/*

 * Copyright (c) 2008, 2018, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package sun.nio.ch;

import java.nio.channels.Channel;

import java.nio.channels.AsynchronousChannelGroup;

import java.nio.channels.spi.AsynchronousChannelProvider;

import java.io.IOException;

import java.io.FileDescriptor;

import java.util.Queue;

import java.util.concurrent.*;

import java.util.concurrent.atomic.AtomicInteger;

import java.util.concurrent.atomic.AtomicBoolean;

import java.security.PrivilegedAction;

import java.security.AccessController;

import java.security.AccessControlContext;

import sun.security.action.GetIntegerAction;

/**

 * Base implementation of AsynchronousChannelGroup

 */

abstract class AsynchronousChannelGroupImpl

    extends AsynchronousChannelGroup implements Executor

{

    // number of internal threads handling I/O events when using an unbounded

    // thread pool. Internal threads do not dispatch to completion handlers.

    private static final int internalThreadCount = AccessController.doPrivileged(

        new GetIntegerAction("sun.nio.ch.internalThreadPoolSize", 1));

    // associated thread pool

    private final ThreadPool pool;

    // number of tasks running (including internal)

    private final AtomicInteger threadCount = new AtomicInteger();

    // associated Executor for timeouts

    private ScheduledThreadPoolExecutor timeoutExecutor;

    // task queue for when using a fixed thread pool. In that case, a thread

    // waiting on I/O events must be awoken to poll tasks from this queue.

    private final Queue<Runnable> taskQueue;

    // group shutdown

    private final AtomicBoolean shutdown = new AtomicBoolean();

    private final Object shutdownNowLock = new Object();

    private volatile boolean terminateInitiated;

    AsynchronousChannelGroupImpl(AsynchronousChannelProvider provider,

                                 ThreadPool pool)

    {

        super(provider);

        this.pool = pool;

        if (pool.isFixedThreadPool()) {

            taskQueue = new ConcurrentLinkedQueue<>();

        } else {

            taskQueue = null;   // not used

        }

        // use default thread factory as thread should not be visible to

        // application (it doesn't execute completion handlers).

        this.timeoutExecutor = (ScheduledThreadPoolExecutor)

            Executors.newScheduledThreadPool(1, ThreadPool.defaultThreadFactory());

        this.timeoutExecutor.setRemoveOnCancelPolicy(true);

    }

    final ExecutorService executor() {

        return pool.executor();

    }

    final boolean isFixedThreadPool() {

        return pool.isFixedThreadPool();

    }

    final int fixedThreadCount() {

        if (isFixedThreadPool()) {

            return pool.poolSize();

        } else {

            return pool.poolSize() + internalThreadCount;

        }

    }

    private Runnable bindToGroup(final Runnable task) {

        final AsynchronousChannelGroupImpl thisGroup = this;

        return new Runnable() {

            public void run() {

                Invoker.bindToGroup(thisGroup);

                task.run();

            }

        };

    }

    private void startInternalThread(final Runnable task) {

        AccessController.doPrivileged(new PrivilegedAction<>() {

            @Override

            public Void run() {

                // internal threads should not be visible to application so

                // cannot use user-supplied thread factory

                ThreadPool.defaultThreadFactory().newThread(task).start();

                return null;

            }

         });

    }

    protected final void startThreads(Runnable task) {

        if (!isFixedThreadPool()) {

            for (int i=0; i<internalThreadCount; i++) {

                startInternalThread(task);

                threadCount.incrementAndGet();

            }

        }

        if (pool.poolSize() > 0) {

            task = bindToGroup(task);

            try {

                for (int i=0; i<pool.poolSize(); i++) {

                    pool.executor().execute(task);

                    threadCount.incrementAndGet();

                }

            } catch (RejectedExecutionException  x) {

                // nothing we can do

            }

        }

    }

    final int threadCount() {

        return threadCount.get();

    }

    /**

     * Invoked by tasks as they terminate

     */

    final int threadExit(Runnable task, boolean replaceMe) {

        if (replaceMe) {

            try {

                if (Invoker.isBoundToAnyGroup()) {

                    // submit new task to replace this thread

                    pool.executor().execute(bindToGroup(task));

                } else {

                    // replace internal thread

                    startInternalThread(task);

                }

                return threadCount.get();

            } catch (RejectedExecutionException x) {

                // unable to replace

            }

        }

        return threadCount.decrementAndGet();

    }

    /**

     * Wakes up a thread waiting for I/O events to execute the given task.

