preface
This article belongs to the column "100 problems to solve Java concurrency". This column is original by the author. Please indicate the source of quotation. Please help point out the deficiencies and errors in the comment area. Thank you!
Please refer to table of contents and references for this column 100 problems to solve Java concurrency
text
Class annotation
/**
* 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:
*
* <ul>
* <li> Methods that create and return an {@link ExecutorService}
* set up with commonly useful configuration settings.
* <li> Methods that create and return a {@link ScheduledExecutorService}
* set up with commonly useful configuration settings.
* <li> Methods that create and return a "wrapped" ExecutorService, that
* disables reconfiguration by making implementation-specific methods
* inaccessible.
* <li> Methods that create and return a {@link ThreadFactory}
* that sets newly created threads to a known state.
* <li> Methods that create and return a {@link Callable}
* out of other closure-like forms, so they can be used
* in execution methods requiring {@code Callable}.
* </ul>
*
* @since 1.5
* @author Doug Lea
*/
public class Executors {
Factories and utility methods of Executor, ExecutorService, ScheduledExecutorService, ThreadFactory, and Callable classes defined in the current package.
This class supports the following types of methods:
- Create and return ExecutorService methods that use common configuration settings.
- Create and return a ScheduledExecutorService method that uses common configuration settings.
- Creates and returns a "wrapped" ExecutorService that disables reconfiguration by making implementation specific methods inaccessible.
- Creates and returns a ThreadFactory method that sets the newly created thread to a known state.
- These methods create and return Callable methods from other closure like forms, so they can be used in execution methods that need to be Callable.
Fixed size thread pool
/**
* Creates a thread pool that reuses a fixed number of threads
* operating off a shared unbounded queue. At any point, at most
* {@code 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 {@code nThreads <= 0}
*/
public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>());
}
Create a thread pool that reuses a fixed number of threads running on a shared unbounded queue.
At any time, up to N active threads are processing tasks.
If other tasks are submitted while all threads are active, they will wait in the queue until a thread is available.
If any thread terminates due to failure during execution before shutdown, a new thread will be used to replace it if subsequent tasks need to be performed.
Threads in the pool will exist until they are explicitly closed.
/**
* 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 {@code 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 {@code nThreads <= 0}
*/
public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>(),
threadFactory);
}
The difference from the above is that you can use the provided ThreadFactory to create new threads when needed.
Worker stealing thread pool
/**
* 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.
*
* @param parallelism the targeted parallelism level
* @return the newly created thread pool
* @throws IllegalArgumentException if {@code parallelism <= 0}
* @since 1.8
*/
public static ExecutorService newWorkStealingPool(int parallelism) {
return new ForkJoinPool
(parallelism,
ForkJoinPool.defaultForkJoinWorkerThreadFactory,
null, true);
}
Create a thread pool that maintains enough threads to support a given level of parallelism and can use multiple queues to reduce contention.
The parallelism level corresponds to the maximum number of threads that actively participate or can participate in task processing.
The actual number of threads may grow and shrink dynamically.
The work stealing pool does not guarantee the execution order of submitted tasks.
/**
* Creates a work-stealing thread pool using all
* {@link Runtime#availableProcessors available processors}
* as its target parallelism level.
* @return the newly created thread pool
* @see #newWorkStealingPool(int)
* @since 1.8
*/
public static ExecutorService newWorkStealingPool() {
return new ForkJoinPool
(Runtime.getRuntime().availableProcessors(),
ForkJoinPool.defaultForkJoinWorkerThreadFactory,
null, true);
}
Create a worker thread pool using all available processors as their target parallelism level.
Thread pool for a single thread
/**
* 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
* {@code newFixedThreadPool(1)} the returned executor is
* guaranteed not to be reconfigurable to use additional threads.
*
* @return the newly created single-threaded Executor
*/
public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>()));
}
Create an actuator that uses a single worker thread running on an unbounded queue.
