Adding comments and refactoring further

src/main/java/com/hithomelabs/dsa/concurrency/DeadLockExampleWithLock.java

@@ -13,14 +13,22 @@ import java.util.concurrent.locks.ReentrantLock;
 class Paper{
 
     private static Lock lock = new ReentrantLock();
-    private String message;
 
     public String procurePaper() {
-        boolean hasLock = false;
         try{
             if(lock.tryLock(500, TimeUnit.MILLISECONDS)){
-                hasLock = true;
+
+                // * * Inner try block if lock is acquired successfully
+                // * * To ensure the lock is always unlocked in the finally block
+
+                try{
                     return "writing on paper ...";
+                } catch (Exception e) {
+                    throw e; // * * Inner catch block just throws the exception for outer block to handle
+                }
+                finally {
+                    lock.unlock();
+                }
             }
             else{
                 return "Could not get lock";
@@ -28,10 +36,6 @@ class Paper{
         }catch (Exception e){
             System.out.println(e.getMessage());
         }
-        finally {
-            if (hasLock)
-                lock.unlock();
-        }
         return "";
     }
 
@@ -39,16 +43,31 @@ class Paper{
 
 class Pen{
 
-    private String message;
     private static Lock lock = new ReentrantLock();
 
     public String procurePen(){
-        boolean hasLock = false;
+
+        // * * Outer try block, required because a tryLock with timeout needs to handle interrupts
         try{
             if(lock.tryLock(500,TimeUnit.MILLISECONDS)){
-                hasLock = true;
+
-                Thread.sleep(5000);
+                // * * Inner try block if lock is acquired successfully
+                // * * to ensure the lock is always unlocked in the finally block
+
+                try {
+
+                    // * * After gaining lock, thread sleeps
+                    // * * Causing the other thread to timeOut waiting to procurePen
+
+                    Thread.sleep(1000);
                     return "Writing with pen ...";
+                } catch (InterruptedException e) {
+                    throw e;
+                }
+                finally {
+                    lock.unlock();
+                }
+
             }
             else{
                 return "Could not get lock";
@@ -57,13 +76,8 @@ class Pen{
         catch(Exception e){
             System.out.println(e.getMessage());
         }
-        finally {
-            if(hasLock)
-                lock.unlock();
-        }
         return "";
     }
-
 }
 
 @AllArgsConstructor
@@ -74,8 +88,8 @@ class VendorWithLock1 implements Runnable{
 
     @Override
     public void run() {
-        System.out.println(Thread.currentThread() + paper.procurePaper());
+        System.out.println(Thread.currentThread() + ":" + paper.procurePaper());
-        System.out.println(Thread.currentThread() + pen.procurePen());
+        System.out.println(Thread.currentThread() +  ":" + pen.procurePen());
     }
 }