Executors

public class Executors extends Object

Factory and utility methods for Executor, ExecutorService, ScheduledExecutorService, ThreadFactory, and Callable classes defined in this package. This class supports the following kinds of methods:

• Methods that create and return an ExecutorService set up with commonly useful configuration settings.
• Methods that create and return a ScheduledExecutorService set up with commonly useful configuration settings.
• Methods that create and return a "wrapped" ExecutorService, that disables reconfiguration by making implementation-specific methods inaccessible.
• Methods that create and return a ThreadFactory that sets newly created threads to a known state.
• Methods that create and return a Callable out of other closure-like forms, so they can be used in execution methods requiring Callable.

Public Method Summary

static Callable<Object>	callable(Runnable task) Returns a Callable object that, when called, runs the given task and returns null.
static Callable<Object>	callable(PrivilegedAction<?> action) Returns a Callable object that, when called, runs the given privileged action and returns its result.
static Callable<Object>	callable(PrivilegedExceptionAction<?> action) Returns a Callable object that, when called, runs the given privileged exception action and returns its result.
static <T> Callable<T>	callable(Runnable task, T result) Returns a Callable object that, when called, runs the given task and returns the given result.
static ThreadFactory	defaultThreadFactory() Returns a default thread factory used to create new threads.
static ExecutorService	newCachedThreadPool() Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they are available.
static ExecutorService	newCachedThreadPool(ThreadFactory threadFactory) Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they are available, and uses the provided ThreadFactory to create new threads when needed.
static ExecutorService	newFixedThreadPool(int nThreads, ThreadFactory threadFactory) Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue, using the provided ThreadFactory to create new threads when needed.
static ExecutorService	newFixedThreadPool(int nThreads) Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue.
static ScheduledExecutorService	newScheduledThreadPool(int corePoolSize) Creates a thread pool that can schedule commands to run after a given delay, or to execute periodically.
static ScheduledExecutorService	newScheduledThreadPool(int corePoolSize, ThreadFactory threadFactory) Creates a thread pool that can schedule commands to run after a given delay, or to execute periodically.
static ExecutorService	newSingleThreadExecutor(ThreadFactory threadFactory) Creates an Executor that uses a single worker thread operating off an unbounded queue, and uses the provided ThreadFactory to create a new thread when needed.
static ExecutorService	newSingleThreadExecutor() Creates an Executor that uses a single worker thread operating off an unbounded queue.
static ScheduledExecutorService	newSingleThreadScheduledExecutor() Creates a single-threaded executor that can schedule commands to run after a given delay, or to execute periodically.
static ScheduledExecutorService	newSingleThreadScheduledExecutor(ThreadFactory threadFactory) Creates a single-threaded executor that can schedule commands to run after a given delay, or to execute periodically.
static ExecutorService	newWorkStealingPool(int parallelism) Creates a thread pool that maintains enough threads to support the given parallelism level, and may use multiple queues to reduce contention.
static ExecutorService	newWorkStealingPool() Creates a work-stealing thread pool using the number of {@linkplain Runtime#availableProcessors available processors} as its target parallelism level.
static <T> Callable<T>	privilegedCallable(Callable<T> callable) Legacy security code; do not use.
static <T> Callable<T>	privilegedCallableUsingCurrentClassLoader(Callable<T> callable) Legacy security code; do not use.
static ThreadFactory	privilegedThreadFactory() Legacy security code; do not use.
static ExecutorService	unconfigurableExecutorService(ExecutorService executor) Returns an object that delegates all defined ExecutorService methods to the given executor, but not any other methods that might otherwise be accessible using casts.
static ScheduledExecutorService	unconfigurableScheduledExecutorService(ScheduledExecutorService executor) Returns an object that delegates all defined ScheduledExecutorService methods to the given executor, but not any other methods that might otherwise be accessible using casts.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Methods

public static Callable<Object> callable (Runnable task)

Returns a Callable object that, when called, runs the given task and returns null.

Parameters

task	the task to run

Returns

• a callable object

Throws

NullPointerException	if task null

public static Callable<Object> callable (PrivilegedAction<?> action)

Returns a Callable object that, when called, runs the given privileged action and returns its result.

