I have a method startServer() which starts a simple cpp grpc server.
I want to make server->Wait() call non-blocking, without handling any extra overheads of maintaining the completion queue or handling RPC calls.
I dug around the async flavour of grpc server but did not find any simple example to do this without adding any extra overheads. Is there any easy/simple way to make this function non-blocking apart from running this on a separate thread?
void GrpcIface::startServer() {
std::string address("0.0.0.0:5000");
GrpcIface service;
grpc::ServerBuilder builder;
builder.AddListeningPort(address, grpc::InsecureServerCredentials());
builder.RegisterService(&service);
std::unique_ptr<grpc::Server> server(builder.BuildAndStart());
std::cout << "GrpcIface :: Server listening on port: " << address << std::endl;
server->Wait();
}
Correct me if I'm wrong, but I dont think Wait() is mandatory. It at least does not look like it in the source code. Or what do you mean by
without handling any extra overheads of maintaining the completion queue or handling RPC calls.
?
The easiest way to do this is to spawn a new thread for the Wait;
std::unique_ptr<std::thread> worker(new std::thread([&]
{
server->Wait();
}));
When you want to exit, use this:
server->Shutdown();
if (worker->joinable())
{
worker->join();
}
Related
example websocket :
std::thread{ wsserver }.detach();
void()
{
boost::asio::ip::tcp::socket socket{ ioc };
acceptor.accept(socket);
}
The thread process is running separately from the server.
I think this may lead to erroneous results in some interlinked operations.
so I want to put this process into an infinite loop.
In short, I should not use multi-threads.
I want.
example:
while(loop());
int loop()
{
boost::asio::ip::tcp::socket socket{ ioc };
acceptor.accept(socket);
return 1;
}
but not work idle loop.
because "acceptor.accept" is all time waiting connect.
How to use a different command instead of the "accept" command.
How I can also get rid of your thread command.
Can I do this with smart data?
I hope I can explained.
I'm using gRPC for inter-process communication between C++ App (gRPC Server) and Java App (gRPC Client). Everything run on one machine. I want to provide client possibility to shut down the server. My idea is to add RPC function to service in proto which would do it.
The C++ Implementation would be:
class Service : public grpcGeneratedService
{
public:
......
private:
grpc::Server* m_pServer;
};
grpc::Status Service::ShutDown(grpc::ServerContext* pContext, const ShutDownRequest* pRequest, ShutDownResponse* pResponse)
{
if (m_pServer)
m_pServer->Shutdown();
return grpc::Status(grpc::StatusCode::OK, "");
}
However the ShutDown blocks until all RPC calls are processed what means dead-lock. Is there any elegant way how to implement it?
I'm using a std::promise with a method almost exactly like yours.
// Somewhere in the global scope :/
std::promise<void> exit_requested;
// My method looks nearly identical to yours
Status CoreServiceImpl::shutdown(ServerContext *context, const SystemRequest *request, Empty*)
{
LOG(INFO) << context->peer() << " - Shutdown request acknowledged.";
exit_requested.set_value();
return Status::OK;
}
In order to make this work, I call server->Wait() in a second thread and wait on the future for the exit_requested promise to block a shutdown call:
auto serveFn = [&]() {
server->Wait();
};
std::thread serving_thread(serveFn);
auto f = exit_requested.get_future();
f.wait();
server->Shutdown();
serving_thread.join();
Once I had this I was also able to support a clean shutdown via signal handlers as well:
auto handler = [](int s) {
exit_requested.set_value();
};
std::signal(SIGINT, handler);
std::signal(SIGTERM, handler);
std::signal(SIGQUIT, handler);
I've been satisfied with this approach so far and it's kept me within the bounds of gRPC and the standard c++ libs. Rather than use some globally scoped promise (I have to declare it as an external in my service implementation source) I should probably think of something more elegant.
One thing to note here is that setting the value of the promise more than once will throw an exception. This could happen if you somehow send the shutdown message and also pkill -2 my_awesome_service at the same time. I actually ran into this when there was a deadlock in my persistence layer preventing shutdown from finishing, when I tried to send a SIGINT again the service aborted instead! For my needs this is still an acceptable solution but I'd love to hear about alternatives that work around or solve that little problem.
