/**
    *
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF 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 org.apache.hadoop.hbase;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.LinkedHashMap;
  import java.util.Map.Entry;
  import java.util.concurrent.ScheduledFuture;
  import java.util.concurrent.ScheduledThreadPoolExecutor;
  import java.util.concurrent.ThreadFactory;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import com.google.common.annotations.VisibleForTesting;
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.ScheduledChore.ChoreServicer;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  
  /**
   * ChoreService is a service that can be used to schedule instances of {@link ScheduledChore} to run
   * periodically while sharing threads. The ChoreService is backed by a
   * {@link ScheduledThreadPoolExecutor} whose core pool size changes dynamically depending on the
   * number of {@link ScheduledChore} scheduled. All of the threads in the core thread pool of the
   * underlying {@link ScheduledThreadPoolExecutor} are set to be daemon threads.
   * <p>
   * The ChoreService provides the ability to schedule, cancel, and trigger instances of
   * {@link ScheduledChore}. The ChoreService also provides the ability to check on the status of
   * scheduled chores. The number of threads used by the ChoreService changes based on the scheduling
   * load and whether or not the scheduled chores are executing on time. As more chores are scheduled,
   * there may be a need to increase the number of threads if it is noticed that chores are no longer
   * meeting their scheduled start times. On the other hand, as chores are cancelled, an attempt is
   * made to reduce the number of running threads to see if chores can still meet their start times
   * with a smaller thread pool.
   * <p>
   * When finished with a ChoreService it is good practice to call {@link ChoreService#shutdown()}.
   * Calling this method ensures that all scheduled chores are cancelled and cleaned up properly.
   */
  @InterfaceAudience.Private
  public class ChoreService implements ChoreServicer {
    private static final Log LOG = LogFactory.getLog(ChoreService.class);
  
    /**
     * The minimum number of threads in the core pool of the underlying ScheduledThreadPoolExecutor
     */
    public final static int MIN_CORE_POOL_SIZE = 1;
  
    /**
     * This thread pool is used to schedule all of the Chores
     */
    private final ScheduledThreadPoolExecutor scheduler;
  
    /**
     * Maps chores to their futures. Futures are used to control a chore's schedule
     */
    private final HashMap<ScheduledChore, ScheduledFuture<?>> scheduledChores;
  
    /**
     * Maps chores to Booleans which indicate whether or not a chore has caused an increase in the
     * core pool size of the ScheduledThreadPoolExecutor. Each chore should only be allowed to
     * increase the core pool size by 1 (otherwise a single long running chore whose execution is
     * longer than its period would be able to spawn too many threads).
     */
    private final HashMap<ScheduledChore, Boolean> choresMissingStartTime;
  
    /**
     * The coreThreadPoolPrefix is the prefix that will be applied to all threads within the
     * ScheduledThreadPoolExecutor. The prefix is typically related to the Server that the service is
     * running on. The prefix is useful because it allows us to monitor how the thread pool of a
     * particular service changes over time VIA thread dumps.
     */
    private final String coreThreadPoolPrefix;
  
    /**
     *
     * @param coreThreadPoolPrefix Prefix that will be applied to the Thread name of all threads
     *          spawned by this service
     */
    @VisibleForTesting
    public ChoreService(final String coreThreadPoolPrefix) {
      this(coreThreadPoolPrefix, MIN_CORE_POOL_SIZE, false);
    }
  
   /**
    * @param jitter Should chore service add some jitter for all of the scheduled chores. When set
    *               to true this will add -10% to 10% jitter.
    */
   public ChoreService(final String coreThreadPoolPrefix, final boolean jitter) {
     this(coreThreadPoolPrefix, MIN_CORE_POOL_SIZE, jitter);
   }
 
   /**
    * @param coreThreadPoolPrefix Prefix that will be applied to the Thread name of all threads
    *          spawned by this service
    * @param corePoolSize The initial size to set the core pool of the ScheduledThreadPoolExecutor 
    *          to during initialization. The default size is 1, but specifying a larger size may be
    *          beneficial if you know that 1 thread will not be enough.
    */
   public ChoreService(final String coreThreadPoolPrefix, int corePoolSize, boolean jitter) {
     this.coreThreadPoolPrefix = coreThreadPoolPrefix;
     if (corePoolSize < MIN_CORE_POOL_SIZE)  {
       corePoolSize = MIN_CORE_POOL_SIZE;
     }
 
     final ThreadFactory threadFactory = new ChoreServiceThreadFactory(coreThreadPoolPrefix);
     if (jitter) {
       scheduler = new JitterScheduledThreadPoolExecutorImpl(corePoolSize, threadFactory, 0.1);
     } else {
       scheduler = new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
     }
 
     scheduler.setRemoveOnCancelPolicy(true);
     scheduledChores = new HashMap<ScheduledChore, ScheduledFuture<?>>();
     choresMissingStartTime = new HashMap<ScheduledChore, Boolean>();
   }
 
