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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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*/ |
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|
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package java.util.concurrent; |
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import java.util.concurrent.*; // for javadoc (till 6280605 is fixed) |
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import java.util.*; |
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import java.util.concurrent.atomic.AtomicInteger; |
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import java.security.AccessControlContext; |
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import java.security.AccessController; |
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import java.security.PrivilegedAction; |
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import java.security.PrivilegedExceptionAction; |
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import java.security.AccessControlException; |
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|
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/** |
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* Factory and utility methods for {@link Executor}, {@link |
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* ExecutorService}, {@link ScheduledExecutorService}, {@link |
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* ThreadFactory}, and {@link Callable} classes defined in this |
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* package. This class supports the following kinds of methods: |
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* |
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* <ul> |
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* <li> Methods that create and return an {@link ExecutorService} |
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* set up with commonly useful configuration settings. |
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* <li> Methods that create and return a {@link ScheduledExecutorService} |
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* set up with commonly useful configuration settings. |
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* <li> Methods that create and return a "wrapped" ExecutorService, that |
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* disables reconfiguration by making implementation-specific methods |
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* inaccessible. |
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* <li> Methods that create and return a {@link ThreadFactory} |
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* that sets newly created threads to a known state. |
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* <li> Methods that create and return a {@link Callable} |
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* out of other closure-like forms, so they can be used |
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* in execution methods requiring <tt>Callable</tt>. |
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* </ul> |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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*/ |
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public class Executors { |
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|
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/** |
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* Creates a thread pool that reuses a fixed number of threads |
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* operating off a shared unbounded queue. At any point, at most |
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* <tt>nThreads</tt> threads will be active processing tasks. |
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* If additional tasks are submitted when all threads are active, |
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* they will wait in the queue until a thread is available. |
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* If any thread terminates due to a failure during execution |
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* prior to shutdown, a new one will take its place if needed to |
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* execute subsequent tasks. |
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* |
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* @param nThreads the number of threads in the pool |
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* @return the newly created thread pool |
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*/ |
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public static ExecutorService newFixedThreadPool(int nThreads) { |
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return new ThreadPoolExecutor(nThreads, nThreads, |
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0L, TimeUnit.MILLISECONDS, |
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new LinkedBlockingQueue<Runnable>()); |
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} |
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|
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/** |
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* Creates a thread pool that reuses a fixed number of threads |
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* operating off a shared unbounded queue, using the provided |
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* ThreadFactory to create new threads when needed. At any point, |
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* at most <tt>nThreads</tt> threads will be active processing |
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* tasks. If additional tasks are submitted when all threads are |
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* active, they will wait in the queue until a thread is |
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* available. If any thread terminates due to a failure during |
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* execution prior to shutdown, a new one will take its place if |
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* needed to execute subsequent tasks. |
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* |
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* @param nThreads the number of threads in the pool |
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* @param threadFactory the factory to use when creating new threads |
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* @return the newly created thread pool |
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*/ |
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public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) { |
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return new ThreadPoolExecutor(nThreads, nThreads, |
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0L, TimeUnit.MILLISECONDS, |
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new LinkedBlockingQueue<Runnable>(), |
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threadFactory); |
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} |
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|
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/** |
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* Creates an Executor that uses a single worker thread operating |
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* off an unbounded queue. (Note however that if this single |