You can create an std::function from the ShutDown() handler and run that function in a separate thread (or threadpool). This will allow decoupling the handling of the RPC from the execution of the shutdown logic and eliminate the deadlock.
Referring to HTTP Server- Single threaded Implementation
I am trying to Explicitly control Lifetime of server instance
My Requirements are:
1) I should be able to explicitly destroy the server
2) I need to keep multiple Server Instances alive which should listen to different ports
3) Manager Class maintains list of all active server instances; should be able to create and destroy the server instances by create and drop methods
I am trying to implement Requirement 1 and
I have come up with code:
void server::stop()
{
DEBUG_MSG("Stopped");
io_service_.post(boost::bind(&server::handle_stop, this));
}
where handle_stop() is
void server::handle_stop()
{
// The server is stopped by cancelling all outstanding asynchronous
// operations. Once all operations have finished the io_service::run() call
// will exit.
acceptor_.close();
connection_manager_.stop_all();
}
I try to call it from main() as:
try
{
http::server::server s("127.0.0.1","8973");
// Run the server until stopped.
s.run();
boost::this_thread::sleep_for(boost::chrono::seconds(3));
s.stop();
}
catch (std::exception& e)
{
std::cerr << "exception: " << e.what() << "\n";
}
Question 1)
I am not able to call server::handle_stop().
I suppose io_service_.run() is blocking my s.stop() call.
void server::run()
{
// The io_service::run() call will block until all asynchronous operations
// have finished. While the server is running, there is always at least one
// asynchronous operation outstanding: the asynchronous accept call waiting
// for new incoming connections.
io_service_.run();
}
How do I proceed?
Question 2:
For requirement 2) where I need to have multiple server instances, i think I will need to create an io_service instance in main and must pass the same instance to all server instances. Am I right?
Is it mandatory to have only one io_service instance per process or can I have more than one ?
EDIT
My aim is to implement a class which can control multi server instances:
Something of below sort (Incorrect code // Just giving view, what I try to implement ) I want to achieve-
How do i design?
I have confusion regarding io_Service and how do I cleanly call mng.create(), mng.drop()
Class Manager{
public:
void createServer(ServerPtr)
{
list_.insert(make_shared<Server> (ip, port));
}
void drop()
{
list_.drop((ServerPtr));
}
private:
io_service iO_;
set<server> list_;
};
main()
{
io_service io;
Manager mng(io);
mng.createServer(ip1,port1);
mng.createServer(ip2,port2);
io.run();
mng.drop(ip1,port1);
}
I am not able to call server::handle_stop().
As you say, run() won't return until the service is stopped or runs out of work. There's no point calling stop() after that.
In a single-threaded program, you can call stop() from an I/O handler - for your example, you could use a deadline_timer to call it after three seconds. Or you could do something complicated with poll() rather than run(), but I wouldn't recommend that.
In a multi-threaded program, you could call it from another thread than the one calling run(), as long as you make sure it's thread-safe.
For [multiple servers] I think I will need to create an io_service instance in main
Yes, that's probably the best thing to do.
Is it mandatory to have only one io_service instance per process or can I have more than one?
You can have as many as you like. But I think you can only run one at a time on a single thread, so it would be tricky to have more than one in a single-threaded program. I'd have a single instance that all the servers can use.
You are right, it's not working because you call stop after blocking run, and run blocks until there are some unhandled callbacks. There are multiple ways to solve this and it depands from what part of program stop will be called:
If you can call it from another thread, then run each instance of server in separate thread.
If you need to stop server after some IO operation for example you can simply do as you have tried io_service_.post(boost::bind(&server::handle_stop, this));, but it should be registered from another thread or from another callback in current thread.
You can use io_service::poll(). It is non-blocking version of run, so you create a loop where you call poll until you need to stop server.
