先看一个Executor接口,该接口只有一个方法:void execute(Runnable command),用于在未来某个时刻提交一个command,这个command可以被提交到一个新的线程,或者一个线程池,或者在调用线程中。
ExecutorService接口继承了Executor接口。主要是增加了shutDown、shutDownNow、invokeAll、invokeAny和submit方法。
- invokeAny(Collection<? extends Callable<T>> tasks)
提交所有任务,返回某个已完成的任务的结果 <T> T,有相应带超时版本。 - invokeAll(Collection<? extends Callable<T>> tasks)
提交所有任务,所有任务完成后,返回所有的结果 <T>List<Future<T>>,有相应带超时版本。 - shutdown()
执行器不再接受新的任务。 - List<Runnable> shutDownNow()
尝试结束所有正在执行的任务。 - submit
用于将任务提交给ExecutorService,会返回Future对象,用于查询执行状态。
下面是ExecutorService的源码:
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. */ 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. */ List<Runnable> shutdownNow(); /** * Returns <tt>true</tt> if this executor has been shut down. */ boolean isShutdown(); /** * Returns <tt>true</tt> if all tasks have completed following shut down. * Note that <tt>isTerminated</tt> is never <tt>true</tt> unless * either <tt>shutdown</tt> or <tt>shutdownNow</tt> was called first. */ 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. */ 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 <tt>get</tt> method will return the task's result upon * successful completion. */ <T> Future<T> submit(Callable<T> task); /** * Submits a Runnable task for execution and returns a Future * representing that task. The Future's <tt>get</tt> method will * return the given result upon successful completion. */ <T> Future<T> submit(Runnable task, T result); /** * Submits a Runnable task for execution and returns a Future * representing that task. The Future's <tt>get</tt> method will * return <tt>null</tt> upon <em>successful</em> completion. */ Future<?> submit(Runnable task); /** * Executes the given tasks, returning a list of Futures holding * their status and results when all complete. */ <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 <tt>true</tt> for each * element of the returned list. * Upon return, tasks that have not completed are cancelled. */ <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. */ <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. */ <T> T invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException; }