/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/*
 *
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 *
 * 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 static java.util.concurrent.TimeUnit.NANOSECONDS;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;

/**
 * Provides default implementations of {@link ExecutorService}
 * execution methods. This class implements the {@code submit},
 * {@code invokeAny} and {@code invokeAll} methods using a
 * {@link RunnableFuture} returned by {@code newTaskFor}, which defaults
 * to the {@link FutureTask} class provided in this package. For example,
 * the implementation of {@code submit(Runnable)} creates an
 * associated {@code RunnableFuture} that is executed and
 * returned. Subclasses may override the {@code newTaskFor} methods
 * to return {@code RunnableFuture} implementations other than
 * {@code FutureTask}.
 *
 * <p><b>Extension example</b>. Here is a sketch of a class
 * that customizes {@link ThreadPoolExecutor} to use
 * a {@code CustomTask} class instead of the default {@code FutureTask}:
 * <pre> {@code
 * public class CustomThreadPoolExecutor extends ThreadPoolExecutor {
 *
 * static class CustomTask<V> implements RunnableFuture<V> {...}
 *
 * protected <V> RunnableFuture<V> newTaskFor(Callable<V> c) {
 * return new CustomTask<V>(c);
 * }
 * protected <V> RunnableFuture<V> newTaskFor(Runnable r, V v) {
 * return new CustomTask<V>(r, v);
 * }
 * // ... add constructors, etc.
 * }}</pre>
 *
 * @since 1.5
 * @author Doug Lea
 */
public abstract class AbstractExecutorService implements ExecutorService {

 /**
 * Returns a {@code RunnableFuture} for the given runnable and default
 * value.
 *
 * @param runnable the runnable task being wrapped
 * @param value the default value for the returned future
 * @param <T> the type of the given value
 * @return a {@code RunnableFuture} which, when run, will run the
 * underlying runnable and which, as a {@code Future}, will yield
 * the given value as its result and provide for cancellation of
 * the underlying task
 * @since 1.6
 */
 protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
 return new FutureTask<T>(runnable, value);
 }

 /**
 * Returns a {@code RunnableFuture} for the given callable task.
 *
 * @param callable the callable task being wrapped
 * @param <T> the type of the callable's result
 * @return a {@code RunnableFuture} which, when run, will call the
 * underlying callable and which, as a {@code Future}, will yield
 * the callable's result as its result and provide for
 * cancellation of the underlying task
 * @since 1.6
 */
 protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
 return new FutureTask<T>(callable);
 }

 /**
 * @throws RejectedExecutionException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 */
 public Future<?> submit(Runnable task) {
 if (task == null) throw new NullPointerException();
 RunnableFuture<Void> ftask = newTaskFor(task, null);
 execute(ftask);
 return ftask;
 }

 /**
 * @throws RejectedExecutionException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 */
 public <T> Future<T> submit(Runnable task, T result) {
 if (task == null) throw new NullPointerException();
 RunnableFuture<T> ftask = newTaskFor(task, result);
 execute(ftask);
 return ftask;
 }

 /**
 * @throws RejectedExecutionException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 */
 public <T> Future<T> submit(Callable<T> task) {
 if (task == null) throw new NullPointerException();
 RunnableFuture<T> ftask = newTaskFor(task);
 execute(ftask);
 return ftask;
 }

 /**
 * the main mechanics of invokeAny.
 */
 private <T> T doInvokeAny(Collection<? extends Callable<T>> tasks,
 boolean timed, long nanos)
 throws InterruptedException, ExecutionException, TimeoutException {
 if (tasks == null)
 throw new NullPointerException();
 int ntasks = tasks.size();
 if (ntasks == 0)
 throw new IllegalArgumentException();
 ArrayList<Future<T>> futures = new ArrayList<>(ntasks);
 ExecutorCompletionService<T> ecs =
 new ExecutorCompletionService<T>(this);

 // For efficiency, especially in executors with limited
 // parallelism, check to see if previously submitted tasks are
 // done before submitting more of them. This interleaving
 // plus the exception mechanics account for messiness of main
 // loop.

