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Executors.javaAPI DocJava SE 6 API28629Tue Jun 10 00:25:56 BST 2008java.util.concurrent

Executors

public class Executors extends Object
Factory and utility methods for {@link Executor}, {@link ExecutorService}, {@link ScheduledExecutorService}, {@link ThreadFactory}, and {@link Callable} classes defined in this package. This class supports the following kinds of methods:
  • Methods that create and return an {@link ExecutorService} set up with commonly useful configuration settings.
  • Methods that create and return a {@link 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 {@link ThreadFactory} that sets newly created threads to a known state.
  • Methods that create and return a {@link Callable} out of other closure-like forms, so they can be used in execution methods requiring Callable.
since
1.5
author
Doug Lea

Fields Summary
Constructors Summary
private Executors()
Cannot instantiate.

Methods Summary
public static java.util.concurrent.Callablecallable(java.lang.Runnable task, T result)
Returns a {@link 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.

param
task the task to run
param
result the result to return
return
a callable object
throws
NullPointerException if task null

        if (task == null)
            throw new NullPointerException();
        return new RunnableAdapter<T>(task, result);
    
public static java.util.concurrent.Callablecallable(java.lang.Runnable task)
Returns a {@link Callable} object that, when called, runs the given task and returns null.

param
task the task to run
return
a callable object
throws
NullPointerException if task null

        if (task == null)
            throw new NullPointerException();
        return new RunnableAdapter<Object>(task, null);
    
public static java.util.concurrent.Callablecallable(java.security.PrivilegedAction action)
Returns a {@link Callable} object that, when called, runs the given privileged action and returns its result.

param
action the privileged action to run
return
a callable object
throws
NullPointerException if action null

        if (action == null)
            throw new NullPointerException();
        return new Callable<Object>() {
	    public Object call() { return action.run(); }};
    
public static java.util.concurrent.Callablecallable(java.security.PrivilegedExceptionAction action)
Returns a {@link Callable} object that, when called, runs the given privileged exception action and returns its result.

param
action the privileged exception action to run
return
a callable object
throws
NullPointerException if action null

        if (action == null)
            throw new NullPointerException();
	return new Callable<Object>() {
	    public Object call() throws Exception { return action.run(); }};
    
public static java.util.concurrent.ThreadFactorydefaultThreadFactory()
Returns a default thread factory used to create new threads. This factory creates all new threads used by an Executor in the same {@link ThreadGroup}. If there is a {@link java.lang.SecurityManager}, it uses the group of {@link 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 {@link 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.

return
a thread factory

        return new DefaultThreadFactory();
    
public static java.util.concurrent.ExecutorServicenewCachedThreadPool()
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 {@link ThreadPoolExecutor} constructors.

return
the newly created thread pool

        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
    
public static java.util.concurrent.ExecutorServicenewCachedThreadPool(java.util.concurrent.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.

param
threadFactory the factory to use when creating new threads
return
the newly created thread pool
throws
NullPointerException if threadFactory is null

        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>(),
                                      threadFactory);
    
public static java.util.concurrent.ExecutorServicenewFixedThreadPool(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 {@link ExecutorService#shutdown shutdown}.

param
nThreads the number of threads in the pool
return
the newly created thread pool
throws
IllegalArgumentException if nThreads <= 0

        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>());
    
public static java.util.concurrent.ExecutorServicenewFixedThreadPool(int nThreads, java.util.concurrent.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 {@link ExecutorService#shutdown shutdown}.

param
nThreads the number of threads in the pool
param
threadFactory the factory to use when creating new threads
return
the newly created thread pool
throws
NullPointerException if threadFactory is null
throws
IllegalArgumentException if nThreads <= 0

        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>(),
                                      threadFactory);
    
public static java.util.concurrent.ScheduledExecutorServicenewScheduledThreadPool(int corePoolSize, java.util.concurrent.ThreadFactory threadFactory)
Creates a thread pool that can schedule commands to run after a given delay, or to execute periodically.

