boolean unregisterListeners(final Signal signal) {
    assertNotNull(signal, "The signal from which to unregister all listeners cannot be null!");

    Set<SignalListener> listeners = signalListeners.get(signal);

    synchronized (listeners) {
      listeners.clear();
      return listeners.isEmpty();
    }
  }
Map used to register SignalListeners with SignalHandlers...
geode-core/src/main/java/org/apache/geode/internal/process/signal/AbstractSignalNotificationHandler.java