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* thread terminates due to a failure during execution prior to |
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* shutdown, a new one will take its place if needed to execute |
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* subsequent tasks.) Tasks are guaranteed to execute |
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* sequentially, and no more than one task will be active at any |
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* given time. Unlike the otherwise equivalent |
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* <tt>newFixedThreadPool(1)</tt> the returned executor is |
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* guaranteed not to be reconfigurable to use additional threads. |
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* |
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* @return the newly created single-threaded Executor |
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*/ |
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public static ExecutorService newSingleThreadExecutor() { |
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return new DelegatedExecutorService |
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(new ThreadPoolExecutor(1, 1, |
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0L, TimeUnit.MILLISECONDS, |
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new LinkedBlockingQueue<Runnable>())); |
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} |
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|
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/** |
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* Creates an Executor that uses a single worker thread operating |
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* off an unbounded queue, and uses the provided ThreadFactory to |
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* create a new thread when needed. Unlike the otherwise |
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* equivalent <tt>newFixedThreadPool(1, threadFactory)</tt> the |
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* returned executor is guaranteed not to be reconfigurable to use |
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* additional threads. |
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* |
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* @param threadFactory the factory to use when creating new |
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* threads |
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* |
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* @return the newly created single-threaded Executor |
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*/ |
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public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) { |
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return new DelegatedExecutorService |
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(new ThreadPoolExecutor(1, 1, |
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0L, TimeUnit.MILLISECONDS, |
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new LinkedBlockingQueue<Runnable>(), |
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threadFactory)); |
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} |
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|
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/** |
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* Creates a thread pool that creates new threads as needed, but |
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* will reuse previously constructed threads when they are |
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* available. These pools will typically improve the performance |
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* of programs that execute many short-lived asynchronous tasks. |
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* Calls to <tt>execute</tt> will reuse previously constructed |
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* threads if available. If no existing thread is available, a new |
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* thread will be created and added to the pool. Threads that have |
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* not been used for sixty seconds are terminated and removed from |
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* the cache. Thus, a pool that remains idle for long enough will |
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* not consume any resources. Note that pools with similar |
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* properties but different details (for example, timeout parameters) |
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* may be created using {@link ThreadPoolExecutor} constructors. |
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* |
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* @return the newly created thread pool |
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*/ |
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public static ExecutorService newCachedThreadPool() { |
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return new ThreadPoolExecutor(0, Integer.MAX_VALUE, |
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60L, TimeUnit.SECONDS, |
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new SynchronousQueue<Runnable>()); |
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} |
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|
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/** |
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* Creates a thread pool that creates new threads as needed, but |
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* will reuse previously constructed threads when they are |
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* available, and uses the provided |
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* ThreadFactory to create new threads when needed. |
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* @param threadFactory the factory to use when creating new threads |
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* @return the newly created thread pool |
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*/ |
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public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) { |
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return new ThreadPoolExecutor(0, Integer.MAX_VALUE, |
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60L, TimeUnit.SECONDS, |
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new SynchronousQueue<Runnable>(), |
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threadFactory); |
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} |
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|
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/** |
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* Creates a single-threaded executor that can schedule commands |
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* to run after a given delay, or to execute periodically. |
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* (Note however that if this single |
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* thread terminates due to a failure during execution prior to |
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* shutdown, a new one will take its place if needed to execute |
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* subsequent tasks.) Tasks are guaranteed to execute |
