/*
 * Copyright (c) 2010, 2020 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package org.glassfish.grizzly.threadpool;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.concurrent.AbstractExecutorService;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.glassfish.grizzly.Grizzly;
import org.glassfish.grizzly.localization.LogMessages;
import org.glassfish.grizzly.memory.MemoryManager;
import org.glassfish.grizzly.memory.ThreadLocalPoolProvider;
import org.glassfish.grizzly.monitoring.DefaultMonitoringConfig;
import org.glassfish.grizzly.monitoring.MonitoringAware;
import org.glassfish.grizzly.monitoring.MonitoringConfig;
import org.glassfish.grizzly.monitoring.MonitoringUtils;
import org.glassfish.grizzly.utils.DelayedExecutor;

Abstract ExecutorService implementation. 
Author:
Alexey Stashok/**
 * Abstract {@link java.util.concurrent.ExecutorService} implementation.
 *
 * @author Alexey Stashok
 */
public abstract class AbstractThreadPool extends AbstractExecutorService implements Thread.UncaughtExceptionHandler, MonitoringAware<ThreadPoolProbe> {

    private static final Logger logger = Grizzly.logger(AbstractThreadPool.class);
    // Min number of worker threads in a pool
    public static final int DEFAULT_MIN_THREAD_COUNT;
    // Max number of worker threads in a pool
    public static final int DEFAULT_MAX_THREAD_COUNT;

    // "Never stop the thread by timeout" value
    private static final Long NEVER_TIMEOUT = Long.MAX_VALUE;

    static {
        int processorsBasedThreadCount = Runtime.getRuntime().availableProcessors();
        DEFAULT_MIN_THREAD_COUNT = processorsBasedThreadCount > 5 ? processorsBasedThreadCount : 5;
        DEFAULT_MAX_THREAD_COUNT = Integer.MAX_VALUE;
    }

    // Max number of tasks thread pool can enqueue
    public static final int DEFAULT_MAX_TASKS_QUEUED = -1;
    // Timeout, after which idle thread will be stopped and excluded from pool
    public static final int DEFAULT_IDLE_THREAD_KEEPALIVE_TIMEOUT = 30000;

    protected static final Runnable poison = new Runnable() {

        @Override
        public void run() {
        }
    };

    protected final Object stateLock = new Object();

    protected final Map<Worker, Long> workers = new HashMap<>();
    protected volatile boolean running = true;
    protected final ThreadPoolConfig config;
    protected final long transactionTimeoutMillis;
    protected final DelayedExecutor.DelayQueue<Worker> delayedQueue;

    private static final DelayedExecutor.Resolver<Worker> transactionResolver = new DelayedExecutor.Resolver<Worker>() {

        @Override
        public boolean removeTimeout(final Worker element) {
            element.transactionExpirationTime = -1;
            return true;
        }

        @Override
        public long getTimeoutMillis(final Worker element) {
            return element.transactionExpirationTime;
        }

        @Override
        public void setTimeoutMillis(final Worker element, final long timeoutMillis) {
            element.transactionExpirationTime = timeoutMillis;
        }
    };

    
ThreadPool probes
/**
     * ThreadPool probes
     */
    protected final DefaultMonitoringConfig<ThreadPoolProbe> monitoringConfig = new DefaultMonitoringConfig<ThreadPoolProbe>(ThreadPoolProbe.class) {

        @Override
        public Object createManagementObject() {
            return createJmxManagementObject();
        }

    };

    public AbstractThreadPool(ThreadPoolConfig config) {
        if (config.getMaxPoolSize() < 1) {
            throw new IllegalArgumentException("poolsize < 1");
        }

        this.config = config;
        if (config.getInitialMonitoringConfig().hasProbes()) {
            monitoringConfig.addProbes(config.getInitialMonitoringConfig().getProbes());
        }

        if (config.getThreadFactory() == null) {
            config.setThreadFactory(getDefaultThreadFactory());
        }

        transactionTimeoutMillis = config.getTransactionTimeout(TimeUnit.MILLISECONDS);
        final DelayedExecutor transactionMonitor = transactionTimeoutMillis > 0 ? config.getTransactionMonitor() : null;

        if (transactionMonitor != null) {
            final DelayedExecutor.Worker<Worker> transactionWorker = new DelayedExecutor.Worker<Worker>() {

