/*
 * Copyright 2013 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.util.concurrent;

import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

import java.util.ArrayDeque;
import java.util.Queue;
import java.util.concurrent.TimeUnit;

Executes Runnable objects in the caller's thread. If the execute(Runnable) is reentrant it will be queued until the original Runnable finishes execution. 
 All Throwable objects thrown from execute(Runnable) will be swallowed and logged. This is to ensure that all queued Runnable objects have the chance to be run. /**
 * Executes {@link Runnable} objects in the caller's thread. If the {@link #execute(Runnable)} is reentrant it will be
 * queued until the original {@link Runnable} finishes execution.
 * <p>
 * All {@link Throwable} objects thrown from {@link #execute(Runnable)} will be swallowed and logged. This is to ensure
 * that all queued {@link Runnable} objects have the chance to be run.
 */
public final class ImmediateEventExecutor extends AbstractEventExecutor {
    private static final InternalLogger logger = InternalLoggerFactory.getInstance(ImmediateEventExecutor.class);
    public static final ImmediateEventExecutor INSTANCE = new ImmediateEventExecutor();
    
A Runnable will be queued if we are executing a Runnable. This is to prevent a StackOverflowError. /**
     * A Runnable will be queued if we are executing a Runnable. This is to prevent a {@link StackOverflowError}.
     */
    private static final FastThreadLocal<Queue<Runnable>> DELAYED_RUNNABLES = new FastThreadLocal<Queue<Runnable>>() {
        @Override
        protected Queue<Runnable> initialValue() throws Exception {
            return new ArrayDeque<Runnable>();
        }
    };
    
Set to true if we are executing a runnable. /**
     * Set to {@code true} if we are executing a runnable.
     */
    private static final FastThreadLocal<Boolean> RUNNING = new FastThreadLocal<Boolean>() {
        @Override
        protected Boolean initialValue() throws Exception {
            return false;
        }
    };

    private final Future<?> terminationFuture = new FailedFuture<Object>(
            GlobalEventExecutor.INSTANCE, new UnsupportedOperationException());

    private ImmediateEventExecutor() { }

    @Override
    public boolean inEventLoop() {
        return true;
    }

    @Override
    public boolean inEventLoop(Thread thread) {
        return true;
    }

    @Override
    public Future<?> shutdownGracefully(long quietPeriod, long timeout, TimeUnit unit) {
        return terminationFuture();
    }

    @Override
    public Future<?> terminationFuture() {
        return terminationFuture;
    }

    @Override
    @Deprecated
    public void shutdown() { }

    @Override
    public boolean isShuttingDown() {
        return false;
    }

    @Override
    public boolean isShutdown() {
        return false;
    }

    @Override
    public boolean isTerminated() {
        return false;
    }

    @Override
    public boolean awaitTermination(long timeout, TimeUnit unit) {
        return false;
    }

    @Override
    public void execute(Runnable command) {
        if (command == null) {
            throw new NullPointerException("command");
        }
        if (!RUNNING.get()) {
            RUNNING.set(true);
            try {
                command.run();
            } catch (Throwable cause) {
                logger.info("Throwable caught while executing Runnable {}", command, cause);
            } finally {
                Queue<Runnable> delayedRunnables = DELAYED_RUNNABLES.get();
                Runnable runnable;
                while ((runnable = delayedRunnables.poll()) != null) {
                    try {
                        runnable.run();
                    } catch (Throwable cause) {
                        logger.info("Throwable caught while executing Runnable {}", runnable, cause);
                    }
                }
                RUNNING.set(false);
            }
        } else {
            DELAYED_RUNNABLES.get().add(command);
        }
    }

    @Override
    public <V> Promise<V> newPromise() {
        return new ImmediatePromise<V>(this);
    }

    @Override
    public <V> ProgressivePromise<V> newProgressivePromise() {
        return new ImmediateProgressivePromise<V>(this);
    }

    static class ImmediatePromise<V> extends DefaultPromise<V> {
        ImmediatePromise(EventExecutor executor) {
            super(executor);
        }

        @Override
        protected void checkDeadLock() {
            // No check
        }
    }

    static class ImmediateProgressivePromise<V> extends DefaultProgressivePromise<V> {
        ImmediateProgressivePromise(EventExecutor executor) {
            super(executor);
        }

        @Override
        protected void checkDeadLock() {
            // No check
        }
    }
}