core-edge: minor reader pool improvements

enterprise/core-edge/src/main/java/org/neo4j/coreedge/raft/log/segmented/ReaderPool.java

@@ -36,7 +36,7 @@
 // TODO: Prune stale readers with a recurring job.
 class ReaderPool
 {
-    private final ArrayList<Reader> pool;
+    private ArrayList<Reader> pool;
     private final int maxSize;
     private final Log log;
     private final FileNames fileNames;
@@ -125,16 +125,23 @@ private void dispose( Reader reader )
         }
     }
 
-    synchronized void disposeAll() throws IOException
+    synchronized void close() throws IOException
     {
         for ( Reader reader : pool )
         {
             reader.close();
         }
+        pool.clear();
+        pool = null;
     }
 
     public synchronized void prune( long version )
     {
+        if ( pool == null )
+        {
+            return;
+        }
+
         Iterator<Reader> itr = pool.iterator();
         while ( itr.hasNext() )
         {

enterprise/core-edge/src/main/java/org/neo4j/coreedge/raft/log/segmented/SegmentedRaftLog.java

@@ -104,7 +104,7 @@ public synchronized void start() throws IOException, DamagedLogStorageException,
     @Override
     public synchronized void stop() throws DisposedException, IOException
     {
-        readerPool.disposeAll();
+        readerPool.close();
         state.segments.close();
     }
 

enterprise/core-edge/src/test/java/org/neo4j/coreedge/raft/log/segmented/ReaderPoolTest.java

@@ -147,7 +147,7 @@ public void shouldDisposeAllReleasedReaders() throws Exception
         pool.release( readerC );
 
         // when
-        pool.disposeAll();
+        pool.close();
 
         // then
         verify( readerA ).close();