NioEventLoopGroup 之ExecutorService
NioEventLoopGroup
ExecutorService JAVA-DOC 翻译
/*
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package java.util.concurrent;
import java.util.List;
import java.util.Collection;
/**
* An {@link Executor} that provides methods to manage termination and
* methods that can produce a {@link Future} for tracking progress of
* one or more asynchronous tasks.
这个接口提供一些管理任务中止的方法，另外还提供一些具有Future 返回对象的方法，这些方法跟踪一个或多们异步任务的执行行过程。
*
* <p>An {@code ExecutorService} can be shut down, which will cause
* it to reject new tasks. Two different methods are provided for
* shutting down an {@code ExecutorService}. The {@link #shutdown}
* method will allow previously submitted tasks to execute before
* terminating, while the {@link #shutdownNow} method prevents waiting
* tasks from starting and attempts to stop currently executing tasks.
* Upon termination, an executor has no tasks actively executing, no
* tasks awaiting execution, and no new tasks can be submitted. An
* unused {@code ExecutorService} should be shut down to allow
* reclamation of its resources.
ExecutorService能够被shutdown(关闭),这个方法会导致新任务被拒绝加入，关闭有两个不同的方法，
分别是shutdown 和shutdownNow。
shutdown方法允许在中止之前提供的任务继续执行，而shutdownNow方法阻止等待中的任务，并试图阻止正在执行的任务,
当一个executor要中止的时侯，没有活动的任务执行，没有任务等待执行，没有新的任务被提交，一个未使用的ExecutorService 将被shutdown,以允许资源被回收。
* <p>Method {@code submit} extends base method {@link
* Executor#execute(Runnable)} by creating and returning a {@link Future}
* that can be used to cancel execution and/or wait for completion.
* Methods {@code invokeAny} and {@code invokeAll} perform the most
* commonly useful forms of bulk execution, executing a collection of
* tasks and then waiting for at least one, or all, to
* complete. (Class {@link ExecutorCompletionService} can be used to
* write customized variants of these methods.)
submit 方法基于execute 方法的扩展，通过创建并返回一个Future 对象,
这个Future对象通常可以取消执行或等待直到任务完成。
invokeAny和invokeAll执行最普便有用的批量处理形式，执行一批任务然后等待一个或多个任务执行结束。
ExecutorCompletionService通常用于写这些方法的自定义变量。
* <p>The {@link Executors} class provides factory methods for the
* executor services provided in this package.
在这个包下 Executors 这个类提供工厂方法为了提供executor 服务
* <h3>Usage Examples</h3>
*
* Here is a sketch of a network service in which threads in a thread
* pool service incoming requests. It uses the preconfigured {@link
* Executors#newFixedThreadPool} factory method:
下边这段代码是一个网络服务的大概描述,在这个服务里的线程中的所有线程为传送的请示提供服务，它就用了Executors#newFixedThreadPool的工厂方法。
*
* <pre> {@code
* class NetworkService implements Runnable {
* private final ServerSocket serverSocket;
* private final ExecutorService pool;
*
* public NetworkService(int port, int poolSize)
* throws IOException {
* serverSocket = new ServerSocket(port);
* pool = Executors.newFixedThreadPool(poolSize);
* }
*
* public void run() { // run the service
* try {
* for (;;) {
* pool.execute(new Handler(serverSocket.accept()));
* }
* } catch (IOException ex) {
* pool.shutdown();
* }
* }
* }
*
* class Handler implements Runnable {
* private final Socket socket;
* Handler(Socket socket) { this.socket = socket; }
* public void run() {
* // read and service request on socket
* }
* }}</pre>
*
* The following method shuts down an {@code ExecutorService} in two phases,
* first by calling {@code shutdown} to reject incoming tasks, and then
* calling {@code shutdownNow}, if necessary, to cancel any lingering tasks:
下面的方法分两个阶段关闭ExecutorService,首先通过调用shutdown方法先拒绝所有任务的提交，然后调用shutdownNow方法，如果有必须，则取消任何一个徘徊的任务。
* <pre> {@code
* void shutdownAndAwaitTermination(ExecutorService pool) {
* pool.shutdown(); // Disable new tasks from being submitted
* try {
* // Wait a while for existing tasks to terminate
* if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
* pool.shutdownNow(); // Cancel currently executing tasks
* // Wait a while for tasks to respond to being cancelled
* if (!pool.awaitTermination(60, TimeUnit.SECONDS))
* System.err.println("Pool did not terminate");
* }
* } catch (InterruptedException ie) {
* // (Re-)Cancel if current thread also interrupted
* pool.shutdownNow();
* // Preserve interrupt status
* Thread.currentThread().interrupt();
* }
* }}</pre>
*
* <p>Memory consistency effects: Actions in a thread prior to the
* submission of a {@code Runnable} or {@code Callable} task to an
* {@code ExecutorService}
* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
* any actions taken by that task, which in turn <i>happen-before</i> the
* result is retrieved via {@code Future.get()}.