However, please note that if this single thread terminates due to failure during execution before shutdown, a new thread will be replaced when subsequent tasks need to be performed.
Tasks are guaranteed to be executed in sequence, and no more than one task will be active at any given time.
Unlike the newFixedThreadPool above, the returned executor is guaranteed not to be reconfigured to use other threads.
/**
* 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 {@code 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
*/
public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>(),
threadFactory));
}
The difference from the above is that you can use the provided ThreadFactory to create new threads when needed.
Adaptive adjustment, cache unlimited thread pool
/**
* 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 {@code 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
*/
public static ExecutorService newCachedThreadPool() {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>());
}
Create a thread pool that creates new threads as needed, but reuses previously constructed threads when they are available.
These pools typically improve the performance of programs that perform many short-term asynchronous tasks.
Calling execute reuses the previously constructed thread, if available.
If no existing thread is available, a new thread is created and added to the pool.
Threads that are not used for 60 seconds are terminated and removed from the cache.
Therefore, a pool that has been idle long enough does not consume any resources.
Note that you can use the ThreadPoolExecutor constructor to create pools with similar properties but different details, such as timeout parameters.
/**
* 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
*/
public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
threadFactory);
}
The difference from the above is that you can use the provided ThreadFactory to create new threads when needed.
Single thread cycle scheduling thread pool
/**
* 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
* {@code newScheduledThreadPool(1)} the returned executor is
* guaranteed not to be reconfigurable to use additional threads.
* @return the newly created scheduled executor
*/
public static ScheduledExecutorService newSingleThreadScheduledExecutor() {
return new DelegatedScheduledExecutorService
(new ScheduledThreadPoolExecutor(1));
}
Create a single threaded actuator that can schedule commands to run after a given delay or execute periodically.
However, please note that if this single thread terminates due to failure during execution before shutdown, a new thread will be replaced when subsequent tasks need to be performed.
Tasks are guaranteed to be executed in sequence, and no more than one task will be active at any given time.
Unlike the following newScheduledThreadPool, the returned executor is guaranteed not to be reconfigured to use other threads.
/**
* 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 {@code 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
*/
public static ScheduledExecutorService newSingleThreadScheduledExecutor(ThreadFactory threadFactory) {
return new DelegatedScheduledExecutorService
(new ScheduledThreadPoolExecutor(1, threadFactory));
}
The difference from the above is that you can use the provided ThreadFactory to create new threads when needed.
Periodic scheduling thread pool
/**
* 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 {@code corePoolSize < 0}
*/
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
return new ScheduledThreadPoolExecutor(corePoolSize);
}
Create a thread pool that can schedule commands to run after a given delay or execute periodically.
Parameter: corePoolSize – the number of threads to keep in the pool, even if they are idle
/**
* 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 {@code corePoolSize < 0}
* @throws NullPointerException if threadFactory is null
*/
public static ScheduledExecutorService newScheduledThreadPool(
int corePoolSize, ThreadFactory threadFactory) {
return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
}
The difference from the above is that you can use the provided ThreadFactory to create new threads when needed.
The proxy thread pool is not configurable
/**
* 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 {@code ExecutorService} instance
* @throws NullPointerException if executor null
*/
public static ExecutorService unconfigurableExecutorService(ExecutorService executor) {
if (executor == null)
throw new NullPointerException();
return new DelegatedExecutorService(executor);
}
Returns an object that delegates all defined ExecutorService methods to the given executor, but does not delegate any other methods that can be accessed using cast.
This provides a way to safely "freeze" the configuration and prohibit tuning a given concrete implementation.
Non configurable periodic scheduling thread pool
/**
* 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 {@code ScheduledExecutorService} instance
* @throws NullPointerException if executor null
*/
public static ScheduledExecutorService unconfigurableScheduledExecutorService(ScheduledExecutorService executor) {
if (executor == null)
throw new NullPointerException();
return new DelegatedScheduledExecutorService(executor);
}
The difference from the above is that it is for the ScheduledExecutorService
Default thread factory
/**
* 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 {@code defaultThreadFactory} method. Each new
* thread is created as a non-daemon thread with priority set to
* the smaller of {@code Thread.NORM_PRIORITY} and the maximum
* priority permitted in the thread group. New threads have names
* accessible via {@link Thread#getName} of
* <em>pool-N-thread-M</em>, where <em>N</em> is the sequence
* number of this factory, and <em>M</em> is the sequence number
* of the thread created by this factory.
