I am designing a server that accepts incoming connections, the clients occasionally send requests which the server needs to respond, but mostly the server detects some events and broadcasts the event to all the connected clients. Basically what I have is this:
#include <ace/Acceptor.h>
#include <ace/INET_Addr.h>
#include <ace/Reactor.h>
#include <ace/SOCK_Acceptor.h>
#include <ace/SOCK_Stream.h>
#include <ace/Svc_Handler.h>
#include <iostream>
#include <thread>
// XXX: for simplicity
HANDLE const hEvent = ::CreateEvent(NULL, FALSE, FALSE, NULL);
class MyService
: public ACE_Svc_Handler<ACE_SOCK_STREAM, ACE_NULL_SYNCH>
{
public:
MyService() : signalCount_(0) { }
int open(void*) override
{
ACE_Reactor::instance()->register_handler(
this,
ACE_Event_Handler::READ_MASK);
ACE_Reactor::instance()->register_handler(
this,
hEvent);
return 0;
}
int handle_input(ACE_HANDLE) override
{
// Handle stuff coming in from clients.
return 0;
}
int handle_signal(int, siginfo_t*, ucontext_t*) override
{
// handle the detected event, send to client.
std::cout
<< signalCount_++ << " "
<< this << " "
<< __FUNCTION__
<< std::endl;
return 0;
}
unsigned signalCount_;
};
typedef ACE_Acceptor<MyService, ACE_SOCK_ACCEPTOR> MyAcceptor;
int main()
{
WSADATA wsData;
WSAStartup(MAKEWORD(2, 0), &wsData);
std::thread thr([=]()
{
// simulate the events.
Sleep(1000);
SetEvent(hEvent);
});
auto r = ACE_Reactor::instance();
MyAcceptor acceptor(ACE_INET_Addr(1234), r);
r->run_reactor_event_loop();
}
The problem here is that whenever hEvent is set, only the first instance of MyService gets its handle_signal called. It looks like only one handler is allowed for one event, bit a handler can handle multiple events. How can I make multiple handlers handler a single event?
If I make the event manual-reset-event, then all the handlers get their handle_signal called as long as the event is set. But that is really not what I want - I don't want a client to be notified of the same event multiple times.
I kind of achieved my goal by using a semaphore instead of an event:
HANDLE const hEvent = ::CreateSemaphore(NULL, 0, 16, NULL);
And made construtor and destructor of MyService count the number of connected clients so that I could release the semaphore correct number of times:
std::thread thr([=]()
{
while (true)
{
Sleep(1000);
ReleaseSemaphore(hEvent, clientCount, nullptr);
}
});
This seems wrong and smells a lot like a hack. Is there a proper way of doing this with ACE?
Related
UPDATE:
Well it appears that I need to address my issue with an asynchronous implementation. I will update my posting with a new direction, once I've completed testing
Original:
I'm currently writing a multiserver application that will collect, share, and request information from multiple machines. In some cases, Machine A will request information from Machine B but will need to send it to Machine C, which will reply to A. Without getting too deep into what the application is going to do I need some help with my client application.
I have my client application designed with two threads. I used this example from boost, as the basis for my design.
