📚 Main Topics

1. Multi-threaded Application

   • Example of a movie theater booking system.
   • Multiple users accessing the application simultaneously.

2. Lock Concept

   • Ensures that only one thread can book a seat at a time.
   • Threads that cannot acquire the lock enter a waiting state.

3. Reentrant Lock

   • Allows a thread to call the lock method multiple times on the same object.
   • Maintains a hold count to track how many times the lock has been acquired.

4. Fair vs. Unfair Locks

   • Fair locks ensure first-come, first-served access.
   • Unfair locks may allow a thread to acquire the lock out of order for speed.

5. Try Lock Methods

   • tryLock(): Attempts to acquire the lock without blocking.
   • tryLock(long timeout, TimeUnit unit): Attempts to acquire the lock within a specified timeout.

6. Exception Handling

   • Importance of using try-catch-finally to ensure locks are released even in case of exceptions.

7. Additional Lock Features

   • Methods to check if the lock is held by the current thread and to get the length of the waiting queue.

✨ Key Takeaways

• Locks are essential in multi-threaded applications to prevent race conditions when accessing shared resources.
• The ReentrantLock class provides more flexibility than the synchronized keyword, allowing for more complex locking mechanisms.
• Fair locks prevent thread starvation but may be slower due to queue management.
• Exception handling is crucial to avoid deadlocks caused by unhandled exceptions preventing lock release.

🧠 Lessons

• Always ensure that locks are released in a finally block to maintain application stability.
• Understand the differences between fair and unfair locks to choose the appropriate locking strategy based on application needs.
• Utilize tryLock() methods to avoid blocking threads when a lock is not available, allowing for more responsive applications.