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. 
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package com.google.protobuf;


Abstract interface for a blocking RPC channel. BlockingRpcChannel is the blocking equivalent to RpcChannel. 
Author:kenton@google.com Kenton Varda, cpovirk@google.com Chris Povirk
/**
 * Abstract interface for a blocking RPC channel. {@code BlockingRpcChannel} is the blocking
 * equivalent to {@link RpcChannel}.
 *
 * @author kenton@google.com Kenton Varda
 * @author cpovirk@google.com Chris Povirk
 */
public interface BlockingRpcChannel {
  
Call the given method of the remote service and blocks until it returns. 
callBlockingMethod() is the blocking equivalent to RpcChannel.callMethod. 
/**
   * Call the given method of the remote service and blocks until it returns. {@code
   * callBlockingMethod()} is the blocking equivalent to {@link RpcChannel#callMethod}.
   */
  Message callBlockingMethod(
      Descriptors.MethodDescriptor method,
      RpcController controller,
      Message request,
      Message responsePrototype)
      throws ServiceException;
}