context/src/main/java/io/grpc/ThreadLocalContextStorage.java

/*
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 *
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 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
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 *
 * 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
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 */

package 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<Context> localContext = new ThreadLocal<Context>();

  @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();
  }
}