/*
    *
    * 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.coprocessor;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Set;
  import java.util.TreeSet;
  import java.util.UUID;
  import java.util.concurrent.ConcurrentSkipListSet;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.Abortable;
  import org.apache.hadoop.hbase.Coprocessor;
  import org.apache.hadoop.hbase.CoprocessorEnvironment;
  import org.apache.hadoop.hbase.DoNotRetryIOException;
  import org.apache.hadoop.hbase.HBaseInterfaceAudience;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.client.HTable;
  import org.apache.hadoop.hbase.client.HTableInterface;
  import org.apache.hadoop.hbase.client.HTableWrapper;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.util.CoprocessorClassLoader;
  import org.apache.hadoop.hbase.util.SortedList;
  import org.apache.hadoop.hbase.util.VersionInfo;
  
  /**
   * Provides the common setup framework and runtime services for coprocessor
   * invocation from HBase services.
   * @param <E> the specific environment extension that a concrete implementation
   * provides
   */
  @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
  @InterfaceStability.Evolving
  public abstract class CoprocessorHost<E extends CoprocessorEnvironment> {
    public static final String REGION_COPROCESSOR_CONF_KEY =
        "hbase.coprocessor.region.classes";
    public static final String REGIONSERVER_COPROCESSOR_CONF_KEY =
        "hbase.coprocessor.regionserver.classes";
    public static final String USER_REGION_COPROCESSOR_CONF_KEY =
        "hbase.coprocessor.user.region.classes";
    public static final String MASTER_COPROCESSOR_CONF_KEY =
        "hbase.coprocessor.master.classes";
    public static final String WAL_COPROCESSOR_CONF_KEY =
      "hbase.coprocessor.wal.classes";
    public static final String ABORT_ON_ERROR_KEY = "hbase.coprocessor.abortonerror";
    public static final boolean DEFAULT_ABORT_ON_ERROR = true;
    public static final String COPROCESSORS_ENABLED_CONF_KEY = "hbase.coprocessor.enabled";
    public static final boolean DEFAULT_COPROCESSORS_ENABLED = true;
    public static final String USER_COPROCESSORS_ENABLED_CONF_KEY =
      "hbase.coprocessor.user.enabled";
    public static final boolean DEFAULT_USER_COPROCESSORS_ENABLED = true;
    public static final String SKIP_LOAD_DUPLICATE_TABLE_COPROCESSOR =
        "hbase.skip.load.duplicate.table.coprocessor";
    public static final boolean DEFAULT_SKIP_LOAD_DUPLICATE_TABLE_COPROCESSOR = false;
  
    private static final Log LOG = LogFactory.getLog(CoprocessorHost.class);
    protected Abortable abortable;
    /** Ordered set of loaded coprocessors with lock */
    protected SortedList<E> coprocessors =
        new SortedList<E>(new EnvironmentPriorityComparator());
    protected Configuration conf;
    // unique file prefix to use for local copies of jars when classloading
    protected String pathPrefix;
    protected AtomicInteger loadSequence = new AtomicInteger();
  
    public CoprocessorHost(Abortable abortable) {
      this.abortable = abortable;
      this.pathPrefix = UUID.randomUUID().toString();
    }
 
   /**
    * Not to be confused with the per-object _coprocessors_ (above),
    * coprocessorNames is static and stores the set of all coprocessors ever
    * loaded by any thread in this JVM. It is strictly additive: coprocessors are
    * added to coprocessorNames, by loadInstance() but are never removed, since
    * the intention is to preserve a history of all loaded coprocessors for
    * diagnosis in case of server crash (HBASE-4014).
    */
   private static Set<String> coprocessorNames =
       Collections.synchronizedSet(new HashSet<String>());
 
   public static Set<String> getLoadedCoprocessors() {
     synchronized (coprocessorNames) {
       return new HashSet(coprocessorNames);
     }
   }
 
