The java.util.concurrent package in Java is a part of the java.util subpackages, introduced in Java 5. It provides a comprehensive set of concurrency utilities designed to simplify the development of multi-threaded applications and improve performance. The package includes classes and interfaces for thread management, synchronization, and coordination.
Key Components of java.util.concurrent
Executors framework
The Executors framework is designed for managing and controlling thread execution. It provides a high-level API for creating and managing thread pools.
- ExecutorService: This interface represents an advanced replacement for the traditional java.lang.Thread class. It provides methods for submitting tasks and managing the lifecycle of threads. Key implementations include ThreadPoolExecutor and ScheduledThreadPoolExecutor.
- Executors Class: This utility class contains static factory methods for creating different types of thread pools, such as fixed-thread pools, cached-thread pools, and single-threaded executors.
Concurrent Collections
java.util.concurrent provides several thread-safe collection classes that simplify concurrent programming. These include:
- ConcurrentHashMap: A thread-safe implementation of Map that allows concurrent reads and updates without locking the entire map.
- CopyOnWriteArrayList: A thread-safe implementation of List that creates a new copy of the list for every write operation.
- BlockingQueue: An interface for queues that support operations that wait for the queue to become non-empty when retrieving elements and wait for space to become available when storing elements. Implementations include ArrayBlockingQueue, LinkedBlockingQueue, and PriorityBlockingQueue.
Locks
java.util.concurrent.locks provides explicit locking mechanisms that offer more flexibility compared to synchronized blocks and methods.
- ReentrantLock: A lock that allows the same thread to acquire the lock multiple times without causing a deadlock.
- ReadWriteLock: An interface that allows multiple threads to read data concurrently but ensures exclusive access for write operations. Implementations include ReentrantReadWriteLock.
Synchronization Utilities
- CountDownLatch: A synchronization aid that allows one or more threads to wait until a set of operations in other threads completes.
- CyclicBarrier: A synchronization aid that allows a set of threads to wait for each other to reach a common barrier point.
- Semaphore: A counting semaphore that controls access to a resource through counting permits.
The java.util.concurrent package is a robust toolkit for concurrent programming in Java. It provides high-level APIs for managing threads, handling concurrent data structures, and synchronizing operations. By leveraging these utilities, developers can build more efficient, scalable, and maintainable multi-threaded applications.