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<b>Warning</b>:  session_start(): open(/var/lib/php/sessions/sess_mc2ec97328pdkulmu8o5aee0ct, O_RDWR) failed: No space left on device (28) in <b>/var/www/tb-usercake/models/config.php</b> on line <b>51</b><br />
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<b>Warning</b>:  session_start(): Failed to read session data: files (path: /var/lib/php/sessions) in <b>/var/www/tb-usercake/models/config.php</b> on line <b>51</b><br />
/** this class is fully thread-safe */
class Flag {
  private boolean up;
  private Trigger listeners = new Trigger();

  /** returns true if flag was down before */
  public synchronized boolean raise() {
    boolean result = doRaise();
    if (result) {
      listeners.trigger();
      listeners = null;
    }
    return result;
  }

  private synchronized boolean doRaise() {
    if (!up) {
      up = true;
      notifyAll();
      return true;
    } else
      return false;
  }

  public synchronized void waitUntilUp() {
    if (!up) {
      try {
        wait();
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
    }
  }

  public void onRaise(Runnable listener) {
    if (!addListener(listener))
      listener.run();
  }

  private synchronized boolean addListener(Runnable listener) {
    if (!up) {
      listeners.addListener(listener);
      return true;
    } else
      return false;
  }

  public synchronized boolean isUp() {
    return up;
  }

  public String toString() {
    return isUp() ? "up" : "down";
  }

  // currently does a semi-active wait with latency = 50 ms
  public void waitForThisOr(Flag otherFlag) {
    while (!isUp() && !otherFlag.isUp())
      MultiCoreUtil.sleep(50);
  }
}