   /**
    * Used to create a parameter to the HServerLoad constructor so that
    * HServerLoad can provide information about the coprocessors loaded by this
    * regionserver.
    * (HBASE-4070: Improve region server metrics to report loaded coprocessors
    * to master).
    */
   public Set<String> getCoprocessors() {
     Set<String> returnValue = new TreeSet<String>();
     for (CoprocessorEnvironment e: coprocessors) {
       returnValue.add(e.getInstance().getClass().getSimpleName());
     }
     return returnValue;
   }
 
   /**
    * Load system coprocessors once only. Read the class names from configuration.
    * Called by constructor.
    */
   protected void loadSystemCoprocessors(Configuration conf, String confKey) {
     boolean coprocessorsEnabled = conf.getBoolean(COPROCESSORS_ENABLED_CONF_KEY,
       DEFAULT_COPROCESSORS_ENABLED);
     if (!coprocessorsEnabled) {
       return;
     }
 
     Class<?> implClass = null;
 
     // load default coprocessors from configure file
     String[] defaultCPClasses = conf.getStrings(confKey);
     if (defaultCPClasses == null || defaultCPClasses.length == 0)
       return;
 
     int currentSystemPriority = Coprocessor.PRIORITY_SYSTEM;
     for (String className : defaultCPClasses) {
       String[] classNameAndPriority = className.split("\\|");
       boolean hasPriorityOverride = false;
       className = classNameAndPriority[0];
       int overridePriority = Coprocessor.PRIORITY_SYSTEM;
       if (classNameAndPriority.length > 1){
         overridePriority = Integer.parseInt(classNameAndPriority[1]);
         hasPriorityOverride = true;
       }
       className = className.trim();
       if (findCoprocessor(className) != null) {
         // If already loaded will just continue
         LOG.warn("Attempted duplicate loading of " + className + "; skipped");
         continue;
       }
       ClassLoader cl = this.getClass().getClassLoader();
       Thread.currentThread().setContextClassLoader(cl);
       try {
         implClass = cl.loadClass(className);
         // Add coprocessors as we go to guard against case where a coprocessor is specified twice
         // in the configuration
         int coprocPriority = hasPriorityOverride ? overridePriority : currentSystemPriority;
         this.coprocessors.add(loadInstance(implClass, coprocPriority, conf));
         LOG.info("System coprocessor " + className + " was loaded " +
             "successfully with priority (" + coprocPriority + ").");
         if (!hasPriorityOverride) {
           ++currentSystemPriority;
         }
       } catch (Throwable t) {
         // We always abort if system coprocessors cannot be loaded
         abortServer(className, t);
       }
     }
   }
 
   /**
    * Load a coprocessor implementation into the host
    * @param path path to implementation jar
    * @param className the main class name
    * @param priority chaining priority
    * @param conf configuration for coprocessor
    * @throws java.io.IOException Exception
    */
   public E load(Path path, String className, int priority,
       Configuration conf) throws IOException {
     String[] includedClassPrefixes = null;
     if (conf.get(HConstants.CP_HTD_ATTR_INCLUSION_KEY) != null){
       String prefixes = conf.get(HConstants.CP_HTD_ATTR_INCLUSION_KEY);
       includedClassPrefixes = prefixes.split(";");
     }
     return load(path, className, priority, conf, includedClassPrefixes);
   }
 
   /**
    * Load a coprocessor implementation into the host
    * @param path path to implementation jar
    * @param className the main class name
    * @param priority chaining priority
    * @param conf configuration for coprocessor
    * @param includedClassPrefixes class name prefixes to include
    * @throws java.io.IOException Exception
    */
   public E load(Path path, String className, int priority,
       Configuration conf, String[] includedClassPrefixes) throws IOException {
     Class<?> implClass = null;
     LOG.debug("Loading coprocessor class " + className + " with path " +
         path + " and priority " + priority);
 
     boolean skipLoadDuplicateCoprocessor = conf.getBoolean(SKIP_LOAD_DUPLICATE_TABLE_COPROCESSOR,
       DEFAULT_SKIP_LOAD_DUPLICATE_TABLE_COPROCESSOR);
     if (skipLoadDuplicateCoprocessor && findCoprocessor(className) != null) {
       // If already loaded will just continue
       LOG.warn("Attempted duplicate loading of " + className + "; skipped");
       return null;
     }
 
