Merge pull request 'first test' (#2) from SL_U2_SJ into main

Reviewed-on: #2

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

@@ -1,5 +1,6 @@
 package pp;
 
+
 public class Main {
     static SimplifiedList<Integer> list;
 

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

@@ -1,19 +1,15 @@
 package pp;
 
-import lombok.Synchronized;
-import net.jcip.annotations.ThreadSafe;
-
-@ThreadSafe
 public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
   private Node<T> first;
 
-  private class Node<U> {
-    private U element;
-    private Node<U> prev;
-    private Node<U> next;
+  private static class Node<U> {
+    U element;
+    Node<U> prev;
+    Node<U> next;
+    final Object lock = new Object();
 
-    private Node(U element, Node<U> prev, Node<U> next) {
-      super();
+    Node(U element, Node<U> prev, Node<U> next) {
       this.element = element;
       this.prev = prev;
       this.next = next;
@@ -21,78 +17,84 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
   }
 
   public ThreadsafeSimplifiedList() {
-    super();
     this.first = null;
   }
 
-  /**
-   * Returns the element at the specified position in this list.
-   *
-   * @param index index of the element to return
-   * @return the element at the specified position in this list
-   */
   @Override
-  @Synchronized
-  public T get(int index) {
-    var ptr = this.first;
-    for (var j = 0; j < index; j++) {
-      ptr = ptr.next;
-    }
-    return delay(ptr.element);
-  }
-
-  /**
-   * Appends the specified element to the end of this list. There are no
-   * limitations on what elements may be added to this list.
-   * 
-   * @param element element to be appended to this list
-   * @return true
-   * @see java.util.Collection#add(Object)
-   *
-   */
-  @Override
-  @Synchronized
   public boolean add(T element) {
-    if (this.first != null) {
-      var ptr = this.first;
-      while (ptr.next != null) {
-        ptr = ptr.next;
+    synchronized (this) {
+      if (first == null) {
+        first = new Node<>(element, null, 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) {
+            // letztes Element erreicht → neues anhängen
+            curr.next = new Node<>(element, curr, null);
+            return true;
+          }
+        }
+        synchronized (next.lock) {
+          curr = next;
+        }
       }
-      ptr.next = new Node<>(element, ptr, null);
-    } else {
-      this.first = new Node<>(element, null, null);
     }
-    return true;
   }
 
-  /**
-   * Replaces the element at the specified position in this list with the
-   * specified element.
-   * 
-   * @param index   index of the element to replace
-   * @param element element to be stored at the specified position
-   * @return the element previously at the specified position
-   */
   @Override
-  @Synchronized
+  public T get(int index) {
+    Node<T> curr;
+    synchronized (this) {
+      if (first == null) throw new IndexOutOfBoundsException();
+      curr = first;
+    }
+
+    synchronized (curr.lock) {
+      for (int i = 0; i < index; i++) {
+        Node<T> next = curr.next;
+        if (next == null) throw new IndexOutOfBoundsException();
+        synchronized (next.lock) {
+          curr = next;
+        }
+      }
+      return delay(curr.element);
+    }
+  }
+
+  @Override
   public T set(int index, T element) {
-    var ptr = this.first;
-    for (var j = 0; j < index; j++) {
-      ptr = ptr.next;
+    Node<T> curr;
+    synchronized (this) {
+      if (first == null) throw new IndexOutOfBoundsException();
+      curr = first;
+    }
+
+    synchronized (curr.lock) {
+      for (int i = 0; i < index; i++) {
+        Node<T> next = curr.next;
+        if (next == null) throw new IndexOutOfBoundsException();
+        synchronized (next.lock) {
+          curr = next;
+        }
+      }
+      T old = curr.element;
+      curr.element = element;
+      return old;
     }
-    var prevElement = ptr.element;
-    ptr.element = element;
-    return prevElement;
   }
 
-  /**
-   * Returns true if this list contains no elements.
-   * 
-   * @return true if this list contains no elements
-   */
   @Override
-  @Synchronized
   public boolean isEmpty() {
-    return this.first == null;
+    synchronized (this) {
+      return first == null;
+    }
   }
 }