* 略
* @since 1.5
* @author Doug Lea
*/
public interface ExecutorService extends Executor {
/**
* Initiates an orderly shutdown in which previously submitted
* tasks are executed, but no new tasks will be accepted.
* Invocation has no additional effect if already shut down.
启动一个有秩序的shutdown,在这种场景下之前提供的任务都被执行，但没有新的任务被接受。
如果已经关闭，再次调用没有其他影响。
* <p>This method does not wait for previously submitted tasks to
* complete execution. Use {@link #awaitTermination awaitTermination}
* to do that.
这个方法不会等待已经提交的任务被执行完成，你可以用awaitTermination 方法去这样做。
* @throws SecurityException if a security manager exists and
* shutting down this ExecutorService may manipulate
* threads that the caller is not permitted to modify
* because it does not hold {@link
* java.lang.RuntimePermission}{@code ("modifyThread")},
* or the security manager's {@code checkAccess} method
* denies access.
*/
void shutdown();
/**
* Attempts to stop all actively executing tasks, halts the
* 的 of waiting tasks, and returns a list of the tasks
* that were awaiting execution.
试图停止所有活动的正在执行的任务，中止等待中的任务处理，并返回等待执行任务的列表。
* <p>This method does not wait for actively executing tasks to
* terminate. Use {@link #awaitTermination awaitTermination} to
* do that.
本方法不会等待活动的执行中的任务中止，用awaitTermination方法可以。
* <p>There are no guarantees beyond best-effort attempts to stop
* processing actively executing tasks. For example, typical
* implementations will cancel via {@link Thread#interrupt}, so any
* task that fails to respond to interrupts may never terminate.
除了尽量去尝试去中止处理活动的执行中的任务，没有任何保证。举例了，经典的实现通过Thread#interrupt方法取消一个线程的执行，
所以对interrupt方法响应失败的任务可能永远无法中止。
* @return list of tasks that never commenced execution
* @throws SecurityException if a security manager exists and
* shutting down this ExecutorService may manipulate
* threads that the caller is not permitted to modify
* because it does not hold {@link
* java.lang.RuntimePermission}{@code ("modifyThread")},
* or the security manager's {@code checkAccess} method
* denies access.
*/
List<Runnable> shutdownNow();
/**
* Returns {@code true} if this executor has been shut down.
*
* @return {@code true} if this executor has been shut down
* 如果executor 已经关闭则返回true
*/
boolean isShutdown();
/**
* Returns {@code true} if all tasks have completed following shut down.
* Note that {@code isTerminated} is never {@code true} unless
* either {@code shutdown} or {@code shutdownNow} was called first.
如果所有任务在shutdown 之后全部执行完成则返回true
注意：isTerminated 可能永远为true,除非调用了shutdown或shutdownNow 方法被调用
* @return {@code true} if all tasks have completed following shut down
*/
boolean isTerminated();
/**
* Blocks until all tasks have completed execution after a shutdown
* request, or the timeout occurs, or the current thread is
* interrupted, whichever happens first.
阻塞直到
- 在shutdown 方法执行之后，所有任务完成执行
- 时间超时
- 当前线程interrupted
三个条件任一个先发生
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
* @return {@code true} if this executor terminated and
* {@code false} if the timeout elapsed before termination
* @throws InterruptedException if interrupted while waiting
*/
boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException;
/**
* Submits a value-returning task for execution and returns a
* Future representing the pending results of the task. The
* Future's {@code get} method will return the task's result upon
* successful completion.
提交一个有返回值的任务，执行并返回一个Future对象，代表着任务的待定结果。Future的get 方法会返回成功完成任务的执行结果。
* <p>
* If you would like to immediately block waiting
* for a task, you can use constructions of the form
* {@code result = exec.submit(aCallable).get();}
如果你想立刻地阻塞等待任务的结果，你可以用如下构造形式。
* <p>Note: The {@link Executors} class includes a set of methods
* that can convert some other common closure-like objects,
* for example, {@link java.security.PrivilegedAction} to
* {@link Callable} form so they can be submitted.
Executors 这个类包含一组方法，这些方法能转换成一些其他的闭包对象，比如将PrivilegedAction转成Callable形式，所以它们也可以被提交
/**
* 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(); }};
}
*
* @param task the task to submit
* @param <T> the type of the task's result
* @return a Future representing pending completion of the task
* @throws RejectedExecutionException if the task cannot be
* scheduled for execution
* @throws NullPointerException if the task is null
*/
<T> Future<T> submit(Callable<T> task);
/**
* Submits a Runnable task for execution and returns a Future
* representing that task. The Future's {@code get} method will
* return the given result upon successful completion.
