ConfX created CASSANDRA-21096:
---------------------------------
Summary: TableMetricTest might cause NPE
Key: CASSANDRA-21096
URL: https://issues.apache.org/jira/browse/CASSANDRA-21096
Project: Apache Cassandra
Issue Type: Bug
Components: Test/dtest/java
Reporter: ConfX
The `MapMBeanWrapper.queryNames()` method in `TableMetricTest` returns `null`
instead of an empty `Set`, violating the `MBeanWrapper` interface contract.
This causes a `NullPointerException` when `GCInspector` is instantiated during
nodetool operations.
{code:java}
@Override
public Set<ObjectName> queryNames(ObjectName name, QueryExp query)
{
return null;
}
{code}
With this, we might meet NPE if queryNames() is called, for example, if we
restart a node and create a new GCInspector, then the GCInspector constructor
queries MBeans.
{code:java}
// GCInspector.java:144-146
ObjectName gcName = new
ObjectName(ManagementFactory.GARBAGE_COLLECTOR_MXBEAN_DOMAIN_TYPE + ",*");
for (ObjectName name : MBeanWrapper.instance.queryNames(gcName, null)) //
NPE HERE {code}
h2. StackTrace:
{code:java}
java.lang.NullPointerException: Cannot invoke "java.util.Set.iterator()"
because the return value of
"org.apache.cassandra.utils.MBeanWrapper.queryNames(javax.management.ObjectName,
javax.management.QueryExp)" is null
at org.apache.cassandra.service.GCInspector.<init>(GCInspector.java:145)
at
org.apache.cassandra.distributed.mock.nodetool.InternalNodeProbe.connect(InternalNodeProbe.java:79)
at
org.apache.cassandra.distributed.mock.nodetool.InternalNodeProbe.<init>(InternalNodeProbe.java:58)
at
org.apache.cassandra.distributed.impl.Instance$DTestNodeTool.<init>(Instance.java:1079)
at
org.apache.cassandra.distributed.impl.Instance.lambda$nodetoolResult$51(Instance.java:986)
{code}
A better way would be:
Change `MapMBeanWrapper.queryNames()` to return an empty set instead of null:
{code:java}
@Override
public Set<ObjectName> queryNames(ObjectName name, QueryExp query)
{
return Collections.emptySet(); // FIX: Return empty set, not null
} {code}
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