* @return a thread factory
*/
public static ThreadFactory defaultThreadFactory() {
return new DefaultThreadFactory();
}
Returns the default thread factory used to create new threads.
This factory creates all new threads used by the executor in the same thread group.
If there is a SecurityManager, use the System.getSecurityManager group; otherwise, use the thread group that calls this defaultThreadFactory method.
Each new thread is created as a non daemon thread with priority set to thread.norm_ The lesser of priority and the maximum priority allowed in the thread group.
The name of the new thread can be accessed through the Thread.getName of pool-N-Thread-M, where N is the serial number of the factory and M is the serial number of the thread created by the factory.
Privileged thread factory
/**
* 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
* {@code privilegedThreadFactory} method. A new
* {@code privilegedThreadFactory} can be created within an
* {@link AccessController#doPrivileged AccessController.doPrivileged}
* action setting the current thread's access control context to
* create threads with the selected permission settings holding
* within that action.
*
* <p>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(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.
*
* @return a thread factory
* @throws AccessControlException if the current access control
* context does not have permission to both get and set context
* class loader
*/
public static ThreadFactory privilegedThreadFactory() {
return new PrivilegedThreadFactory();
}
Returns the thread factory used to create a new thread with the same permissions as the current thread.
This factory creates a thread with the same settings as defaultThreadFactory, and sets the AccessControlContext and contextClassLoader of the new thread to be the same as the thread calling this privilegedThreadFactory method.
You can create a new privilegedThreadFactory in the AccessController.doPrivileged operation, which sets the access control context of the current thread to create a thread that retains the selected permission settings in the operation.
Note that although tasks running in such threads will have the same access control and classloader settings as the current thread, they do not need to have the same ThreadLocal or InheritableThreadLocal values.
If necessary, you can use ThreadPoolExecutor.beforeExecute (thread, Runnable) to set or reset specific values of thread local variables before running any tasks in the ThreadPoolExecutor subclass.
In addition, if you need to initialize the worker thread to have the same InheritableThreadLocal settings as other specified threads, you can create a custom ThreadFactory in which the thread waits and service requests to create other threads that will inherit its values.
Callable
/**
* 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
* {@code Callable} to an otherwise resultless action.
* @param task the task to run
* @param result the result to return
* @param <T> the type of the result
* @return a callable object
* @throws NullPointerException if task null
*/
public static <T> Callable<T> callable(Runnable task, T result) {
if (task == null)
throw new NullPointerException();
return new RunnableAdapter<T>(task, result);
}
Returns a Callable object that runs the given task and returns the given result when called.
This is useful when applying methods that require Callable to other fruitless operations.
/**
* Returns a {@link Callable} object that, when
* called, runs the given task and returns {@code null}.
* @param task the task to run
* @return a callable object
* @throws NullPointerException if task null
*/
public static Callable<Object> callable(Runnable task) {
if (task == null)
throw new NullPointerException();
return new RunnableAdapter<Object>(task, null);
}
Returns a Callable object that runs the given task and returns null when called.
/**
* 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
*/
public static Callable<Object> callable(final PrivilegedAction<?> action) {
if (action == null)
throw new NullPointerException();
return new Callable<Object>() {
public Object call() { return action.run(); }};
}
Returns a Callable object that runs the given privileged operation and returns its result when called.
/**
* 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
*/
public static Callable<Object> callable(final PrivilegedExceptionAction<?> action) {
if (action == null)
throw new NullPointerException();
return new Callable<Object>() {
public Object call() throws Exception { return action.run(); }};
}
Returns a Callable object that runs the given privileged exception operation and returns its result when called.