                @Override
                public boolean doWork(final Worker worker) {
                    worker.t.interrupt();
                    delayedQueue.add(worker, NEVER_TIMEOUT, TimeUnit.MILLISECONDS);
                    return true;
                }
            };
            delayedQueue = transactionMonitor.createDelayQueue(transactionWorker, transactionResolver);
        } else {
            delayedQueue = null;
        }
    }

    
must hold statelock while calling this method.
Params:
worker – /**
     * must hold statelock while calling this method.
     * 
     * @param worker
     */
    protected void startWorker(final Worker worker) {
        final Thread thread = config.getThreadFactory().newThread(worker);

        worker.t = thread;
        workers.put(worker, System.currentTimeMillis());
        worker.t.start();
    }

    
Returns:
the thread pool configuration/**
     * @return the thread pool configuration
     */
    public ThreadPoolConfig getConfig() {
        return config;
    }

    
Returns:
the task Queue/**
     * @return the task {@link Queue}
     */
    public Queue<Runnable> getQueue() {
        return config.getQueue();
    }

    
Returns:
the number of allocated threads in the thread pool/**
     * @return the number of allocated threads in the thread pool
     */
    public final int getSize() {
        synchronized (stateLock) {
            return workers.size();
        }
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public List<Runnable> shutdownNow() {
        synchronized (stateLock) {
            List<Runnable> drained = new ArrayList<>();
            if (running) {
                running = false;
                drain(getQueue(), drained);
                for (Runnable task : drained) {
                    onTaskDequeued(task);
                    onTaskCancelled(task);
                }
                poisonAll();
                // try to interrupt their current work so they can get their poison fast
                for (Worker w : workers.keySet()) {
                    w.t.interrupt();
                }

                ProbeNotifier.notifyThreadPoolStopped(this);
            }
            return drained;
        }
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public void shutdown() {
        synchronized (stateLock) {
            if (running) {
                running = false;
                poisonAll();
                stateLock.notifyAll();
                ProbeNotifier.notifyThreadPoolStopped(this);
            }
        }
    }

    @Override
    public boolean isShutdown() {
        return !running;
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public boolean isTerminated() {
        synchronized (stateLock) {
            return !running && workers.isEmpty();
        }
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public boolean awaitTermination(final long timeout, final TimeUnit unit) throws InterruptedException {
        // see {@link java.util.concurrent.ThreadPoolExecutor#awaitTermination(long, TimeUnit)}

        long millis = unit.toMillis(timeout);
        final long timeEnd = System.currentTimeMillis() + millis;

        synchronized (stateLock) {
            if (isTerminated()) {
                return true;
            }

            for (;;) {
                if (millis < 20) {
                    return false;
                }

                stateLock.wait(millis);

                if (isTerminated()) {
                    return true;
                }

                millis = timeEnd - System.currentTimeMillis();
            }
        }
    }

    protected void poisonAll() {
        int size = Math.max(config.getMaxPoolSize(), workers.size()) * 4 / 3;
        final Queue<Runnable> q = getQueue();
        while (size-- > 0) {
            q.offer(poison);
        }
    }

    protected static void drain(Queue<Runnable> from, Collection<Runnable> to) {
        boolean cont = true;
        while (cont) {
            Runnable r = from.poll();
            if (cont = r != null) {
                // resizable fixedpool can have poison
                // from runtime resize (shrink) operation
                if (r != AbstractThreadPool.poison) {
                    to.add(r);// bypassing pool queuelimit
                }
            }
        }
    }

    protected void validateNewPoolSize(int corePoolsize, int maxPoolSize) {
        if (maxPoolSize < 1) {
            throw new IllegalArgumentException("maxPoolsize < 1 :" + maxPoolSize);
        }
        if (corePoolsize < 1) {
            throw new IllegalArgumentException("corePoolsize < 1 :" + corePoolsize);
        }
        if (corePoolsize > maxPoolSize) {
            throw new IllegalArgumentException("corePoolsize > maxPoolSize: " + corePoolsize + " > " + maxPoolSize);
        }
    }

    
Method invoked prior to executing the given Runnable in the given thread. This method is invoked by thread t
that will execute task r, and may be used to re-initialize ThreadLocals, or to perform logging.

