//
   //  ========================================================================
   //  Copyright (c) 1995-2016 Mort Bay Consulting Pty. Ltd.
   //  ------------------------------------------------------------------------
   //  All rights reserved. This program and the accompanying materials
   //  are made available under the terms of the Eclipse Public License v1.0
   //  and Apache License v2.0 which accompanies this distribution.
   //
   //      The Eclipse Public License is available at
  //      http://www.eclipse.org/legal/epl-v10.html
  //
  //      The Apache License v2.0 is available at
  //      http://www.opensource.org/licenses/apache2.0.php
  //
  //  You may elect to redistribute this code under either of these licenses.
  //  ========================================================================
  //
  
  package org.eclipse.jetty.server;
  
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.concurrent.Executor;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicBoolean;
  
  import org.eclipse.jetty.io.EndPoint;
  import org.eclipse.jetty.util.annotation.ManagedAttribute;
  import org.eclipse.jetty.util.annotation.ManagedObject;
  import org.eclipse.jetty.util.annotation.Name;
  import org.eclipse.jetty.util.component.AbstractLifeCycle;
  import org.eclipse.jetty.util.log.Log;
  import org.eclipse.jetty.util.log.Logger;
  import org.eclipse.jetty.util.thread.ScheduledExecutorScheduler;
  import org.eclipse.jetty.util.thread.Scheduler;
  import org.eclipse.jetty.util.thread.ThreadPool;
  
  
  /**
   * A monitor for low resources
   * <p>
   * An instance of this class will monitor all the connectors of a server (or a set of connectors
   * configured with {@link #setMonitoredConnectors(Collection)}) for a low resources state.
   * <p>
   * Low resources can be detected by:
   * <ul>
   * <li>{@link ThreadPool#isLowOnThreads()} if {@link Connector#getExecutor()} is
   * an instance of {@link ThreadPool} and {@link #setMonitorThreads(boolean)} is true.<li>
   * <li>If {@link #setMaxMemory(long)} is non zero then low resources is detected if the JVMs
   * {@link Runtime} instance has {@link Runtime#totalMemory()} minus {@link Runtime#freeMemory()}
   * greater than {@link #getMaxMemory()}</li>
   * <li>If {@link #setMaxConnections(int)} is non zero then low resources is dected if the total number
   * of connections exceeds {@link #getMaxConnections()}</li>
   * </ul>
   * <p>
   * Once low resources state is detected, the cause is logged and all existing connections returned
   * by {@link Connector#getConnectedEndPoints()} have {@link EndPoint#setIdleTimeout(long)} set
   * to {@link #getLowResourcesIdleTimeout()}.  New connections are not affected, however if the low
   * resources state persists for more than {@link #getMaxLowResourcesTime()}, then the
   * {@link #getLowResourcesIdleTimeout()} to all connections again.  Once the low resources state is
   * cleared, the idle timeout is reset to the connector default given by {@link Connector#getIdleTimeout()}.
   */
  @ManagedObject ("Monitor for low resource conditions and activate a low resource mode if detected")
  public class LowResourceMonitor extends AbstractLifeCycle
  {
      private static final Logger LOG = Log.getLogger(LowResourceMonitor.class);
      private final Server _server;
      private Scheduler _scheduler;
      private Connector[] _monitoredConnectors;
      private int _period=1000;
      private int _maxConnections;
      private long _maxMemory;
      private int _lowResourcesIdleTimeout=1000;
      private int _maxLowResourcesTime=0;
      private boolean _monitorThreads=true;
      private final AtomicBoolean _low = new AtomicBoolean();
      private String _cause;
      private String _reasons;
      private long _lowStarted;
  
      private final Runnable _monitor = new Runnable()
      {
          @Override
          public void run()
          {
              if (isRunning())
              {
                  monitor();
                  _scheduler.schedule(_monitor,_period,TimeUnit.MILLISECONDS);
              }
          }
      };
  
      public LowResourceMonitor(@Name("server") Server server)
      {
          _server=server;
      }
  
     @ManagedAttribute("Are the monitored connectors low on resources?")
     public boolean isLowOnResources()
     {
         return _low.get();
     }
 
     @ManagedAttribute("The reason(s) the monitored connectors are low on resources")
     public String getLowResourcesReasons()
     {
         return _reasons;
     }
 
     @ManagedAttribute("Get the timestamp in ms since epoch that low resources state started")
     public long getLowResourcesStarted()
     {
         return _lowStarted;
     }
 
     @ManagedAttribute("The monitored connectors. If null then all server connectors are monitored")
     public Collection<Connector> getMonitoredConnectors()
     {
         if (_monitoredConnectors==null)
             return Collections.emptyList();
         return Arrays.asList(_monitoredConnectors);
     }
 
     /**
      * @param monitoredConnectors The collections of Connectors that should be monitored for low resources.
      */
     public void setMonitoredConnectors(Collection<Connector> monitoredConnectors)
     {
         if (monitoredConnectors==null || monitoredConnectors.size()==0)
             _monitoredConnectors=null;
         else
             _monitoredConnectors = monitoredConnectors.toArray(new Connector[monitoredConnectors.size()]);
     }
 
     @ManagedAttribute("The monitor period in ms")
     public int getPeriod()
     {
         return _period;
     }
 
     /**
      * @param periodMS The period in ms to monitor for low resources
      */
     public void setPeriod(int periodMS)
     {
         _period = periodMS;
     }
 
     @ManagedAttribute("True if low available threads status is monitored")
     public boolean getMonitorThreads()
     {
         return _monitorThreads;
     }
 
     /**
      * @param monitorThreads If true, check connectors executors to see if they are
      * {@link ThreadPool} instances that are low on threads.
      */
     public void setMonitorThreads(boolean monitorThreads)
     {
         _monitorThreads = monitorThreads;
     }
 