 try {
 // Record exceptions so that if we fail to obtain any
 // result, we can throw the last exception we got.
 ExecutionException ee = null;
 final long deadline = timed ? System.nanoTime() + nanos : 0L;
 Iterator<? extends Callable<T>> it = tasks.iterator();

 // Start one task for sure; the rest incrementally
 futures.add(ecs.submit(it.next()));
 --ntasks;
 int active = 1;

 for (;;) {
 Future<T> f = ecs.poll();
 if (f == null) {
 if (ntasks > 0) {
 --ntasks;
 futures.add(ecs.submit(it.next()));
 ++active;
 }
 else if (active == 0)
 break;
 else if (timed) {
 f = ecs.poll(nanos, NANOSECONDS);
 if (f == null)
 throw new TimeoutException();
 nanos = deadline - System.nanoTime();
 }
 else
 f = ecs.take();
 }
 if (f != null) {
 --active;
 try {
 return f.get();
 } catch (ExecutionException eex) {
 ee = eex;
 } catch (RuntimeException rex) {
 ee = new ExecutionException(rex);
 }
 }
 }

 if (ee == null)
 ee = new ExecutionException();
 throw ee;

 } finally {
 cancelAll(futures);
 }
 }

 public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
 throws InterruptedException, ExecutionException {
 try {
 return doInvokeAny(tasks, false, 0);
 } catch (TimeoutException cannotHappen) {
 assert false;
 return null;
 }
 }

 public <T> T invokeAny(Collection<? extends Callable<T>> tasks,
 long timeout, TimeUnit unit)
 throws InterruptedException, ExecutionException, TimeoutException {
 return doInvokeAny(tasks, true, unit.toNanos(timeout));
 }

 public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
 throws InterruptedException {
 if (tasks == null)
 throw new NullPointerException();
 ArrayList<Future<T>> futures = new ArrayList<>(tasks.size());
 try {
 for (Callable<T> t : tasks) {
 RunnableFuture<T> f = newTaskFor(t);
 futures.add(f);
 execute(f);
 }
 for (int i = 0, size = futures.size(); i < size; i++) {
 Future<T> f = futures.get(i);
 if (!f.isDone()) {
 try { f.get(); }
 catch (CancellationException | ExecutionException ignore) {}
 }
 }
 return futures;
 } catch (Throwable t) {
 cancelAll(futures);
 throw t;
 }
 }

 public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
 long timeout, TimeUnit unit)
 throws InterruptedException {
 if (tasks == null)
 throw new NullPointerException();
 final long nanos = unit.toNanos(timeout);
 final long deadline = System.nanoTime() + nanos;
 ArrayList<Future<T>> futures = new ArrayList<>(tasks.size());
 int j = 0;
 timedOut: try {
 for (Callable<T> t : tasks)
 futures.add(newTaskFor(t));

 final int size = futures.size();

 // Interleave time checks and calls to execute in case
 // executor doesn't have any/much parallelism.
 for (int i = 0; i < size; i++) {
 if (((i == 0) ? nanos : deadline - System.nanoTime()) <= 0L)
 break timedOut;
 execute((Runnable)futures.get(i));
 }

 for (; j < size; j++) {
 Future<T> f = futures.get(j);
 if (!f.isDone()) {
 try { f.get(deadline - System.nanoTime(), NANOSECONDS); }
 catch (CancellationException | ExecutionException ignore) {}
 catch (TimeoutException timedOut) {
 break timedOut;
 }
 }
 }
 return futures;
 } catch (Throwable t) {
 cancelAll(futures);
 throw t;
 }
 // Timed out before all the tasks could be completed; cancel remaining
 cancelAll(futures, j);
 return futures;
 }

 private static <T> void cancelAll(ArrayList<Future<T>> futures) {
 cancelAll(futures, 0);
 }

 /** Cancels all futures with index at least j. */
 private static <T> void cancelAll(ArrayList<Future<T>> futures, int j) {
 for (int size = futures.size(); j < size; j++)
 futures.get(j).cancel(true);
 }
}