     ClassLoader cl = null;
     if (path == null) {
       try {
         implClass = getClass().getClassLoader().loadClass(className);
       } catch (ClassNotFoundException e) {
         throw new IOException("No jar path specified for " + className);
       }
     } else {
       cl = CoprocessorClassLoader.getClassLoader(
         path, getClass().getClassLoader(), pathPrefix, conf);
       try {
         implClass = ((CoprocessorClassLoader)cl).loadClass(className, includedClassPrefixes);
       } catch (ClassNotFoundException e) {
         throw new IOException("Cannot load external coprocessor class " + className, e);
       }
     }
 
     //load custom code for coprocessor
     Thread currentThread = Thread.currentThread();
     ClassLoader hostClassLoader = currentThread.getContextClassLoader();
     try{
       // switch temporarily to the thread classloader for custom CP
       currentThread.setContextClassLoader(cl);
       E cpInstance = loadInstance(implClass, priority, conf);
       return cpInstance;
     } finally {
       // restore the fresh (host) classloader
       currentThread.setContextClassLoader(hostClassLoader);
     }
   }
 
   /**
    * @param implClass Implementation class
    * @param priority priority
    * @param conf configuration
    * @throws java.io.IOException Exception
    */
   public void load(Class<?> implClass, int priority, Configuration conf)
       throws IOException {
     E env = loadInstance(implClass, priority, conf);
     coprocessors.add(env);
   }
 
   /**
    * @param implClass Implementation class
    * @param priority priority
    * @param conf configuration
    * @throws java.io.IOException Exception
    */
   public E loadInstance(Class<?> implClass, int priority, Configuration conf)
       throws IOException {
     if (!Coprocessor.class.isAssignableFrom(implClass)) {
       throw new IOException("Configured class " + implClass.getName() + " must implement "
           + Coprocessor.class.getName() + " interface ");
     }
 
     // create the instance
     Coprocessor impl;
     Object o = null;
     try {
       o = implClass.getDeclaredConstructor().newInstance();
       impl = (Coprocessor)o;
     } catch (Exception e) {
       throw new IOException(e);
     }
     // create the environment
     E env = createEnvironment(implClass, impl, priority, loadSequence.incrementAndGet(), conf);
     if (env instanceof Environment) {
       ((Environment)env).startup();
     }
     // HBASE-4014: maintain list of loaded coprocessors for later crash analysis
     // if server (master or regionserver) aborts.
     coprocessorNames.add(implClass.getName());
     return env;
   }
 
   /**
    * Called when a new Coprocessor class is loaded
    */
   public abstract E createEnvironment(Class<?> implClass, Coprocessor instance,
       int priority, int sequence, Configuration conf);
 
   public void shutdown(CoprocessorEnvironment e) {
     if (e instanceof Environment) {
       if (LOG.isDebugEnabled()) {
         LOG.debug("Stop coprocessor " + e.getInstance().getClass().getName());
       }
       ((Environment)e).shutdown();
     } else {
       LOG.warn("Shutdown called on unknown environment: "+
           e.getClass().getName());
     }
   }
 
   /**
    * Find a coprocessor implementation by class name
    * @param className the class name
    * @return the coprocessor, or null if not found
    */
   public Coprocessor findCoprocessor(String className) {
     for (E env: coprocessors) {
       if (env.getInstance().getClass().getName().equals(className) ||
           env.getInstance().getClass().getSimpleName().equals(className)) {
         return env.getInstance();
       }
     }
     return null;
   }
 
   /**
    * Find list of coprocessors that extend/implement the given class/interface
    * @param cls the class/interface to look for
    * @return the list of coprocessors, or null if not found
    */
   public <T extends Coprocessor> List<T> findCoprocessors(Class<T> cls) {
     ArrayList<T> ret = new ArrayList<T>();
 
     for (E env: coprocessors) {
       Coprocessor cp = env.getInstance();
 
       if(cp != null) {
         if (cls.isAssignableFrom(cp.getClass())) {
           ret.add((T)cp);
         }
       }
     }
     return ret;
   }
 