     @ManagedAttribute("The maximum connections allowed for the monitored connectors before low resource handling is activated")
     public int getMaxConnections()
     {
         return _maxConnections;
     }
 
     /**
      * @param maxConnections The maximum connections before low resources state is triggered
      */
     public void setMaxConnections(int maxConnections)
     {
         _maxConnections = maxConnections;
     }
 
     @ManagedAttribute("The maximum memory (in bytes) that can be used before low resources is triggered.  Memory used is calculated as (totalMemory-freeMemory).")
     public long getMaxMemory()
     {
         return _maxMemory;
     }
 
     /**
      * @param maxMemoryBytes The maximum memory in bytes in use before low resources is triggered.
      */
     public void setMaxMemory(long maxMemoryBytes)
     {
         _maxMemory = maxMemoryBytes;
     }
 
     @ManagedAttribute("The idletimeout in ms to apply to all existing connections when low resources is detected")
     public int getLowResourcesIdleTimeout()
     {
         return _lowResourcesIdleTimeout;
     }
 
     /**
      * @param lowResourcesIdleTimeoutMS The timeout in ms to apply to EndPoints when in the low resources state.
      */
     public void setLowResourcesIdleTimeout(int lowResourcesIdleTimeoutMS)
     {
         _lowResourcesIdleTimeout = lowResourcesIdleTimeoutMS;
     }
 
     @ManagedAttribute("The maximum time in ms that low resources condition can persist before lowResourcesIdleTimeout is applied to new connections as well as existing connections")
     public int getMaxLowResourcesTime()
     {
         return _maxLowResourcesTime;
     }
 
     /**
      * @param maxLowResourcesTimeMS The time in milliseconds that a low resource state can persist before the low resource idle timeout is reapplied to all connections
      */
     public void setMaxLowResourcesTime(int maxLowResourcesTimeMS)
     {
         _maxLowResourcesTime = maxLowResourcesTimeMS;
     }
 
     @Override
     protected void doStart() throws Exception
     {
         _scheduler = _server.getBean(Scheduler.class);
 
         if (_scheduler==null)
         {
             _scheduler=new LRMScheduler();
             _scheduler.start();
         }
         super.doStart();
 
         _scheduler.schedule(_monitor,_period,TimeUnit.MILLISECONDS);
     }
 
     @Override
     protected void doStop() throws Exception
     {
         if (_scheduler instanceof LRMScheduler)
             _scheduler.stop();
         super.doStop();
     }
 
     protected Connector[] getMonitoredOrServerConnectors()
     {
         if (_monitoredConnectors!=null && _monitoredConnectors.length>0)
             return _monitoredConnectors;
         return _server.getConnectors();
     }
 
     protected void monitor()
     {
         String reasons=null;
         String cause="";
         int connections=0;
 
         ThreadPool serverThreads = _server.getThreadPool();
         if (_monitorThreads && serverThreads.isLowOnThreads())
         {
             reasons=low(reasons,"Server low on threads: "+serverThreads);
             cause+="S";
         }
 
         for(Connector connector : getMonitoredOrServerConnectors())
         {
             connections+=connector.getConnectedEndPoints().size();
 
             Executor executor = connector.getExecutor();
             if (executor instanceof ThreadPool && executor!=serverThreads)
             {
                 ThreadPool connectorThreads=(ThreadPool)executor;
                 if (_monitorThreads && connectorThreads.isLowOnThreads())
                 {
                     reasons=low(reasons,"Connector low on threads: "+connectorThreads);
                     cause+="T";
                 }
             }
         }
 
         if (_maxConnections>0 && connections>_maxConnections)
         {
             reasons=low(reasons,"Max Connections exceeded: "+connections+">"+_maxConnections);
             cause+="C";
         }
 
         long memory=Runtime.getRuntime().totalMemory()-Runtime.getRuntime().freeMemory();
         if (_maxMemory>0 && memory>_maxMemory)
         {
             reasons=low(reasons,"Max memory exceeded: "+memory+">"+_maxMemory);
             cause+="M";
         }
 
         if (reasons!=null)
         {
             // Log the reasons if there is any change in the cause
             if (!cause.equals(_cause))
             {
                 LOG.warn("Low Resources: {}",reasons);
                 _cause=cause;
             }
 
             // Enter low resources state?
             if (_low.compareAndSet(false,true))
             {
                 _reasons=reasons;
                 _lowStarted=System.currentTimeMillis();
                 setLowResources();
             }
 
             // Too long in low resources state?
             if (_maxLowResourcesTime>0 && (System.currentTimeMillis()-_lowStarted)>_maxLowResourcesTime)
                 setLowResources();
         }
         else
         {
             if (_low.compareAndSet(true,false))
             {
                 LOG.info("Low Resources cleared");
                 _reasons=null;
                 _lowStarted=0;
                 _cause=null;
                 clearLowResources();
             }
         }
     }
 
     protected void setLowResources()
     {
         for(Connector connector : getMonitoredOrServerConnectors())
         {
             for (EndPoint endPoint : connector.getConnectedEndPoints())
                 endPoint.setIdleTimeout(_lowResourcesIdleTimeout);
         }
     }
 
     protected void clearLowResources()
     {
         for(Connector connector : getMonitoredOrServerConnectors())
         {
             for (EndPoint endPoint : connector.getConnectedEndPoints())
                 endPoint.setIdleTimeout(connector.getIdleTimeout());
         }
     }
 
     private String low(String reasons, String newReason)
     {
         if (reasons==null)
             return newReason;
         return reasons+", "+newReason;
     }
 
 
     private static class LRMScheduler extends ScheduledExecutorScheduler
     {
     }
 }