fairness of locks

rahulXbarnwal · rahulXbarnwal · commit c1eb4e7068b0 · 2026-01-20T16:03:42.000+05:30
diff --git a/src/multithreading/locks/FairnessLockExample.java b/src/multithreading/locks/FairnessLockExample.java
@@ -0,0 +1,60 @@
+package multithreading.locks;
+
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+/*
+locking me fairness hoti hai, order determine hoti hai ki kon se thread ko lock milega, kyuki multiple thread wants lock,
+to sbse phle kisko milega fir kisko milega, to wo order jo hai usko fairness kehte
+
+jo pehle aaya hai usko pehle lock milega
+
+Fair Lock: Jo pehle aya, usko lock milega (FIFO)
+Unfair Lock: Jo fast hai wo ghus jata hai, chahe baad me aaya ho
+
+let's say 20 threads hai and unme se ek to lock mil hi nhi rha hai baaki sb race krrhe hai, (starvation)
+this doesn't happen in fairness, mauka sbko milega, order to FIFO rhega hi but mauka sbko milega
+
+Disadvantages of synchronization:
+- synchronized me fairness ki guarantee nhi hai
+- indefinitely blocking hoti hai
+- interruptibility bhi nhi hai
+- synchronized ko pta hi nhi hai kon sa read / write hai to wo to poora block krke rkhega
+ */
+
+public class FairnessLockExample {
+//    private  final Lock unfairLock = new ReentrantLock();
+    private final Lock lock = new ReentrantLock(true);
+
+    public void accessResource() {
+        lock.lock();
+        try {
+            System.out.println(Thread.currentThread().getName() + " acquired the lock");
+            Thread.sleep(1000);
+        } catch(InterruptedException e) {
+            Thread.currentThread().interrupt();
+        } finally {
+            System.out.println(Thread.currentThread().getName() + " released the lock");
+            lock.unlock();
+        }
+    }
+
+    public static void main(String[] args) {
+        FairnessLockExample example = new FairnessLockExample();
+
+        Runnable task = new Runnable() {
+            @Override
+            public void run() {
+                example.accessResource();
+            }
+        };
+
+        Thread thread1 = new Thread(task, "Thread 1");
+        Thread thread2 = new Thread(task, "Thread 2");
+        Thread thread3 = new Thread(task, "Thread 3");
+
+        thread1.start();
+        thread2.start();
+        thread3.start();
+    }
+}
