Finished writing ThreadsafeSimplifiedList

src/main/java/io/dama/ffi/hoh/Main.java

@@ -8,10 +8,14 @@ public class Main {
             var sum = 0;
             for (var i = start; i < end; i++) {
                 sum += list.get(i);
+                if (i % 250 == 0) {
+                    System.out.println("Progress in " + Thread.currentThread().getName() + ": " + sum + " " + i);
+                }
             }
             if (sum != expected) {
-                System.out.println("Fehler in "
-                        + Thread.currentThread().getName() + ": " + sum);
+                System.err.println("Fehler in " + Thread.currentThread().getName() + ": " + sum);
+            } else {
+                System.out.println("Ok in " + Thread.currentThread().getName() + ": " + sum);
             }
         };
     }
@@ -21,6 +25,9 @@ public class Main {
         for (int i = 0; i < 5000; i++) {
             list.add(i);
         }
+
+        System.out.println("Liste: " + list);
+
         var thread0 = new Thread(sliceSum(0, 1250, 780625));
         var thread1 = new Thread(sliceSum(1250, 2500, 2343125));
         var thread2 = new Thread(sliceSum(2500, 3750, 3905625));

src/main/java/io/dama/ffi/hoh/ThreadsafeSimplifiedList.java

@@ -1,5 +1,8 @@
 package io.dama.ffi.hoh;
 
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
 public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
     private Node<T> first;
 
@@ -7,6 +10,7 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
         private U element;
         private Node<U> prev;
         private Node<U> next;
+        private final Lock lock = new ReentrantLock();
 
         private Node(U element, Node<U> prev, Node<U> next) {
             super();
@@ -14,6 +18,18 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
             this.prev = prev;
             this.next = next;
         }
+
+        @Override
+        public String toString() {
+            StringBuilder builder = new StringBuilder();
+            builder.append("'").append(this.element).append("'");
+            var node = this;
+            while (node.next != null) {
+                node = node.next;
+                builder.append(" -> '").append(node.element).append("'");
+            }
+            return builder.toString();
+        }
     }
 
     public ThreadsafeSimplifiedList() {
@@ -28,31 +44,54 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
      * @return the element at the specified position in this list
      */
     @Override
-    public synchronized T get(int index) {
-        var ptr = this.first;
-        for (var j = 0; j < index; j++) {
-            ptr = ptr.next;
+    public T get(int index) {
+        Node<T> ptr = this.first;
+
+        ptr.lock.lock();
+        try {
+            for (var j = 0; j < index; j++) {
+                ptr.next.lock.lock();
+                ptr = ptr.next;
+                ptr.prev.lock.unlock();
+            }
+
+            return delay(ptr.element);
+        } finally {
+            ptr.lock.unlock();
+            if (ptr.prev != null && ptr.prev.lock.tryLock()) {
+                ptr.prev.lock.unlock();
+            }
         }
-        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
-    public synchronized boolean add(T element) {
+    public boolean add(T element) {
         if (this.first != null) {
             var ptr = this.first;
-            while (ptr.next != null) {
-                ptr = ptr.next;
+
+            ptr.lock.lock();
+            try {
+                while (ptr.next != null) {
+                    ptr.next.lock.lock();
+                    ptr = ptr.next;
+                    ptr.prev.lock.unlock();
+                }
+
+                ptr.next = new Node<>(element, ptr, null);
+            } finally {
+                ptr.lock.unlock();
+                if (ptr.prev != null && ptr.prev.lock.tryLock()) {
+                    ptr.prev.lock.unlock();
+                }
             }
-            ptr.next = new Node<>(element, ptr, null);
         } else {
             this.first = new Node<>(element, null, null);
         }
@@ -62,29 +101,46 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
     /**
      * 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
-    public synchronized T set(int index, T element) {
-        var ptr = this.first;
-        for (var j = 0; j < index; j++) {
-            ptr = ptr.next;
+    public T set(int index, T element) {
+        Node<T> ptr = this.first;
+
+        ptr.lock.lock();
+        try {
+            for (var j = 0; j < index; j++) {
+                ptr.next.lock.lock();
+                ptr = ptr.next;
+                ptr.prev.lock.unlock();
+            }
+
+            var prevElement = ptr.element;
+            ptr.element = element;
+            return prevElement;
+        } finally {
+            ptr.lock.unlock();
+            if (ptr.prev != null && ptr.prev.lock.tryLock()) {
+                ptr.prev.lock.unlock();
+            }
         }
-        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
-    public synchronized boolean isEmpty() {
+    public boolean isEmpty() {
         return this.first == null;
     }
+
+    @Override
+    public String toString() {
+        return this.first != null ? "[" + this.first + "]" : "[]";
+    }
 }