   /**
    * Find a coprocessor environment by class name
    * @param className the class name
    * @return the coprocessor, or null if not found
    */
   public CoprocessorEnvironment findCoprocessorEnvironment(String className) {
     for (E env: coprocessors) {
       if (env.getInstance().getClass().getName().equals(className) ||
           env.getInstance().getClass().getSimpleName().equals(className)) {
         return env;
       }
     }
     return null;
   }
 
   /**
    * Retrieves the set of classloaders used to instantiate Coprocessor classes defined in external
    * jar files.
    * @return A set of ClassLoader instances
    */
   Set<ClassLoader> getExternalClassLoaders() {
     Set<ClassLoader> externalClassLoaders = new HashSet<ClassLoader>();
     final ClassLoader systemClassLoader = this.getClass().getClassLoader();
     for (E env : coprocessors) {
       ClassLoader cl = env.getInstance().getClass().getClassLoader();
       if (cl != systemClassLoader ){
         //do not include system classloader
         externalClassLoaders.add(cl);
       }
     }
     return externalClassLoaders;
   }
 
   /**
    * Environment priority comparator.
    * Coprocessors are chained in sorted order.
    */
   static class EnvironmentPriorityComparator
       implements Comparator<CoprocessorEnvironment> {
     @Override
     public int compare(final CoprocessorEnvironment env1,
         final CoprocessorEnvironment env2) {
       if (env1.getPriority() < env2.getPriority()) {
         return -1;
       } else if (env1.getPriority() > env2.getPriority()) {
         return 1;
       }
       if (env1.getLoadSequence() < env2.getLoadSequence()) {
         return -1;
       } else if (env1.getLoadSequence() > env2.getLoadSequence()) {
         return 1;
       }
       return 0;
     }
   }
 
   /**
    * Encapsulation of the environment of each coprocessor
    */
   public static class Environment implements CoprocessorEnvironment {
 
     /** The coprocessor */
     public Coprocessor impl;
     /** Chaining priority */
     protected int priority = Coprocessor.PRIORITY_USER;
     /** Current coprocessor state */
     Coprocessor.State state = Coprocessor.State.UNINSTALLED;
     /** Accounting for tables opened by the coprocessor */
     protected final List<HTableInterface> openTables =
       Collections.synchronizedList(new ArrayList<HTableInterface>());
     private int seq;
     private Configuration conf;
     private ClassLoader classLoader;
 
     /**
      * Constructor
      * @param impl the coprocessor instance
      * @param priority chaining priority
      */
     public Environment(final Coprocessor impl, final int priority,
         final int seq, final Configuration conf) {
       this.impl = impl;
       this.classLoader = impl.getClass().getClassLoader();
       this.priority = priority;
       this.state = Coprocessor.State.INSTALLED;
       this.seq = seq;
       this.conf = conf;
     }
 
     /** Initialize the environment */
     public void startup() throws IOException {
       if (state == Coprocessor.State.INSTALLED ||
           state == Coprocessor.State.STOPPED) {
         state = Coprocessor.State.STARTING;
         Thread currentThread = Thread.currentThread();
         ClassLoader hostClassLoader = currentThread.getContextClassLoader();
         try {
           currentThread.setContextClassLoader(this.getClassLoader());
           impl.start(this);
           state = Coprocessor.State.ACTIVE;
         } finally {
           currentThread.setContextClassLoader(hostClassLoader);
         }
       } else {
         LOG.warn("Not starting coprocessor "+impl.getClass().getName()+
             " because not inactive (state="+state.toString()+")");
       }
     }
 
