/*

 * Copyright (c) 2008, 2009, 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.*;

import java.util.concurrent.*;

import java.security.AccessController;

import sun.security.action.GetIntegerAction;

/**

 * Defines static methods to invoke a completion handler or arbitrary task.

 */

class Invoker {

    private Invoker() { }

    // maximum number of completion handlers that may be invoked on the current

    // thread before it re-directs invocations to the thread pool. This helps

    // avoid stack overflow and lessens the risk of starvation.

    private static final int maxHandlerInvokeCount = AccessController.doPrivileged(

        new GetIntegerAction("sun.nio.ch.maxCompletionHandlersOnStack", 16));

    // Per-thread object with reference to channel group and a counter for

    // the number of completion handlers invoked. This should be reset to 0

    // when all completion handlers have completed.

    static class GroupAndInvokeCount {

        private final AsynchronousChannelGroupImpl group;

        private int handlerInvokeCount;

        GroupAndInvokeCount(AsynchronousChannelGroupImpl group) {

            this.group = group;

        }

        AsynchronousChannelGroupImpl group() {

            return group;

        }

        int invokeCount() {

            return handlerInvokeCount;

        }

        void setInvokeCount(int value) {

            handlerInvokeCount = value;

        }

        void resetInvokeCount() {

            handlerInvokeCount = 0;

        }

        void incrementInvokeCount() {

            handlerInvokeCount++;

        }

    }

    private static final ThreadLocal<GroupAndInvokeCount> myGroupAndInvokeCount =

        new ThreadLocal<GroupAndInvokeCount>() {

            @Override protected GroupAndInvokeCount initialValue() {

                return null;

            }

        };

    /**

     * Binds this thread to the given group

     */

    static void bindToGroup(AsynchronousChannelGroupImpl group) {

        myGroupAndInvokeCount.set(new GroupAndInvokeCount(group));

    }

    /**

     * Returns the GroupAndInvokeCount object for this thread.

     */

    static GroupAndInvokeCount getGroupAndInvokeCount() {

        return myGroupAndInvokeCount.get();

    }

    /**

     * Returns true if the current thread is in a channel group's thread pool

     */

    static boolean isBoundToAnyGroup() {

        return myGroupAndInvokeCount.get() != null;

    }

    /**

     * Returns true if the current thread is in the given channel's thread

     * pool and we haven't exceeded the maximum number of handler frames on

     * the stack.

     */

    static boolean mayInvokeDirect(GroupAndInvokeCount myGroupAndInvokeCount,

                                   AsynchronousChannelGroupImpl group)

    {

        if ((myGroupAndInvokeCount != null) &&

            (myGroupAndInvokeCount.group() == group) &&

            (myGroupAndInvokeCount.invokeCount() < maxHandlerInvokeCount))

        {

            return true;

        }

        return false;

    }

    /**

     * Invoke handler without checking the thread identity or number of handlers

     * on the thread stack.

     */

    static <V,A> void invokeUnchecked(CompletionHandler<V,? super A> handler,

                                      A attachment,

                                      V value,

                                      Throwable exc)

    {

        if (exc == null) {

            handler.completed(value, attachment);

        } else {

            handler.failed(exc, attachment);

        }

        // clear interrupt

        Thread.interrupted();

    }

    /**

     * Invoke handler assuming thread identity already checked

     */

    static <V,A> void invokeDirect(GroupAndInvokeCount myGroupAndInvokeCount,

                                   CompletionHandler<V,? super A> handler,

                                   A attachment,

                                   V result,

                                   Throwable exc)

    {

        myGroupAndInvokeCount.incrementInvokeCount();

        Invoker.invokeUnchecked(handler, attachment, result, exc);

    }

    /**

     * Invokes the handler. If the current thread is in the channel group's

     * thread pool then the handler is invoked directly, otherwise it is

     * invoked indirectly.

