HDDS-10971. Replace ConcurrentHashMap with HashMap in PipelineStateMap (

#6765)

hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/pipeline/PipelineStateMap.java

@@ -36,8 +36,6 @@
 import java.util.NavigableSet;
 import java.util.Set;
 import java.util.TreeSet;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.CopyOnWriteArrayList;
 
 import static java.lang.String.format;
 
@@ -46,24 +44,19 @@
  * its state.
  * Invariant: If a pipeline exists in PipelineStateMap, both pipelineMap and
  * pipeline2container would have a non-null mapping for it.
+ *
+ * Concurrency consideration:
+ *   - thread-unsafe
  */
 class PipelineStateMap {
+  private static final Logger LOG = LoggerFactory.getLogger(PipelineStateMap.class);
 
-  private static final Logger LOG = LoggerFactory.getLogger(
-      PipelineStateMap.class);
-
-  private final Map<PipelineID, Pipeline> pipelineMap;
-  private final Map<PipelineID, NavigableSet<ContainerID>> pipeline2container;
-  private final Map<ReplicationConfig, List<Pipeline>> query2OpenPipelines;
-
-  PipelineStateMap() {
+  // TODO: Use TreeMap for range operations?
+  private final Map<PipelineID, Pipeline> pipelineMap = new HashMap<>();
+  private final Map<PipelineID, NavigableSet<ContainerID>> pipeline2container = new HashMap<>();
+  private final Map<ReplicationConfig, List<Pipeline>> query2OpenPipelines = new HashMap<>();
 
-    // TODO: Use TreeMap for range operations?
-    pipelineMap = new ConcurrentHashMap<>();
-    pipeline2container = new ConcurrentHashMap<>();
-    query2OpenPipelines = new HashMap<>();
-
-  }
+  PipelineStateMap() { }
 
   /**
    * Adds provided pipeline in the data structures.
@@ -87,8 +80,8 @@ void addPipeline(Pipeline pipeline) throws IOException {
     }
     pipeline2container.put(pipeline.getId(), new TreeSet<>());
     if (pipeline.getPipelineState() == PipelineState.OPEN) {
-      query2OpenPipelines.computeIfAbsent(pipeline.getReplicationConfig(),
-          any -> new CopyOnWriteArrayList<>()).add(pipeline);
+      query2OpenPipelines.computeIfAbsent(pipeline.getReplicationConfig(), any -> new ArrayList<>())
+          .add(pipeline);
     }
   }
 
@@ -416,7 +409,7 @@ Pipeline updatePipelineState(PipelineID pipelineID, PipelineState state)
     if (updatedPipeline.getPipelineState() == PipelineState.OPEN) {
       // for transition to OPEN state add pipeline to query2OpenPipelines
       if (pipelineList == null) {
-        pipelineList = new CopyOnWriteArrayList<>();
+        pipelineList = new ArrayList<>();
         query2OpenPipelines.put(pipeline.getReplicationConfig(), pipelineList);
       }
       pipelineList.add(updatedPipeline);