edu.emory.mathcs.backport.java.util.concurrent

Class 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:

Since: 1.5

Author: Doug Lea

Method Summary
static Callablecallable(Runnable task, Object result)
Returns a Callable object that, when called, runs the given task and returns the given result.
static Callablecallable(Runnable task)
Returns a Callable object that, when called, runs the given task and returns null.
static Callablecallable(PrivilegedAction action)
Returns a Callable object that, when called, runs the given privileged action and returns its result.
static Callablecallable(PrivilegedExceptionAction action)
Returns a Callable object that, when called, runs the given privileged exception action and returns its result.
static ThreadFactorydefaultThreadFactory()
Returns a default thread factory used to create new threads.
static ExecutorServicenewCachedThreadPool()
Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they are available.
static ExecutorServicenewCachedThreadPool(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 ExecutorServicenewFixedThreadPool(int nThreads)
Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue.
static ExecutorServicenewFixedThreadPool(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 ScheduledExecutorServicenewScheduledThreadPool(int corePoolSize)
Creates a thread pool that can schedule commands to run after a given delay, or to execute periodically.
static ScheduledExecutorServicenewScheduledThreadPool(int corePoolSize, ThreadFactory threadFactory)
Creates a thread pool that can schedule commands to run after a given delay, or to execute periodically.
static ExecutorServicenewSingleThreadExecutor()
Creates an Executor that uses a single worker thread operating off an unbounded queue.
static ExecutorServicenewSingleThreadExecutor(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 ScheduledExecutorServicenewSingleThreadScheduledExecutor()
Creates a single-threaded executor that can schedule commands to run after a given delay, or to execute periodically.
static ScheduledExecutorServicenewSingleThreadScheduledExecutor(ThreadFactory threadFactory)
Creates a single-threaded executor that can schedule commands to run after a given delay, or to execute periodically.
static CallableprivilegedCallable(Callable callable)
Returns a Callable object that will, when called, execute the given callable under the current access control context.
static CallableprivilegedCallableUsingCurrentClassLoader(Callable callable)
Returns a Callable object that will, when called, execute the given callable under the current access control context, with the current context class loader as the context class loader.
static ThreadFactoryprivilegedThreadFactory()
Returns a thread factory used to create new threads that have the same permissions as the current thread.
static ExecutorServiceunconfigurableExecutorService(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 ScheduledExecutorServiceunconfigurableScheduledExecutorService(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.

Method Detail

callable

public static Callable callable(Runnable task, Object 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

callable

public static Callable 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

callable

public static Callable 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

callable

public static Callable 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

defaultThreadFactory

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. If there is a java.lang.SecurityManager, it uses the group of System#getSecurityManager, else the group of the thread invoking this defaultThreadFactory method. 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

newCachedThreadPool

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

newCachedThreadPool

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

newFixedThreadPool

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

newFixedThreadPool

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

newScheduledThreadPool

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

newScheduledThreadPool

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

newSingleThreadExecutor

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

newSingleThreadExecutor

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

newSingleThreadScheduledExecutor

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

newSingleThreadScheduledExecutor

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

privilegedCallable

public static Callable privilegedCallable(Callable callable)
Returns a Callable object that will, when called, execute the given callable under the current access control context. This method should normally be invoked within an AccessController#doPrivileged action to create callables that will, if possible, execute under the selected permission settings holding within that action; or if not possible, throw an associated AccessControlException.

Parameters: callable the underlying task

Returns: a callable object

Throws: NullPointerException if callable null

privilegedCallableUsingCurrentClassLoader

public static Callable privilegedCallableUsingCurrentClassLoader(Callable callable)
Returns a Callable object that will, when called, execute the given callable under the current access control context, with the current context class loader as the context class loader. This method should normally be invoked within an AccessController#doPrivileged action to create callables that will, if possible, execute under the selected permission settings holding within that action; or if not possible, throw an associated AccessControlException.

Parameters: callable the underlying task

Returns: a callable object

Throws: NullPointerException if callable null AccessControlException if the current access control context does not have permission to both set and get context class loader.

privilegedThreadFactory

public static ThreadFactory privilegedThreadFactory()
Returns a thread factory used to create new threads that have the same permissions as the current thread. This factory creates threads with the same settings as Executors, additionally setting the AccessControlContext and contextClassLoader of new threads to be the same as the thread invoking this privilegedThreadFactory method. A new privilegedThreadFactory can be created within an AccessController#doPrivileged action setting the current thread's access control context to create threads with the selected permission settings holding within that action.

Note that while tasks running within such threads will have the same access control and class loader settings as the current thread, they need not have the same java.lang.ThreadLocal or java.lang.InheritableThreadLocal values. If necessary, particular values of thread locals can be set or reset before any task runs in ThreadPoolExecutor subclasses using ThreadPoolExecutor. Also, if it is necessary to initialize worker threads to have the same InheritableThreadLocal settings as some other designated thread, you can create a custom ThreadFactory in which that thread waits for and services requests to create others that will inherit its values.

Returns: a thread factory

Throws: AccessControlException if the current access control context does not have permission to both get and set context class loader.

unconfigurableExecutorService

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

unconfigurableScheduledExecutorService

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