param
corePoolSize the number of threads to keep in the pool, even if they are idle.
param
threadFactory the factory to use when the executor creates a new thread.
return
a newly created scheduled thread pool
throws
IllegalArgumentException if corePoolSize < 0
throws
NullPointerException if threadFactory is null

        return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
    
public static java.util.concurrent.ScheduledExecutorServicenewScheduledThreadPool(int corePoolSize)
Creates a thread pool that can schedule commands to run after a given delay, or to execute periodically.

param
corePoolSize the number of threads to keep in the pool, even if they are idle.
return
a newly created scheduled thread pool
throws
IllegalArgumentException if corePoolSize < 0

        return new ScheduledThreadPoolExecutor(corePoolSize);
    
public static java.util.concurrent.ExecutorServicenewSingleThreadExecutor()
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.

return
the newly created single-threaded Executor

        return new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>()));
    
public static java.util.concurrent.ExecutorServicenewSingleThreadExecutor(java.util.concurrent.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.

param
threadFactory the factory to use when creating new threads
return
the newly created single-threaded Executor
throws
NullPointerException if threadFactory is null

        return new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>(),
                                    threadFactory));
    
public static java.util.concurrent.ScheduledExecutorServicenewSingleThreadScheduledExecutor()
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.

return
the newly created scheduled executor

        return new DelegatedScheduledExecutorService
            (new ScheduledThreadPoolExecutor(1));
    
public static java.util.concurrent.ScheduledExecutorServicenewSingleThreadScheduledExecutor(java.util.concurrent.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.

param
threadFactory the factory to use when creating new threads
return
a newly created scheduled executor
throws
NullPointerException if threadFactory is null

        return new DelegatedScheduledExecutorService
            (new ScheduledThreadPoolExecutor(1, threadFactory));
    
public static java.util.concurrent.CallableprivilegedCallable(java.util.concurrent.Callable callable)
Returns a {@link Callable} object that will, when called, execute the given callable under the current access control context. This method should normally be invoked within an {@link 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 {@link AccessControlException}.

param
callable the underlying task
return
a callable object
throws
NullPointerException if callable null

        if (callable == null)
            throw new NullPointerException();
        return new PrivilegedCallable<T>(callable);
    
public static java.util.concurrent.CallableprivilegedCallableUsingCurrentClassLoader(java.util.concurrent.Callable callable)
Returns a {@link 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 {@link 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 {@link AccessControlException}.

param
callable the underlying task
return
a callable object
throws
NullPointerException if callable null
throws
AccessControlException if the current access control context does not have permission to both set and get context class loader.

        if (callable == null)
            throw new NullPointerException();
        return new PrivilegedCallableUsingCurrentClassLoader<T>(callable);
    
public static java.util.concurrent.ThreadFactoryprivilegedThreadFactory()
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 {@link Executors#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 {@link 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 {@link java.lang.ThreadLocal} or {@link java.lang.InheritableThreadLocal} values. If necessary, particular values of thread locals can be set or reset before any task runs in {@link ThreadPoolExecutor} subclasses using {@link ThreadPoolExecutor#beforeExecute}. 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.

return
a thread factory
throws
AccessControlException if the current access control context does not have permission to both get and set context class loader.

        return new PrivilegedThreadFactory();
    
public static java.util.concurrent.ExecutorServiceunconfigurableExecutorService(java.util.concurrent.ExecutorService executor)
Returns an object that delegates all defined {@link 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.

param
executor the underlying implementation
return
an ExecutorService instance
throws
NullPointerException if executor null

        if (executor == null)
            throw new NullPointerException();
        return new DelegatedExecutorService(executor);
    
public static java.util.concurrent.ScheduledExecutorServiceunconfigurableScheduledExecutorService(java.util.concurrent.ScheduledExecutorService executor)
Returns an object that delegates all defined {@link 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.

param
executor the underlying implementation
return
a ScheduledExecutorService instance
throws
NullPointerException if executor null

        if (executor == null)
            throw new NullPointerException();
        return new DelegatedScheduledExecutorService(executor);