Parameters

action	the privileged action to run

Returns

• a callable object

Throws

NullPointerException	if action null

public static Callable<Object> callable (PrivilegedExceptionAction<?> action)

Returns a Callable object that, when called, runs the given privileged exception action and returns its result.

Parameters

action	the privileged exception action to run

Returns

• a callable object

Throws

NullPointerException	if action null

public static Callable<T> callable (Runnable task, T result)

Returns a Callable object that, when called, runs the given task and returns the given result. This can be useful when applying methods requiring a Callable to an otherwise resultless action.

Parameters

task	the task to run
result	the result to return

Returns

• a callable object

Throws

NullPointerException	if task null

public static ThreadFactory defaultThreadFactory ()

Returns a default thread factory used to create new threads. This factory creates all new threads used by an Executor in the same ThreadGroup. Each new thread is created as a non-daemon thread with priority set to the smaller of Thread.NORM_PRIORITY and the maximum priority permitted in the thread group. New threads have names accessible via Thread.getName() of pool-N-thread-M, where N is the sequence number of this factory, and M is the sequence number of the thread created by this factory.

Returns

• a thread factory

public static ExecutorService newCachedThreadPool ()

Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they are available. These pools will typically improve the performance of programs that execute many short-lived asynchronous tasks. Calls to execute will reuse previously constructed threads if available. If no existing thread is available, a new thread will be created and added to the pool. Threads that have not been used for sixty seconds are terminated and removed from the cache. Thus, a pool that remains idle for long enough will not consume any resources. Note that pools with similar properties but different details (for example, timeout parameters) may be created using ThreadPoolExecutor constructors.

Returns

• the newly created thread pool

public static ExecutorService newCachedThreadPool (ThreadFactory threadFactory)

Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they are available, and uses the provided ThreadFactory to create new threads when needed.

Parameters

threadFactory	the factory to use when creating new threads

Returns

• the newly created thread pool

Throws

NullPointerException	if threadFactory is null

public static ExecutorService newFixedThreadPool (int nThreads, ThreadFactory threadFactory)

Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue, using the provided ThreadFactory to create new threads when needed. At any point, at most nThreads threads will be active processing tasks. If additional tasks are submitted when all threads are active, they will wait in the queue until a thread is available. If any thread terminates due to a failure during execution prior to shutdown, a new one will take its place if needed to execute subsequent tasks. The threads in the pool will exist until it is explicitly shutdown.

Parameters

nThreads	the number of threads in the pool
threadFactory	the factory to use when creating new threads

Returns

• the newly created thread pool

Throws

NullPointerException	if threadFactory is null
IllegalArgumentException	if nThreads <= 0

public static ExecutorService newFixedThreadPool (int nThreads)

Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue. At any point, at most nThreads threads will be active processing tasks. If additional tasks are submitted when all threads are active, they will wait in the queue until a thread is available. If any thread terminates due to a failure during execution prior to shutdown, a new one will take its place if needed to execute subsequent tasks. The threads in the pool will exist until it is explicitly shutdown.

Parameters

nThreads	the number of threads in the pool

Returns

• the newly created thread pool

Throws

IllegalArgumentException	if nThreads <= 0

public static ScheduledExecutorService newScheduledThreadPool (int corePoolSize)

Creates a thread pool that can schedule commands to run after a given delay, or to execute periodically.

Parameters

corePoolSize	the number of threads to keep in the pool, even if they are idle

Returns

• a newly created scheduled thread pool

Throws

IllegalArgumentException	if corePoolSize < 0

public static ScheduledExecutorService newScheduledThreadPool (int corePoolSize, ThreadFactory threadFactory)

Creates a thread pool that can schedule commands to run after a given delay, or to execute periodically.

Parameters

corePoolSize	the number of threads to keep in the pool, even if they are idle
threadFactory	the factory to use when the executor creates a new thread

Returns

• a newly created scheduled thread pool

Throws

IllegalArgumentException	if corePoolSize < 0
NullPointerException	if threadFactory is null

public static ExecutorService newSingleThreadExecutor (ThreadFactory threadFactory)

Creates an Executor that uses a single worker thread operating off an unbounded queue, and uses the provided ThreadFactory to create a new thread when needed. Unlike the otherwise equivalent newFixedThreadPool(1, threadFactory) the returned executor is guaranteed not to be reconfigurable to use additional threads.