     */

    static <V,A> void invoke(AsynchronousChannel channel,

                             CompletionHandler<V,? super A> handler,

                             A attachment,

                             V result,

                             Throwable exc)

    {

        boolean invokeDirect = false;

        boolean identityOkay = false;

        GroupAndInvokeCount thisGroupAndInvokeCount = myGroupAndInvokeCount.get();

        if (thisGroupAndInvokeCount != null) {

            if ((thisGroupAndInvokeCount.group() == ((Groupable)channel).group()))

                identityOkay = true;

            if (identityOkay &&

                (thisGroupAndInvokeCount.invokeCount() < maxHandlerInvokeCount))

            {

                // group match

                invokeDirect = true;

            }

        }

        if (invokeDirect) {

            invokeDirect(thisGroupAndInvokeCount, handler, attachment, result, exc);

        } else {

            try {

                invokeIndirectly(channel, handler, attachment, result, exc);

            } catch (RejectedExecutionException ree) {

                // channel group shutdown; fallback to invoking directly

                // if the current thread has the right identity.

                if (identityOkay) {

                    invokeDirect(thisGroupAndInvokeCount,

                                 handler, attachment, result, exc);

                } else {

                    throw new ShutdownChannelGroupException();

                }

            }

        }

    }

    /**

     * Invokes the handler indirectly via the channel group's thread pool.

     */

    static <V,A> void invokeIndirectly(AsynchronousChannel channel,

                                       final CompletionHandler<V,? super A> handler,

                                       final A attachment,

                                       final V result,

                                       final Throwable exc)

    {

        try {

            ((Groupable)channel).group().executeOnPooledThread(new Runnable() {

                public void run() {

                    GroupAndInvokeCount thisGroupAndInvokeCount =

                        myGroupAndInvokeCount.get();

                    if (thisGroupAndInvokeCount != null)

                        thisGroupAndInvokeCount.setInvokeCount(1);

                    invokeUnchecked(handler, attachment, result, exc);

                }

            });

        } catch (RejectedExecutionException ree) {

            throw new ShutdownChannelGroupException();

        }

    }

    /**

     * Invokes the handler "indirectly" in the given Executor

     */

    static <V,A> void invokeIndirectly(final CompletionHandler<V,? super A> handler,

                                       final A attachment,

                                       final V value,

                                       final Throwable exc,

                                       Executor executor)

    {

         try {

            executor.execute(new Runnable() {

                public void run() {

                    invokeUnchecked(handler, attachment, value, exc);

                }

            });

        } catch (RejectedExecutionException ree) {

            throw new ShutdownChannelGroupException();

        }

    }

    /**

     * Invokes the given task on the thread pool associated with the given

     * channel. If the current thread is in the thread pool then the task is

     * invoked directly.

     */

    static void invokeOnThreadInThreadPool(Groupable channel,

                                           Runnable task)

    {

        boolean invokeDirect;

        GroupAndInvokeCount thisGroupAndInvokeCount = myGroupAndInvokeCount.get();

        AsynchronousChannelGroupImpl targetGroup = channel.group();

        if (thisGroupAndInvokeCount == null) {

            invokeDirect = false;

        } else {

            invokeDirect = (thisGroupAndInvokeCount.group == targetGroup);

        }

        try {

            if (invokeDirect) {

                task.run();

            } else {

                targetGroup.executeOnPooledThread(task);

            }

        } catch (RejectedExecutionException ree) {

            throw new ShutdownChannelGroupException();

        }

    }

    /**

     * Invoke handler with completed result. This method does not check the

     * thread identity or the number of handlers on the thread stack.

     */

    static <V,A> void invokeUnchecked(PendingFuture<V,A> future) {

        assert future.isDone();

        CompletionHandler<V,? super A> handler = future.handler();

        if (handler != null) {

            invokeUnchecked(handler,

                            future.attachment(),

                            future.value(),

                            future.exception());

        }

    }

    /**

     * Invoke handler with completed result. If the current thread is in the

     * channel group's thread pool then the handler is invoked directly,

     * otherwise it is invoked indirectly.

     */

    static <V,A> void invoke(PendingFuture<V,A> future) {

        assert future.isDone();

        CompletionHandler<V,? super A> handler = future.handler();

        if (handler != null) {

            invoke(future.channel(),

                   handler,

                   future.attachment(),

                   future.value(),

                   future.exception());

        }

    }

    /**

     * Invoke handler with completed result. The handler is invoked indirectly,

     * via the channel group's thread pool.

     */

    static <V,A> void invokeIndirectly(PendingFuture<V,A> future) {

        assert future.isDone();

        CompletionHandler<V,? super A> handler = future.handler();

        if (handler != null) {

            invokeIndirectly(future.channel(),

                             handler,

                             future.attachment(),

                             future.value(),

                             future.exception());

        }

    }

}