+ * Extensible bundle tracker. Takes several BundleTrackerCustomizers and
+ * propagates bundle events to all of them.
+ *
+ * Primary customizer may return tracking object,
+ * which will be passed to it during invocation of
+ * {@link BundleTrackerCustomizer#removedBundle(Bundle, BundleEvent, Future)}
+ *
+ *
+ * This extender modifies behaviour to not leak platform thread
+ * in {@link BundleTrackerCustomizer#addingBundle(Bundle, BundleEvent)}
+ * but deliver this event from its own single threaded executor.
+ *
+ * If bundle is removed before event for adding bundle was executed,
+ * that event is cancelled. If addingBundle event is currently in progress
+ * or was already executed, platform thread is block untill addingBundle
+ * finishes so bundle could be removed correctly in platform thread.
+ *
+ *
+ * Method {@link BundleTrackerCustomizer#removedBundle(Bundle, BundleEvent, Object)}
+ * is never invoked on registered trackers.