Usage of Collections.unmodifiableCollection is unsafe

This is a follow-up to https://git.opendaylight.org/gerrit/#/c/51583/
wrt a review comment questioning why I returned a new ArrayList instead
of returning the Set directly. One reason was to avoid mutation of the
internal set by the caller but also to capture the state of the set at
that point in time and avoid concurrent mods which may not be safe.
Where a concurrent set is used, it would be thread-safe to return the
set directly but the set may by modified as the caller is iterating it
which may not be desired. For the other class whose set is a keySet
from a non-threadsafe Map, the caller could get a ConcurrentMod
exception while iterating. Based on the review, I changed the call
sites to return a Collections.unmodifiableCollection but this is also
incorrect and is susceptible to the same issues as that impl reads-thru
to the underlying collection. Therefore I changed the call sites back
to returning a new ArrayList.

Change-Id: I504f38c5bfc4c707180ac301eb10acd0ac24f872
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>
(cherry picked from commit d98bea5d456be31205b64dc8f0c5f3ae2b1a4cd0)

diff --git a/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/DataChangeListenerSupport.java b/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/DataChangeListenerSupport.java
index 57e20059e69cfed0229a15ae67f642b3a385d684..cae4559bdcd74a3e163fde496daa74091cbac4ab 100644 (file)
--- a/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/DataChangeListenerSupport.java
+++ b/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/DataChangeListenerSupport.java
@@ -11,8 +11,8 @@ import akka.actor.ActorRef;
 import akka.actor.ActorSelection;
 import com.google.common.base.Optional;
 import com.google.common.collect.Sets;
+import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Map.Entry;
 import java.util.Set;
 import org.opendaylight.controller.cluster.datastore.messages.EnableNotification;
@@ -38,7 +38,7 @@ final class DataChangeListenerSupport extends AbstractDataListenerSupport<
     }
 
     Collection<ActorSelection> getListenerActors() {
-        return Collections.unmodifiableCollection(listenerActors);
+        return new ArrayList<>(listenerActors);
     }
 
     @Override

diff --git a/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/DataTreeChangeListenerSupport.java b/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/DataTreeChangeListenerSupport.java
index abafae80493bf74ca2ec3580739bf8cab98fd682..f6208193f11017dedec8da025d76baa0a23cd12d 100644 (file)
--- a/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/DataTreeChangeListenerSupport.java
+++ b/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/DataTreeChangeListenerSupport.java
@@ -11,8 +11,8 @@ import akka.actor.ActorRef;
 import akka.actor.ActorSelection;
 import com.google.common.base.Optional;
 import com.google.common.collect.Sets;
+import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Map.Entry;
 import java.util.Set;
 import org.opendaylight.controller.cluster.datastore.messages.EnableNotification;
@@ -32,7 +32,7 @@ final class DataTreeChangeListenerSupport extends AbstractDataListenerSupport<DO
     }
 
     Collection<ActorSelection> getListenerActors() {
-        return Collections.unmodifiableCollection(listenerActors);
+        return new ArrayList<>(listenerActors);
     }
 
     @Override

diff --git a/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/DataTreeCohortActorRegistry.java b/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/DataTreeCohortActorRegistry.java
index e232e4fa849283b1ba0ab710e29f89931f795451..28fe93e38ab976af43b1abaf644fdd6ef98ee410 100644 (file)
--- a/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/DataTreeCohortActorRegistry.java
+++ b/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/DataTreeCohortActorRegistry.java
@@ -15,7 +15,6 @@ import akka.util.Timeout;
 import com.google.common.base.Preconditions;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -50,7 +49,7 @@ class DataTreeCohortActorRegistry extends AbstractRegistrationTree<ActorRef> {
     private final Map<ActorRef, RegistrationTreeNode<ActorRef>> cohortToNode = new HashMap<>();
 
     Collection<ActorRef> getCohortActors() {
-        return Collections.unmodifiableCollection(cohortToNode.keySet());
+        return new ArrayList<>(cohortToNode.keySet());
     }
 
     void registerCohort(final ActorRef sender, final RegisterCohort cohort) {