pp.A4-HandOverHandLocking/src/main/java/pp/ThreadsafeSimplifiedList.java

@@ -2,7 +2,6 @@ package pp;
 
 public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
   private Node<T> first;
-  private final Object headLock = new Object();
 
   private static class Node<U> {
     U element;
@@ -23,33 +22,36 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
 
   @Override
   public boolean add(T element) {
-    Node<T> curr;
-
-    synchronized (headLock) {
+    synchronized (this) {
       if (first == null) {
         first = new Node<>(element, null, null);
         return true;
       }
-      curr = first;
     }
 
-    while (true) {
-      Node<T> next;
-      synchronized (curr.lock) {
-        next = curr.next;
-        if (next == null) {
-          curr.next = new Node<>(element, curr, null);
-          return true;
+    Node<T> curr;
+    synchronized (first.lock) {
+      curr = first;
+      while (true) {
+        Node<T> next;
+        synchronized (curr.lock) {
+          next = curr.next;
+          if (next == null) {
+            curr.next = new Node<>(element, curr, null);
+            return true;
+          }
+        }
+        synchronized (next.lock) {
+          curr = next;
         }
       }
-      curr = next;
     }
   }
 
   @Override
   public T get(int index) {
     Node<T> curr;
-    synchronized (headLock) {
+    synchronized (this) {
       if (first == null) throw new IndexOutOfBoundsException();
       curr = first;
     }
@@ -69,7 +71,7 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
   @Override
   public T set(int index, T element) {
     Node<T> curr;
-    synchronized (headLock) {
+    synchronized (this) {
       if (first == null) throw new IndexOutOfBoundsException();
       curr = first;
     }
@@ -90,7 +92,7 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
 
   @Override
   public boolean isEmpty() {
-    synchronized (headLock) {
+    synchronized (this) {
       return first == null;
     }
   }