Thread one will open a Client Websocket with Machine-A, it will stream a series of data points and commands. Here is a stripped-down version of my code
#include "Poco/Clock.h"
#include "Poco/Task.h"
#include "Poco/Thread.h"
#include <boost/asio.hpp>
#include <boost/beast.hpp>
#include <jsoncons/json.hpp>
namespace beast = boost::beast; // from <boost/beast.hpp>
namespace http = beast::http; // from <boost/beast/http.hpp>
namespace websocket = beast::websocket; // from <boost/beast/websocket.hpp>
namespace net = boost::asio; // from <boost/asio.hpp>
using tcp = net::ip::tcp; // from <boost/asio/ip/tcp.hpp>
class ResponseChannel : public Poco::Runnable {
void do_session(tcp::socket socket)
{
try {
websocket::stream<tcp::socket> ws{std::move(socket)};
ws.set_option(websocket::stream_base::decorator(
[](websocket::response_type& res) {
res.set(http::field::server,
std::string(BOOST_BEAST_VERSION_STRING) +
" websocket-server-sync");
}));
ws.accept();
for (;;) {
beast::flat_buffer buffer;
ws.read(buffer);
if (ws.got_binary()) {
// do something
}
}
} catch (beast::system_error const& se) {
if (se.code() != websocket::error::closed) {
std::cerr << "do_session1 ->: " << se.code().message()
<< std::endl;
return;
}
} catch (std::exception const& e) {
std::cerr << "do_session2 ->: " << e.what() << std::endl;
return;
}
}
virtual void run()
{
auto const address = net::ip::make_address(host);
auto const port = static_cast<unsigned short>(respPort);
try {
net::io_context ioc{1};
tcp::acceptor acceptor{ioc, {address, port}};
tcp::socket socket{ioc};
for (; keep_running;) {
acceptor.accept(socket);
std::thread(&ResponseChannel::do_session, this,
std::move(socket))
.detach();
}
} catch (const std::exception& e) {
std::cout << "run: " << e.what() << std::endl;
}
}
void _terminate() { keep_running = false; }
public:
std::string host;
int respPort;
bool keep_running = true;
int responseCount = 0;
std::vector<long long int> latency_times;
long long int time_sum;
Poco::Clock* responseClock;
};
int main()
{
using namespace std::chrono_literals;
Poco::Clock clock = Poco::Clock();
Poco::Thread response_thread;
ResponseChannel response_channel;
response_channel.responseClock = &clock;
response_channel.host = "0.0.0.0";
response_channel.respPort = 8080;
response_thread.start(response_channel);
response_thread.setPriority(Poco::Thread::Priority::PRIO_HIGH);
// doing some work here. work will vary depending on command-line arguments
std::this_thread::sleep_for(30s);
response_channel.keep_running = false;
response_thread.join();
}
The way I have designed the multiple machines works as expected regarding sending commands to Machine-B and receiving results from Machine-C.
The issue I'm facing is closing out Thread 2, which contains my local response channel.
I went back and forth between Poco::Thread and Poco::Task, but I decided that I do not want to use Task, as it would be a mistake to be able to close the 2nd thread/task from the main thread. I need to know that all packets have been received before closing down the 2nd thread.
So I need to close events down only once I have received a websocket::error::closed flag from Machine-C. Shutting down the websocket, detached, thread is no issue, as when the flag arrives it takes care of that for me.
However, as part of the loop process for reconnecting after a closed socket, the thread just waits for a new connection.
acceptor.accept(socket);
It's blocking, and through the documentation, there doesn't seem to be a timeout feature. I see that there is a close option, but my attempt to use close simply threw an exception. Which ultimately added complexity, I didn't want.
Ultimately, I want the Server to continuously loop through a series of connections from both Machine-B and Machine-C, but only after my client application has ended. The last thing I do before waiting for the Poco::Thread to complete is to set the flag that I no longer want the Websocket server to run.
I've put that flag before the blocking accept() call. This would work, only with perfect timing of the flag going up, a new connection is opened and then closed, before looping back to wait for a new connection.
Ideally, there would be a timeout so that it would loop around, first checking if it timed out, allow for a periodic check if I wanted the thread to remain open.
Has anyone ever run into this?
I work on a C++ server where I wait for an network connection. If I get one I put the socket into a new thread and listen for further inputs. But the problem is that as soon as I have the socket in a new thread the TCP connection is disconnected. I'm using the SFML library.
Here's some code:
main.cpp:
int main() {
std::list<std::thread> user_connections;
sf::TcpListener listener;
listener.listen(PORT);
while (true)
{
sf::TcpSocket client;
listener.accept(client);
Protocol user_connection;
std::thread new_con (&Protocol::connect, &user_connection, std::ref(client));
new_con.detach();
user_connections.push_back(std::move(new_con)); // user_connections is a list
}
protocol.cpp:
class Protocol {
public:
void connect(sf::TcpSocket& client)
{
std::cout << "Address: " << client.getRemoteAddress() << ":" << client.getRemotePort() << std::endl;
}
}
This prints out:
Address: 0.0.0.0:0
And if I try to send any kind of message I get the status 4 which is according to the documentation disconnected.