You can do it both ways. Even with the link you provided you can take a look at:
HTTP Server 3 - An HTTP server using a single io_service and a thread pool
and HTTP Server 2 - An HTTP server using an io_service-per-CPU design
I currently have a very simple boost::asio server that sends a status update upon connecting (using google proto buffers):
try
{
boost::asio::io_service io_service;
tcp::acceptor acceptor(io_service,tcp::endpoint(tcp::v4(), 13));
for (;;)
{
tcp::socket socket(io_service);
acceptor.accept(socket);
...
std::stringstream message;
protoMsg.SerializeToOstream(&message);
boost::system::error_code ignored_error;
boost::asio::write(socket, boost::asio::buffer(message.str()), ignored_error);
}
}
catch (std::exception& e) { }
I would like to extend it to first read after accepting a new connection, check what request was received, and send different messages back depending on this message. I'd also like to keep the TCP connection open so the client doesn't have to re-connect, and would like to handle multiple clients (not many, maybe 2 or 3).
I had a look at a few examples on boost asio, namely the async time tcp server and the chat server, but both are a bit over my head tbh. I don't even understand whether I need an async server. I guess I could just do a read after acceptor.accept(socket), but I guess then I wouldn't keep on listening for further requests. And if I go into a loop I guess that would mean I could only handle one client. So I guess that means I have to go async? Is there a simpler example maybe that isn't 250 lines of code? Or do I just have to bite my way through those examples? Thanks
The examples you mention from the Boost.Asio documentation are actually pretty good to see how things work. You're right that at first it might look a bit difficult to understand, especially if you're new to these concepts. However, I would recommend that you start with the chat server example and get that built on your machine. This will allow you to closer look into things and start changing things in order to learn how it works. Let me guide you through a few things I find important to get started.
From your description what you want to do, it seems that the chat server gives you a good starting point as it already has similar pieces you need. Having the server asynchronous is what you want as you then quite easily can handle multiple clients with a single thread. Nothing too complicated from the start.
Simplified, asynchronous in this case means that your server works off a queue, taking a handler (task) and executes it. If there is nothing on the queue, it just waits for something to be put on the queue. In your case that means it could be a connect from a client, a new read of a message from a client or something like this. In order for this to work, each handler (the function handling the reaction to a particular event) needs to be set up.
Let me explain a bit using code from the chat server example.
In the server source file, you see the chat_server class which calls start_accept in the constructor. Here the accept handler gets set up.
void start_accept()
{
chat_session_ptr new_session(new chat_session(io_service_, room_)); // 1
acceptor_.async_accept(new_session->socket(), // 2
boost::bind(&chat_server::handle_accept, this, new_session, // 3
boost::asio::placeholders::error)); // 4
}
Line 1: A chat_session object is created which represents a session between one client and the server. A session is created for the accept (no client has connected yet).
Line 2: An asynchronous accept for the socket...
Line 3: ...bound to call chat_server::handle_accept when it happens. The session is passed along to be used by the first client which connects.
Now, if we look at the handle_accept we see that upon client connect, start is called for the session (this just starts stuff between the server and this client). Lastly a new accept is put outstanding in case other clients want to connect as well.
void handle_accept(chat_session_ptr session,
const boost::system::error_code& error)
{
if (!error)
{
session->start();
}
start_accept();
}
This is what you want to have as well. An outstanding accept for incoming connections. And if multiple clients can connect, there should always be one of these outstanding so the server can handle the accept.
How the server and the client(s) interact is all in the session and you could follow the same design and modify this to do what you want. You mention that the server needs to look at what is sent and do different things. Take a look at chat_session and the start function which was called by the server in handle_accept.
void start()
{
room_.join(shared_from_this());
boost::asio::async_read(socket_,
boost::asio::buffer(read_msg_.data(), chat_message::header_length),
boost::bind(
&chat_session::handle_read_header, shared_from_this(),
boost::asio::placeholders::error));
}
What is important here is the call to boost::asio::async_read. This is what you want too. This puts an outstanding read on the socket, so the server can read what the client sends. There is a handler (function) which is bound to this event chat_session::handle_read_header. This will be called whenever the server reads something on the socket. In this handler function you could start putting your specific code to determine what to do if a specific message is sent and so on.