     */

    abstract void executeOnHandlerTask(Runnable task);

    /**

     * For a fixed thread pool the task is queued to a thread waiting on I/O

     * events. For other thread pools we simply submit the task to the thread

     * pool.

     */

    final void executeOnPooledThread(Runnable task) {

        if (isFixedThreadPool()) {

            executeOnHandlerTask(task);

        } else {

            pool.executor().execute(bindToGroup(task));

        }

    }

    final void offerTask(Runnable task) {

        taskQueue.offer(task);

    }

    final Runnable pollTask() {

        return (taskQueue == null) ? null : taskQueue.poll();

    }

    final Future<?> schedule(Runnable task, long timeout, TimeUnit unit) {

        try {

            return timeoutExecutor.schedule(task, timeout, unit);

        } catch (RejectedExecutionException rej) {

            if (terminateInitiated) {

                // no timeout scheduled as group is terminating

                return null;

            }

            throw new AssertionError(rej);

        }

    }

    @Override

    public final boolean isShutdown() {

        return shutdown.get();

    }

    @Override

    public final boolean isTerminated()  {

        return pool.executor().isTerminated();

    }

    /**

     * Returns true if there are no channels in the group

     */

    abstract boolean isEmpty();

    /**

     * Attaches a foreign channel to this group.

     */

    abstract Object attachForeignChannel(Channel channel, FileDescriptor fdo)

        throws IOException;

    /**

     * Detaches a foreign channel from this group.

     */

    abstract void detachForeignChannel(Object key);

    /**

     * Closes all channels in the group

     */

    abstract void closeAllChannels() throws IOException;

    /**

     * Shutdown all tasks waiting for I/O events.

     */

    abstract void shutdownHandlerTasks();

    private void shutdownExecutors() {

        AccessController.doPrivileged(

            new PrivilegedAction<>() {

                public Void run() {

                    pool.executor().shutdown();

                    timeoutExecutor.shutdown();

                    return null;

                }

            },

            null,

            new RuntimePermission("modifyThread"));

    }

    @Override

    public final void shutdown() {

        if (shutdown.getAndSet(true)) {

            // already shutdown

            return;

        }

        // if there are channels in the group then shutdown will continue

        // when the last channel is closed

        if (!isEmpty()) {

            return;

        }

        // initiate termination (acquire shutdownNowLock to ensure that other

        // threads invoking shutdownNow will block).

        synchronized (shutdownNowLock) {

            if (!terminateInitiated) {

                terminateInitiated = true;

                shutdownHandlerTasks();

                shutdownExecutors();

            }

        }

    }

    @Override

    public final void shutdownNow() throws IOException {

        shutdown.set(true);

        synchronized (shutdownNowLock) {

            if (!terminateInitiated) {

                terminateInitiated = true;

                closeAllChannels();

                shutdownHandlerTasks();

                shutdownExecutors();

            }

        }

    }

    /**

     * For use by AsynchronousFileChannel to release resources without shutting

     * down the thread pool.

     */

    final void detachFromThreadPool() {

        if (shutdown.getAndSet(true))

            throw new AssertionError("Already shutdown");

        if (!isEmpty())

            throw new AssertionError("Group not empty");

        shutdownHandlerTasks();

    }

    @Override

    public final boolean awaitTermination(long timeout, TimeUnit unit)

        throws InterruptedException

    {

        return pool.executor().awaitTermination(timeout, unit);

    }

    /**

     * Executes the given command on one of the channel group's pooled threads.

     */

    @Override

    public final void execute(Runnable task) {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            // when a security manager is installed then the user's task

            // must be run with the current calling context

            final AccessControlContext acc = AccessController.getContext();

            final Runnable delegate = task;

            task = new Runnable() {

                @Override

                public void run() {

                    AccessController.doPrivileged(new PrivilegedAction<>() {

                        @Override

                        public Void run() {

                            delegate.run();

                            return null;

                        }

                    }, acc);

                }

            };

        }

        executeOnPooledThread(task);

    }

}