Unify lifecycle of StatementLocksFactory implementations

And improve setting description.

community/kernel/src/main/java/org/neo4j/kernel/impl/factory/DataSourceModule.java

@@ -397,7 +397,7 @@ private static StatementLocksFactory createStatementLocksFactory( Locks locks, C
         List<StatementLocksFactory> factories = Iterables.toList( Service.load( StatementLocksFactory.class ) );
         if ( factories.isEmpty() )
         {
-            statementLocksFactory = new SimpleStatementLocksFactory( locks );
+            statementLocksFactory = new SimpleStatementLocksFactory();
 
             log.info( "No services implementing " + serviceName + " found. " +
                       "Using " + SimpleStatementLocksFactory.class.getSimpleName() );

community/kernel/src/main/java/org/neo4j/kernel/impl/locking/SimpleStatementLocksFactory.java

@@ -28,27 +28,37 @@
  */
 public class SimpleStatementLocksFactory implements StatementLocksFactory
 {
-    private final Locks locks;
+    private Locks locks;
 
-    public SimpleStatementLocksFactory( Locks locks )
+    public SimpleStatementLocksFactory()
     {
-        this.locks = requireNonNull( locks );
     }
 
     /**
-     * Inherited from the {@link StatementLocksFactory} interface but does nothing for this factory.
+     * Creates a new factory initialized with given {@code locks}.
+     * <b>Note:</b> should be used for tests only.
      *
-     * @param locks will not be used.
-     * @param config will not be used.
+     * @param locks the locks to use.
      */
+    public SimpleStatementLocksFactory( Locks locks )
+    {
+        initialize( locks, null );
+    }
+
     @Override
     public void initialize( Locks locks, Config config )
     {
+        this.locks = requireNonNull( locks );
     }
 
     @Override
     public StatementLocks newInstance()
     {
+        if ( locks == null )
+        {
+            throw new IllegalStateException( "Factory has not been initialized" );
+        }
+
         return new SimpleStatementLocks( locks.newClient() );
     }
 }

community/kernel/src/test/java/org/neo4j/kernel/impl/locking/SimpleStatementLocksFactoryTest.java

@@ -21,6 +21,8 @@
 
 import org.junit.Test;
 
+import org.neo4j.kernel.configuration.Config;
+
 import static org.hamcrest.Matchers.instanceOf;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertThat;
@@ -59,4 +61,34 @@ public void createSimpleStatementLocks()
         assertSame( client, statementLocks.optimistic() );
         assertSame( client, statementLocks.pessimistic() );
     }
+
+    @Test
+    public void newInstanceThrowsWhenNotInitialized()
+    {
+        SimpleStatementLocksFactory factory = new SimpleStatementLocksFactory();
+        try
+        {
+            factory.newInstance();
+            fail( "Exception expected" );
+        }
+        catch ( Exception e )
+        {
+            assertThat( e, instanceOf( IllegalStateException.class ) );
+        }
+    }
+
+    @Test
+    public void initializeThrowsForNullLocks()
+    {
+        SimpleStatementLocksFactory factory = new SimpleStatementLocksFactory();
+        try
+        {
+            factory.initialize( null, new Config() );
+            fail( "Exception expected" );
+        }
+        catch ( Exception e )
+        {
+            assertThat( e, instanceOf( NullPointerException.class ) );
+        }
+    }
 }

enterprise/deferred-locks/src/main/java/org/neo4j/kernel/impl/locking/DeferringStatementLocksFactory.java

@@ -35,9 +35,8 @@
 public class DeferringStatementLocksFactory implements StatementLocksFactory
 {
     @Internal
-    @Description( "Enable deferring of locks to commit time. This feature is really dangerous and impacts the " +
-                  "isolation level. It can result in both domain and storage level inconsistencies if used " +
-                  "without an additional transaction management layer on top." )
+    @Description( "Enable deferring of locks to commit time. This feature weakens the isolation level. " +
+                  "It can result in both domain and storage level inconsistencies." )
     public static final Setting<Boolean> deferred_locks_enabled =
             setting( "unsupported.dbms.deferred_locks.enabled", Settings.BOOLEAN, Settings.FALSE );