WS08'

src/main/java/workshop/exercises/DeadlockPreventionWorkshop.java

@@ -21,7 +21,14 @@ public class DeadlockPreventionWorkshop {
 
     public static void useResources(Resource r1, Resource r2) {
         // TODO: Prevent deadlock by enforcing a consistent lock acquisition order
-        // Hint: Compare resource IDs and always synchronize on the resource with the smaller ID first.
+        Resource first = r1;
+        Resource second = r2;
+        if (r1.getId() > r2.getId()) {
+            first = r2;
+            second = r1;
+        }
+        r1 = first;
+        r2 = second;
         
         System.out.println(Thread.currentThread().getName() + " is attempting to lock " + r1.getName());
         synchronized (r1) {

src/main/java/workshop/exercises/LockWorkshop.java

@@ -5,8 +5,9 @@ import java.util.concurrent.locks.ReentrantLock;
 
 public class LockWorkshop {
     public static int counter = 0;
-    
+
     // TODO: Create a ReentrantLock instance to protect the critical section
+    public static final Lock lock = new ReentrantLock();
 
     public static class MyRunnable implements Runnable {
         @Override
@@ -14,24 +15,30 @@ public class LockWorkshop {
             int i;
             for (i = 0; i < 1_000_000; i++) {
                 // TODO: Acquire the lock, increment the counter, and release the lock safely in a finally block
-                counter += 1;
+                lock.lock();
+                try {
+                    counter += 1;
+                } finally {
+                    lock.unlock();
+                }
+
+                System.out.println("Increments completed by " + Thread.currentThread().getName() + ": " + i);
             }
-            System.out.println("Increments completed by " + Thread.currentThread().getName() + ": " + i);
+        }
+
+        public static void main(String[] args) throws InterruptedException {
+            counter = 0;
+
+            Thread thread1 = new Thread(new MyRunnable(), "Thread-1");
+            Thread thread2 = new Thread(new MyRunnable(), "Thread-2");
+
+            thread1.start();
+            thread2.start();
+
+            thread1.join();
+            thread2.join();
+
+            System.out.println("Final counter value (expected 2000000): " + counter);
         }
     }
-
-    public static void main(String[] args) throws InterruptedException {
-        counter = 0;
-
-        Thread thread1 = new Thread(new MyRunnable(), "Thread-1");
-        Thread thread2 = new Thread(new MyRunnable(), "Thread-2");
-        
-        thread1.start();
-        thread2.start();
-
-        thread1.join();
-        thread2.join();
-        
-        System.out.println("Final counter value (expected 2000000): " + counter);
-    }
 }

src/main/java/workshop/exercises/SynchronizedWorkshop.java

@@ -2,8 +2,9 @@ package workshop.exercises;
 
 public class SynchronizedWorkshop {
     public static int counter = 0;
-    
+
     // TODO: Define a lock object to prevent race condition
+    public static final Object lock = new Object();
 
     public static class MyRunnable implements Runnable {
         @Override
@@ -11,24 +12,26 @@ public class SynchronizedWorkshop {
             int i;
             for (i = 0; i < 1_000_000; i++) {
                 // TODO: Use a synchronized block to protect the counter increment
-                counter += 1;
+                synchronized (lock) {
+                    counter += 1;
+                }
+                System.out.println("Increments completed by " + Thread.currentThread().getName() + ": " + i);
             }
-            System.out.println("Increments completed by " + Thread.currentThread().getName() + ": " + i);
+        }
+
+        public static void main(String[] args) throws InterruptedException {
+            counter = 0;
+
+            Thread thread1 = new Thread(new MyRunnable(), "Thread-1");
+            Thread thread2 = new Thread(new MyRunnable(), "Thread-2");
+
+            thread1.start();
+            thread2.start();
+
+            thread1.join();
+            thread2.join();
+
+            System.out.println("Final counter value (expected 2000000): " + counter);
         }
     }
-
-    public static void main(String[] args) throws InterruptedException {
-        counter = 0;
-
-        Thread thread1 = new Thread(new MyRunnable(), "Thread-1");
-        Thread thread2 = new Thread(new MyRunnable(), "Thread-2");
-        
-        thread1.start();
-        thread2.start();
-
-        thread1.join();
-        thread2.join();
-        
-        System.out.println("Final counter value (expected 2000000): " + counter);
-    }
 }

src/main/java/workshop/exercises/TaylorSeries.java

@@ -8,7 +8,7 @@ import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 
 public class TaylorSeries {
-    
+
     public static class CalculateSin implements Runnable {
         private final MathContext mc = new MathContext(1000);
         private final BigDecimal x;
@@ -22,54 +22,67 @@ public class TaylorSeries {
         @Override
         public void run() {
             // TODO: Calculate the n-th term of the Taylor series for sin(x):
-            // term = (-1)^n * (x^(2n+1)) / (2n+1)!
-            // Add the term to the global sum ensuring thread-safety.
+            BigDecimal numerator = x.pow(2 * n + 1, mc);
+            BigDecimal denominator = factorial(2 * n + 1);
+
+            BigDecimal term = numerator.divide(denominator, mc);
+
+            if (n % 2 != 0) {
+                term = term.negate();
+            }
+
+            synchronized (TaylorSeries.class) {
+                sum = sum.add(term, mc);
+            }
         }
-
-        // TODO: Implement factorial(k) using BigDecimal
-        private BigDecimal factorial(int k) {
-            return BigDecimal.ZERO;
+            // TODO: Implement factorial(k) using BigDecimal
+            private BigDecimal factorial(int k) {
+                BigDecimal result = BigDecimal.ONE;
+                for (int i = 2; i <= k; i++) {
+                    result = result.multiply(BigDecimal.valueOf(i));
+                }
+                return result;
+            }
         }
-    }
+            public static BigDecimal sum = BigDecimal.ZERO;
 