EDIT:
According to #Ted Lyngmo it's because I need to put client in a list, because otherwise it runs out of scope. Now if I try to put it in a list via:
std::list<sf::TcpSocket> clients; // executed before while loop
// [...]
clients.push_back(client); // in the while loop
I get the error: (pastebin).
This is something built on your current threaded code. It may be a good idea to use a single threaded design and use the sf::SocketSelector to wait for events on the listener and all the connected clients instead.
In this lazy solution disconnected clients will not be removed from the servers list of clients until a new client is connected.
I've tried to explain it with comments in the code which is an echoing kind of server, so you can telnet to it, send messages and get them back.
#include <SFML/Network.hpp>
#include <atomic>
#include <iostream>
#include <list>
#include <thread>
constexpr uint16_t PORT = 2048; // what you have in your code.
// A simple struct to keep a client and thread
struct client_thread {
sf::TcpSocket client{};
std::thread thread{};
// The main thread can check "done" to remove this client_thread from its list:
std::atomic<bool> done{false};
~client_thread() {
// instead of detaching, join()
if(thread.joinable()) thread.join();
}
};
// the connect function gets a reference to a client_thread instead
void connect(client_thread& clith) {
constexpr std::size_t BufSize = 1024;
auto& [client, thread, done] = clith; // for convenience
std::cout << "thread: Address: " << client.getRemoteAddress() << ":"
<< client.getRemotePort() << std::endl;
std::string buffer(BufSize, '\0');
std::size_t received;
while(client.receive(buffer.data(), buffer.size(), received) == sf::Socket::Done) {
// remove ASCII control chars (cr and newline etc.)
while(received && buffer[received - 1] < ' ') --received;
buffer.resize(received);
std::cout << buffer << std::endl;
// send something back
buffer = "You sent >" + buffer + "<\n";
client.send(buffer.c_str(), buffer.size());
// restore the size
buffer.resize(BufSize);
}
std::cout << "thread: client disconnected\n";
client.disconnect();
// set done to true so the main thread can remove the client_thread
done = true;
}
int main() {
sf::TcpListener listener;
// check that listening actually works
if(listener.listen(PORT) != sf::Socket::Done) return 1;
// now a list of client_thread instead:
std::list<client_thread> user_connections;
while(true) {
// create a client_thread to use when listening
auto& clith = user_connections.emplace_back();
auto& [client, thread, _] = clith; // for convenience
std::cout << "main: listening ...\n";
sf::Socket::Status status = listener.accept(client);
if(status == sf::Socket::Done) {
std::cout << "main: got connection\n";
thread = std::thread(connect, std::ref(clith));
} else {
std::cout << "main: accept not done\n";
}
// remove disconnected clients, pre C++20
for(auto it = user_connections.begin(); it != user_connections.end();) {
// check the atomic bool in all threads
if(it->done) {
std::cout << "main: removing old connection\n";
it = user_connections.erase(it);
} else {
++it;
}
}
// remove disconnected clients, >= C++20
//
// std::erase_if(user_connections,
// [](auto& clith) -> bool { return clith.done; });
}
}
Edit regarding your edited question where you're trying to put the client in a list:
You're trying to copy the sf::TcpSocket and it's not copyable. What's worse, it's not even moveable. The reason the code in my answer works is because it avoids both copying and moving by using std::list::emplace_back to construct the element in place in the list.
It is apparently both sf::TcpSocket client and Protocol user_connection are destroyed. It's no use to only keep the thread alive, your thread only holds references to client and user_connection, but both of them are destroyed soon after your thread is created (and maybe not even started running).
I read a little bit on the SMFL library and unfortunately, at least the client, which is an object of TCPSocket, is not copyable, nor movable. The SMFL library must be a very old library. Any modern socket library will design socket to be at least movable, meaning that you can move your socket into the thread, or move it to the std::list or std::vector you created.
So, to use SMFL library, which was written without modern C++11 support (the copy & move in C++ was introduced in C++ 2011), together with C++11 library (std::thread), will be quite painful.