This implementation does nothing, but may be customized in subclasses. Note: To properly nest multiple overridings,
subclasses should generally invoke super.beforeExecute at the end of this method.
Params:
worker – the Worker, running the the thread t
t – the thread that will run task r.
r – the task that will be executed./**
     * Method invoked prior to executing the given Runnable in the given thread. This method is invoked by thread <tt>t</tt>
     * that will execute task <tt>r</tt>, and may be used to re-initialize ThreadLocals, or to perform logging.
     *
     * <p>
     * This implementation does nothing, but may be customized in subclasses. Note: To properly nest multiple overridings,
     * subclasses should generally invoke <tt>super.beforeExecute</tt> at the end of this method.
     *
     * @param worker the {@link Worker}, running the the thread t
     * @param t the thread that will run task r.
     * @param r the task that will be executed.
     */
    protected void beforeExecute(final Worker worker, final Thread t, final Runnable r) {
        if (delayedQueue != null) {
            worker.transactionExpirationTime = System.currentTimeMillis() + transactionTimeoutMillis;
        }

        final ClassLoader initial = config.getInitialClassLoader();
        if (initial != null) {
            t.setContextClassLoader(initial);
        }
    }

    
Method invoked upon completion of execution of the given Runnable. This method is invoked by the thread that executed
the task. If non-null, the Throwable is the uncaught RuntimeException or Error that caused
execution to terminate abruptly.

Note: When actions are enclosed in tasks (such as FutureTask) either explicitly or via methods such as submit, these task objects catch and maintain computational exceptions, and so they
do not cause abrupt termination, and the internal exceptions are not passed to this method.

This implementation does nothing, but may be customized in subclasses. Note: To properly nest multiple overridings,
subclasses should generally invoke super.afterExecute at the beginning of this method.
Params:
worker – the Worker, running the the thread t
thread – 
r – the runnable that has completed.
t – the exception that caused termination, or null if execution completed normally./**
     * Method invoked upon completion of execution of the given Runnable. This method is invoked by the thread that executed
     * the task. If non-null, the Throwable is the uncaught <tt>RuntimeException</tt> or <tt>Error</tt> that caused
     * execution to terminate abruptly.
     *
     * <p>
     * <b>Note:</b> When actions are enclosed in tasks (such as {@link java.util.concurrent.FutureTask}) either explicitly
     * or via methods such as <tt>submit</tt>, these task objects catch and maintain computational exceptions, and so they
     * do not cause abrupt termination, and the internal exceptions are <em>not</em> passed to this method.
     *
     * <p>
     * This implementation does nothing, but may be customized in subclasses. Note: To properly nest multiple overridings,
     * subclasses should generally invoke <tt>super.afterExecute</tt> at the beginning of this method.
     *
     * @param worker the {@link Worker}, running the the thread t
     * @param thread
     * @param r the runnable that has completed.
     * @param t the exception that caused termination, or null if execution completed normally.
     */
    protected void afterExecute(final Worker worker, final Thread thread, final Runnable r, final Throwable t) {
        if (delayedQueue != null) {
            worker.transactionExpirationTime = NEVER_TIMEOUT;
        }
    }

    
 This method will be invoked when a the specified Runnable has completed execution. 
Params:
task – the unit of work that has completed processing/**
     * <p>
     * This method will be invoked when a the specified {@link Runnable} has completed execution.
     * </p>
     *
     * @param task the unit of work that has completed processing
     */
    protected void onTaskCompletedEvent(Runnable task) {
        ProbeNotifier.notifyTaskCompleted(this, task);
    }

    
Method is called by Worker, when it's starting Worker.run() method execution, which means, that ThreadPool's thread is getting active and ready to process tasks. This method is called from Worker's thread. 
Params:
worker – /**
     * Method is called by {@link Worker}, when it's starting {@link Worker#run()} method execution, which means, that
     * ThreadPool's thread is getting active and ready to process tasks. This method is called from {@link Worker}'s thread.
     *
     * @param worker
     */
    protected void onWorkerStarted(final Worker worker) {
        if (delayedQueue != null) {
            delayedQueue.add(worker, NEVER_TIMEOUT, TimeUnit.MILLISECONDS);
        }

        ProbeNotifier.notifyThreadAllocated(this, worker.t);
    }

    
Method is called by Worker, when it's completing Worker.run() method execution, which in most cases means, that ThreadPool's thread will be released. This method is called from Worker's thread. 
Params:
worker – /**
     * Method is called by {@link Worker}, when it's completing {@link Worker#run()} method execution, which in most cases
     * means, that ThreadPool's thread will be released. This method is called from {@link Worker}'s thread.
     *
     * @param worker
     */
    protected void onWorkerExit(Worker worker) {
        synchronized (stateLock) {
            workers.remove(worker);
            if (delayedQueue != null) {
                delayedQueue.remove(worker);
            }
            if (workers.isEmpty()) {
                // notify awaitTermination threads
                stateLock.notifyAll();
            }
        }

        ProbeNotifier.notifyThreadReleased(this, worker.t);
    }

    
Method is called by AbstractThreadPool, when maximum number of worker threads is reached and task will need
to wait in task queue, until one of the threads will be able to process it.
/**
     * Method is called by <tt>AbstractThreadPool</tt>, when maximum number of worker threads is reached and task will need
     * to wait in task queue, until one of the threads will be able to process it.
     */
    protected void onMaxNumberOfThreadsReached() {
        ProbeNotifier.notifyMaxNumberOfThreads(this, config.getMaxPoolSize());
    }