     /** Clean up the environment */
     protected void shutdown() {
       if (state == Coprocessor.State.ACTIVE) {
         state = Coprocessor.State.STOPPING;
         Thread currentThread = Thread.currentThread();
         ClassLoader hostClassLoader = currentThread.getContextClassLoader();
         try {
           currentThread.setContextClassLoader(this.getClassLoader());
           impl.stop(this);
           state = Coprocessor.State.STOPPED;
         } catch (IOException ioe) {
           LOG.error("Error stopping coprocessor "+impl.getClass().getName(), ioe);
         } finally {
           currentThread.setContextClassLoader(hostClassLoader);
         }
       } else {
         LOG.warn("Not stopping coprocessor "+impl.getClass().getName()+
             " because not active (state="+state.toString()+")");
       }
       synchronized (openTables) {
         // clean up any table references
         for (HTableInterface table: openTables) {
           try {
             ((HTableWrapper)table).internalClose();
           } catch (IOException e) {
             // nothing can be done here
             LOG.warn("Failed to close " +
                 Bytes.toStringBinary(table.getTableName()), e);
           }
         }
       }
     }
 
     @Override
     public Coprocessor getInstance() {
       return impl;
     }
 
     @Override
     public ClassLoader getClassLoader() {
       return classLoader;
     }
 
     @Override
     public int getPriority() {
       return priority;
     }
 
     @Override
     public int getLoadSequence() {
       return seq;
     }
 
     /** @return the coprocessor environment version */
     @Override
     public int getVersion() {
       return Coprocessor.VERSION;
     }
 
     /** @return the HBase release */
     @Override
     public String getHBaseVersion() {
       return VersionInfo.getVersion();
     }
 
     @Override
     public Configuration getConfiguration() {
       return conf;
     }
 
     /**
      * Open a table from within the Coprocessor environment
      * @param tableName the table name
      * @return an interface for manipulating the table
      * @exception java.io.IOException Exception
      */
     @Override
     public HTableInterface getTable(TableName tableName) throws IOException {
       return this.getTable(tableName, HTable.getDefaultExecutor(getConfiguration()));
     }
 
     /**
      * Open a table from within the Coprocessor environment
      * @param tableName the table name
      * @return an interface for manipulating the table
      * @exception java.io.IOException Exception
      */
     @Override
     public HTableInterface getTable(TableName tableName, ExecutorService pool) throws IOException {
       return HTableWrapper.createWrapper(openTables, tableName, this, pool);
     }
   }
 
   protected void abortServer(final CoprocessorEnvironment environment, final Throwable e) {
     abortServer(environment.getInstance().getClass().getName(), e);
   }
 
   protected void abortServer(final String coprocessorName, final Throwable e) {
     String message = "The coprocessor " + coprocessorName + " threw " + e.toString();
     LOG.error(message, e);
     if (abortable != null) {
       abortable.abort(message, e);
     } else {
       LOG.warn("No available Abortable, process was not aborted");
     }
   }
 
   /**
    * This is used by coprocessor hooks which are declared to throw IOException
    * (or its subtypes). For such hooks, we should handle throwable objects
    * depending on the Throwable's type. Those which are instances of
    * IOException should be passed on to the client. This is in conformance with
    * the HBase idiom regarding IOException: that it represents a circumstance
    * that should be passed along to the client for its own handling. For
    * example, a coprocessor that implements access controls would throw a
    * subclass of IOException, such as AccessDeniedException, in its preGet()
    * method to prevent an unauthorized client's performing a Get on a particular
    * table.
    * @param env Coprocessor Environment
    * @param e Throwable object thrown by coprocessor.
    * @exception IOException Exception
    */
   protected void handleCoprocessorThrowable(final CoprocessorEnvironment env, final Throwable e)
       throws IOException {
     if (e instanceof IOException) {
       throw (IOException)e;
     }
     // If we got here, e is not an IOException. A loaded coprocessor has a
     // fatal bug, and the server (master or regionserver) should remove the
     // faulty coprocessor from its set of active coprocessors. Setting
     // 'hbase.coprocessor.abortonerror' to true will cause abortServer(),
     // which may be useful in development and testing environments where
     // 'failing fast' for error analysis is desired.
     if (env.getConfiguration().getBoolean(ABORT_ON_ERROR_KEY, DEFAULT_ABORT_ON_ERROR)) {
       // server is configured to abort.
       abortServer(env, e);
     } else {
       // If available, pull a table name out of the environment
       if(env instanceof RegionCoprocessorEnvironment) {
         String tableName = ((RegionCoprocessorEnvironment)env).getRegionInfo().getTable().getNameAsString();
         LOG.error("Removing coprocessor '" + env.toString() + "' from table '"+ tableName + "'", e);
       } else {
         LOG.error("Removing coprocessor '" + env.toString() + "' from " +
                 "environment",e);
       }
 
