我使用此示例的代码来创建我的 GRPC 异步服务器：
#include <memory>
#include <iostream>
#include <string>
#include <thread>
#include <grpcpp/grpcpp.h>
#include <grpc/support/log.h>
#ifdef BAZEL_BUILD
#include "examples/protos/helloworld.grpc.pb.h"
#else
#include "helloworld.grpc.pb.h"
#endif
using grpc::Server;
using grpc::ServerAsyncResponseWriter;
using grpc::ServerBuilder;
using grpc::ServerContext;
using grpc::ServerCompletionQueue;
using grpc::Status;
using helloworld::HelloRequest;
using helloworld::HelloReply;
using helloworld::Greeter;
class ServerImpl final {
public:
~ServerImpl() {
server_->Shutdown();
// Always shutdown the completion queue after the server.
cq_->Shutdown();
}
// There is no shutdown handling in this code.
void Run() {
std::string server_address("0.0.0.0:50051");
ServerBuilder builder;
// Listen on the given address without any authentication mechanism.
builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
// Register "service_" as the instance through which we'll communicate with
// clients. In this case it corresponds to an *asynchronous* service.
//LINES ADDED BY ME TO IMPLEMENT KEEPALIVE
builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
builder.AddChannelArgument(GRPC_ARG_KEEPALIVE_TIME_MS, 2000);
builder.AddChannelArgument(GRPC_ARG_KEEPALIVE_TIMEOUT_MS, 3000);
builder.AddChannelArgument(GRPC_ARG_KEEPALIVE_PERMIT_WITHOUT_CALLS, 1);
//END OF LINES ADDED BY ME
builder.RegisterService(&service_);
// Get hold of the completion queue used for the asynchronous communication
// with the gRPC runtime.
cq_ = builder.AddCompletionQueue();
// Finally assemble the server.
server_ = builder.BuildAndStart();
std::cout << "Server listening on " << server_address << std::endl;
// Proceed to the server's main loop.
HandleRpcs();
}
private:
// Class encompasing the state and logic needed to serve a request.
class CallData {
public:
// Take in the "service" instance (in this case representing an asynchronous
// server) and the completion queue "cq" used for asynchronous communication
// with the gRPC runtime.
CallData(Greeter::AsyncService* service, ServerCompletionQueue* cq)
: service_(service), cq_(cq), responder_(&ctx_), status_(CREATE) {
// Invoke the serving logic right away.
Proceed();
}
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.
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 {
GPR_ASSERT(status_ == FINISH);
// Once in the FINISH state, deallocate ourselves (CallData).
delete this;
}
}
private:
// The means of communication with the gRPC runtime for an asynchronous
// server.
Greeter::AsyncService* service_;
// The producer-consumer queue where for asynchronous server notifications.
ServerCompletionQueue* cq_;
// Context for the rpc, allowing to tweak aspects of it such as the use
// of compression, authentication, as well as to send metadata back to the
// client.
ServerContext ctx_;
// What we get from the client.
HelloRequest request_;
// What we send back to the client.
HelloReply reply_;
// The means to get back to the client.
ServerAsyncResponseWriter<HelloReply> responder_;
// Let's implement a tiny state machine with the following states.
enum CallStatus { CREATE, PROCESS, FINISH };
CallStatus status_; // The current serving state.
};
// This can be run in multiple threads if needed.
void HandleRpcs() {
// Spawn a new CallData instance to serve new clients.
new CallData(&service_, cq_.get());
void* tag; // uniquely identifies a request.
bool ok;
while (true) {
// 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();
}
}
std::unique_ptr<ServerCompletionQueue> cq_;
Greeter::AsyncService service_;
std::unique_ptr<Server> server_;
};
int main(int argc, char** argv) {
ServerImpl server;
server.Run();
return 0;
}
因为我做了一项研究，发现我必须实现 KeepAlive ( https://grpc.github.io/grpc/cpp/md_doc_keepalive.html )，我添加了这些行：
builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
builder.AddChannelArgument(GRPC_ARG_KEEPALIVE_TIME_MS, 2000);
builder.AddChannelArgument(GRPC_ARG_KEEPALIVE_TIMEOUT_MS, 3000);
builder.AddChannelArgument(GRPC_ARG_KEEPALIVE_PERMIT_WITHOUT_CALLS, 1);
到目前为止一切顺利，服务器工作并且通信流畅。但是我如何检测客户端已断开连接？我添加的行使所谓的KeepAlive方法似乎对我不起作用。
我的错误在哪里？当客户端因任何原因断开连接时，如何在异步服务器上检测到？
小智 8
让我先介绍一些背景信息。
关于 gRPC 需要了解的一件重要事情是，它使用 HTTP/2 在单个 TCP 连接上复用许多流。每个 gRPC 调用都是一个单独的流，无论调用是一元的还是流式的。一般来说，任何 gRPC 调用都可以有零个或多个从双方发送的消息；一元调用只是一种特殊情况，它只有一条从客户端到服务器的消息，后面紧接着一条从服务器到客户端的消息。
我们通常使用“断开连接”一词来指 TCP 连接断开，而不是单个流终止，尽管有时人们以相反的含义使用该词。我不确定你指的是哪一个，所以我会回答两个。
gRPC API 向应用程序公开流生命周期，但不公开 TCP 连接生命周期。目的是该库处理管理 TCP 连接的所有细节并向应用程序隐藏它们——我们实际上并没有公开一种方法来判断连接何时断开，并且您不需要关心，因为图书馆将自动为您重新连接。:) 应用程序可见的唯一情况是，如果单个 TCP 连接失败时已有流正在运行，那么这些流将失败。
正如我所说，该库确实向应用程序公开了各个流的生命周期；流的生命周期基本上就是CallData上面代码中对象的生命周期。有两种方法可以确定流是否已终止。一种是显式调用ServerContext::IsCancelled(). 另一种是在 CQ 上请求事件，通过 异步通知应用程序取消ServerContext::AsyncNotifyWhenDone()。
请注意，一般来说，像上面的 HelloWorld 这样的一元示例实际上并不需要担心检测流取消，因为从服务器的角度来看，整个流实际上不会持续很长时间。它通常在流式调用的情况下更有用。但也有一些例外，例如，如果您有一个一元调用，在发送响应之前必须执行大量昂贵的异步工作。
我希望这些信息有帮助。