    
Method is called by a thread pool each time new task has been queued to a task queue.
Params:
task – /**
     * Method is called by a thread pool each time new task has been queued to a task queue.
     *
     * @param task
     */
    protected void onTaskQueued(Runnable task) {
        ProbeNotifier.notifyTaskQueued(this, task);
    }

    
Method is called by a thread pool each time a task has been dequeued from a task queue.
Params:
task – /**
     * Method is called by a thread pool each time a task has been dequeued from a task queue.
     *
     * @param task
     */
    protected void onTaskDequeued(Runnable task) {
        ProbeNotifier.notifyTaskDequeued(this, task);
    }

    
Method is called by a thread pool each time a dequeued task has been canceled instead of being processed.
Params:
task – /**
     * Method is called by a thread pool each time a dequeued task has been canceled instead of being processed.
     *
     * @param task
     */
    protected void onTaskCancelled(Runnable task) {
        ProbeNotifier.notifyTaskCancelled(this, task);
    }

    
Method is called by a thread pool, when new task could not be added to a task queue, because task queue is full. throws RejectedExecutionException /**
     * Method is called by a thread pool, when new task could not be added to a task queue, because task queue is full.
     * throws {@link RejectedExecutionException}
     */
    protected void onTaskQueueOverflow() {
        ProbeNotifier.notifyTaskQueueOverflow(this);

        throw new RejectedExecutionException("The thread pool's task queue is full, limit: " + config.getQueueLimit());
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public MonitoringConfig<ThreadPoolProbe> getMonitoringConfig() {
        return monitoringConfig;
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public void uncaughtException(Thread thread, Throwable throwable) {
        logger.log(Level.WARNING, LogMessages.WARNING_GRIZZLY_THREADPOOL_UNCAUGHT_EXCEPTION(thread), throwable);
    }

    Object createJmxManagementObject() {
        return MonitoringUtils.loadJmxObject("org.glassfish.grizzly.threadpool.jmx.ThreadPool", this, AbstractThreadPool.class);
    }

    protected final ThreadFactory getDefaultThreadFactory() {
        final AtomicInteger counter = new AtomicInteger();

        return new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {
                final MemoryManager mm = config.getMemoryManager();
                final ThreadLocalPoolProvider threadLocalPoolProvider;

                if (mm instanceof ThreadLocalPoolProvider) {
                    threadLocalPoolProvider = (ThreadLocalPoolProvider) mm;
                } else {
                    threadLocalPoolProvider = null;
                }

                final DefaultWorkerThread thread = new DefaultWorkerThread(Grizzly.DEFAULT_ATTRIBUTE_BUILDER,
                        config.getPoolName() + '(' + counter.incrementAndGet() + ')',
                        threadLocalPoolProvider != null ? threadLocalPoolProvider.createThreadLocalPool() : null, r);

                thread.setUncaughtExceptionHandler(AbstractThreadPool.this);
                thread.setPriority(config.getPriority());
                thread.setDaemon(config.isDaemon());
                final ClassLoader initial = config.getInitialClassLoader();
                if (initial != null) {
                    thread.setContextClassLoader(initial);
                }

                return thread;
            }
        };
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder(256);
        sb.append(getClass().getSimpleName());
        sb.append(" config: [").append(config.toString()).append("]\r\n");
        sb.append(", is-shutdown=").append(isShutdown());
        return sb.toString();
    }

    public abstract class Worker implements Runnable {

        protected Thread t;
        protected volatile long transactionExpirationTime;

        @Override
        public void run() {
            try {
                onWorkerStarted(this);// inside try, to ensure balance
                doWork();
            } finally {
                onWorkerExit(this);
            }
        }

        protected void doWork() {
            final Thread thread = t;

            while (true) {
                try {
                    Thread.interrupted();
                    final Runnable r = getTask();
                    if (r == poison || r == null) {
                        return;
                    }
                    onTaskDequeued(r);
                    Throwable error = null;
                    try {
                        beforeExecute(this, thread, r); // inside try. to ensure balance
                        r.run();
                        onTaskCompletedEvent(r);
                    } catch (Exception e) {
                        error = e;
                    } finally {
                        afterExecute(this, thread, r, error);
                    }
                } catch (Exception ignore) {
                }
            }
        }

        protected abstract Runnable getTask() throws InterruptedException;
    }
}