提交一个任务执行并返回一个Future对象，Future的get 方法在任务执行成功并完成时获取返回结果
问题：为什么runnable不需要返回结果，还需要传result 对象?
@param task the task to submit
* @param result the result to return
* @param <T> the type of the result
* @return a Future representing pending completion of the task
* @throws RejectedExecutionException if the task cannot be
* scheduled for execution
* @throws NullPointerException if the task is null
*/
<T> Future<T> submit(Runnable task, T result);
/**
* Submits a Runnable task for execution and returns a Future
* representing that task. The Future's {@code get} method will
* return {@code null} upon <em>successful</em> completion.
*
* @param task the task to submit
* @return a Future representing pending completion of the task
* @throws RejectedExecutionException if the task cannot be
* scheduled for execution
* @throws NullPointerException if the task is null
*/
Future<?> submit(Runnable task);
/**
* Executes the given tasks, returning a list of Futures holding
* their status and results when all complete.
* {@link Future#isDone} is {@code true} for each
* element of the returned list.
* Note that a <em>completed</em> task could have
* terminated either normally or by throwing an exception.
* The results of this method are undefined if the given
* collection is modified while this operation is in progress.
执行给定义的任务列表，当所有任务都执行完的时侯,返回Future 列表，这些Future 保留任务的状态和结果。返回结果列表(FutureList)的每个Future的isDone 结果都为true
注意：这个已经完成的任务已经中止，或者正常的执行完成，或者抛出异常。
如果在该操作的进行过程中，给定的任务集合被修改，那么返回结果为undefined
*
* @param tasks the collection of tasks
* @param <T> the type of the values returned from the tasks
* @return a list of Futures representing the tasks, in the same
* sequential order as produced by the iterator for the
* given task list, each of which has completed
* @throws InterruptedException if interrupted while waiting, in
* which case unfinished tasks are cancelled
* @throws NullPointerException if tasks or any of its elements are {@code null}
* @throws RejectedExecutionException if any task cannot be
* scheduled for execution
*/
<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
throws InterruptedException;
/**
* Executes the given tasks, returning a list of Futures holding
* their status and results
* when all complete or the timeout expires, whichever happens first.
* {@link Future#isDone} is {@code true} for each
* element of the returned list.
* Upon return, tasks that have not completed are cancelled.
* Note that a <em>completed</em> task could have
* terminated either normally or by throwing an exception.
* The results of this method are undefined if the given
* collection is modified while this operation is in progress.
*
* @param tasks the collection of tasks
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
* @param <T> the type of the values returned from the tasks
* @return a list of Futures representing the tasks, in the same
* sequential order as produced by the iterator for the
* given task list. If the operation did not time out,
* each task will have completed. If it did time out, some
* of these tasks will not have completed.
* @throws InterruptedException if interrupted while waiting, in
* which case unfinished tasks are cancelled
* @throws NullPointerException if tasks, any of its elements, or
* unit are {@code null}
* @throws RejectedExecutionException if any task cannot be scheduled
* for execution
*/
<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException;
/**
* Executes the given tasks, returning the result
* of one that has completed successfully (i.e., without throwing
* an exception), if any do. Upon normal or exceptional return,
* tasks that have not completed are cancelled.
* The results of this method are undefined if the given
* collection is modified while this operation is in progress.
执行一些给定的任务
- 返回任一个已经成功完成任务的结果，也就是说没有抛出异常。
- 在正常或者异常返回时，未完成的任务将被取消。
- 在执行过程中如果任务列表被修改，则方法的返回结果为undefined
* @param tasks the collection of tasks
* @param <T> the type of the values returned from the tasks
* @return the result returned by one of the tasks
* @throws InterruptedException if interrupted while waiting
* @throws NullPointerException if tasks or any element task
* subject to execution is {@code null}
* @throws IllegalArgumentException if tasks is empty
* @throws ExecutionException if no task successfully completes
* @throws RejectedExecutionException if tasks cannot be scheduled
* for execution
*/
<T> T invokeAny(Collection<? extends Callable<T>> tasks)
throws InterruptedException, ExecutionException;
/**
* Executes the given tasks, returning the result
* of one that has completed successfully (i.e., without throwing
* an exception), if any do before the given timeout elapses.
* Upon normal or exceptional return, tasks that have not
* completed are cancelled.
* The results of this method are undefined if the given
* collection is modified while this operation is in progress.
*
* @param tasks the collection of tasks
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
* @param <T> the type of the values returned from the tasks
* @return the result returned by one of the tasks
* @throws InterruptedException if interrupted while waiting
* @throws NullPointerException if tasks, or unit, or any element
* task subject to execution is {@code null}
* @throws TimeoutException if the given timeout elapses before
* any task successfully completes
* @throws ExecutionException if no task successfully completes
* @throws RejectedExecutionException if tasks cannot be scheduled
* for execution
*/
<T> T invokeAny(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException;
}
网友评论