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* sequentially, and no more than one task will be active at any |
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* given time. Unlike the otherwise equivalent |
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* <tt>newScheduledThreadPool(1)</tt> the returned executor is |
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* guaranteed not to be reconfigurable to use additional threads. |
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* @return the newly created scheduled executor |
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*/ |
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public static ScheduledExecutorService newSingleThreadScheduledExecutor() { |
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return new DelegatedScheduledExecutorService |
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(new ScheduledThreadPoolExecutor(1)); |
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} |
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|
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/** |
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* Creates a single-threaded executor that can schedule commands |
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* to run after a given delay, or to execute periodically. (Note |
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* however that if this single thread terminates due to a failure |
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* during execution prior to shutdown, a new one will take its |
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* place if needed to execute subsequent tasks.) Tasks are |
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* guaranteed to execute sequentially, and no more than one task |
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* will be active at any given time. Unlike the otherwise |
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* equivalent <tt>newScheduledThreadPool(1, threadFactory)</tt> |
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* the returned executor is guaranteed not to be reconfigurable to |
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* use additional threads. |
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* @param threadFactory the factory to use when creating new |
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* threads |
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* @return a newly created scheduled executor |
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*/ |
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public static ScheduledExecutorService newSingleThreadScheduledExecutor(ThreadFactory threadFactory) { |
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return new DelegatedScheduledExecutorService |
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(new ScheduledThreadPoolExecutor(1, threadFactory)); |
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} |
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|
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/** |
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* Creates a thread pool that can schedule commands to run after a |
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* given delay, or to execute periodically. |
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* @param corePoolSize the number of threads to keep in the pool, |
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* even if they are idle. |
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* @return a newly created scheduled thread pool |
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*/ |
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public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) { |
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return new ScheduledThreadPoolExecutor(corePoolSize); |
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} |
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|
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/** |
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* Creates a thread pool that can schedule commands to run after a |
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* given delay, or to execute periodically. |
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* @param corePoolSize the number of threads to keep in the pool, |
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* even if they are idle. |
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* @param threadFactory the factory to use when the executor |
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* creates a new thread. |
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* @return a newly created scheduled thread pool |
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*/ |
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public static ScheduledExecutorService newScheduledThreadPool( |
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int corePoolSize, ThreadFactory threadFactory) { |
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return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory); |
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} |
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|
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|
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/** |
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* Returns an object that delegates all defined {@link |
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* ExecutorService} methods to the given executor, but not any |
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* other methods that might otherwise be accessible using |
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* casts. This provides a way to safely "freeze" configuration and |
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* disallow tuning of a given concrete implementation. |
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* @param executor the underlying implementation |
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* @return an <tt>ExecutorService</tt> instance |
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* @throws NullPointerException if executor null |
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*/ |
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public static ExecutorService unconfigurableExecutorService(ExecutorService executor) { |
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if (executor == null) |
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throw new NullPointerException(); |
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return new DelegatedExecutorService(executor); |
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} |
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|
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/** |
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* Returns an object that delegates all defined {@link |
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* ScheduledExecutorService} methods to the given executor, but |
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* not any other methods that might otherwise be accessible using |
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* casts. This provides a way to safely "freeze" configuration and |
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* disallow tuning of a given concrete implementation. |
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* @param executor the underlying implementation |
