Question

我试图了解grpc c ++异步模型流程。本文（link）已经解释了我的许多疑问。这是grpc_asycn_server的代码。为了了解CompletionQueue何时获取请求，我添加了一些打印语句，如下所示：

首先在HandleRpcs（）函数内部。

void HandleRpcs() {
    // Spawn a new CallData instance to serve new clients.
    new CallData(&service_, cq_.get());
    void* tag;  // uniquely identifies a request.
    bool ok;
    int i = 0;
    while (true) {
      std::cout << i << std::endl; ///////////////////////////////
      // Block waiting to read the next event from the completion queue. The
      // event is uniquely identified by its tag, which in this case is the
      // memory address of a CallData instance.
      // The return value of Next should always be checked. This return value
      // tells us whether there is any kind of event or cq_ is shutting down.
      GPR_ASSERT(cq_->Next(&tag, &ok));
      GPR_ASSERT(ok);
      static_cast<CallData*>(tag)->Proceed();
      i++;
    }
  }

以及proceed（）函数内部：

void Proceed() {
  if (status_ == CREATE) {
    // Make this instance progress to the PROCESS state.
    status_ = PROCESS;

    // As part of the initial CREATE state, we *request* that the system
    // start processing SayHello requests. In this request, "this" acts are
    // the tag uniquely identifying the request (so that different CallData
    // instances can serve different requests concurrently), in this case
    // the memory address of this CallData instance.
    std::cout<<"RequestSayHello called"<<std::endl; ////////////////////////////
    service_->RequestSayHello(&ctx_, &request_, &responder_, cq_, cq_,
                              this);
  } else if (status_ == PROCESS) {
    // Spawn a new CallData instance to serve new clients while we process
    // the one for this CallData. The instance will deallocate itself as
    // part of its FINISH state.
    new CallData(service_, cq_);

    // The actual processing.
    std::string prefix("Hello ");
    reply_.set_message(prefix + request_.name());

    // And we are done! Let the gRPC runtime know we've finished, using the
    // memory address of this instance as the uniquely identifying tag for
    // the event.
    status_ = FINISH;
    responder_.Finish(reply_, Status::OK, this);
  } else {
    std::cout<<"deallocated"<<std::endl; ////////////////////////////
    GPR_ASSERT(status_ == FINISH);
    // Once in the FINISH state, deallocate ourselves (CallData).
    delete this;
  }
}

一旦我运行服务器和一个客户端（client），服务器就会打印以下内容：

RequestSayHello called
i = 0
RequestSayHello called
i = 1
deallocated
i = 2

第二个RequestSayHello called之所以有意义，是因为创建了新的CallData实例。 我的问题是第二次执行proceed()函数并打印deallocated的结果吗？

Answer 1

完成队列（cq_）结构处理几种类型的事件，包括请求和响应事件。对proceed()的第一次调用进入了PROCESS对象的状态机的CallData阶段。

在此阶段：
1.创建一个新的CallData对象；正如您提到的，这会将请求事件插入cq_中
2. responder_与回复对象一起调用；这会将响应事件插入cq_

在收到来自cq_的响应事件后，在第一个proceed()对象（现在处于CallData状态）上再次调用FINISH，因此执行清理并打印出deallocated。

grpc c ++异步完成队列事件

1 个答案: