message: Add a fixme for an invalid change
  Releasing the realm mutex between the cache lookup and adding the new Realm to
  the cache can result in two Realms for the same Scheduler being created.
diff: @@ -362,6 +362,9 @@ void RealmCoordinator::do_get_realm(Realm::Config config, std::shared_ptr<Realm>
  // Creating ExternalCommitHelper with mutex locked creates a potential deadlock
  // as the commit helper calls back on the Realm::on_change (not in the constructor,
  // but the thread sanitizer warns anyway)
  + // FIXME: this introduced a race condition, as getting a cached Realm requires
  + // that the lock be held from when the cache lookup is done until when the
  + // new Realm is added to the cache
  realm_lock.unlock_unchecked();
  std::unique_ptr<ExternalCommitHelper> notifier;
  try {
  