diff --git a/src/main/java/workshop/exercises/DeadlockPreventionWorkshop.java b/src/main/java/workshop/exercises/DeadlockPreventionWorkshop.java index 91ba6a8..0897b84 100644 --- a/src/main/java/workshop/exercises/DeadlockPreventionWorkshop.java +++ b/src/main/java/workshop/exercises/DeadlockPreventionWorkshop.java @@ -20,17 +20,18 @@ 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. - - System.out.println(Thread.currentThread().getName() + " is attempting to lock " + r1.getName()); - synchronized (r1) { - System.out.println("+ " + Thread.currentThread().getName() + " locked " + r1.getName()); + + Resource first = (r1.getId() < r2.getId()) ? r1 : r2; + Resource second = (r1.getId() < r2.getId()) ? r2 : r1; + + System.out.println(Thread.currentThread().getName() + " is attempting to lock " + first.getName()); + synchronized (first) { + System.out.println("+ " + Thread.currentThread().getName() + " locked " + first.getName()); try { Thread.sleep(100); } catch (InterruptedException ignored) {} - - System.out.println(Thread.currentThread().getName() + " is attempting to lock " + r2.getName()); - synchronized (r2) { - System.out.println("+ " + Thread.currentThread().getName() + " locked " + r2.getName()); + + System.out.println(Thread.currentThread().getName() + " is attempting to lock " + second.getName()); + synchronized (second) { + System.out.println("+ " + Thread.currentThread().getName() + " locked " + second.getName()); System.out.println(Thread.currentThread().getName() + " using " + r1.getName() + " and " + r2.getName()); } } @@ -40,7 +41,7 @@ public class DeadlockPreventionWorkshop { Resource resA = new Resource(1, "ResourceA"); Resource resB = new Resource(2, "ResourceB"); - // Thread 1 locks A then B; Thread 2 locks B then A (causing deadlock if unordered) + Thread t1 = new Thread(() -> useResources(resA, resB), "Thread-1"); Thread t2 = new Thread(() -> useResources(resB, resA), "Thread-2"); diff --git a/src/main/java/workshop/exercises/LockWorkshop.java b/src/main/java/workshop/exercises/LockWorkshop.java index ec24ecf..5384206 100644 --- a/src/main/java/workshop/exercises/LockWorkshop.java +++ b/src/main/java/workshop/exercises/LockWorkshop.java @@ -5,16 +5,21 @@ import java.util.concurrent.locks.ReentrantLock; public class LockWorkshop { public static int counter = 0; - - // TODO: Create a ReentrantLock instance to protect the critical section + + + private static final Lock lock = new ReentrantLock(); public static class MyRunnable implements Runnable { @Override public void run() { 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); } @@ -25,13 +30,13 @@ public class LockWorkshop { 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); } } diff --git a/src/main/java/workshop/exercises/SynchronizedWorkshop.java b/src/main/java/workshop/exercises/SynchronizedWorkshop.java index 9259d8e..d91532e 100644 --- a/src/main/java/workshop/exercises/SynchronizedWorkshop.java +++ b/src/main/java/workshop/exercises/SynchronizedWorkshop.java @@ -2,16 +2,18 @@ package workshop.exercises; public class SynchronizedWorkshop { public static int counter = 0; - - // TODO: Define a lock object to prevent race condition + + private static final Object lock = new Object(); public static class MyRunnable implements Runnable { @Override public void run() { 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); } @@ -22,13 +24,13 @@ public class SynchronizedWorkshop { 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); } } diff --git a/src/main/java/workshop/exercises/TaylorSeries.java b/src/main/java/workshop/exercises/TaylorSeries.java index d63a18e..495dfad 100644 --- a/src/main/java/workshop/exercises/TaylorSeries.java +++ b/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; @@ -21,14 +21,32 @@ public class TaylorSeries { @Override public void run() { - // TODO: Calculate the n-th term of the Taylor series for sin(x): + // 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. + int exponent = 2 * n + 1; + + BigDecimal numerator = x.pow(exponent, mc); + if (n % 2 == 1) { + numerator = numerator.negate(); + } + + BigDecimal denominator = factorial(exponent); + BigDecimal term = numerator.divide(denominator, mc); + + // Add the term to the global sum, ensuring thread-safety by + // synchronizing on the shared class object that guards `sum`. + synchronized (TaylorSeries.class) { + sum = sum.add(term, mc); + } } - // TODO: Implement factorial(k) using BigDecimal + private BigDecimal factorial(int k) { - return BigDecimal.ZERO; + BigDecimal result = BigDecimal.ONE; + for (int i = 2; i <= k; i++) { + result = result.multiply(BigDecimal.valueOf(i)); + } + return result; } } @@ -39,9 +57,8 @@ public class TaylorSeries { 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)); } threadPool.shutdown(); @@ -51,7 +68,6 @@ public class TaylorSeries { Thread.currentThread().interrupt(); } - // Pre-calculated accurate value of sin(0.01) up to 1000 decimal places BigDecimal accurateValue = new BigDecimal("0.009999833334166664682542438269099729038964385360169151033879" + "1124794097345090639159659426367929614989901525182568937606738071143914781018343679925045223748779233" + "4633395662957704288475175228160558357110105077439518716860615533070998720636987509269668842490541364" +