sclass TestPhantomCleanUp {

  settable bool withGC;

  settable double maxWait = 60.0; // how many seconds

  gettable bool referenceWasCleared;

  gettable Duration delayBeforeClearance;

  // The object to be referenced & cleared by the GC.

  // Don't keep any references to it, of course!

  swappable O createReferent() {

    ret new S("copy of a string");

  }

  run {

    temp new RunnablesReferenceQueue queue;

    class MyPhantomRef<A> extends PhantomReference<A> is Runnable {

      new Flag flag;

      *(A a, RunnablesReferenceQueue queue) {

        super(a, queue!);

      }

      run {

        printWithMS("Behold the phantom!");

        flag.raise();

      }

    }

    var ref = new MyPhantomRef<O>(createReferent(), queue);

    printWithMS("Made the object.");

    if (withGC) {

      print("GC.");

      timedGC();

    }

    long time = sysNow();

    printWithMS("Now waiting...");

    if (ref.flag.waitUntilUp(toMS_int(maxWait))) {

      delayBeforeClearance = msToDuration(sysNow()-time);

      referenceWasCleared = true;

      printWithMS("Cool! Reference was cleared after "

        + renderElapsedSecondsPleasantly(delayBeforeClearance)

        + " (" + withOrWithout(withGC) + " GC)");

    } else

      printWithMS("Ouch. Reference not cleared even after " + maxWait + " s");

  }

  svoid allTests {

    testSmallObject();

    testHumungousObject();

  }

  svoid testSmallObject {

    for (gc : falseTrue()) {

      printAfterNL("Small object test!");

      new TestPhantomCleanUp().withGC(gc).run();

    }

  }

  svoid testHumungousObject {

    for (gc : falseTrue()) {

      printAfterNL("Humungous object test!");

      var tpcu = new TestPhantomCleanUp().withGC(gc);

      // pretty likely to be humungous

      // Def. humungous: an array bigger than (G1 region size/2)

      // Check "jinfo -flags $pid" to see the region size

      tpcu.createReferent = -> new byte[8*oneMegabyte_int()];

      tpcu.run();

    }

  }

}