// In the newest pinging system (with flag PingV3), a ping source

// is the object that "allows" some code to run.

// When that code calls ping(), the ping source's action (if defined)

// is triggered.

// This allows randomly interrupting code execution, for example.

sclass PingSource {

  // returns true if it slept

  settable volatile IF0<Bool> action;

  // optional description of this ping source

  S text;

  // optional thread pool that this ping source likes to run in

  ThreadPool threadPool;

  *() {}

  *(ThreadPool *threadPool) {}

  *(ThreadPool *threadPool, S *text) {}

  *(IF0<Bool> *action) {}

  // returns true if it slept

  final bool get() {

    var a = action;

    ret a != null && a!;

  }

  final void ping { 

    var a = action;

    if (a != null) a!;

  }

  void cancel {

    action = new Cancelled;

  }

  class Cancelled is IF0<Bool> {

    public Bool get() { throw new PingSourceCancelledException(PingSource.this); }

  }

  record noeq Encapsulated(Runnable r) is Runnable {

    run {

      //System.out.println("Encapsulated running: " + r);

      try {

        pingSource_tl().set(PingSource.this);

        //System.out.println("Ping source set");

        ping();

        r.run();

        //System.out.println("Done running");

      } finally {

        //System.out.println("Finally");

        pingSource_tl().set(null);

      }

    }

    toString { ret PingSource.this + ": " + r; }

  }

  void do(Runnable r) {

    if (r == null) ret;

    threadPool.acquireThreadOrQueue(new Encapsulated(r));

  }

  toString { S t = text; ret nempty(t) ? t : super.toString(); }

  ISleeper_v2 sleeper() { ret threadPool.sleeper(); }

}