You can probably use std::shared_ptr to hold a newly created protocol & client, and pass shared_ptr into thread or into the list you created.
I don't know what Protocol exactly does, a rough pseudo code is as follows,
std::shared_ptr<TcpSocket> client = std::make_shared<TcpSocket>();
listener.accept(*client);
std::shared_ptr<Protocol> protocol = std::make_shared<Protocol>();
// copy the pointer into thread, they will be deleted after the thread is done
std::thread new_con ( [client, protocol] () { protocol->connect(*client); } );
or, protocol can probably be defined in the thread,
std::shared_ptr<TcpSocket> client = std::make_shared<TcpSocket>();
listener.accept(*client);
std::thread new_con ( [client] () {
Protocol protocol;
protocol.connect(*client);
} );
Consider a situation where you need to maintain 256 tcp connections with devices just for ocassionally sending commands. I want to do this in parallel(It needs to block until it gets the response), I'm trying to use QThreadPool for this purpose but I have some doubts if it is possible.
I tried to use QRunnable but I'm not sure how sockets will behave between threads (sockets should be used only in thread that they were created in?)
I'm also worried about efficiency of this solution, I would be glad if somebody could propose some alternatives, not necessarily using QT.
Below I'm posting some snippets of the code.
class Task : public QRunnable {
Task(){
//creating TaskSubclass instance and socket in it
}
private:
TaskSubclass *sub;
void run() override {
//some debug info and variable setting...
sub->doSomething( args );
return;
}
};
class TaskSubclass {
Socket *sock; // socket instance
//...
void doSomething( args )
{
//writing to socket here
}
}
class MainProgram : public QObject{
Q_OBJECT
private:
QThreadPool *pool;
Task *tasks;
public:
MainProgram(){
pool = new QThreadPool(this);
//create tasks here
}
void run(){
//decide which task to start
pool->start(tasks[i]);
}
};
My favorite solution for this problem is by multiplexing your sockets using select(). That way you don't need to create additional threads, and it is a "very POSIX" way to do it.
See for example see this tutorial:
http://www.binarytides.com/multiple-socket-connections-fdset-select-linux/
Or a related question in:
Using select(..) on client
As OMD_AT has allready pointed out the best solution is to use Select() and let the kernel do the job for you :-)
here you have an example of an Async approach and an Syncron multi thread approach.
In this example we create 10 connection to a google webservice and make a simple get request to the server, we measure how long all connections in each approach needed to receive the response from the google server.
Be aware that you should use a more faster webserver to make a real test, like the localhost because the network latency has a big impact on the result.
#include <QCoreApplication>
#include <QTcpSocket>
#include <QtConcurrent/QtConcurrentRun>
#include <QElapsedTimer>
#include <QAtomicInt>
class Task : public QRunnable
{
public:
Task() : QRunnable() {}
static QAtomicInt counter;
static QElapsedTimer timer;
virtual void run() override
{
QTcpSocket* socket = new QTcpSocket();
socket->connectToHost("www.google.com", 80);
socket->write("GET / HTTP/1.1\r\nHost: www.google.com\r\n\r\n");
socket->waitForReadyRead();
if(!--counter) {
qDebug("Multiple Threads elapsed: %lld nanoseconds", timer.nsecsElapsed());
}
}
};
QAtomicInt Task::counter;
QElapsedTimer Task::timer;
int main(int argc, char *argv[])
{
QCoreApplication app(argc, argv);
// init
int connections = 10;
Task::counter = connections;
QElapsedTimer timer;
/// Async via One Thread (Select)
// handle the data
auto dataHandler = [&timer,&connections](QByteArray data) {
Q_UNUSED(data);
if(!--connections) qDebug(" Single Threads elapsed: %lld nanoseconds", timer.nsecsElapsed());
};
// create 10 connection to google.com and send an http get request
timer.start();
for(int i = 0; i < connections; i++) {
QTcpSocket* socket = new QTcpSocket();
socket->connectToHost("www.google.com", 80);
socket->write("GET / HTTP/1.1\r\nHost: www.google.com\r\n\r\n");
QObject::connect(socket, &QTcpSocket::readyRead, [dataHandler,socket]() {
dataHandler(socket->readAll());
});
}
/// Async via Multiple Threads
Task::timer.start();
for(int i = 0; i < connections; i++) {
QThreadPool::globalInstance()->start(new Task());
}
return app.exec();
}
Prints:
Multiple Threads elapsed: 62324598 nanoseconds
Single Threads elapsed: 63613967 nanoseconds
Although, the answer is already accepted, I would like to share my)
What I understood from your question: Having 256 currently active connections, from time to time you send a request ("command" as you named it) to one of them and wait for the response. Meanwhile, you want to make this process multithreaded and, though you said "It needs to block until it gets the response", I assume you implied blocking a thread which handles request-response process, but not the main thread.