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* @return a <tt>ScheduledExecutorService</tt> instance |
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* @throws NullPointerException if executor null |
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*/ |
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public static ScheduledExecutorService unconfigurableScheduledExecutorService(ScheduledExecutorService executor) { |
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if (executor == null) |
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throw new NullPointerException(); |
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return new DelegatedScheduledExecutorService(executor); |
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} |
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|
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/** |
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* Returns a default thread factory used to create new threads. |
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* This factory creates all new threads used by an Executor in the |
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* same {@link ThreadGroup}. If there is a {@link |
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* java.lang.SecurityManager}, it uses the group of {@link |
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* System#getSecurityManager}, else the group of the thread |
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* invoking this <tt>defaultThreadFactory</tt> method. Each new |
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* thread is created as a non-daemon thread with priority set to |
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* the smaller of <tt>Thread.NORM_PRIORITY</tt> and the maximum |
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* priority permitted in the thread group. New threads have names |
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* accessible via {@link Thread#getName} of |
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* <em>pool-N-thread-M</em>, where <em>N</em> is the sequence |
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* number of this factory, and <em>M</em> is the sequence number |
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* of the thread created by this factory. |
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* @return a thread factory |
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*/ |
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public static ThreadFactory defaultThreadFactory() { |
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return new DefaultThreadFactory(); |
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} |
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|
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/** |
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* Returns a thread factory used to create new threads that |
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* have the same permissions as the current thread. |
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* This factory creates threads with the same settings as {@link |
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* Executors#defaultThreadFactory}, additionally setting the |
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* AccessControlContext and contextClassLoader of new threads to |
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* be the same as the thread invoking this |
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* <tt>privilegedThreadFactory</tt> method. A new |
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* <tt>privilegedThreadFactory</tt> can be created within an |
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* {@link AccessController#doPrivileged} action setting the |
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* current thread's access control context to create threads with |
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* the selected permission settings holding within that action. |
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* |
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* <p> Note that while tasks running within such threads will have |
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* the same access control and class loader settings as the |
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* current thread, they need not have the same {@link |
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* java.lang.ThreadLocal} or {@link |
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* java.lang.InheritableThreadLocal} values. If necessary, |
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* particular values of thread locals can be set or reset before |
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* any task runs in {@link ThreadPoolExecutor} subclasses using |
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* {@link ThreadPoolExecutor#beforeExecute}. Also, if it is |
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* necessary to initialize worker threads to have the same |
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* InheritableThreadLocal settings as some other designated |
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* thread, you can create a custom ThreadFactory in which that |
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* thread waits for and services requests to create others that |
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* will inherit its values. |
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* |
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* @return a thread factory |
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* @throws AccessControlException if the current access control |
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* context does not have permission to both get and set context |
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* class loader. |
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*/ |
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public static ThreadFactory privilegedThreadFactory() { |
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return new PrivilegedThreadFactory(); |
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} |
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|
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/** |
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* Returns a {@link Callable} object that, when |
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* called, runs the given task and returns the given result. This |
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* can be useful when applying methods requiring a |
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* <tt>Callable</tt> to an otherwise resultless action. |
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* @param task the task to run |
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* @param result the result to return |
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* @throws NullPointerException if task null |
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* @return a callable object |
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*/ |
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public static <T> Callable<T> callable(Runnable task, T result) { |
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if (task == null) |
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throw new NullPointerException(); |
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return new RunnableAdapter<T>(task, result); |