       coprocessors.remove(env);
       try {
         shutdown(env);
       } catch (Exception x) {
         LOG.error("Uncaught exception when shutting down coprocessor '"
             + env.toString() + "'", x);
       }
       throw new DoNotRetryIOException("Coprocessor: '" + env.toString() +
           "' threw: '" + e + "' and has been removed from the active " +
           "coprocessor set.", e);
     }
   }
 
   /**
    * Used to gracefully handle fallback to deprecated methods when we
    * evolve coprocessor APIs.
    *
    * When a particular Coprocessor API is updated to change methods, hosts can support fallback
    * to the deprecated API by using this method to determine if an instance implements the new API.
    * In the event that said support is partial, then in the face of a runtime issue that prevents
    * proper operation {@link #legacyWarning(Class, String)} should be used to let operators know.
    *
    * For examples of this in action, see the implementation of
    * <ul>
    *   <li>{@link org.apache.hadoop.hbase.regionserver.RegionCoprocessorHost}
    *   <li>{@link org.apache.hadoop.hbase.regionserver.wal.WALCoprocessorHost}
    * </ul>
    *
    * @param clazz Coprocessor you wish to evaluate
    * @param methodName the name of the non-deprecated method version
    * @param parameterTypes the Class of the non-deprecated method's arguments in the order they are
    *     declared.
    */
   @InterfaceAudience.Private
   protected static boolean useLegacyMethod(final Class<? extends Coprocessor> clazz,
       final String methodName, final Class<?>... parameterTypes) {
     boolean useLegacy;
     // Use reflection to see if they implement the non-deprecated version
     try {
       clazz.getDeclaredMethod(methodName, parameterTypes);
       LOG.debug("Found an implementation of '" + methodName + "' that uses updated method " +
           "signature. Skipping legacy support for invocations in '" + clazz +"'.");
       useLegacy = false;
     } catch (NoSuchMethodException exception) {
       useLegacy = true;
     } catch (SecurityException exception) {
       LOG.warn("The Security Manager denied our attempt to detect if the coprocessor '" + clazz +
           "' requires legacy support; assuming it does. If you get later errors about legacy " +
           "coprocessor use, consider updating your security policy to allow access to the package" +
           " and declared members of your implementation.");
       LOG.debug("Details of Security Manager rejection.", exception);
       useLegacy = true;
     }
     return useLegacy;
   }
 
   /**
    * Used to limit legacy handling to once per Coprocessor class per classloader.
    */
   private static final Set<Class<? extends Coprocessor>> legacyWarning =
       new ConcurrentSkipListSet<Class<? extends Coprocessor>>(
           new Comparator<Class<? extends Coprocessor>>() {
             @Override
             public int compare(Class<? extends Coprocessor> c1, Class<? extends Coprocessor> c2) {
               if (c1.equals(c2)) {
                 return 0;
               }
               return c1.getName().compareTo(c2.getName());
             }
           });
 
   /**
    * limits the amount of logging to once per coprocessor class.
    * Used in concert with {@link #useLegacyMethod(Class, String, Class[])} when a runtime issue
    * prevents properly supporting the legacy version of a coprocessor API.
    * Since coprocessors can be in tight loops this serves to limit the amount of log spam we create.
    */
   @InterfaceAudience.Private
   protected void legacyWarning(final Class<? extends Coprocessor> clazz, final String message) {
     if(legacyWarning.add(clazz)) {
       LOG.error("You have a legacy coprocessor loaded and there are events we can't map to the " +
           " deprecated API. Your coprocessor will not see these events.  Please update '" + clazz +
           "'. Details of the problem: " + message);
     }
   }
 }