If I indeed understand the question right, here is how I suggest to do it using Qt:
#include <functional>
#include <QObject> // need to add "QT += core" in .pro
#include <QTcpSocket> // QT += network
#include <QtConcurrent> // QT += concurrent
#include <QFuture>
#include <QFutureWatcher>
class CommandSender : public QObject
{
public:
// Sends a command via connection and blocks
// until the response arrives or timeout occurs
// then passes the response to a handler
// when the handler is done - unblocks
void SendCommand(
QTcpSocket* connection,
const Command& command,
void(*responseHandler)(Response&&))
{
const int timeout = 1000; // milliseconds, set it to -1 if you want no timeouts
// Sending a command (blocking)
connection.write(command.ToByteArray()); // Look QByteArray for more details
if (connection.waitForBytesWritten(timeout) {
qDebug() << connection.errorString() << endl;
emit error(connection);
return;
}
// Waiting for a response (blocking)
QDataStream in{ connection, QIODevice::ReadOnly };
QString message;
do {
if (!connection.waitForReadyRead(timeout)) {
qDebug() << connection.errorString() << endl;
emit error(connection);
return;
}
in.startTransaction();
in >> message;
} while (!in.commitTransaction());
responseHandler(Response{ message }); // Translate message to a response and handle it
}
// Non-blocking version of SendCommand
void SendCommandAsync(
QTcpSocket* connection,
const Command& command,
void(*responseHandler) (Response&&))
{
QFutureWatcher<void>* watcher = new QFutureWatcher<void>{ this };
connect(watcher, &QFutureWatcher<void>::finished, [connection, watcher] ()
{
emit done(connection);
watcher->deleteLater();
});
// Does not block,
// emits "done" when finished
QFuture<void> future
= QtConcurrent::run(this, &CommandSender::SendCommand, connection, command, responseHandler);
watcher->setFuture(future);
}
signals:
void done(QTcpSocket* connection);
void error(QTcpSocket* connection);
}
Now you can send a command to a socket using a separate thread taken from a thread pool: under the hood QtConcurrent::run() uses the global instance of QThreadPool provided by Qt for you. That thread blocks until it gets a response back and than handles it with responseHandler . Meanwhile, your main thread managing all your commands and sockets stays unblocked. Just catch done() signal which tells that response was received and handled successfully.
One thing to note: asynchronous version sends request only when there is a free thread in the thread pool and waits for it otherwise. Of course, that is the behavior for any thread pool (that is exactly the point of such pattern) but just do not forget about that.
Also I was writing code without Qt in handy so may contain some errors.
Edit: As it turned out, this is not thread safe as sockets are not reentrant in Qt.
What you can do about it is to associate a mutex with a socket and lock it each time you execute its function. This can be done easily creating a wrapper around QTcpSocket class. Please, correct me if I wrong.
I am using the HTML Server 3 example from boost as my learning tool (http://www.boost.org/doc/libs/1_53_0/doc/html/boost_asio/examples.html#boost_asio.examples.http_server_3) for asynchronous message handling.
I have taken the example, and turned it into a library with a server object I can instantiate in my programs. The only thing I have done to the above example is remove the main.cpp and compile it as a library. And it works to the extend that I can instantiate the server object in my code, and pass messages to it from the command line.
