Advanced Java Concurrency: Phaser, CompletableFuture, and ForkJoinPool

This guide explores advanced Java concurrency tools: `Phaser` for multi-phase synchronization, `CompletableFuture` for asynchronous programming, and `ForkJoinPool` for parallel task execution. Learn how to use these powerful features to build efficient and scalable concurrent applications.

Java Concurrency: Advanced Techniques and Concepts

`Phaser` Class

Question 14: `Phaser` Class

The `Phaser` class in Java 8 is a versatile synchronization tool for managing multiple threads across phases. It offers finer control than `CountDownLatch` or `CyclicBarrier`, allowing for dynamic registration and deregistration of threads and more sophisticated synchronization patterns.

`CompletableFuture`

Question 25: `CompletableFuture` Class

CompletableFuture provides a way to perform and manage asynchronous computations. It offers methods for composing asynchronous operations and handling results and exceptions efficiently.

CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
    return "Hello";
}).thenApply(s -> s + " world");

System.out.println(future.join()); // Output: Hello world

`ForkJoinPool`

Question 26: `ForkJoinPool` Class

ForkJoinPool is a specialized thread pool designed for parallel execution of `ForkJoinTask`s. It's particularly well-suited for recursive tasks that can be broken down into smaller subtasks, using work stealing for load balancing.

`Future` Interface

Question 27: `Future` Interface

The `Future` interface represents the asynchronous result of a computation. It's used to get the result of a task, check if it's done, and cancel it. It is typically returned by methods such as `submit()` in the `ExecutorService`.

`Lock` and `ReentrantLock`

Question 28: `Lock` and `ReentrantLock` Classes

The `Lock` interface and `ReentrantLock` class provide more flexible and powerful locking mechanisms than the `synchronized` keyword. They're particularly useful for complex synchronization scenarios. `ReentrantLock` allows a thread to acquire the same lock multiple times.

Atomic Classes

Question 29: Atomic Classes

Java's atomic classes (`AtomicInteger`, `AtomicLong`, `AtomicBoolean`, etc.) provide methods for performing atomic operations on variables. This is crucial for ensuring thread safety without explicit synchronization.

`Semaphore` Class

Question 30: `Semaphore` Class

A `Semaphore` controls access to a shared resource by managing a pool of permits. Threads acquire a permit before accessing the resource and release it afterward. If no permits are available, the thread blocks until a permit becomes free.

`ThreadLocal` Class

Question 31: `ThreadLocal` Class

ThreadLocal creates thread-local variables. Each thread has its own copy of the variable; this prevents data corruption or race conditions in concurrent applications.

`Thread.join()`

Question 32: `Thread.join()` Method

The `join()` method is used to wait for a thread to complete its execution before continuing the execution of the calling thread. The calling thread blocks until the thread on which you call `join()` completes.

Thread t = new Thread(()->{
    System.out.println("Thread 1 is running"); //Output: Thread 1 is running
});
t.start();
t.join();
System.out.println("Thread 1 is finished"); //Output: Thread 1 is finished

`Thread.yield()`

Question 33: `Thread.yield()` Method

The `yield()` method politely requests the scheduler to relinquish the CPU to another thread. It's not guaranteed that another thread will run immediately.

`Thread.sleep()`

Question 34: `Thread.sleep()` Method

The `sleep()` method pauses the execution of a thread for a specified time (in milliseconds). It throws an `InterruptedException` if the thread is interrupted while sleeping.

try {
    Thread.sleep(1000); // Sleep for 1 second
    System.out.println("Woke up after 1 second!"); // Output: Woke up after 1 second! (after a 1-second pause)
} catch (InterruptedException e) {
    Thread.currentThread().interrupt();
}

`ThreadPoolExecutor`

Question 35: `ThreadPoolExecutor` Class

ThreadPoolExecutor provides fine-grained control over thread pool configuration (core pool size, maximum pool size, keep-alive time, queueing policy, rejection policy).

`Executors` Class

Question 36: `Executors` Class

The `Executors` class provides factory methods for creating common thread pool types (e.g., `newFixedThreadPool()`, `newCachedThreadPool()`).

`Callable` Interface

Question 37: `Callable` Interface

The `Callable` interface represents a task that returns a value and can throw checked exceptions. This is useful for asynchronous tasks that need to produce a result. It's used with `ExecutorService`.