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();
    }
  }
}