars or the Java Fork/Join framework will.

---

The GPars solution. Note that the compress() function could be modified to properly accept source dir/target dir/etc, but since all my names are consistent, I'm just using the one argument for now. I was able to cut my build time from 7.3s to 5.4s with only 3 files being minified. I've seen build times spiral out of control, so I'm always wary of performance with this kind of behavior.

import groovyx.gpars.GParsPool

buildscript {
    repositories {
        mavenCentral()
    }

    dependencies {
        classpath 'org.codehaus.gpars:gpars:0.12'
    }
}

def compress(String type) {
    def elementsToMinify = []
    fileTree {
        from type
        include "**/*.$type"
    }.visit { element ->
        if (element.file.isFile()) {
            elementsToMinify << element
        }
    }

    GParsPool.withPool(8) {
        elementsToMinify.eachParallel { element ->
            println "Minifying ${element.relativePath}"
            def outputFileLocation = "build/$type/${element.relativePath}"
            new File(outputFileLocation).parentFile.mkdirs()
            ant.java(jar: "lib/yuicompressor-2.4.6.jar", fork: true) {
                arg(value: "$type/${element.relativePath}")
                arg(value: "-o")
                arg(value: outputFileLocation)
            }
        }
    }
}

task compressJs {
    inputs.dir new File('js')
    outputs.dir new File('build/js')

    doLast {
        compress('js')
    }
}

task compressCss {
    inputs.dir new File('css')
    outputs.dir new File('build/css')

    doLast {
       compress('css')
    }
}