grpc/include/grpc++/completion_queue.h

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#ifndef GRPCXX_COMPLETION_QUEUE_H
#define GRPCXX_COMPLETION_QUEUE_H

#include <grpc++/impl/client_unary_call.h>

struct grpc_completion_queue;

namespace grpc {

template <class R>
class ClientReader;
template <class W>
class ClientWriter;
template <class R, class W>
class ClientReaderWriter;
template <class R>
class ServerReader;
template <class W>
class ServerWriter;
template <class R, class W>
class ServerReaderWriter;

class CompletionQueue;
class Server;
class ServerContext;

class CompletionQueueTag {
 public:
  virtual ~CompletionQueueTag() {}
  // Called prior to returning from Next(), return value
  // is the status of the operation (return status is the default thing
  // to do)
  // If this function returns false, the tag is dropped and not returned
  // from the completion queue
  virtual bool FinalizeResult(void **tag, bool *status) = 0;
};

// grpc_completion_queue wrapper class
class CompletionQueue {
 public:
  CompletionQueue();
  explicit CompletionQueue(grpc_completion_queue *take);
  ~CompletionQueue();

  // Blocking read from queue.
  // Returns true if an event was received, false if the queue is ready
  // for destruction.
  bool Next(void **tag, bool *ok);

  // Shutdown has to be called, and the CompletionQueue can only be
  // destructed when false is returned from Next().
  void Shutdown();

  grpc_completion_queue *cq() { return cq_; }

 private:
  // Friend synchronous wrappers so that they can access Pluck(), which is
  // a semi-private API geared towards the synchronous implementation.
  template <class R>
  friend class ::grpc::ClientReader;
  template <class W>
  friend class ::grpc::ClientWriter;
  template <class R, class W>
  friend class ::grpc::ClientReaderWriter;
  template <class R>
  friend class ::grpc::ServerReader;
  template <class W>
  friend class ::grpc::ServerWriter;
  template <class R, class W>
  friend class ::grpc::ServerReaderWriter;
  friend class ::grpc::Server;
  friend class ::grpc::ServerContext;
  friend Status BlockingUnaryCall(ChannelInterface *channel,
                                  const RpcMethod &method,
                                  ClientContext *context,
                                  const google::protobuf::Message &request,
                                  google::protobuf::Message *result);

  // Wraps grpc_completion_queue_pluck.
  // Cannot be mixed with calls to Next().
  bool Pluck(CompletionQueueTag *tag);

  // Does a single polling pluck on tag
  void TryPluck(CompletionQueueTag *tag);

  grpc_completion_queue *cq_;  // owned
};

}  // namespace grpc

#endif  // GRPCXX_COMPLETION_QUEUE_H