content: /*
   * Copyright 1999-2017 Alibaba Group Holding Ltd.
   *
   * 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 com.alibaba.druid.sql.parser;
  
  import com.alibaba.druid.sql.ast.SQLExpr;
  import com.alibaba.druid.util.FnvHash;
  
  import java.util.List;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  
  public class InsertColumnsCache {
      public static InsertColumnsCache global;
  
      static {
          global = new InsertColumnsCache(8192);
      }
  
      public ConcurrentMap<Long, Entry> cache = new ConcurrentHashMap<Long, Entry>();
  
      private final Entry[] buckets;
      private final int indexMask;
  
      public InsertColumnsCache(int tableSize) {
          this.indexMask = tableSize - 1;
          this.buckets = new Entry[tableSize];
      }
  
      public final Entry get(long hashCode64) {
          final int bucket = ((int) hashCode64) & indexMask;
          for (Entry entry = buckets[bucket]; entry != null; entry = entry.next) {
              if (hashCode64 == entry.hashCode64) {
                  return entry;
              }
          }
  
          return null;
      }
  
      public boolean put(long hashCode64, String columnsString, String columnsFormattedString, List<SQLExpr> columns) {
          final int bucket = ((int) hashCode64) & indexMask;
  
          for (Entry entry = buckets[bucket]; entry != null; entry = entry.next) {
              if (hashCode64 == entry.hashCode64) {
                  return true;
              }
          }
  
          Entry entry = new Entry(hashCode64, columnsString, columnsFormattedString, columns, buckets[bucket]);
          buckets[bucket] = entry;  // 并发是处理时会可能导致缓存丢失，但不影响正确性
  
          return false;
      }
  
      public static final class Entry {
          public final long hashCode64;
          public final String columnsString;
          public final String columnsFormattedString;
          public final long columnsFormattedStringHash;
          public final List<SQLExpr> columns;
          public final Entry next;
  
          public Entry(long hashCode64,
                       String columnsString,
                       String columnsFormattedString,
                       List<SQLExpr> columns,
                       Entry next) {
              this.hashCode64 = hashCode64;
              this.columnsString = columnsString;
              this.columnsFormattedString = columnsFormattedString;
              this.columnsFormattedStringHash = FnvHash.fnv1a_64_lower(columnsFormattedString);
              this.columns = columns;
              this.next = next;
          }
      }
  }
  