grpc/include/grpc++/completion_queue.h

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/// A completion queue implements a concurrent producer-consumer queue, with two
/// main methods, \a Next and \a AsyncNext.
#ifndef GRPCXX_COMPLETION_QUEUE_H
#define GRPCXX_COMPLETION_QUEUE_H

#include <grpc/support/time.h>
#include <grpc++/impl/grpc_library.h>
#include <grpc++/support/status.h>
#include <grpc++/support/time.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;
template <class ServiceType, class RequestType, class ResponseType>
class RpcMethodHandler;
template <class ServiceType, class RequestType, class ResponseType>
class ClientStreamingHandler;
template <class ServiceType, class RequestType, class ResponseType>
class ServerStreamingHandler;
template <class ServiceType, class RequestType, class ResponseType>
class BidiStreamingHandler;
class UnknownMethodHandler;

class Channel;
class ClientContext;
class CompletionQueueTag;
class CompletionQueue;
class RpcMethod;
class Server;
class ServerBuilder;
class ServerContext;

/// A thin wrapper around \a grpc_completion_queue (see / \a
/// src/core/surface/completion_queue.h).
class CompletionQueue : public GrpcLibrary {
 public:
  /// Default constructor. Implicitly creates a \a grpc_completion_queue
  /// instance.
  CompletionQueue();

  /// Wrap \a take, taking ownership of the instance.
  ///
  /// \param take The completion queue instance to wrap. Ownership is taken.
  explicit CompletionQueue(grpc_completion_queue* take);

  /// Destructor. Destroys the owned wrapped completion queue / instance.
  ~CompletionQueue() GRPC_OVERRIDE;

  /// Tri-state return for AsyncNext: SHUTDOWN, GOT_EVENT, TIMEOUT.
  enum NextStatus {
    SHUTDOWN,   ///< The completion queue has been shutdown.
    GOT_EVENT,  ///< Got a new event; \a tag will be filled in with its
                ///< associated value; \a ok indicating its success.
    TIMEOUT     ///< deadline was reached.
  };

  /// Read from the queue, blocking up to \a deadline (or the queue's shutdown).
  /// Both \a tag and \a ok are updated upon success (if an event is available
  /// within the \a deadline).  A \a tag points to an arbitrary location usually
  /// employed to uniquely identify an event.
  ///
  /// \param tag[out] Upon sucess, updated to point to the event's tag.
  /// \param ok[out] Upon sucess, true if read a regular event, false otherwise.
  /// \param deadline[in] How long to block in wait for an event.
  ///
  /// \return The type of event read.
  template <typename T>
  NextStatus AsyncNext(void** tag, bool* ok, const T& deadline) {
    TimePoint<T> deadline_tp(deadline);
    return AsyncNextInternal(tag, ok, deadline_tp.raw_time());
  }

  /// Read from the queue, blocking until an event is available or the queue is
  /// shutting down.
  ///
  /// \param tag[out] Updated to point to the read event's tag.
  /// \param ok[out] true if read a regular event, false otherwise.
  ///
  /// \return true if read a regular event, false if the queue is shutting down.
  bool Next(void** tag, bool* ok) {
    return (AsyncNextInternal(tag, ok, gpr_inf_future(GPR_CLOCK_REALTIME)) !=
            SHUTDOWN);
  }

  /// Request the shutdown of the queue.
  ///
  /// \warning This method must be called at some point. Once invoked, \a Next
  /// will start to return false and \a AsyncNext will return \a
  /// NextStatus::SHUTDOWN. Only once either one of these methods does that
  /// (that is, once the queue has been \em drained) can an instance of this
  /// class be destroyed.
  void Shutdown();

  /// Returns a \em raw pointer to the underlying \a grpc_completion_queue
  /// instance.
  ///
  /// \warning Remember that the returned instance is owned. No transfer of
  /// owership is performed.
  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;
  template <class ServiceType, class RequestType, class ResponseType>
  friend class RpcMethodHandler;
  template <class ServiceType, class RequestType, class ResponseType>
  friend class ClientStreamingHandler;
  template <class ServiceType, class RequestType, class ResponseType>
  friend class ServerStreamingHandler;
  template <class ServiceType, class RequestType, class ResponseType>
  friend class BidiStreamingHandler;
  friend class UnknownMethodHandler;
  friend class ::grpc::Server;
  friend class ::grpc::ServerContext;
  template <class InputMessage, class OutputMessage>
  friend Status BlockingUnaryCall(Channel* channel, const RpcMethod& method,
                                  ClientContext* context,
                                  const InputMessage& request,
                                  OutputMessage* result);

  NextStatus AsyncNextInternal(void** tag, bool* ok, gpr_timespec deadline);

  /// Wraps \a grpc_completion_queue_pluck.
  /// \warning Must not be mixed with calls to \a Next.
  bool Pluck(CompletionQueueTag* tag);

  /// Performs a single polling pluck on \a tag.
  void TryPluck(CompletionQueueTag* tag);

  grpc_completion_queue* cq_;  // owned
};

/// An interface allowing implementors to process and filter event tags.
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;
};

/// A specific type of completion queue used by the processing of notifications
/// by servers. Instantiated by \a ServerBuilder.
class ServerCompletionQueue : public CompletionQueue {
 private:
  friend class ServerBuilder;
  ServerCompletionQueue() {}
};

}  // namespace grpc

#endif  // GRPCXX_COMPLETION_QUEUE_H