Package java.util.concurrent

Package java.util.concurrent

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Java 5.0

This package includes a number of powerful utilities for multithreaded programming. Most of these utilities fall into three main categories:

Collections

This package extends the Java Collections Framework, adding the threadsafe classes ConcurrentHashMap , CopyOnWriteArrayList , CopyOnWriteArraySet , and ConcurrentLinkedQueue . These classes achieve threadsafety without relying exclusively on synchronized methods , greatly increasing the number of threads that can safely use them concurrently. ConcurrentHashMap implements the ConcurrentMap interface, which adds important atomic methods to the base java.util.Map interface.

In addition to these Map , List , Set , and Queue implementations , this package also defines the BlockingQueue interface. Blocking queues are important in many concurrent algorithms, and this package provides a variety of useful implementations: ArrayBlockingQueue , DelayQueue , LinkedBlockingQueue , PriorityBlockingQueue , and SynchronousQueue .

Asynchronous Execution with Thread Pools

java.util.concurrent provides a robust framework for asynchronous execution of tasks defined by the existing java.lang.Runnable interface or the new Callable interface. The Executor , ExecutorService , and ScheduledExecutorService interfaces define methods for executing (or scheduling for future execution) Runnable and Callable tasks. The Future interface represents the future result of the asynchronous execution of a task. ThreadPoolExecutor and ScheduledThreadPoolExecutor are executor implementations based on highly configurable thread pools. The Executors class provides convenient factory methods for obtaining instances of these thread pool implementations.

Synchronizers

A number of classes in this package are useful for synchronizing two or more concurrent threads. See CountDownLatch , CyclicBarrier , Exchanger , and Semaphore .

Interfaces

 public interface  BlockingQueue  <E> extends java.util.Queue<E>; public interface  Callable  <V>; public interface  CompletionService  <V>; public interface  ConcurrentMap  <K, V> extends java.util.Map<K, V>; public interface  Delayed  extends Comparable<Delayed>; public interface  Executor  ; public interface  ExecutorService  extends Executor; public interface  Future  <V>; public interface  RejectedExecutionHandler  ; public interface  ScheduledExecutorService  extends ExecutorService; public interface  ScheduledFuture  <V> extends Delayed, Future<V>; public interface  ThreadFactory  ; 

Enumerated Types

 public enum  TimeUnit  ; 

Collections

 public class  ArrayBlockingQueue  <E> extends java.util.AbstractQueue<E>          implements BlockingQueue<E>, Serializable; public class  ConcurrentHashMap  <K, V> extends java.util.AbstractMap<K, V>         implements ConcurrentMap<K, V> Serializable; public class  ConcurrentLinkedQueue  <E> extends java.util.AbstractQueue<E>          implements java.util.Queue<E>, Serializable; public class  CopyOnWriteArrayList  <E> implements java.util.List<E>, java.util.RandomAccess, Cloneable, Serializable; public class  CopyOnWriteArraySet  <E> extends java.util.AbstractSet<E>          implements Serializable; public class  DelayQueue  <E extends Delayed> extends java.util.AbstractQueue<E>          implements BlockingQueue<E>; public class  LinkedBlockingQueue  <E> extends java.util.AbstractQueue<E>          implements BlockingQueue<E>, Serializable; public class  PriorityBlockingQueue  <E> extends java.util.AbstractQueue<E>          implements BlockingQueue<E>, Serializable; public class  SynchronousQueue  <E> extends java.util.AbstractQueue<E>          implements BlockingQueue<E>, Serializable; 

Other Classes

 public abstract class  AbstractExecutorService  implements ExecutorService;    public class  ThreadPoolExecutor  extends AbstractExecutorService;       public class  ScheduledThreadPoolExecutor  extends ThreadPoolExecutor           implements ScheduledExecutorService; public class  CountDownLatch  ; public class  CyclicBarrier  ; public class  Exchanger  <V>; public class  ExecutorCompletionService  <V> implements CompletionService<V>; public class  Executors  ; public class  FutureTask  <V> implements Future<V>, Runnable; public class  Semaphore  implements Serializable; public static class  ThreadPoolExecutor.AbortPolicy  implements RejectedExecutionHandler; public static class  ThreadPoolExecutor.CallerRunsPolicy  implements RejectedExecutionHandler; public static class  ThreadPoolExecutor.DiscardOldestPolicy  implements RejectedExecutionHandler; public static class  ThreadPoolExecutor.DiscardPolicy  implements RejectedExecutionHandler; 

Exceptions

 public class  BrokenBarrierException  extends Exception; public class  CancellationException  extends IllegalStateException; public class  ExecutionException  extends Exception; public class  RejectedExecutionException  extends RuntimeException; public class  TimeoutException  extends Exception;