   /**
    * @param coreThreadPoolPrefix Prefix that will be applied to the Thread name of all threads
    *          spawned by this service
    */
   public static ChoreService getInstance(final String coreThreadPoolPrefix) {
     return new ChoreService(coreThreadPoolPrefix);
   }
 
   /**
    * @param chore Chore to be scheduled. If the chore is already scheduled with another ChoreService
    *          instance, that schedule will be cancelled (i.e. a Chore can only ever be scheduled
    *          with a single ChoreService instance).
    * @return true when the chore was successfully scheduled. false when the scheduling failed
    *         (typically occurs when a chore is scheduled during shutdown of service)
    */
   public synchronized boolean scheduleChore(ScheduledChore chore) {
     if (chore == null) {
       return false;
     }
 
     try {
       chore.setChoreServicer(this);
       ScheduledFuture<?> future =
           scheduler.scheduleAtFixedRate(chore, chore.getInitialDelay(), chore.getPeriod(),
             chore.getTimeUnit());
       scheduledChores.put(chore, future);
       return true;
     } catch (Exception exception) {
       if (LOG.isInfoEnabled()) {
         LOG.info("Could not successfully schedule chore: " + chore.getName());
       }
       return false;
     }
   }
 
   /**
    * @param chore The Chore to be rescheduled. If the chore is not scheduled with this ChoreService
    *          yet then this call is equivalent to a call to scheduleChore.
    */
   private synchronized void rescheduleChore(ScheduledChore chore) {
     if (chore == null) return;
 
     if (scheduledChores.containsKey(chore)) {
       ScheduledFuture<?> future = scheduledChores.get(chore);
       future.cancel(false);
     }
     scheduleChore(chore);
   }
 
   @Override
   public synchronized void cancelChore(ScheduledChore chore) {
     cancelChore(chore, true);
   }
 
   @Override
   public synchronized void cancelChore(ScheduledChore chore, boolean mayInterruptIfRunning) {
     if (chore != null && scheduledChores.containsKey(chore)) {
       ScheduledFuture<?> future = scheduledChores.get(chore);
       future.cancel(mayInterruptIfRunning);
       scheduledChores.remove(chore);
 
       // Removing a chore that was missing its start time means it may be possible
       // to reduce the number of threads
       if (choresMissingStartTime.containsKey(chore)) {
         choresMissingStartTime.remove(chore);
         requestCorePoolDecrease();
       }
     }
   }
 
   @Override
   public synchronized boolean isChoreScheduled(ScheduledChore chore) {
     return chore != null && scheduledChores.containsKey(chore)
         && !scheduledChores.get(chore).isDone();
   }
 
   @Override
   public synchronized boolean triggerNow(ScheduledChore chore) {
     if (chore == null) {
       return false;
     } else {
       rescheduleChore(chore);
       return true;
     }
   }
 
   /**
    * @return number of chores that this service currently has scheduled
    */
   int getNumberOfScheduledChores() {
     return scheduledChores.size();
   }
 
   /**
    * @return number of chores that this service currently has scheduled that are missing their
    *         scheduled start time
    */
   int getNumberOfChoresMissingStartTime() {
     return choresMissingStartTime.size();
   }
 
   /**
    * @return number of threads in the core pool of the underlying ScheduledThreadPoolExecutor
    */
   int getCorePoolSize() {
     return scheduler.getCorePoolSize();
   }
 
   /**
    * Custom ThreadFactory used with the ScheduledThreadPoolExecutor so that all the threads are
    * daemon threads, and thus, don't prevent the JVM from shutting down
    */
   static class ChoreServiceThreadFactory implements ThreadFactory {
     private final String threadPrefix;
     private final static String THREAD_NAME_SUFFIX = "_ChoreService_";
     private AtomicInteger threadNumber = new AtomicInteger(1);
 
     /**
      * @param threadPrefix The prefix given to all threads created by this factory
      */
     public ChoreServiceThreadFactory(final String threadPrefix) {
       this.threadPrefix = threadPrefix;
     }
 
     @Override
     public Thread newThread(Runnable r) {
       Thread thread =
           new Thread(r, threadPrefix + THREAD_NAME_SUFFIX + threadNumber.getAndIncrement());
       thread.setDaemon(true);
       return thread;
     }
   }
 
