https://developers.google.com/protocol-buffers/protobuf-java/: Core Protocol Buffers library. Protocol Buffers are a way of encoding structured data in an efficient yet extensible format. 
// Protocol Buffers - Google's data interchange format
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package com.google.protobuf;


Blocking equivalent to Service. 
Author:kenton@google.com Kenton Varda, cpovirk@google.com Chris Povirk
/**
 * Blocking equivalent to {@link Service}.
 *
 * @author kenton@google.com Kenton Varda
 * @author cpovirk@google.com Chris Povirk
 */
public interface BlockingService {
  /** Equivalent to {@link Service#getDescriptorForType}. */
  Descriptors.ServiceDescriptor getDescriptorForType();

  
Equivalent to Service.callMethod, except that callBlockingMethod() returns the result of the RPC or throws a ServiceException if there is a failure, rather than passing the information to a callback. 
/**
   * Equivalent to {@link Service#callMethod}, except that {@code callBlockingMethod()} returns the
   * result of the RPC or throws a {@link ServiceException} if there is a failure, rather than
   * passing the information to a callback.
   */
  Message callBlockingMethod(
      Descriptors.MethodDescriptor method, RpcController controller, Message request)
      throws ServiceException;

  /** Equivalent to {@link Service#getRequestPrototype}. */
  Message getRequestPrototype(Descriptors.MethodDescriptor method);

  /** Equivalent to {@link Service#getResponsePrototype}. */
  Message getResponsePrototype(Descriptors.MethodDescriptor method);
}