Utility classes commonly useful in concurrent programming.
See: Description
Interface Summary | |
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BlockingDeque | A Deque that additionally supports blocking operations that wait for the deque to become non-empty when retrieving an element, and wait for space to become available in the deque when storing an element. |
BlockingQueue | A Queue that additionally supports operations that wait for the queue to become non-empty when retrieving an element, and wait for space to become available in the queue when storing an element. |
Callable | A task that returns a result and may throw an exception. |
CompletionService | A service that decouples the production of new asynchronous tasks from the consumption of the results of completed tasks. |
ConcurrentMap | A java.util.Map providing additional atomic putIfAbsent, remove, and replace methods. |
ConcurrentNavigableMap | A ConcurrentMap supporting NavigableMap operations, and recursively so for its navigable sub-maps. |
Delayed | A mix-in style interface for marking objects that should be acted upon after a given delay. |
Executor | An object that executes submitted Runnable tasks. |
ExecutorService | An Executor that provides methods to manage termination and methods that can produce a Future for tracking progress of one or more asynchronous tasks. |
Future | A Future represents the result of an asynchronous computation. |
RejectedExecutionHandler | A handler for tasks that cannot be executed by a ThreadPoolExecutor. |
RunnableFuture | A Future that is Runnable. |
RunnableScheduledFuture | A ScheduledFuture that is Runnable. |
ScheduledExecutorService | An ExecutorService that can schedule commands to run after a given delay, or to execute periodically. |
ScheduledFuture | A delayed result-bearing action that can be cancelled. |
ThreadFactory | An object that creates new threads on demand. |
Class Summary | |
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AbstractExecutorService | Provides default implementations of ExecutorService execution methods. |
ArrayBlockingQueue | A bounded blocking queue backed by an array. |
BrokenBarrierException | Exception thrown when a thread tries to wait upon a barrier that is in a broken state, or which enters the broken state while the thread is waiting. |
CancellationException | Exception indicating that the result of a value-producing task, such as a FutureTask, cannot be retrieved because the task was cancelled. |
ConcurrentHashMap | A hash table supporting full concurrency of retrievals and adjustable expected concurrency for updates. |
ConcurrentLinkedQueue | An unbounded thread-safe queue based on linked nodes. |
ConcurrentSkipListMap | A scalable concurrent ConcurrentNavigableMap implementation. |
ConcurrentSkipListSet | A scalable concurrent NavigableSet implementation based on a ConcurrentSkipListMap. |
CopyOnWriteArrayList | |
CopyOnWriteArraySet | A java.util.Set that uses an internal CopyOnWriteArrayList for all of its operations. |
CountDownLatch | A synchronization aid that allows one or more threads to wait until a set of operations being performed in other threads completes. |
CyclicBarrier | A synchronization aid that allows a set of threads to all wait for each other to reach a common barrier point. |
DelayQueue | An unbounded blocking queue of Delayed elements, in which an element can only be taken when its delay has expired. |
Exchanger | A synchronization point at which threads can pair and swap elements within pairs. |
ExecutionException | Exception thrown when attempting to retrieve the result of a task that aborted by throwing an exception. |
ExecutorCompletionService | A CompletionService that uses a supplied Executor to execute tasks. |
Executors | Factory and utility methods for Executor, ExecutorService, ScheduledExecutorService, ThreadFactory, and Callable classes defined in this package. |
FutureTask | A cancellable asynchronous computation. |
LinkedBlockingDeque | An optionally-bounded blocking deque based on linked nodes. |
LinkedBlockingQueue | An optionally-bounded blocking queue based on linked nodes. |
PriorityBlockingQueue | An unbounded blocking queue that uses the same ordering rules as class PriorityQueue and supplies blocking retrieval operations. |
RejectedExecutionException | Exception thrown by an Executor when a task cannot be accepted for execution. |
ScheduledThreadPoolExecutor | A ThreadPoolExecutor that can additionally schedule commands to run after a given delay, or to execute periodically. |
Semaphore | A counting semaphore. |
SynchronousQueue | A blocking queue in which each insert operation must wait for a corresponding remove operation by another thread, and vice versa. |
ThreadPoolExecutor | An ExecutorService that executes each submitted task using one of possibly several pooled threads, normally configured using Executors factory methods. |
ThreadPoolExecutor.AbortPolicy | A handler for rejected tasks that throws a {@code RejectedExecutionException}. |
ThreadPoolExecutor.CallerRunsPolicy | A handler for rejected tasks that runs the rejected task directly in the calling thread of the {@code execute} method, unless the executor has been shut down, in which case the task is discarded. |
ThreadPoolExecutor.DiscardOldestPolicy | A handler for rejected tasks that discards the oldest unhandled request and then retries {@code execute}, unless the executor is shut down, in which case the task is discarded. |
ThreadPoolExecutor.DiscardPolicy | A handler for rejected tasks that silently discards the rejected task. |
TimeoutException | Exception thrown when a blocking operation times out. |
TimeUnit | A TimeUnit represents time durations at a given unit of granularity and provides utility methods to convert across units, and to perform timing and delay operations in these units. |
Utility classes commonly useful in concurrent programming. This package includes a few small standardized extensible frameworks, as well as some classes that provide useful functionality and are otherwise tedious or difficult to implement. Here are brief descriptions of the main components. See also the locks and atomic packages.
Implementations. Classes ThreadPoolExecutor and ScheduledThreadPoolExecutor provide tunable, flexible thread pools. The Executors class provides factory methods for the most common kinds and configurations of Executors, as well as a few utility methods for using them. Other utilities based on Executors include the concrete class FutureTask providing a common extensible implementation of Futures, and ExecutorCompletionService, that assists in coordinating the processing of groups of asynchronous tasks.
The "Concurrent" prefix used with some classes in this package is a shorthand indicating several differences from similar "synchronized" classes. For example java.util.Hashtable and Collections.synchronizedMap(new HashMap()) are synchronized. But ConcurrentHashMap is "concurrent". A concurrent collection is thread-safe, but not governed by a single exclusion lock. In the particular case of ConcurrentHashMap, it safely permits any number of concurrent reads as well as a tunable number of concurrent writes. "Synchronized" classes can be useful when you need to prevent all access to a collection via a single lock, at the expense of poorer scalability. In other cases in which multiple threads are expected to access a common collection, "concurrent" versions are normally preferable. And unsynchronized collections are preferable when either collections are unshared, or are accessible only when holding other locks.
Most concurrent Collection implementations (including most Queues)
also differ from the usual java.util conventions in that their Iterators
provide weakly consistent rather than fast-fail traversal. A
weakly consistent iterator is thread-safe, but does not necessarily
freeze the collection while iterating, so it may (or may not) reflect
any updates since the iterator was created.
Memory Consistency Properties
Chapter 17 of the Java Language Specification defines the
happens-before relation on memory operations such as reads and
writes of shared variables. The results of a write by one thread are
guaranteed to be visible to a read by another thread only if the write
operation happens-before the read operation. The
{@code synchronized} and {@code volatile} constructs, as well as the
{@code Thread.start()} and {@code Thread.join()} methods, can form
happens-before relationships. In particular:
Since: 1.5