Javaconcurrency

Javaconcurrency, commonly referred to as Java concurrency, encompasses the facilities provided by the Java platform for executing multiple tasks in parallel and coordinating their execution. The Java platform supports both low-level synchronization and high-level parallelism through a formal memory model and a comprehensive API. While early Java versions offered basic thread support and synchronized blocks, the java.util.concurrent package, introduced in Java 5, standardized scalable concurrent programming and has been expanded in subsequent releases.

Core concepts include threads, synchronization, and the Java Memory Model. A thread represents an independent path of execution, and visibility and ordering are governed by the happens-before relationships defined in the memory model. volatile fields provide visibility for writes to and reads from a shared variable, while synchronized blocks establish mutual exclusion and a happens-before relation. Correct concurrent code relies on proper synchronization to avoid data races, visibility problems, and deadlocks.

Key APIs reside in java.util.concurrent, including the Executor framework (ExecutorService, Executors, ThreadPoolExecutor), and the Future and Callable abstractions for asynchronous results. The ForkJoinPool enables work-stealing parallelism for divide-and-conquer tasks. Concurrency utilities such as CountDownLatch, CyclicBarrier, Semaphore, Exchanger, and Phaser help coordinate threads. Concurrent collections like ConcurrentHashMap and CopyOnWriteArrayList, along with blocking queues, provide thread-safe data sharing. Atomic classes in java.util.concurrent.atomic offer lock-free counters, references, and other atomic operations.

Parallelism in Java is further exposed through streams, which can run in parallel by using a parallel stream and the common ForkJoinPool. Practical guidance emphasizes choosing appropriate pool sizes, reducing contention, and avoiding unnecessary synchronization. Common pitfalls include deadlock, livelock, starvation, and subtle memory-visibility bugs. The Javaconcurrency landscape favors high-level abstractions for most tasks while reserving low-level primitives for specialized, performance-critical code.