code: /*
   * Copyright 2012-2018 Chronicle Map Contributors
   *
   * Licensed 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 net.openhft.chronicle.hash.impl;
  
  import net.openhft.chronicle.core.Jvm;
  import net.openhft.chronicle.core.shutdown.PriorityHook;
  
  import java.util.TreeMap;
  import java.util.WeakHashMap;
  
  final class ChronicleHashCloseOnExitHook {
  
      private static WeakHashMap<VanillaChronicleHash<?, ?, ?, ?>.Identity, Long> maps = new WeakHashMap<>();
      private static long order = 0;
  
      static {
          PriorityHook.add(80, ChronicleHashCloseOnExitHook::closeAll);
      }
  
      private ChronicleHashCloseOnExitHook() {
      }
  
      static synchronized void add(VanillaChronicleHash<?, ?, ?, ?> hash) {
          if (maps == null)
              throw new IllegalStateException("Shutdown in progress");
          maps.put(hash.identity, order++);
      }
  
      static synchronized void remove(VanillaChronicleHash<?, ?, ?, ?> hash) {
          if (maps == null)
              return; // we are already in shutdown
          maps.remove(hash.identity);
      }
  
      private static void closeAll() {
          try {
              WeakHashMap<VanillaChronicleHash<?, ?, ?, ?>.Identity, Long> maps;
              synchronized (ChronicleHashCloseOnExitHook.class) {
                  maps = ChronicleHashCloseOnExitHook.maps;
                  ChronicleHashCloseOnExitHook.maps = null;
              }
  
              TreeMap<Long, VanillaChronicleHash<?, ?, ?, ?>> orderedMaps = new TreeMap<>();
              maps.forEach((identity, order) -> orderedMaps.put(order, identity.hash()));
              // close later added maps first
              orderedMaps.descendingMap().values().forEach(h -> {
                  try {
                      Runnable preShutdownAction = h.getPreShutdownAction();
                      if (preShutdownAction != null) {
                          try {
                              preShutdownAction.run();
                          } catch (Throwable throwable) {
                              try {
                                  Jvm.error().on(ChronicleHashCloseOnExitHook.class,
                                          "Error running pre-shutdown action for " + h.toIdentityString() +
                                          " :", throwable);
                              } catch (Throwable t2) {
                                  throwable.addSuppressed(t2);
                                  throwable.printStackTrace();
                              }
                          }
                      }
                      h.close();
                  } catch (Throwable throwable) {
                      try {
                          Jvm.error().on(ChronicleHashCloseOnExitHook.class,
                                  "Error while closing " + h.toIdentityString() +
                                  " during shutdown hook:", throwable);
                      } catch (Throwable t2) {
                          // This may occur if the log service has already been shut down. Try to fall
                          // back to printStackTrace().
                          throwable.addSuppressed(t2);
                          throwable.printStackTrace();
                      }
                  }
              });
          } catch (Throwable throwable) {
              try {
                  Jvm.error().on(ChronicleHashCloseOnExitHook.class,
                          "Error while closing maps during shutdown hook:", throwable);
              } catch (Throwable t2) {
                  throwable.addSuppressed(t2);
                  throwable.printStackTrace();
              }
          }
      }
  }
  