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} |
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|
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/** |
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* Returns a {@link Callable} object that, when |
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* called, runs the given task and returns <tt>null</tt>. |
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* @param task the task to run |
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* @return a callable object |
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* @throws NullPointerException if task null |
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*/ |
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public static Callable<Object> callable(Runnable task) { |
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if (task == null) |
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throw new NullPointerException(); |
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return new RunnableAdapter<Object>(task, null); |
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} |
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|
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/** |
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* Returns a {@link Callable} object that, when |
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* called, runs the given privileged action and returns its result. |
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* @param action the privileged action to run |
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* @return a callable object |
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* @throws NullPointerException if action null |
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*/ |
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public static Callable<Object> callable(final PrivilegedAction<?> action) { |
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if (action == null) |
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throw new NullPointerException(); |
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return new Callable<Object>() { |
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public Object call() { return action.run(); }}; |
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} |
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|
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/** |
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* Returns a {@link Callable} object that, when |
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* called, runs the given privileged exception action and returns |
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* its result. |
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* @param action the privileged exception action to run |
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* @return a callable object |
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* @throws NullPointerException if action null |
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*/ |
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public static Callable<Object> callable(final PrivilegedExceptionAction<?> action) { |
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if (action == null) |
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throw new NullPointerException(); |
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return new Callable<Object>() { |
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public Object call() throws Exception { return action.run(); }}; |
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} |
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|
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/** |
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* Returns a {@link Callable} object that will, when |
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* called, execute the given <tt>callable</tt> under the current |
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* access control context. This method should normally be |
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* invoked within an {@link AccessController#doPrivileged} action |
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* to create callables that will, if possible, execute under the |
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* selected permission settings holding within that action; or if |
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* not possible, throw an associated {@link |
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* AccessControlException}. |
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* @param callable the underlying task |
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* @return a callable object |
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* @throws NullPointerException if callable null |
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* |
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*/ |
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public static <T> Callable<T> privilegedCallable(Callable<T> callable) { |
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if (callable == null) |
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throw new NullPointerException(); |
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return new PrivilegedCallable<T>(callable); |
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} |
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|
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/** |
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* Returns a {@link Callable} object that will, when |
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* called, execute the given <tt>callable</tt> under the current |
395 |
* access control context, with the current context class loader |
396 |
* as the context class loader. This method should normally be |
397 |
* invoked within an {@link AccessController#doPrivileged} action |
398 |
* to create callables that will, if possible, execute under the |
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* selected permission settings holding within that action; or if |
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* not possible, throw an associated {@link |
401 |
* AccessControlException}. |
402 |
* @param callable the underlying task |
403 |
* |
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* @return a callable object |
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* @throws NullPointerException if callable null |
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* @throws AccessControlException if the current access control |
407 |
* context does not have permission to both set and get context |
408 |
* class loader. |
409 |
*/ |
410 |
public static <T> Callable<T> privilegedCallableUsingCurrentClassLoader(Callable<T> callable) { |
411 |
if (callable == null) |
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throw new NullPointerException(); |
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return new PrivilegedCallableUsingCurrentClassLoader<T>(callable); |
414 |
} |
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|
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// Non-public classes supporting the public methods |
417 |
|
418 |
/** |
419 |
* A callable that runs given task and returns given result |
420 |
*/ |
421 |
static final class RunnableAdapter<T> implements Callable<T> { |
422 |
final Runnable task; |
423 |
final T result; |
424 |
RunnableAdapter(Runnable task, T result) { |