/**
* Returns a {@link Callable} object that will, when called,
* execute the given {@code callable} under the current access
* control context. This method should normally be invoked within
* an {@link AccessController#doPrivileged 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
* @param <T> the type of the callable's result
* @return a callable object
* @throws NullPointerException if callable null
*/
public static <T> Callable<T> privilegedCallable(Callable<T> callable) {
if (callable == null)
throw new NullPointerException();
return new PrivilegedCallable<T>(callable);
}
Returns a Callable object that will execute the given Callable object under the current access control context when called.
This method should normally be invoked in the AccessController.doPrivileged operation to create callable items.
If possible, the callable item will be executed under the selected permission settings reserved in the operation;
Or, if not possible, throw the associated AccessControlException.
/**
* Returns a {@link Callable} object that will, when called,
* execute the given {@code 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 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
* @param <T> the type of the callable's result
* @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
*/
public static <T> Callable<T> privilegedCallableUsingCurrentClassLoader(Callable<T> callable) {
if (callable == null)
throw new NullPointerException();
return new PrivilegedCallableUsingCurrentClassLoader<T>(callable);
}
Returns a Callable object that will execute the given Callable object under the current access control context when called, and takes the current context class loader as the context class loader.
This method should normally be invoked in the AccessController.doPrivileged operation to create callable items.
If possible, the callable item will be executed under the selected permission settings reserved in the operation;
Or, if not possible, throw the associated AccessControlException.
The following are non-public methods that support the above public methods
A callable class that runs a given task and returns a given result
/**
* A callable that runs given task and returns given result
*/
static final class RunnableAdapter<T> implements Callable<T> {
final Runnable task;
final T result;
RunnableAdapter(Runnable task, T result) {
this.task = task;
this.result = result;
}
public T call() {
task.run();
return result;
}
}
Callable classes that run under established access control settings
/**
* A callable that runs under established access control settings
*/
static final class PrivilegedCallable<T> implements Callable<T> {
private final Callable<T> task;
private final AccessControlContext acc;
PrivilegedCallable(Callable<T> task) {
this.task = task;
this.acc = AccessController.getContext();
}
public T call() throws Exception {
try {
return AccessController.doPrivileged(
new PrivilegedExceptionAction<T>() {
public T run() throws Exception {
return task.call();
}
}, acc);
} catch (PrivilegedActionException e) {
throw e.getException();
}
}
}
Callable classes running under the established access control settings and the current class loader
/**
* A callable that runs under established access control settings and
* current ClassLoader
*/
static final class PrivilegedCallableUsingCurrentClassLoader<T> implements Callable<T> {
private final Callable<T> task;
private final AccessControlContext acc;
private final ClassLoader ccl;
PrivilegedCallableUsingCurrentClassLoader(Callable<T> task) {
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
// Calls to getContextClassLoader from this class
// never trigger a security check, but we check
// whether our callers have this permission anyways.
sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
// Whether setContextClassLoader turns out to be necessary
// or not, we fail fast if permission is not available.
