public Object retrieve(int id) {
    Object o = null;
    if (useWeakRefs) {
      final WeakReference<?> ref = (WeakReference<?>) map.get(id);
      if (ref != null) {
        o = ref.get();
        if (o == null) {
          // Clean up
          map.remove(id, ref);
        }
      }
    } else {
      o = map.get(id);
    }
    // System.out.println("ProcessorKeeper.retrieve(" + int + ") returning " + processor);
    return o;
  }
Retrieve a processor that was previously put() in this keeper. The id is the value returned
from put(). If there is no processor by that id, or it has been garbage collected, null is
returned.
geode-core/src/main/java/org/apache/geode/distributed/internal/ProcessorKeeper21.java