Excecutor的實現(xiàn)通常會創(chuàng)建線程來執(zhí)行任務(wù)荚坞。但JVM只有在所有線程全部終止后才會退出戳鹅。因此，如果無法正確地關(guān)閉Executor,那么JVM將無法結(jié)束团滥。
為了解決執(zhí)行服務(wù)的生命周期問題竿屹，Excecutor擴(kuò)展了ExecutorService接口，添加了一些用于生命周期管理的方法灸姊。
/**
* 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.
提供用于管理終止的方法以及可以產(chǎn)生Future來跟蹤一個或多個異步任務(wù)的進(jìn)度的方法的執(zhí)行器
*
* <p>An {@code ExecutorService} can be shut down, which will cause
* it to reject new tasks.
ExecutorService可以關(guān)閉拱燃，這將會導(dǎo)致它拒絕新的任務(wù)
* Two different methods are provided for
* shutting down an {@code ExecutorService}.
ExecutorService提供了兩種不同的關(guān)閉方法
* The {@link #shutdown}
* method will allow previously submitted tasks to execute before
* terminating,
shutdown方法將允許先前提交的任務(wù)在終止之前執(zhí)行
* while the {@link #shutdownNow} method prevents waiting
* tasks from starting and attempts to stop currently executing tasks.
而shutdownNow方法阻止等待的任務(wù)啟動并嘗試停止當(dāng)前正在執(zhí)行的任務(wù)
* Upon termination, an executor has no tasks actively executing, no
* tasks awaiting execution, and no new tasks can be submitted.
終止后，執(zhí)行者將沒有正在執(zhí)行的任務(wù)力惯，沒有正在等待執(zhí)行的任務(wù)碗誉，并且無法提交新任務(wù)
* An unused {@code ExecutorService} should be shut down to allow
* reclamation of its resources.
應(yīng)該關(guān)閉未使用的ExecutorService以便回收其資源
* <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.)
*
* <p>The {@link Executors} class provides factory methods for the
* executor services provided in this package.
*
* <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:
*
* <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:
以下方法分兩個階段關(guān)閉ExecutorService：
首先通過調(diào)用shutdown來拒絕傳入的任務(wù)，然后
如有必要父晶，調(diào)用shutdownNow取消所有延遲的任務(wù)
*
* <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()}.
*
* @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.
*
* <p>This method does not wait for previously submitted tasks to
* complete execution. Use {@link #awaitTermination awaitTermination}
* to do that.
此方法不會等待先前提交的任務(wù)完成后執(zhí)行哮缺。
使用awaitTermination awaitTermination可以做到這一點。
*
* @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
* processing of waiting tasks, and returns a list of the tasks
* that were awaiting execution.
嘗試停止所有正在執(zhí)行的任務(wù)甲喝，
暫停正在等待的任務(wù)的處理蝴蜓，
并返回正在等待執(zhí)行的任務(wù)的列表
*
* <p>This method does not wait for actively executing tasks to
* terminate. Use {@link #awaitTermination awaitTermination} to
* do that.
此方法不等待主動執(zhí)行的任務(wù)終止。
使用awaitTermination可以做到這一點
*
* <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.
除了盡最大努力嘗試停止處理正在執(zhí)行的任務(wù)之外俺猿，沒有任何保證茎匠。
例如，典型的實現(xiàn)將通過線程中斷取消押袍，因此任何無法響應(yīng)中斷的任務(wù)都可能永遠(yuǎn)不會終止诵冒。
*
* @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
*/
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.
*
* @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.
阻塞直到所有的任務(wù)在執(zhí)行關(guān)閉請求或者超時發(fā)生或者當(dāng)前線程中斷后完成
*
* @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.
*
* <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();}
*
* <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.
*
* @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.
*
* @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.
提交一個Runnable任務(wù)以執(zhí)行并返回一個代表該任務(wù)的Future
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.
執(zhí)行給定的任務(wù)，當(dāng)所有任務(wù)完成時谊惭，返回保存其狀態(tài)和結(jié)果的列表
* {@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.
*
* @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.
執(zhí)行給定的任務(wù)汽馋，返回持有它們的狀態(tài)和結(jié)果（當(dāng)全部完成或超時到期時侮东，以先
發(fā)生者為準(zhǔn)）的列表。
* {@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.
*
* @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;
}
