Fix ExceptionsTable when stacktrace has zero elements

patch by Stefan Miklosovic; reviewed by Brandon Williams, Dmitry Konstantinov for CASSANDRA-20992

Author: smiklosovic

CHANGES.txt

@@ -1,4 +1,5 @@
 5.1
+ * Fix ExceptionsTable when stacktrace has zero elements (CASSANDRA-20992)
  * Replace blocking wait with non-blocking delay in paxos repair (CASSANDRA-20983)
  * Implementation of CEP-55 - Generation of role names (CASSANDRA-20897)
  * Add cqlsh autocompletion for the identity mapping feature (CASSANDRA-20021)

src/java/org/apache/cassandra/db/virtual/ExceptionsTable.java

@@ -171,15 +171,15 @@ public static void persist(Throwable t)
         if (INSTANCE != null)
         {
             INSTANCE.add(toPersist.getClass().getName(),
-                         stackTrace.get(0),
+                         stackTrace.isEmpty() ? "unknown" : stackTrace.get(0),
                          toPersist.getMessage(),
                          stackTrace,
                          now);
         }
         else
         {
             preInitialisationBuffer.add(new ExceptionRow(toPersist.getClass().getName(),
-                                                         stackTrace.get(0),
+                                                         stackTrace.isEmpty() ? "unknown" : stackTrace.get(0),
                                                          0,
                                                          toPersist.getMessage(),
                                                          stackTrace,

test/unit/org/apache/cassandra/db/virtual/ExceptionsTableTest.java

@@ -264,6 +264,28 @@ public void testTruncation()
         });
     }
 
+    @Test
+    public void testEmptyStacktrace()
+    {
+        doWithVTable(4, table ->
+        {
+            // register after treating exception, so it goes to pre-initialisation buffer first
+            VirtualKeyspaceRegistry.instance.register(new VirtualKeyspace(KS_NAME, ImmutableList.of(table)));
+            ExceptionsTable.INSTANCE = getVirtualTable(ExceptionsTable.class, KS_NAME, EXCEPTIONS_TABLE_NAME);
+
+            JVMStabilityInspector.uncaughtException(currentThread(), new MyUncaughtExceptionWithoutStacktrace("my exception"));
+
+            ExceptionsTable.BoundedMap buffer = table.buffer;
+            assertEquals(1, buffer.size());
+
+            LinkedHashMap<String, ExceptionRow> partition = buffer.get(MyUncaughtExceptionWithoutStacktrace.class.getName());
+            ExceptionRow clustering = partition.get("unknown");
+            assertNotNull(clustering);
+            assertEquals(1, clustering.count);
+            assertEquals("my exception", clustering.message);
+        });
+    }
+
     private List<UntypedResultSet.Row> rows(String query)
     {
         return execute(query).stream().collect(toList());
@@ -306,4 +328,12 @@ public MyUncaughtException2(String message)
             super(message);
         }
     }
+
+    public static class MyUncaughtExceptionWithoutStacktrace extends Throwable
+    {
+        public MyUncaughtExceptionWithoutStacktrace(String message)
+        {
+            super(message, null, false, false);
+        }
+    }
 }