   /**
    * Represents a request to increase the number of core pool threads. Typically a request
    * originates from the fact that the current core pool size is not sufficient to service all of
    * the currently running Chores
    * @return true when the request to increase the core pool size succeeds
    */
   private synchronized boolean requestCorePoolIncrease() {
     // There is no point in creating more threads than scheduledChores.size since scheduled runs
     // of the same chore cannot run concurrently (i.e. happen-before behavior is enforced
     // amongst occurrences of the same chore).
     if (scheduler.getCorePoolSize() < scheduledChores.size()) {
       scheduler.setCorePoolSize(scheduler.getCorePoolSize() + 1);
       printChoreServiceDetails("requestCorePoolIncrease");
       return true;
     }
     return false;
   }
 
   /**
    * Represents a request to decrease the number of core pool threads. Typically a request
    * originates from the fact that the current core pool size is more than sufficient to service the
    * running Chores.
    */
   private synchronized void requestCorePoolDecrease() {
     if (scheduler.getCorePoolSize() > MIN_CORE_POOL_SIZE) {
       scheduler.setCorePoolSize(scheduler.getCorePoolSize() - 1);
       printChoreServiceDetails("requestCorePoolDecrease");
     }
   }
 
   @Override
   public synchronized void onChoreMissedStartTime(ScheduledChore chore) {
     if (chore == null || !scheduledChores.containsKey(chore)) return;
 
     // If the chore has not caused an increase in the size of the core thread pool then request an
     // increase. This allows each chore missing its start time to increase the core pool size by
     // at most 1.
     if (!choresMissingStartTime.containsKey(chore) || !choresMissingStartTime.get(chore)) {
       choresMissingStartTime.put(chore, requestCorePoolIncrease());
     }
 
     // Must reschedule the chore to prevent unnecessary delays of chores in the scheduler. If
     // the chore is NOT rescheduled, future executions of this chore will be delayed more and
     // more on each iteration. This hurts us because the ScheduledThreadPoolExecutor allocates
     // idle threads to chores based on how delayed they are.
     rescheduleChore(chore);
     printChoreDetails("onChoreMissedStartTime", chore);
   }
 
   /**
    * shutdown the service. Any chores that are scheduled for execution will be cancelled. Any chores
    * in the middle of execution will be interrupted and shutdown. This service will be unusable
    * after this method has been called (i.e. future scheduling attempts will fail).
    */
   public synchronized void shutdown() {
     scheduler.shutdownNow();
     if (LOG.isInfoEnabled()) {
       LOG.info("Chore service for: " + coreThreadPoolPrefix + " had " + scheduledChores.keySet()
           + " on shutdown");
     }
     cancelAllChores(true);
     scheduledChores.clear();
     choresMissingStartTime.clear();
   }
   
   /**
    * @return true when the service is shutdown and thus cannot be used anymore
    */
   public boolean isShutdown() {
     return scheduler.isShutdown();
   }
 
   /**
    * @return true when the service is shutdown and all threads have terminated
    */
   public boolean isTerminated() {
     return scheduler.isTerminated();
   }
 
   private void cancelAllChores(final boolean mayInterruptIfRunning) {
     ArrayList<ScheduledChore> choresToCancel = new ArrayList<ScheduledChore>();
     // Build list of chores to cancel so we can iterate through a set that won't change
     // as chores are cancelled. If we tried to cancel each chore while iterating through
     // keySet the results would be undefined because the keySet would be changing
     for (ScheduledChore chore : scheduledChores.keySet()) {
       choresToCancel.add(chore);
     }
     for (ScheduledChore chore : choresToCancel) {
       cancelChore(chore, mayInterruptIfRunning);
     }
     choresToCancel.clear();
   }
 
   /**
    * Prints a summary of important details about the chore. Used for debugging purposes
    */
   private void printChoreDetails(final String header, ScheduledChore chore) {
     LinkedHashMap<String, String> output = new LinkedHashMap<String, String>();
     output.put(header, "");
     output.put("Chore name: ", chore.getName());
     output.put("Chore period: ", Integer.toString(chore.getPeriod()));
     output.put("Chore timeBetweenRuns: ", Long.toString(chore.getTimeBetweenRuns()));
 
     for (Entry<String, String> entry : output.entrySet()) {
       if (LOG.isTraceEnabled()) LOG.trace(entry.getKey() + entry.getValue());
     }
   }
 
   /**
    * Prints a summary of important details about the service. Used for debugging purposes
    */
   private void printChoreServiceDetails(final String header) {
     LinkedHashMap<String, String> output = new LinkedHashMap<String, String>();
     output.put(header, "");
     output.put("ChoreService corePoolSize: ", Integer.toString(getCorePoolSize()));
     output.put("ChoreService scheduledChores: ", Integer.toString(getNumberOfScheduledChores()));
     output.put("ChoreService missingStartTimeCount: ",
       Integer.toString(getNumberOfChoresMissingStartTime()));
 
     for (Entry<String, String> entry : output.entrySet()) {
       if (LOG.isTraceEnabled()) LOG.trace(entry.getKey() + entry.getValue());
     }
   }
 }