What is important to know is that whenever calling these asynchronous boost::asio functions things will not happen within that call (i.e. the socket is not read if you call the function read). This is the asynchronous aspect. You just kind of register a handler for something and your code is called back when this happens. Hence, when this read is called it will immediately return and you're back in the handle_accept for the server (if you follow how things get called). And if you remember there we also call start_accept to set up another asynchronous accept. At this point you have two outstanding handlers waiting for either another client to connect or the first client to send something. Depending on what happens first, that specific handler will be called.
Also what is important to understand is that whenever something is run, it will run uninterrupted until everything it needs to do has been done. Other handlers have to wait even if there is are outstanding events which trigger them.
Finally, in order to run the server you'll need the io_service which is a central concept in Asio.
io_service.run();
This is one line you see in the main function. This just says that the thread (only one in the example) should run the io_service, which is the queue where handlers get enqueued when there is work to be done. When nothing, the io_service just waits (blocking the main thread there of course).
I hope this helps you get started with what you want to do. There is a lot of stuff you can do and things to learn. I find it a great piece of software! Good luck!
In case anyone else wants to do this, here is the minimum to get above going: (similar to the tutorials, but a bit shorter and a bit different)
class Session : public boost::enable_shared_from_this<Session>
{
tcp::socket socket;
char buf[1000];
public:
Session(boost::asio::io_service& io_service)
: socket(io_service) { }
tcp::socket& SocketRef() { return socket; }
void Read() {
boost::asio::async_read( socket,boost::asio::buffer(buf),boost::asio::transfer_at_least(1),boost::bind(&Session::Handle_Read,shared_from_this(),boost::asio::placeholders::error));
}
void Handle_Read(const boost::system::error_code& error) {
if (!error)
{
//read from buffer and handle requests
//if you want to write sth, you can do it sync. here: e.g. boost::asio::write(socket, ..., ignored_error);
Read();
}
}
};
typedef boost::shared_ptr<Session> SessionPtr;
class Server
{
boost::asio::io_service io_service;
tcp::acceptor acceptor;
public:
Server() : acceptor(io_service,tcp::endpoint(tcp::v4(), 13)) { }
~Server() { }
void operator()() { StartAccept(); io_service.run(); }
void StartAccept() {
SessionPtr session_ptr(new Session(io_service));
acceptor.async_accept(session_ptr->SocketRef(),boost::bind(&Server::HandleAccept,this,session_ptr,boost::asio::placeholders::error));
}
void HandleAccept(SessionPtr session,const boost::system::error_code& error) {
if (!error)
session->Read();
StartAccept();
}
};
From what I gathered through trial and error and reading: I kick it off in the operator()() so you can have it run in the background in an additional thread. You run one Server instance. To handle multiple clients, you need an extra class, I called this a session class. For asio to clean up dead sessions, you need a shared pointer as pointed out above. Otherwise the code should get you started.
I'm using Boost.Asio for network operations, they have to (and actually, can, there's no complex data structures or anything) remain pretty low level since I can't afford the luxury of serialization overhead (and the libs I found that did offer well enough performance seemed to be badly suited for my case).
The problem is with an async write I'm doing from the client (in QT, but that should probably be irrelevant here). The callback specified in the async_write doesn't get called, ever, and I'm at a complete loss as to why. The code is:
void SpikingMatrixClient::addMatrix() {
std::cout << "entered add matrix" << std::endl;
int action = protocol::Actions::AddMatrix;
int matrixSize = this->ui->editNetworkSize->text().toInt();
std::ostream out(&buf);
out.write(reinterpret_cast<const char*>(&action), sizeof(action));
out.write(reinterpret_cast<const char*>(&matrixSize), sizeof(matrixSize));
boost::asio::async_write(*connection.socket(), buf.data(),
boost::bind(&SpikingMatrixClient::onAddMatrix, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));
}
which calls the first write. The callback is
void SpikingMatrixClient::onAddMatrix(const boost::system::error_code& error, size_t bytes_transferred) {
std::cout << "entered onAddMatrix" << std::endl;
if (!error) {
buf.consume(bytes_transferred);
requestMatrixList();
} else {
QString message = QString::fromStdString(error.message());
this->ui->statusBar->showMessage(message, 15000);
}
}
The callback never gets called, even though the server receives all the data. Can anyone think of any reason why it might be doing that?