sm.checkPermission(new RuntimePermission("setContextClassLoader"));
}
this.task = task;
this.acc = AccessController.getContext();
this.ccl = Thread.currentThread().getContextClassLoader();
}
public T call() throws Exception {
try {
return AccessController.doPrivileged(
new PrivilegedExceptionAction<T>() {
public T run() throws Exception {
Thread t = Thread.currentThread();
ClassLoader cl = t.getContextClassLoader();
if (ccl == cl) {
return task.call();
} else {
t.setContextClassLoader(ccl);
try {
return task.call();
} finally {
t.setContextClassLoader(cl);
}
}
}
}, acc);
} catch (PrivilegedActionException e) {
throw e.getException();
}
}
}
Default thread factory
/**
* The default thread factory
*/
static class DefaultThreadFactory implements ThreadFactory {
private static final AtomicInteger poolNumber = new AtomicInteger(1);
private final ThreadGroup group;
private final AtomicInteger threadNumber = new AtomicInteger(1);
private final String namePrefix;
DefaultThreadFactory() {
SecurityManager s = System.getSecurityManager();
group = (s != null) ? s.getThreadGroup() :
Thread.currentThread().getThreadGroup();
namePrefix = "pool-" +
poolNumber.getAndIncrement() +
"-thread-";
}
public Thread newThread(Runnable r) {
Thread t = new Thread(group, r,
namePrefix + threadNumber.getAndIncrement(),
0);
if (t.isDaemon())
t.setDaemon(false);
if (t.getPriority() != Thread.NORM_PRIORITY)
t.setPriority(Thread.NORM_PRIORITY);
return t;
}
}
A thread factory that captures the access control context and class loader
/**
* Thread factory capturing access control context and class loader
*/
static class PrivilegedThreadFactory extends DefaultThreadFactory {
private final AccessControlContext acc;
private final ClassLoader ccl;
PrivilegedThreadFactory() {
super();
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
// Calls to getContextClassLoader from this class
// never trigger a security check, but we check
// whether our callers have this permission anyways.
sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
// Fail fast
sm.checkPermission(new RuntimePermission("setContextClassLoader"));
}
this.acc = AccessController.getContext();
this.ccl = Thread.currentThread().getContextClassLoader();
}
public Thread newThread(final Runnable r) {
return super.newThread(new Runnable() {
public void run() {
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
Thread.currentThread().setContextClassLoader(ccl);
r.run();
return null;
}
}, acc);
}
});
}
}
Exposes only the wrapper class of the ExecutorService method implemented by ExecutorService
/**
* A wrapper class that exposes only the ExecutorService methods
* of an ExecutorService implementation.
*/
static class DelegatedExecutorService extends AbstractExecutorService {
private final ExecutorService e;
DelegatedExecutorService(ExecutorService executor) { e = executor; }
public void execute(Runnable command) { e.execute(command); }
public void shutdown() { e.shutdown(); }
public List<Runnable> shutdownNow() { return e.shutdownNow(); }
public boolean isShutdown() { return e.isShutdown(); }
public boolean isTerminated() { return e.isTerminated(); }
public boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException {
return e.awaitTermination(timeout, unit);
}
public Future<?> submit(Runnable task) {
return e.submit(task);
}
public <T> Future<T> submit(Callable<T> task) {
return e.submit(task);
}
public <T> Future<T> submit(Runnable task, T result) {
return e.submit(task, result);
}
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
throws InterruptedException {
return e.invokeAll(tasks);
}
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException {
return e.invokeAll(tasks, timeout, unit);
}
public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
throws InterruptedException, ExecutionException {
return e.invokeAny(tasks);
}
public <T> T invokeAny(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException {
return e.invokeAny(tasks, timeout, unit);
}
}
static class FinalizableDelegatedExecutorService
extends DelegatedExecutorService {
FinalizableDelegatedExecutorService(ExecutorService executor) {
super(executor);
}
protected void finalize() {
super.shutdown();
}
}
Exposes only the wrapper class of the ScheduledExecutorService method implemented by ScheduledExecutorService
/**
* A wrapper class that exposes only the ScheduledExecutorService
* methods of a ScheduledExecutorService implementation.
*/
static class DelegatedScheduledExecutorService
extends DelegatedExecutorService
implements ScheduledExecutorService {
private final ScheduledExecutorService e;
DelegatedScheduledExecutorService(ScheduledExecutorService executor) {
super(executor);
e = executor;
}
public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
return e.schedule(command, delay, unit);
}
public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) {
return e.schedule(callable, delay, unit);
}
public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) {
return e.scheduleAtFixedRate(command, initialDelay, period, unit);
}
public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) {
return e.scheduleWithFixedDelay(command, initialDelay, delay, unit);
}
}
/** Cannot instantiate. */
private Executors() {}
}