boolean registerListener(final SignalListener listener, final Signal signal) {
    assertNotNull(signal, "The signal to register the listener for cannot be null!");
    assertNotNull(listener,
        "The SignalListener being registered to listen for '%1$s' signals cannot be null!",
        signal.getName());

    return signalListeners.get(signal).add(listener);
  }
Map used to register SignalListeners with SignalHandlers...
geode-core/src/main/java/org/apache/geode/internal/process/signal/AbstractSignalNotificationHandler.java