Where I am struggling is how to terminate the server gracefully. From the sample code I see this:
server::server(const std::string& address, const std::string& port,
std::size_t thread_pool_size,
Handler &handler)
: thread_pool_size_(thread_pool_size),
signals_(io_service_),
acceptor_(io_service_),
new_connection_(),
request_handler_(handler)
{
// Register to handle the signals that indicate when the server should exit.
// It is safe to register for the same signal multiple times in a program,
// provided all registration for the specified signal is made through Asio.
signals_.add(SIGINT);
signals_.add(SIGTERM);
signals_.async_wait(boost::bind(&server::handle_stop, this));
So an asynchronous thread is set up to listen for signals and respond to them
I have implemented this server object in a thread in my program as follows:
class ServerWorker
{
public:
ServerWorker(std::string theHost, std::string thePort)
{
Host = theHost;
Port = thePort;
}
void Start()
{
try
{
MYRequestHandler handler;
int nCores = boost::thread::hardware_concurrency();
server *mServer = new server(Host, Port, nCores, handler);
svr->run();
}
catch(std::exception &e) { /* do something */ }
}
void Stop()
{
mServer->stop(); // this should raise a signal and send it to the server
// but don't know how to do it
}
private:
std::string Host;
std::string Port;
server *mServer;
};
TEST(BSGT_LBSSERVER_STRESS, BSGT_SINGLETON)
{
// Launch as server on a new thread
ServerWorker sw(BSGT_DEFAULT_IPADDRESS, BSGT_DEFAULT_PORT_STR);
boost::function<void()> th_func = boost::bind(&ServerWorker::Start, &sw);
boost::thread swThread = boost::thread(th_func);
// DO SOMETHING
// How do I signal the server in the swThread to stop?
}
How do I implement the stop() method on the server object to send the signal to itself? I have tried:
1) raise(SIGTERM) - kills the whole program
2) raise(SIGINT) - kills the whole program
raise() is appropriate for having a process signal itself.
void ServerWorker::Stop()
{
std::raise(SIGTERM);
}
Be aware that raise() is asynchronous. It will issue the signal and return immediately. Hence, control may continue before the io_service processes the enqueued SignalHandler.
void run_server()
{
// Launch as server on a new thread
ServerWorker server_worker(...);
boost::thread worker_thread([&server_worker]() { server_worker.Start(); });
...
// Raises SIGTERM. May return before io_service is stopped.
server_worker.Stop();
// Need to synchronize with worker_thread. The `worker_thread` may still be
// in `ServerWorker::Start()` which would go out of scope. Additionally,
// the `worker_thread` is joinable, so its destructor may invoke
// `std::terminate()`.
}
Here is a minimal example demonstrating using Boost.Asio signal handling, raise(), and synchronization:
#include <cassert>
#include <csignal>
#include <iostream>
#include <thread>
#include <boost/asio.hpp>
int main()
{
boost::asio::io_service io_service;
// Prevent io_service from running out of work.
boost::asio::io_service::work work(io_service);
// Boost.Asio will register an internal handler for SIGTERM.
boost::asio::signal_set signal_set(io_service, SIGTERM);
signal_set.async_wait(
[&io_service](
const boost::system::error_code& error,
int signal_number)
{
std::cout << "Got signal " << signal_number << "; "
"stopping io_service." << std::endl;
io_service.stop();
});
// Raise SIGTERM.
std::raise(SIGTERM);
// By the time raise() returns, Boost.Asio has handled SIGTERM with its
// own internal handler, queuing it internally. At this point, Boost.Asio
// is ready to dispatch this notification to a user signal handler
// (i.e. those provided to signal_set.async_wait()) within the
// io_service event loop.
std::cout << "io_service stopped? " << io_service.stopped() << std::endl;
assert(false == io_service.stopped());
// Initiate thread that will run the io_service. This will invoke
// the queued handler that is ready for completion.
std::thread work_thread([&io_service]() { io_service.run(); });
// Synchornize on the work_thread. Letting it run to completion.
work_thread.join();
// The io_service has been explicitly stopped in the async_wait
// handler.
std::cout << "io_service stopped? " << io_service.stopped() << std::endl;
assert(true == io_service.stopped());
}
Output:
io_service stopped? 0
Got signal 15; stopping io_service.
io_service stopped? 1
I would like to create a c++ webserver that will perform a task for each user that lands on my website. Since the task might be computationally heavy (for now just a long sleep), I'd like to handle each user on a different thread. I'm using mongoose to set up a webserver.
