content: /*
   * 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.cassandra.concurrent;
  
  import io.netty.util.concurrent.FastThreadLocal;
  import org.apache.cassandra.service.ClientWarn;
  import org.apache.cassandra.tracing.TraceState;
  import org.apache.cassandra.utils.Closeable;
  import org.apache.cassandra.utils.WithResources;
  
  /*
   * This class only knows about Tracing and ClientWarn, so if any different executor locals are added, it must be
   * updated.
   *
   * We don't enumerate the ExecutorLocal.all array each time because it would be much slower.
   */
  public class ExecutorLocals implements WithResources, Closeable
  {
      private static final ExecutorLocals none = new ExecutorLocals(null, null);
      private static final FastThreadLocal<ExecutorLocals> locals = new FastThreadLocal<ExecutorLocals>()
      {
          @Override
          protected ExecutorLocals initialValue()
          {
              return none;
          }
      };
  
      public static class Impl
      {
          protected static void set(TraceState traceState, ClientWarn.State clientWarnState)
          {
              if (traceState == null && clientWarnState == null) locals.set(none);
              else locals.set(new ExecutorLocals(traceState, clientWarnState));
          }
      }
  
      public final TraceState traceState;
      public final ClientWarn.State clientWarnState;
  
      protected ExecutorLocals(TraceState traceState, ClientWarn.State clientWarnState)
      {
          this.traceState = traceState;
          this.clientWarnState = clientWarnState;
      }
  
      /**
       * @return an ExecutorLocals object which has the current trace state and client warn state.
       */
      public static ExecutorLocals current()
      {
          return locals.get();
      }
  
      /**
       * The {@link #current}Locals, if any; otherwise {@link WithResources#none()}.
       * Used to propagate current to other executors as a {@link WithResources}.
       */
      public static WithResources propagate()
      {
          ExecutorLocals locals = current();
          return locals == none ? WithResources.none() : locals;
      }
  
      public static ExecutorLocals create(TraceState traceState)
      {
          ExecutorLocals current = locals.get();
          return current.traceState == traceState ? current : new ExecutorLocals(traceState, current.clientWarnState);
      }
  
      public static void clear()
      {
          locals.set(none);
      }
  
      /**
       * Overwrite current locals, and return the previous ones
       */
      public ExecutorLocals get()
      {
          // TODO (desired): add compareAndSet to save one thread local round trip
          ExecutorLocals old = current();
          if (old != this)
              locals.set(this);
          return old;
      }
  
      public void close()
      {
          locals.set(this);
      }
  }
  