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Executors

public class Executors
extends Object

java.lang.Object
   ↳ java.util.concurrent.Executors


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.

Summary

Public methods

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 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 methods

From class java.lang.Object

Public methods

callable

Added in API level 1
Callable<Object> callable (Runnable task)

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

Parameters
task Runnable: the task to run
Returns
Callable<Object> a callable object
Throws
NullPointerException if task null

callable

Added in API level 9
Callable<Object> callable (PrivilegedAction<?> action)

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

Parameters
action PrivilegedAction: the privileged action to run
Returns
Callable<Object> a callable object
Throws
NullPointerException if action null

callable

Added in API level 9
Callable<Object> callable (PrivilegedExceptionAction<?> action)

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

Parameters
action PrivilegedExceptionAction: the privileged exception action to run
Returns
Callable<Object> a callable object
Throws
NullPointerException if action null

callable

Added in API level 1
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 Runnable: the task to run
result T: the result to return
Returns
Callable<T> a callable object
Throws
NullPointerException if task null

defaultThreadFactory

Added in API level 1
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 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
ThreadFactory a thread factory

newCachedThreadPool

Added in API level 1
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
ExecutorService the newly created thread pool

newCachedThreadPool

Added in API level 1
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 ThreadFactory: the factory to use when creating new threads
Returns
ExecutorService the newly created thread pool
Throws
NullPointerException if threadFactory is null

newFixedThreadPool

Added in API level 1
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 int: the number of threads in the pool
threadFactory ThreadFactory: the factory to use when creating new threads
Returns
ExecutorService the newly created thread pool
Throws
NullPointerException if threadFactory is null
IllegalArgumentException if nThreads <= 0

newFixedThreadPool

Added in API level 1
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 int: the number of threads in the pool
Returns
ExecutorService the newly created thread pool
Throws
IllegalArgumentException if nThreads <= 0

newScheduledThreadPool

Added in API level 1
ScheduledExecutorService newScheduledThreadPool (int corePoolSize)

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

Parameters
corePoolSize int: the number of threads to keep in the pool, even if they are idle
Returns
ScheduledExecutorService a newly created scheduled thread pool
Throws
IllegalArgumentException if corePoolSize < 0

newScheduledThreadPool

Added in API level 1
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 int: the number of threads to keep in the pool, even if they are idle
threadFactory ThreadFactory: the factory to use when the executor creates a new thread
Returns
ScheduledExecutorService a newly created scheduled thread pool
Throws
IllegalArgumentException if corePoolSize < 0
NullPointerException if threadFactory is null

newSingleThreadExecutor

Added in API level 1
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 ThreadFactory: the factory to use when creating new threads
Returns
ExecutorService the newly created single-threaded Executor
Throws
NullPointerException if threadFactory is null

newSingleThreadExecutor

Added in API level 1
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
ExecutorService the newly created single-threaded Executor

newSingleThreadScheduledExecutor

Added in API level 1
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
ScheduledExecutorService the newly created scheduled executor

newSingleThreadScheduledExecutor

Added in API level 1
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 ThreadFactory: the factory to use when creating new threads
Returns
ScheduledExecutorService a newly created scheduled executor
Throws
NullPointerException if threadFactory is null

newWorkStealingPool

Added in API level 24
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 int: the targeted parallelism level
Returns
ExecutorService the newly created thread pool
Throws
IllegalArgumentException if parallelism <= 0

newWorkStealingPool

Added in API level 24
ExecutorService newWorkStealingPool ()

Creates a work-stealing thread pool using the number of available processors as its target parallelism level.

Returns
ExecutorService the newly created thread pool

See also:

privilegedCallable

Added in API level 1
Callable<T> privilegedCallable (Callable<T> callable)

Legacy security code; do not use.

Parameters
callable Callable
Returns
Callable<T>

privilegedCallableUsingCurrentClassLoader

Added in API level 1
Callable<T> privilegedCallableUsingCurrentClassLoader (Callable<T> callable)

Legacy security code; do not use.

Parameters
callable Callable
Returns
Callable<T>

privilegedThreadFactory

Added in API level 1
ThreadFactory privilegedThreadFactory ()

Legacy security code; do not use.

Returns
ThreadFactory

unconfigurableExecutorService

Added in API level 1
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 ExecutorService: the underlying implementation
Returns
ExecutorService an ExecutorService instance
Throws
NullPointerException if executor null

unconfigurableScheduledExecutorService

Added in API level 1
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 ScheduledExecutorService: the underlying implementation
Returns
ScheduledExecutorService a ScheduledExecutorService instance
Throws
NullPointerException if executor null
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