Concurrency & Synchronization

Resources:

• Threads: Thread Lifecycle | Java Concurrency and Multithreading in Practice

Concurrency

Concurrency vs Parallelism

TODO: Define

Concurrency Issues

Deadlock: A situation where two or more threads are unable to proceed because each is waiting for the other to release a resource. Ex: Two threads each holding a lock the other needs, causing both to wait indefinitely.

Race Condition: Occurs when multiple threads access shared resources simultaneously, leading to unpredictable outcomes. Ex: Two threads incrementing a shared counter without synchronization, resulting in incorrect values.

Starvation: A situation where a thread is perpetually denied access to resources, preventing it from making progress. Ex: A low-priority thread never getting CPU time because high-priority threads are always running.

Fairness: Ensuring that all threads get a fair chance to execute, preventing starvation. Ex: Using fair locks that ensure threads acquire locks in the order they requested them.

Deadlock

Deadlock occurs when two or more threads are unable to proceed because each is waiting for the other to release a resource.

 public class DeadlockExample {
      private final Object lock1 = new Object();
      private final Object lock2 = new Object();

      public void method1() {
          synchronized (lock1) {
              System.out.println("Thread 1: Holding lock 1...");
              synchronized (lock2) {
                  System.out.println("Thread 1: Holding lock 2...");
              }
          }
      }

      public void method2() {
          synchronized (lock2) {
              System.out.println("Thread 2: Holding lock 2...");
              synchronized (lock1) {
                  System.out.println("Thread 2: Holding lock 1...");
              }
          }
      }
  }