P.S. There was a wrapper for that connection, and yes there will probably be one again. Ditched it a day or two ago because I couldn't find the problem with this callback.
As suggested, posting a solution I found to be the most suitable (at least for now).
The client application is [being] written in QT, and I need the IO to be async. For the most part, the client receives calculation data from the server application and has to render various graphical representations of them.
Now, there's some key aspects to consider:
The GUI has to be responsive, it should not be blocked by the IO.
The client can be connected / disconnected.
The traffic is pretty intense, data gets sent / refreshed to the client every few secs and it has to remain responsive (as per item 1.).
As per the Boost.Asio documentation,
Multiple threads may call io_service::run() to set up a pool of
threads from which completion handlers may be invoked.
Note that all threads that have joined an io_service's pool are considered equivalent, and the io_service may distribute work across them in an arbitrary fashion.
Note that io_service.run() blocks until the io_service runs out of work.
With this in mind, the clear solution is to run io_service.run() from another thread. The relevant code snippets are
void SpikingMatrixClient::connect() {
Ui::ConnectDialog ui;
QDialog *dialog = new QDialog;
ui.setupUi(dialog);
if (dialog->exec()) {
QString host = ui.lineEditHost->text();
QString port = ui.lineEditPort->text();
connection = TcpConnection::create(io);
boost::system::error_code error = connection->connect(host, port);
if (!error) {
io = boost::shared_ptr<boost::asio::io_service>(new boost::asio::io_service);
work = boost::shared_ptr<boost::asio::io_service::work>(new boost::asio::io_service::work(*io));
io_threads.create_thread(boost::bind(&SpikingMatrixClient::runIo, this, io));
}
QString message = QString::fromStdString(error.message());
this->ui->statusBar->showMessage(message, 15000);
}
}
for connecting & starting IO, where:
work is a private boost::shared_ptr to the boost::asio::io_service::work object it was passed,
io is a private boost::shared_ptr to a boost::asio::io_service,
connection is a boost::shared_ptr to my connection wrapper class, and the connect() call uses a resolver etc. to connect the socket, there's plenty examples of that around
and io_threads is a private boost::thread_group.
Surely it could be shortened with some typedefs if needed.
TcpConnection is my own connection wrapper implementation, which sortof lacks functionality for now, and I suppose I could move the whole thread thing into it when it gets reinstated. This snippet should be enough to get the idea anyway...
The disconnecting part goes like this:
void SpikingMatrixClient::disconnect() {
work.reset();
io_threads.join_all();
boost::system::error_code error = connection->disconnect();
if (!error) {
connection.reset();
}
QString message = QString::fromStdString(error.message());
this->ui->statusBar->showMessage(message, 15000);
}
the work object is destroyed, so that the io_service can run out of work eventually,
the threads are joined, meaning that all work gets finished before disconnecting, thus data shouldn't get corrupted,
the disconnect() calls shutdown() and close() on the socket behind the scenes, and if there's no error, destroys the connection pointer.
Note, that there's no error handling in case of an error while disconnecting in this snippet, but it could very well be done, either by checking the error code (which seems more C-like), or throwing from the disconnect() if the error code within it represents an error after trying to disconnect.
I encountered a similar problem (callbacks not fired) but the circumstances are different from this question (io_service had jobs but still would not fire the handlers ). I will post this anyway and maybe it will help someone.
In my program, I set up an async_connect() then followed by io_service.run(), which blocks as expected.
async_connect() goes to on_connect_handler() as expected, which in turn fires async_write().
on_write_complete_handler() does not fire, even though the other end of the connection has received all the data and has even sent back a response.
I discovered that it is caused by me placing program logic in on_connect_handler(). Specifically, after the connection was established and after I called async_write(), I entered an infinite loop to perform arbitrary logic, not allowing on_connect_handler() to exit. I assume this causes the io_service to not be able to execute other handlers, even if their conditions are met because it is stuck here. ( I had many misconceptions, and thought that io_service would automagically spawn threads for each async_x() call )
Hope that helps.