completion_queue.h

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#ifndef GRPCXX_IMPL_CODEGEN_COMPLETION_QUEUE_H
#define GRPCXX_IMPL_CODEGEN_COMPLETION_QUEUE_H

#include <grpc++/impl/codegen/completion_queue_tag.h>
#include <grpc++/impl/codegen/core_codegen_interface.h>
#include <grpc++/impl/codegen/grpc_library.h>
#include <grpc++/impl/codegen/status.h>
#include <grpc++/impl/codegen/time.h>
#include <grpc/impl/codegen/atm.h>

struct grpc_completion_queue;

namespace grpc {

template <class R>
class ClientReader;
template <class W>
class ClientWriter;
template <class W, class R>
class ClientReaderWriter;
template <class R>
class ServerReader;
template <class W>
class ServerWriter;
namespace internal {
template <class W, class R>
class ServerReaderWriterBody;
}
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 ChannelInterface;
class ClientContext;
class CompletionQueueTag;
class CompletionQueue;
class RpcMethod;
class Server;
class ServerBuilder;
class ServerContext;

extern CoreCodegenInterface* g_core_codegen_interface;

class CompletionQueue : private GrpcLibraryCodegen {
 public:
  CompletionQueue() {
    cq_ = g_core_codegen_interface->grpc_completion_queue_create(nullptr);
    InitialAvalanching();  // reserve this for the future shutdown
  }

  explicit CompletionQueue(grpc_completion_queue* take);

  ~CompletionQueue() {
    g_core_codegen_interface->grpc_completion_queue_destroy(cq_);
  }

  enum NextStatus {
    SHUTDOWN,   
    GOT_EVENT,  
    TIMEOUT     
  };

  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());
  }

  bool Next(void** tag, bool* ok) {
    return (AsyncNextInternal(tag, ok, g_core_codegen_interface->gpr_inf_future(
                                           GPR_CLOCK_REALTIME)) != SHUTDOWN);
  }

  void Shutdown();

  grpc_completion_queue* cq() { return cq_; }

  void InitialAvalanching() {
    gpr_atm_rel_store(&avalanches_in_flight_, static_cast<gpr_atm>(1));
  }
  void RegisterAvalanching() {
    gpr_atm_no_barrier_fetch_add(&avalanches_in_flight_,
                                 static_cast<gpr_atm>(1));
  };
  void CompleteAvalanching();

 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 W, class R>
  friend class ::grpc::ClientReaderWriter;
  template <class R>
  friend class ::grpc::ServerReader;
  template <class W>
  friend class ::grpc::ServerWriter;
  template <class W, class R>
  friend class ::grpc::internal::ServerReaderWriterBody;
  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 Streamer, bool WriteNeeded>
  friend class TemplatedBidiStreamingHandler;
  friend class UnknownMethodHandler;
  friend class ::grpc::Server;
  friend class ::grpc::ServerContext;
  template <class InputMessage, class OutputMessage>
  friend Status BlockingUnaryCall(ChannelInterface* channel,
                                  const RpcMethod& method,
                                  ClientContext* context,
                                  const InputMessage& request,
                                  OutputMessage* result);

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

  bool Pluck(CompletionQueueTag* tag) {
    auto deadline =
        g_core_codegen_interface->gpr_inf_future(GPR_CLOCK_REALTIME);
    auto ev = g_core_codegen_interface->grpc_completion_queue_pluck(
        cq_, tag, deadline, nullptr);
    bool ok = ev.success != 0;
    void* ignored = tag;
    GPR_CODEGEN_ASSERT(tag->FinalizeResult(&ignored, &ok));
    GPR_CODEGEN_ASSERT(ignored == tag);
    // Ignore mutations by FinalizeResult: Pluck returns the C API status
    return ev.success != 0;
  }

  void TryPluck(CompletionQueueTag* tag) {
    auto deadline = g_core_codegen_interface->gpr_time_0(GPR_CLOCK_REALTIME);
    auto ev = g_core_codegen_interface->grpc_completion_queue_pluck(
        cq_, tag, deadline, nullptr);
    if (ev.type == GRPC_QUEUE_TIMEOUT) return;
    bool ok = ev.success != 0;
    void* ignored = tag;
    // the tag must be swallowed if using TryPluck
    GPR_CODEGEN_ASSERT(!tag->FinalizeResult(&ignored, &ok));
  }

  grpc_completion_queue* cq_;  // owned

  gpr_atm avalanches_in_flight_;
};

class ServerCompletionQueue : public CompletionQueue {
 public:
  bool IsFrequentlyPolled() { return is_frequently_polled_; }

 private:
  bool is_frequently_polled_;
  friend class ServerBuilder;
  ServerCompletionQueue(bool is_frequently_polled = true)
      : is_frequently_polled_(is_frequently_polled) {}
};

}  // namespace grpc

#endif  // GRPCXX_IMPL_CODEGEN_COMPLETION_QUEUE_H