Class Executors
- java.lang.Object
-
- java.util.concurrent.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 requiringCallable
.
- Since:
- 1.5
Method Summary
Modifier and Type | Method | Description |
---|---|---|
static Callable<Object> | callable(Runnable task) | Returns a |
static <T> Callable<T> | callable(Runnable task,
T result) | Returns a |
static Callable<Object> | callable(PrivilegedAction<?> action) | Returns a |
static Callable<Object> | callable(PrivilegedExceptionAction<?> action) | Returns a |
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) | Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue. |
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 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() | Creates an Executor that uses a single worker thread operating off an unbounded queue. |
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 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() | Creates a work-stealing thread pool using the number of available processors as its target parallelism level. |
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 <T> Callable<T> | privilegedCallable(Callable<T> callable) | Returns a |
static <T> Callable<T> | privilegedCallableUsingCurrentClassLoader(Callable<T> callable) | Returns a |
static ThreadFactory | privilegedThreadFactory() | Returns a thread factory used to create new threads that have the same permissions as the current thread. |
static ExecutorService | unconfigurableExecutorService(ExecutorService executor) | Returns an object that delegates all defined |
static ScheduledExecutorService | unconfigurableScheduledExecutorService(ScheduledExecutorService executor) | Returns an object that delegates all defined |
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Method Detail
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
- ifnThreads <= 0
newWorkStealingPool
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
- ifparallelism <= 0
- Since:
- 1.8
newWorkStealingPool
public static ExecutorService newWorkStealingPool()
Creates a work-stealing thread pool using the number of available processors as its target parallelism level.
- Returns:
- the newly created thread pool
- Since:
- 1.8
- See Also:
newWorkStealingPool(int)
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
- ifnThreads <= 0
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
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
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:
- the newly created scheduled executor
- Throws:
-
NullPointerException
- if threadFactory is null
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:
- the newly created scheduled thread pool
- Throws:
-
IllegalArgumentException
- ifcorePoolSize < 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:
- the newly created scheduled thread pool
- Throws:
-
IllegalArgumentException
- ifcorePoolSize < 0
-
NullPointerException
- if threadFactory is null
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
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 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
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 defaultThreadFactory()
, 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 ThreadLocal
or InheritableThreadLocal
values. If necessary, particular values of thread locals can be set or reset before any task runs in ThreadPoolExecutor
subclasses using ThreadPoolExecutor.beforeExecute(Thread, Runnable)
. 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
callable
public 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. This can be useful when applying methods requiring a Callable
to an otherwise resultless action.
- Type Parameters:
-
T
- the type of the result - Parameters:
-
task
- the task to run -
result
- the result to return - Returns:
- a callable object
- Throws:
-
NullPointerException
- if task null
callable
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
callable
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
callable
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
privilegedCallable
public static <T> Callable<T> privilegedCallable(Callable<T> 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
.
- Type Parameters:
-
T
- the type of the callable's result - Parameters:
-
callable
- the underlying task - Returns:
- a callable object
- Throws:
-
NullPointerException
- if callable null
privilegedCallableUsingCurrentClassLoader
public static <T> Callable<T> privilegedCallableUsingCurrentClassLoader(Callable<T> 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
.
- Type Parameters:
-
T
- the type of the callable's result - 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