Parameters

threadFactory	the factory to use when creating new threads

Returns

• the newly created single-threaded Executor

Throws

NullPointerException	if threadFactory is null

public static ExecutorService newSingleThreadExecutor ()

Creates an Executor that uses a single worker thread operating off an unbounded queue. (Note however that if this single thread terminates due to a failure during execution prior to shutdown, a new one will take its place if needed to execute subsequent tasks.) Tasks are guaranteed to execute sequentially, and no more than one task will be active at any given time. Unlike the otherwise equivalent newFixedThreadPool(1) the returned executor is guaranteed not to be reconfigurable to use additional threads.

Returns

• the newly created single-threaded Executor

public static ScheduledExecutorService newSingleThreadScheduledExecutor ()

Creates a single-threaded executor that can schedule commands to run after a given delay, or to execute periodically. (Note however that if this single thread terminates due to a failure during execution prior to shutdown, a new one will take its place if needed to execute subsequent tasks.) Tasks are guaranteed to execute sequentially, and no more than one task will be active at any given time. Unlike the otherwise equivalent newScheduledThreadPool(1) the returned executor is guaranteed not to be reconfigurable to use additional threads.

Returns

• the newly created scheduled executor

public static ScheduledExecutorService newSingleThreadScheduledExecutor (ThreadFactory threadFactory)

Creates a single-threaded executor that can schedule commands to run after a given delay, or to execute periodically. (Note however that if this single thread terminates due to a failure during execution prior to shutdown, a new one will take its place if needed to execute subsequent tasks.) Tasks are guaranteed to execute sequentially, and no more than one task will be active at any given time. Unlike the otherwise equivalent newScheduledThreadPool(1, threadFactory) the returned executor is guaranteed not to be reconfigurable to use additional threads.

Parameters

threadFactory	the factory to use when creating new threads

Returns

• a newly created scheduled executor

Throws

NullPointerException	if threadFactory is null

public static ExecutorService newWorkStealingPool (int parallelism)

Creates a thread pool that maintains enough threads to support the given parallelism level, and may use multiple queues to reduce contention. The parallelism level corresponds to the maximum number of threads actively engaged in, or available to engage in, task processing. The actual number of threads may grow and shrink dynamically. A work-stealing pool makes no guarantees about the order in which submitted tasks are executed.

Parameters

parallelism	the targeted parallelism level

Returns

• the newly created thread pool

Throws

IllegalArgumentException	if parallelism <= 0

public static ExecutorService newWorkStealingPool ()

Creates a work-stealing thread pool using the number of {@linkplain Runtime#availableProcessors available processors} as its target parallelism level.

Returns

• the newly created thread pool

See Also

• newWorkStealingPool(int)

public static Callable<T> privilegedCallable (Callable<T> callable)

Legacy security code; do not use.

Parameters

callable

public static Callable<T> privilegedCallableUsingCurrentClassLoader (Callable<T> callable)

Legacy security code; do not use.

Parameters

callable

public static ThreadFactory privilegedThreadFactory ()

Legacy security code; do not use.

public static ExecutorService unconfigurableExecutorService (ExecutorService executor)

Returns an object that delegates all defined ExecutorService methods to the given executor, but not any other methods that might otherwise be accessible using casts. This provides a way to safely "freeze" configuration and disallow tuning of a given concrete implementation.

Parameters

executor	the underlying implementation

Returns

• an ExecutorService instance

Throws

NullPointerException	if executor null

public static ScheduledExecutorService unconfigurableScheduledExecutorService (ScheduledExecutorService executor)

Returns an object that delegates all defined ScheduledExecutorService methods to the given executor, but not any other methods that might otherwise be accessible using casts. This provides a way to safely "freeze" configuration and disallow tuning of a given concrete implementation.

Parameters

executor	the underlying implementation

Returns

• a ScheduledExecutorService instance

Throws

NullPointerException	if executor null