PÜ 2

pp.A4-HandOverHandLocking/.gitignore

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+/target/
+/.classpath
+/.project

pp.A4-HandOverHandLocking/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>pp</groupId>
+  <artifactId>pp.A4-HandOverHandLocking</artifactId>
+  <version>1.0-SNAPSHOT</version>
+  <packaging>jar</packaging>
+
+  <properties>	
+    <exec.mainClass>pp.Main</exec.mainClass>
+    <maven.compiler.release>10</maven.compiler.release>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
+  <dependencies>
+    <dependency><!-- für Unit-Tests -->
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter</artifactId>
+      <version>5.10.0</version>
+      <scope>test</scope>
+    </dependency>
+    <dependency><!-- für Lombok -->
+      <groupId>org.projectlombok</groupId>
+      <artifactId>lombok</artifactId>
+      <version>1.18.30</version>
+      <scope>provided</scope>
+    </dependency>
+    <dependency><!-- für net.jcip Annotationen -->
+      <groupId>net.jcip</groupId>
+      <artifactId>jcip-annotations</artifactId>
+      <version>1.0</version>
+      <scope>provided</scope>
+    </dependency>
+  </dependencies>
+  <build>
+    <defaultGoal>clean compile exec:java</defaultGoal>
+    <plugins>
+      <plugin><!-- für Unit-Tests [mvn test] -->
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <version>3.0.0</version>
+      </plugin>
+      <plugin><!-- [mvn compile] -->
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>3.9.0</version>
+      </plugin>
+      <plugin><!-- [mvn exec:java] -->
+        <groupId>org.codehaus.mojo</groupId>
+        <artifactId>exec-maven-plugin</artifactId>
+        <version>3.1.0</version>
+      </plugin>
+      <plugin><!-- [mvn javadoc:javadoc] -->
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-javadoc-plugin</artifactId>
+        <version>3.5.0</version>
+        <configuration>
+          <show>private</show>
+          <locale>en_US</locale>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>

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

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+package pp;
+
+public class Main {
+    static SimplifiedList<Integer> list;
+
+    static Runnable sliceSum(int start, int end, int expected) {
+        return () -> {
+            var sum = 0;
+            for (var i = start; i < end; i++) {
+                sum += list.get(i);
+            }
+            if (sum != expected) {
+                System.out.println("Fehler in "
+                        + Thread.currentThread().getName() + ": " + sum);
+            }
+        };
+    }
+
+    public static void main(String... args) throws InterruptedException {
+        list = new ThreadsafeSimplifiedList<>();
+        for (int i = 0; i < 5000; i++) {
+            list.add(i);
+        }
+        var thread0 = new Thread(sliceSum(0, 1250, 780625));
+        var thread1 = new Thread(sliceSum(1250, 2500, 2343125));
+        var thread2 = new Thread(sliceSum(2500, 3750, 3905625));
+        var thread3 = new Thread(sliceSum(3750, 5000, 5468125));
+        var start = System.currentTimeMillis();
+        thread0.start();
+        thread1.start();
+        thread2.start();
+        thread3.start();
+        thread0.join();
+        thread1.join();
+        thread2.join();
+        thread3.join();
+        System.out.printf("%s: %d ms\n", list.getClass().toString(),
+                System.currentTimeMillis() - start);
+    }
+
+}

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

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+package pp;
+
+public interface SimplifiedList<T> {
+
+    /**
+     * 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
+     */
+    public T get(int index);
+
+    /**
+     * 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)
+     *
+     */
+    public boolean add(T element);
+
+    /**
+     * 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
+     */
+    public T set(int index, T element);
+
+    /**
+     * Returns true if this list contains no elements.
+     * 
+     * @return true if this list contains no elements
+     */
+    public boolean isEmpty();
+
+    /**
+     * delayed passing through of parameter
+     * 
+     * @param element element to pass through
+     * @return passed though element
+     *
+     */
+    public default T delay(T element) {
+        try {
+            Thread.sleep(10);
+        } catch (InterruptedException ex) {
+            Thread.currentThread().interrupt();
+        }
+        return element;
+    }
+}

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

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+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 Node(U element, Node<U> prev, Node<U> next) {
+      super();
+      this.element = element;
+      this.prev = prev;
+      this.next = next;
+    }
+  }
+
+  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;
+      }
+      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 set(int index, T element) {
+    var ptr = this.first;
+    for (var j = 0; j < index; j++) {
+      ptr = ptr.next;
+    }
+    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;
+  }
+}