HDFS-12171. Reduce IIP object allocations for inode lookup. Contributed by Daryn Sharp.

(cherry picked from commit 3d8c7d701b8f22b3b4d67f587f7ff2318c60c541)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/EncryptionZoneManager.java

@@ -209,9 +209,8 @@ public class EncryptionZoneManager {
     if (!hasCreatedEncryptionZone()) {
       return null;
     }
-    List<INode> inodes = iip.getReadOnlyINodes();
-    for (int i = inodes.size() - 1; i >= 0; i--) {
-      final INode inode = inodes.get(i);
+    for (int i = iip.length() - 1; i >= 0; i--) {
+      final INode inode = iip.getINode(i);
       if (inode != null) {
         final EncryptionZoneInt ezi = encryptionZones.get(inode.getId());
         if (ezi != null) {

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/INodesInPath.java

@@ -18,9 +18,6 @@
 package org.apache.hadoop.hdfs.server.namenode;
 
 import java.util.Arrays;
-import java.util.Collections;
-import java.util.List;
-import java.util.NoSuchElementException;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -298,17 +295,9 @@ public class INodesInPath {
    *         otherwise, i < 0, return the (length + i)-th inode.
    */
   public INode getINode(int i) {
-    if (inodes == null || inodes.length == 0) {
-      throw new NoSuchElementException("inodes is null or empty");
-    }
-    int index = i >= 0 ? i : inodes.length + i;
-    if (index < inodes.length && index >= 0) {
-      return inodes[index];
-    } else {
-      throw new NoSuchElementException("inodes.length == " + inodes.length);
-    }
+    return inodes[(i < 0) ? inodes.length + i : i];
   }
-  
+
   /** @return the last inode. */
   public INode getLastINode() {
     return getINode(-1);
@@ -346,10 +335,6 @@ public class INodesInPath {
     return inodes.length;
   }
 
-  public List<INode> getReadOnlyINodes() {
-    return Collections.unmodifiableList(Arrays.asList(inodes));
-  }
-
   public INode[] getINodesArray() {
     INode[] retArr = new INode[inodes.length];
     System.arraycopy(inodes, 0, retArr, 0, inodes.length);

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestSnapshotPathINodes.java

@@ -310,9 +310,8 @@ public class TestSnapshotPathINodes {
   }
 
   private int getNumNonNull(INodesInPath iip) {
-    List<INode> inodes = iip.getReadOnlyINodes();
-    for (int i = inodes.size() - 1; i >= 0; i--) {
-      if (inodes.get(i) != null) {
+    for (int i = iip.length() - 1; i >= 0; i--) {
+      if (iip.getINode(i) != null) {
         return i+1;
       }
     }