Interview Questions and Answers

Deadlock is a situation where two or more threads are blocked forever, waiting for each other to release the locks.

Example:

Thread 1 locks resource A and waits for resource B. Thread 2 locks resource B and waits for resource A.

The wait-notify mechanism is used for inter-thread communication, where one thread can signal the other that a certain condition has been met.

Example:

Using wait(), notify(), and notifyAll() methods in synchronized blocks.

The join() method is used to wait for a thread to die. It causes the current thread to pause execution until the specified thread completes its execution.

Example:

Thread anotherThread = new Thread(() -> { 
/* Thread logic */ }); 
anotherThread.start(); 
anotherThread.join();

A race condition occurs when two or more threads access shared data concurrently, and the final outcome depends on the order of execution.

Example:

When two threads increment a shared counter without proper synchronization.

The ReentrantLock class is a part of the java.util.concurrent package and provides a flexible locking mechanism with the ability to interrupt a thread that is waiting for the lock.

Example:

ReentrantLock lock = new ReentrantLock(); 
lock.lock(); 
try { /* Critical section */ } 
finally { lock.unlock(); }

The producer-consumer problem involves two types of threads: producers that produce data and consumers that consume the data. The challenge is to synchronize their activities.

Example:

Using a shared buffer and synchronization mechanisms to ensure proper communication between producers and consumers.

Thread dumping involves generating a snapshot of all the threads' current state and stack traces. It is useful for diagnosing performance or deadlock issues.

Example:

In Java, you can use tools like jstack or VisualVM to generate thread dumps.

The happens-before relationship is a partial ordering of memory operations in Java. It ensures that the result of one operation is visible to another, providing a consistent view of shared data among threads.

Example:

Using synchronized blocks establishes a happens-before relationship.

The Phaser class in Java provides a more flexible alternative to the CountDownLatch and CyclicBarrier for synchronizing threads. It supports dynamic registration of threads and phase advancement.

Example:

Phaser phaser = new Phaser(); 
phaser.register(); // Register the current thread

The Exchanger class provides a synchronization point at which threads can pair and swap elements within pairs. Each thread presents some object on entry to the exchange method, matches with a partner thread, and receives its partner's object on return.

Example:

Exchanger exchanger = new Exchanger<>();

The ForkJoinPool is a special-purpose ExecutorService designed for parallelizing divide-and-conquer algorithms. It is particularly useful for recursive tasks with multiple subtasks.

Example:

RecursiveTask and RecursiveAction are classes commonly used with ForkJoinPool.