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JDBC Driver for Google Cloud Spanner
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/*
 * Copyright 2016, Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *    * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *    * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *
 *    * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package nl.topicus.jdbc.shaded.io.grpc;

import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * A {@link ThreadLocal}-based context storage implementation.  Used by default.
 */
final class ThreadLocalContextStorage extends Context.Storage {
  private static final Logger log = Logger.getLogger(ThreadLocalContextStorage.class.getName());

  /**
   * Currently bound context.
   */
  private static final ThreadLocal localContext = new ThreadLocal();

  @Override
  public void attach(Context toAttach) {
    localContext.set(toAttach);
  }

  @Override
  public void detach(Context toDetach, Context toRestore) {
    if (current() != toDetach) {
      // Log a severe message instead of throwing an exception as the context to attach is assumed
      // to be the correct one and the unbalanced state represents a coding mistake in a lower
      // layer in the stack that cannot be recovered from here.
      log.log(Level.SEVERE, "Context was not attached when detaching",
          new Throwable().fillInStackTrace());
    }
    attach(toRestore);
  }

  @Override
  public Context current() {
    return localContext.get();
  }
}