425 |
this.task = task; |
426 |
this.result = result; |
427 |
} |
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public T call() { |
429 |
task.run(); |
430 |
return result; |
431 |
} |
432 |
} |
433 |
|
434 |
/** |
435 |
* A callable that runs under established access control settings |
436 |
*/ |
437 |
static final class PrivilegedCallable<T> implements Callable<T> { |
438 |
private final AccessControlContext acc; |
439 |
private final Callable<T> task; |
440 |
private T result; |
441 |
private Exception exception; |
442 |
PrivilegedCallable(Callable<T> task) { |
443 |
this.task = task; |
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this.acc = AccessController.getContext(); |
445 |
} |
446 |
|
447 |
public T call() throws Exception { |
448 |
AccessController.doPrivileged(new PrivilegedAction<T>() { |
449 |
public T run() { |
450 |
try { |
451 |
result = task.call(); |
452 |
} catch (Exception ex) { |
453 |
exception = ex; |
454 |
} |
455 |
return null; |
456 |
} |
457 |
}, acc); |
458 |
if (exception != null) |
459 |
throw exception; |
460 |
else |
461 |
return result; |
462 |
} |
463 |
} |
464 |
|
465 |
/** |
466 |
* A callable that runs under established access control settings and |
467 |
* current ClassLoader |
468 |
*/ |
469 |
static final class PrivilegedCallableUsingCurrentClassLoader<T> implements Callable<T> { |
470 |
private final ClassLoader ccl; |
471 |
private final AccessControlContext acc; |
472 |
private final Callable<T> task; |
473 |
private T result; |
474 |
private Exception exception; |
475 |
PrivilegedCallableUsingCurrentClassLoader(Callable<T> task) { |
476 |
this.task = task; |
477 |
this.ccl = Thread.currentThread().getContextClassLoader(); |
478 |
this.acc = AccessController.getContext(); |
479 |
acc.checkPermission(new RuntimePermission("getContextClassLoader")); |
480 |
acc.checkPermission(new RuntimePermission("setContextClassLoader")); |
481 |
} |
482 |
|
483 |
public T call() throws Exception { |
484 |
AccessController.doPrivileged(new PrivilegedAction<T>() { |
485 |
public T run() { |
486 |
ClassLoader savedcl = null; |
487 |
Thread t = Thread.currentThread(); |
488 |
try { |
489 |
ClassLoader cl = t.getContextClassLoader(); |
490 |
if (ccl != cl) { |
491 |
t.setContextClassLoader(ccl); |
492 |
savedcl = cl; |
493 |
} |
494 |
result = task.call(); |
495 |
} catch (Exception ex) { |
496 |
exception = ex; |
497 |
} finally { |
498 |
if (savedcl != null) |
499 |
t.setContextClassLoader(savedcl); |
500 |
} |
501 |
return null; |
502 |
} |
503 |
}, acc); |
504 |
if (exception != null) |
505 |
throw exception; |
506 |
else |
507 |
return result; |
508 |
} |
509 |
} |
510 |
|
511 |
/** |
512 |
* The default thread factory |
513 |
*/ |
514 |
static class DefaultThreadFactory implements ThreadFactory { |
515 |
static final AtomicInteger poolNumber = new AtomicInteger(1); |
516 |
final ThreadGroup group; |
517 |
final AtomicInteger threadNumber = new AtomicInteger(1); |
518 |
final String namePrefix; |
519 |
|
520 |
DefaultThreadFactory() { |
521 |
SecurityManager s = System.getSecurityManager(); |
522 |
group = (s != null)? s.getThreadGroup() : |
523 |
Thread.currentThread().getThreadGroup(); |
524 |
namePrefix = "pool-" + |
525 |
poolNumber.getAndIncrement() + |
526 |
"-thread-"; |
527 |
} |
528 |
|
529 |
public Thread newThread(Runnable r) { |
530 |
Thread t = new Thread(group, r, |
531 |
namePrefix + threadNumber.getAndIncrement(), |
532 |
0); |
533 |
if (t.isDaemon()) |
534 |
t.setDaemon(false); |
535 |
if (t.getPriority() != Thread.NORM_PRIORITY) |
536 |
t.setPriority(Thread.NORM_PRIORITY); |
537 |
return t; |
538 |
} |
539 |
} |
540 |
|
541 |
/** |
542 |
* Thread factory capturing access control and class loader |
543 |
*/ |
544 |
static class PrivilegedThreadFactory extends DefaultThreadFactory { |
545 |
private final ClassLoader ccl; |
546 |
private final AccessControlContext acc; |
547 |
|
548 |
PrivilegedThreadFactory() { |
549 |
super(); |
550 |
this.ccl = Thread.currentThread().getContextClassLoader(); |
551 |
this.acc = AccessController.getContext(); |
552 |
acc.checkPermission(new RuntimePermission("setContextClassLoader")); |
553 |
} |
554 |
|
555 |
public Thread newThread(final Runnable r) { |
556 |
return super.newThread(new Runnable() { |
557 |
public void run() { |
558 |
AccessController.doPrivileged(new PrivilegedAction<Object>() { |
559 |
public Object run() { |
560 |
Thread.currentThread().setContextClassLoader(ccl); |
561 |
r.run(); |
562 |
return null; |
563 |
} |
564 |
}, acc); |
565 |
} |
566 |
}); |
567 |
} |
568 |
|
569 |
} |
570 |
|
571 |
/** |
572 |
* A wrapper class that exposes only the ExecutorService methods |
573 |
* of an ExecutorService implementation. |
574 |
*/ |
575 |
static class DelegatedExecutorService extends AbstractExecutorService { |
576 |
private final ExecutorService e; |
577 |
DelegatedExecutorService(ExecutorService executor) { e = executor; } |
578 |
public void execute(Runnable command) { e.execute(command); } |
579 |
public void shutdown() { e.shutdown(); } |
580 |
public List<Runnable> shutdownNow() { return e.shutdownNow(); } |
581 |
public boolean isShutdown() { return e.isShutdown(); } |
582 |
public boolean isTerminated() { return e.isTerminated(); } |
583 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
584 |
throws InterruptedException { |
585 |
return e.awaitTermination(timeout, unit); |
586 |
} |
587 |
public Future<?> submit(Runnable task) { |
588 |
return e.submit(task); |
589 |
} |
590 |
public <T> Future<T> submit(Callable<T> task) { |
591 |
return e.submit(task); |
592 |
} |
593 |
public <T> Future<T> submit(Runnable task, T result) { |
594 |
return e.submit(task, result); |
595 |
} |
596 |
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) |
597 |
throws InterruptedException { |
598 |
return e.invokeAll(tasks); |
599 |
} |
600 |
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks, |
601 |
long timeout, TimeUnit unit) |
602 |
throws InterruptedException { |
603 |
return e.invokeAll(tasks, timeout, unit); |
604 |
} |
605 |
public <T> T invokeAny(Collection<? extends Callable<T>> tasks) |
606 |
throws InterruptedException, ExecutionException { |
607 |
return e.invokeAny(tasks); |
608 |
} |
609 |
public <T> T invokeAny(Collection<? extends Callable<T>> tasks, |
610 |
long timeout, TimeUnit unit) |
611 |
throws InterruptedException, ExecutionException, TimeoutException { |
612 |
return e.invokeAny(tasks, timeout, unit); |
613 |
} |
614 |
} |
615 |
|
616 |
/** |
617 |
* A wrapper class that exposes only the ScheduledExecutorService |
618 |
* methods of a ScheduledExecutorService implementation. |
619 |
*/ |
620 |
static class DelegatedScheduledExecutorService |
621 |
extends DelegatedExecutorService |
622 |
implements ScheduledExecutorService { |
623 |
private final ScheduledExecutorService e; |
624 |
DelegatedScheduledExecutorService(ScheduledExecutorService executor) { |
625 |
super(executor); |
626 |
e = executor; |
627 |
} |
628 |
public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) { |
629 |
return e.schedule(command, delay, unit); |
630 |
} |
631 |
public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) { |
632 |
return e.schedule(callable, delay, unit); |
633 |
} |
634 |
public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) { |
635 |
return e.scheduleAtFixedRate(command, initialDelay, period, unit); |
636 |
} |
637 |
public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) { |
638 |
return e.scheduleWithFixedDelay(command, initialDelay, delay, unit); |
639 |
} |
640 |
} |
641 |
|
642 |
|
643 |
/** Cannot instantiate. */ |
644 |
private Executors() {} |
645 |
} |