HBASE-20069 fix existing findbugs errors in hbase-server; ADDENDUM Address review

Revert of the revert, i.e. reapply. Thought this had broken the build
but it was a bad nightly. Putting it back.

Revert "Revert "HBASE-20069 fix existing findbugs errors in hbase-server; ADDENDUM Address review""

This reverts commit 07eae00ec1.

hbase-server/src/main/java/org/apache/hadoop/hbase/master/ClusterStatusPublisher.java

@@ -134,7 +134,7 @@ public class ClusterStatusPublisher extends ScheduledChore {
 
   @Override
   protected void chore() {
-    if (!connected) {
+    if (!isConnected()) {
       return;
     }
 
@@ -170,6 +170,10 @@ public class ClusterStatusPublisher extends ScheduledChore {
     publisher.close();
   }
 
+  private synchronized boolean isConnected() {
+    return this.connected;
+  }
+
   /**
    * Create the dead server to send. A dead server is sent NB_SEND times. We send at max
    * MAX_SERVER_PER_MESSAGE at a time. if there are too many dead servers, we send the newly

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreFlusher.java

@@ -90,17 +90,9 @@ class MemStoreFlusher implements FlushRequester {
   private FlushType flushType;
 
   /**
-   * Singleton instance of this class inserted into flush queue.
+   * Singleton instance inserted into flush queue used for signaling.
    */
-  private static final WakeupFlushThread WAKEUPFLUSH_INSTANCE = new WakeupFlushThread();
-
-  /**
-   * Marker class used as a token inserted into flush queue that ensures the flusher does not sleep.
-   * Create a single instance only.
-   */
-  private static final class WakeupFlushThread implements FlushQueueEntry {
-    private WakeupFlushThread() {}
-
+  private static final FlushQueueEntry WAKEUPFLUSH_INSTANCE = new FlushQueueEntry() {
     @Override
     public long getDelay(TimeUnit unit) {
       return 0;
@@ -120,7 +112,7 @@ class MemStoreFlusher implements FlushRequester {
     public int hashCode() {
       return 42;
     }
-  }
+  };
 
 
   /**

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RegionCoprocessorHost.java

@@ -1119,6 +1119,8 @@ public class RegionCoprocessorHost
    * @return true or false to return to client if default processing should be bypassed, or null
    * otherwise
    */
+  @edu.umd.cs.findbugs.annotations.SuppressWarnings(value="NP_BOOLEAN_RETURN_NULL",
+      justification="Null is legit")
   public Boolean preCheckAndPutAfterRowLock(
       final byte[] row, final byte[] family, final byte[] qualifier, final CompareOperator op,
       final ByteArrayComparable comparator, final Put put) throws IOException {
@@ -1207,7 +1209,7 @@ public class RegionCoprocessorHost
    * or null otherwise
    */
   @edu.umd.cs.findbugs.annotations.SuppressWarnings(value="NP_BOOLEAN_RETURN_NULL",
-      justification="TODO: Fix")
+      justification="Null is legit")
   public Boolean preCheckAndDeleteAfterRowLock(final byte[] row, final byte[] family,
       final byte[] qualifier, final CompareOperator op, final ByteArrayComparable comparator,
       final Delete delete) throws IOException {