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Subject [GitHub] [zookeeper] belugabehr commented on a change in pull request #888: ZOOKEEPER-3347: Improve PathTrie Consistency
Date Wed, 24 Jul 2019 18:30:16 GMT
belugabehr commented on a change in pull request #888: ZOOKEEPER-3347: Improve PathTrie Consistency
URL: https://github.com/apache/zookeeper/pull/888#discussion_r306958715
 
 

 ##########
 File path: zookeeper-server/src/main/java/org/apache/zookeeper/common/PathTrie.java
 ##########
 @@ -40,254 +46,275 @@
  *      (bc)
  *   cf/
  *   (cf)
- */    
+ */
 public class PathTrie {
-    /**
-     * the logger for this class
-     */
+
+    /** Logger for this class */
     private static final Logger LOG = LoggerFactory.getLogger(PathTrie.class);
-    
-    /**
-     * the root node of PathTrie
-     */
-    private final TrieNode rootNode ;
-    
+
+    /** Root node of PathTrie */
+    private final TrieNode rootNode;
+
+    private final ReadWriteLock lock = new ReentrantReadWriteLock(true);
+
+    private final Lock readLock = lock.readLock();
+
+    private final Lock writeLock = lock.writeLock();
+
     static class TrieNode {
-        boolean property = false;
+        final String value;
         final Map<String, TrieNode> children;
-        TrieNode parent = null;
+        boolean property;
+        TrieNode parent;
+
         /**
-         * create a trienode with parent
-         * as parameter
-         * @param parent the parent of this trienode
+         * Create a trie node with parent as parameter.
+         *
+         * @param parent the parent of this node
+         * @param value the value stored in this node
          */
-        private TrieNode(TrieNode parent) {
-            children = new HashMap<String, TrieNode>();
+        private TrieNode(TrieNode parent, String value) {
+            this.value = value;
             this.parent = parent;
+            this.property = false;
+            this.children = new HashMap<>(4);
         }
-        
+
         /**
-         * get the parent of this node
+         * Get the parent of this node.
+         *
          * @return the parent node
          */
         TrieNode getParent() {
             return this.parent;
         }
-        
+
         /**
-         * set the parent of this node
+         * set the parent of this node.
+         *
          * @param parent the parent to set to
          */
         void setParent(TrieNode parent) {
             this.parent = parent;
         }
-        
+
         /**
-         * a property that is set 
-         * for a node - making it 
-         * special.
+         * A property that is set for a node - making it special.
          */
         void setProperty(boolean prop) {
             this.property = prop;
         }
-        
-        /** the property of this
-         * node 
-         * @return the property for this
-         * node
+
+        /**
+         * The property of this node.
+         *
+         * @return the property for this node
          */
-        boolean getProperty() {
+        boolean hasProperty() {
             return this.property;
         }
+
+        /**
+         * The value stored in this node.
+         *
+         * @return the value stored in this node
+         */
+        public String getValue() {
+          return this.value;
+        }
+
         /**
-         * add a child to the existing node
+         * Add a child to the existing node.
+         *
          * @param childName the string name of the child
          * @param node the node that is the child
          */
         void addChild(String childName, TrieNode node) {
-            synchronized(children) {
-                if (children.containsKey(childName)) {
-                    return;
-                }
-                children.put(childName, node);
-            }
+            this.children.putIfAbsent(childName, node);
         }
-     
+
         /**
-         * delete child from this node
-         * @param childName the string name of the child to 
-         * be deleted
+         * Delete child from this node.
+         *
+         * @param childName the name of the child to be deleted
          */
         void deleteChild(String childName) {
-            synchronized(children) {
-                if (!children.containsKey(childName)) {
-                    return;
-                }
-                TrieNode childNode = children.get(childName);
-                // this is the only child node.
-                if (childNode.getChildren().length == 1) { 
+            this.children.computeIfPresent(childName, (key, childNode) -> {
+                // Node no longer has an external property associated
+                childNode.setProperty(false);
+
+                // Delete it if it has no children (is a leaf node)
+                if (childNode.isLeafNode()) {
                     childNode.setParent(null);
-                    children.remove(childName);
+                    return null;
                 }
-                else {
-                    // their are more child nodes
-                    // so just reset property.
-                    childNode.setProperty(false);
-                }
-            }
+
+                return childNode;
+            });
         }
-        
+
         /**
-         * return the child of a node mapping
-         * to the input childname
+         * Return the child of a node mapping to the input child name.
+         *
          * @param childName the name of the child
          * @return the child of a node
          */
         TrieNode getChild(String childName) {
-            synchronized(children) {
-               if (!children.containsKey(childName)) {
-                   return null;
-               }
-               else {
-                   return children.get(childName);
-               }
-            }
+            return this.children.get(childName);
         }
 
         /**
-         * get the list of children of this 
-         * trienode.
-         * @return the string list of its children
+         * Get the list of children of this trienode.
+         *
+         * @return A collection containing the node's children
          */
-        String[] getChildren() {
-           synchronized(children) {
-               return children.keySet().toArray(new String[0]);
-           }
+        Collection<String> getChildren() {
+            return children.keySet();
         }
-        
+
         /**
-         * get the string representation
-         * for this node
+         * Determine if this node is a leaf (has no children).
+         *
+         * @return true if this node is a lead node; otherwise false
          */
+        boolean isLeafNode() {
+            return children.isEmpty();
+        }
+
+        @Override
         public String toString() {
-            StringBuilder sb = new StringBuilder();
-            sb.append("Children of trienode: ");
-            synchronized(children) {
-                for (String str: children.keySet()) {
-                    sb.append(" " + str);
-                }
-            }
-            return sb.toString();
+          return "TrieNode [name=" + value + ", property=" + property
+              + ", children=" + children.keySet() + "]";
         }
     }
-    
+
     /**
-     * construct a new PathTrie with
-     * a root node of /
+     * Construct a new PathTrie with a root node.
      */
     public PathTrie() {
-        this.rootNode = new TrieNode(null);
+        this.rootNode = new TrieNode(null, "");
     }
-    
+
     /**
-     * add a path to the path trie 
-     * @param path
+     * Add a path to the path trie.
+     *
+     * @param path the path to add to the trie
      */
-    public void addPath(String path) {
-        if (path == null) {
-            return;
-        }
-        String[] pathComponents = path.split("/");
-        TrieNode parent = rootNode;
-        String part = null;
-        if (pathComponents.length <= 1) {
-            throw new IllegalArgumentException("Invalid path " + path);
+    public void addPath(final String path) {
+        Objects.requireNonNull(path, "Path cannot be null");
+
+        final String[] pathComponents = StringUtils.split(path, '/');
+        if (pathComponents.length == 0) {
+            throw new IllegalArgumentException("Invalid path: " + path);
         }
-        for (int i=1; i<pathComponents.length; i++) {
-            part = pathComponents[i];
-            if (parent.getChild(part) == null) {
-                parent.addChild(part, new TrieNode(parent));
+
+        writeLock.lock();
+        try {
+            TrieNode parent = rootNode;
+            for (final String part : pathComponents) {
+                TrieNode child = parent.getChild(part);
+                if (child == null) {
+                    child = new TrieNode(parent, part);
+                    parent.addChild(part, child);
+                }
+                parent = child;
             }
-            parent = parent.getChild(part);
+            parent.setProperty(true);
+        } finally {
+            writeLock.lock();
 
 Review comment:
   I pushed new version to fix this.  Thanks for the catch.

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