The different processes (in my code below just one, aka server1) are set up correctly and seem to function correctly. However, the threads seem to be queuing one after the other so if 2 users hit the end point, the second user must wait until the first user finishes. What am I missing? Do the threads run out of scope? Is there a "thread-manager" that I should be using?
#include "../../mongoose.h"
#include <unistd.h>
#include <iostream>
#include <stdlib.h>
#include <thread>
//what happens whenever someone lands on an endpoint
void myEvent(struct mg_connection *conn){
//long delay...
std::thread mythread(usleep, 2*5000000);
mythread.join();
mg_send_header(conn, "Content-Type", "text/plain");
mg_printf_data(conn, "This is a reply from server instance # %s",
(char *) conn->server_param);
}
static int ev_handler(struct mg_connection *conn, enum mg_event ev) {
if (ev == MG_REQUEST) {
myEvent(conn);
return MG_TRUE;
} else if (ev == MG_AUTH) {
return MG_TRUE;
} else {
return MG_FALSE;
}
}
static void *serve(void *server) {
for (;;) mg_poll_server((struct mg_server *) server, 1000);
return NULL;
}
int main(void) {
struct mg_server *server1;
server1 = mg_create_server((void *) "1", ev_handler);
mg_set_option(server1, "listening_port", "8080");
mg_start_thread(serve, server1);
getchar();
return 0;
}
Long running requests should be handled like this:
static void thread_func(struct mg_connection *conn) {
sleep(60); // simulate long processing
conn->user_data = "done"; // Production code must not do that.
// Other thread must never access connection
// structure directly. This example is just
// for demonstration.
}
static int ev_handler(struct mg_connection *conn, enum mg_event ev) {
switch (ev) {
case MG_REQUEST:
conn->user_data = "doing...";
spawn_thread(thread_func, conn);
return MG_MORE; // Important! Signal Mongoose we are not done yet
case MG_POLL:
if (conn->user_data != NULL && !strcmp(conn->user_data, "done")) {
mg_printf(conn, "HTTP/1.0 200 OK\n\n Done !");
return MG_TRUE; // Signal we're finished. Mongoose can close this connection
}
return MG_FALSE; // Still not done
Caveat: I'm not familiar with mongoose
My assumptions:
The serve function is polling for incoming connections
If the thread executing mg_poll_server is the same thread that triggers the call to ev_handler then your problem is the fact that ev_handler calls myEvent which starts a long running operation and blocks the thread (i.e., by calling join). In this case you're also blocking the thread which is handling the incoming connections (i.e., A subsequent client must wait for the first client to finish their work), which seems is the behavior you describe seeing.
I'm not sure what the real task is supposed to do so I can't say for sure how you should fix this. Perhaps in your use-case it may be possible to call detach otherwise you might keep track of executing threads and defer calling join on them until the server is shutdown.
James Adkison is absolutely right. So, if instead the beginning of the code looks like this:
void someFunc(struct mg_connection *conn){
usleep(2*5000000);
std::cout << "hello!" << std::endl;
std::cout<< "This finished from server instance #"<<conn<<std::endl;
mg_send_header(conn, "Content-Type", "application/json");
mg_printf_data(conn, "{\"message\": \"This is a reply from server instance # %s\"}",
// (char *) conn->server_param);
}
void myEvent(struct mg_connection *conn){
std::thread mythread(someFunc,conn);
mythread.detach();
std::cout<< "This is a reply from server instance #"<<(char *) conn->server_param<<std::endl;
}
static int ev_handler(struct mg_connection *conn, enum mg_event ev) {
if (ev == MG_REQUEST) {
myEvent(conn);
return MG_TRUE;
} else if (ev == MG_AUTH) {
//.... exactly as before
//....
then the program works. Basically the difference is replacing .join() with .detach(). someFunc is running now in parallel for 2 users -- so that's great!. Thanks!