-    public static BigDecimal sum = BigDecimal.ZERO;
+            public static void main (String[]args){
+                ExecutorService threadPool = Executors.newFixedThreadPool(4);
+                sum = BigDecimal.ZERO;
+                BigDecimal x = new BigDecimal("0.01");
 
-    public static void main(String[] args) {
-        ExecutorService threadPool = Executors.newFixedThreadPool(4);
-        sum = BigDecimal.ZERO;
-        BigDecimal x = new BigDecimal("0.01");
+                // Submit tasks to calculate terms
+                for (int i = 0; i < 100; i++) {
+                    // TODO: Submit task to the thread pool
+                    threadPool.submit(new CalculateSin(x, i));
+                }
 
-        // Submit tasks to calculate terms
-        for (int i = 0; i < 100; i++) {
-            // TODO: Submit task to the thread pool
+                threadPool.shutdown();
+                try {
+                    threadPool.awaitTermination(10, TimeUnit.SECONDS);
+                } catch (InterruptedException e) {
+                    Thread.currentThread().interrupt();
+                }
+
+                // Pre-calculated accurate value of sin(0.01) up to 1000 decimal places
+                BigDecimal accurateValue = new BigDecimal("0.009999833334166664682542438269099729038964385360169151033879" +
+                        "1124794097345090639159659426367929614989901525182568937606738071143914781018343679925045223748779233" +
+                        "4633395662957704288475175228160558357110105077439518716860615533070998720636987509269668842490541364" +
+                        "2046237535076816415219593915753970609625155007149734343650140126010756472960507873872984042987441343" +
+                        "4632784947709943715670321717675280271359744354619523360203501121465199963741173489051927920551271878" +
+                        "0890799396861427770050764919858890678677220571952090318596147460309593993397336341626522171452145068" +
+                        "2733933417711179372733354590095099959888961964291389175600643442999116373725594047366187408263088683" +
+                        "4976343405988894064532908768068263525544004211332459809773301487980907370431155859574851192235000645" +
+                        "6064003773432638837702651724406011257895842835907410397326351149391214249645075873929695397792073094" +
+                        "1188402364506858174852606021099282767046225114299907364917050686481947141812831031312882254660611456" +
+                        "524573907422800164140884130285721050703575");
+
+                sum = sum.setScale(1000, RoundingMode.HALF_DOWN);
+                accurateValue = accurateValue.setScale(1000, RoundingMode.HALF_DOWN);
+
+                System.out.println("sin(0.01) up to 1000 decimal places:");
+                System.out.println("Calculated Value:  " + sum.toPlainString());
+                System.out.println("Accurate Value:    " + accurateValue.toPlainString());
+                System.out.println("Difference:        " + accurateValue.subtract(sum).abs().toPlainString());
+            }
         }
-
-        threadPool.shutdown();
-        try {
-            threadPool.awaitTermination(10, TimeUnit.SECONDS);
-        } catch (InterruptedException e) {
-            Thread.currentThread().interrupt();
-        }
-
-        // Pre-calculated accurate value of sin(0.01) up to 1000 decimal places
-        BigDecimal accurateValue = new BigDecimal("0.009999833334166664682542438269099729038964385360169151033879" +
-                "1124794097345090639159659426367929614989901525182568937606738071143914781018343679925045223748779233" +
-                "4633395662957704288475175228160558357110105077439518716860615533070998720636987509269668842490541364" +
-                "2046237535076816415219593915753970609625155007149734343650140126010756472960507873872984042987441343" +
-                "4632784947709943715670321717675280271359744354619523360203501121465199963741173489051927920551271878" +
-                "0890799396861427770050764919858890678677220571952090318596147460309593993397336341626522171452145068" +
-                "2733933417711179372733354590095099959888961964291389175600643442999116373725594047366187408263088683" +
-                "4976343405988894064532908768068263525544004211332459809773301487980907370431155859574851192235000645" +
-                "6064003773432638837702651724406011257895842835907410397326351149391214249645075873929695397792073094" +
-                "1188402364506858174852606021099282767046225114299907364917050686481947141812831031312882254660611456" +
-                "524573907422800164140884130285721050703575");
-
-        sum = sum.setScale(1000, RoundingMode.HALF_DOWN);
-        accurateValue = accurateValue.setScale(1000, RoundingMode.HALF_DOWN);
-
-        System.out.println("sin(0.01) up to 1000 decimal places:");
-        System.out.println("Calculated Value:  " + sum.toPlainString());
-        System.out.println("Accurate Value:    " + accurateValue.toPlainString());
-        System.out.println("Difference:        " + accurateValue.subtract(sum).abs().toPlainString());
-    }
-}