private void setAllGatewaySenderIds() {
    if (getGatewaySenderIds().isEmpty() && getAsyncEventQueueIds().isEmpty()) {
      allGatewaySenderIds = Collections.emptySet(); // fix for bug 45774
    }
    Set<String> tmp = new HashSet<>(getGatewaySenderIds());
    for (String asyncQueueId : getAsyncEventQueueIds()) {
      tmp.add(AsyncEventQueueImpl.getSenderIdFromAsyncEventQueueId(asyncQueueId));
    }
    allGatewaySenderIds = Collections.unmodifiableSet(tmp);
  }
Use ONLY imSync for IndexManager get and set.

@return {@link IndexManager} lock.
geode-core/src/main/java/org/apache/geode/internal/cache/AbstractRegion.java