- Boost-users - lists.boost.org

Fwd: Using ASIO to wait on a foreign socket being readable, with a timeout
by Dominique Devienne 19 Jan '24

19 Jan '24

Sorry, sent originally to the wrong list. And this is on Windows 10 too, BTW. Haven't tried Linux with that code yet. --DD ---------- Forwarded message --------- From: Dominique Devienne <ddevienne(a)gmail.com> Date: Thu, Jan 18, 2024 at 7:18 PM Subject: Using ASIO to wait on a foreign socket being readable, with a timeout To: <boost(a)lists.boost.org> Hi, I'm trying to use ASIO to wait until a socket is ready to read, or timeout. This is a blocking wait. But the socket is not "owned" by ASIO, but is from the libpq PostgreSQL connection. So ASIO should NOT consume any of the input on the socket, just notify me when that socket is "read-ready". I've cobbled together the following test code: ``` const int socket2 = PQsocket(conn2.handle()); BOOST_CHECK(socket2 > 0); int timr_err_code = 0; int sock_err_code = 0; bool timr_aborted = false; bool sock_aborted = false; std::string timr_err_msg; std::string sock_err_msg; bool timed_out = true; auto c1 = "C# 1"sv; conn2.listen(c1); conn1->notify(c1, "wake up!"sv); { boost::asio::io_context io_ctx; boost::asio::ip::tcp::socket io_sock(io_ctx); io_sock.assign(boost::asio::ip::tcp::v4(), socket2); boost::asio::steady_timer io_timer(io_ctx); io_timer.expires_from_now(std::chrono::milliseconds(100)); io_sock.async_wait( io_sock.wait_read, [&](const boost::system::error_code& errc) { if (errc) { sock_err_code = errc.value(); sock_err_msg = errc.message(); sock_aborted = (errc == boost::asio::error::operation_aborted); } timed_out = false; //io_timer.cancel(); io_ctx.stop(); } ); io_timer.async_wait( [&](const boost::system::error_code& errc) { if (errc) { timr_err_code = errc.value(); timr_err_msg = errc.message(); timr_aborted = (errc == boost::asio::error::operation_aborted); } io_sock.cancel(); io_ctx.stop(); } ); io_ctx.run(); // blocks until either async op above runs } // there's a notif to read, so io_sock.async_wait should have completed BOOST_CHECK_EQUAL(timr_err_code, 0); BOOST_CHECK_EQUAL(sock_err_code, 0); BOOST_CHECK_EQUAL(timr_err_msg, ""); BOOST_CHECK_EQUAL(sock_err_msg, ""); BOOST_CHECK_EQUAL(timr_aborted, false); BOOST_CHECK_EQUAL(sock_aborted, false); BOOST_CHECK_EQUAL(timed_out, false); auto notif = conn2.notification(); BOOST_REQUIRE(notif); BOOST_CHECK_EQUAL(notif.backend_pid(), pid1); BOOST_CHECK_EQUAL(notif.channel(), c1); BOOST_CHECK_EQUAL(notif.payload(), "wake up!"sv); ``` The io_sock.async_wait(io_sock.wait_read, ...) succeeds, the IO loop stops as expected, but when I try to PQconsumeInput() from the LIBPQ connection next (as shown in the code below) ``` Notification Connection::notification() { auto [lock, hndl] = ensure_handle(); if (1 != PQconsumeInput(hndl)) { throw std::runtime_error(error_msg()); // <<<<<< THROWS } PGnotify_uptr notif{ PQnotifies(hndl) }; return Notification(std::move(notif)); // may be null } ``` that calls fail with this error message: fatal error: in "NotificationTests/test_across_backends": class std::runtime_error: could not receive data from server: Socket operation on non-socket (0x00002736/10038) LIBPQ didn't like what ASIO somehow did on the socket descriptor. The LIBPQ doc says to select() the descriptor, but I thought ASIO would be cleaner, more C++, and perhaps more cross-platform. Can somehow help, telling me if I'm using ASIO incorrectly here? Thanks, --DD

2 2

[Scope] Peer review conclusion
by Дмитрий Архипов 15 Jan '24

15 Jan '24

Dear Boost community, the formal review of Boost.Scope has taken place between 26th of November and 5th of December of the previous year. I have received 5 reviews in total, including 4 here on the mailing list and 1 on Reddit. Two of the reviews recommended unconditional, and 3 conditional acceptance. The reviews came from: - Klemens Morgenstern, - Janko Dedic, - Julien Blanc, - David Sankel, - /u/jonesmz on Reddit. Also, several people have given insightful comments but did not provide a review. I would like to thank all of the people who took their time to write reviews or participate in the discussions. Your effort was very important and valuable. The outcome of the review is that Boost.Scope is ACCEPTED with several minor CONDITIONS. 1. noexcept specification on destructors of scope guards should be properly documented. Andrey has already commented that the technical hurdle that prevented it was eliminated. 2. There should be a good motivating example for scope_success. There was a lot of comments regarding scope_success and its seeming uselessness. Without a good example I see the same pattern occurring with future users. 3. The examples should better describe what they are trying to achieve. Several comments about examples suggested incorrect changes, which signals that readers failed to understand them. After a lot of consideration I decided against requesting the author to remove unique_resource and related functionality from the library. While several reviewers wanted a more "concise" library, all noted that the component is useful. One last thing I wanted to point out is that all reviewers and most commenters were adamant that compatibility with the Technical Specification on which this library was initially based should not be a goal. In fact, Andrzej Krzemienski even noted that such compatibility has prevented him from adequately evaluating the library on its own merit. In my opinion this should be a sign to all of us that people prefer better APIs over standard APIs. I recommend Andrey to re-evaluate those parts of the library's APIs that he copied from the TS and potentially pick better names for member functions. Thanks to Andrey for submitting this library to Boost. And thanks again to the reviewers and everyone who provided feedback, who ultimately made this review possible.

1 0

Using Boost in CLR Class
by 임성준 08 Jan '24

08 Jan '24

Hello, I have question about using Boost. I'm trying to using boost in clr class of Visual Studito 2022 When I build the project, I got following error Error C1189 #error: "This library now requires a C++11 or later compiler - this message was generated as a result of BOOST_NO_CXX11_REF_QUALIFIERS being set" ClassLibrary2 C:\Users\bussly\source\repos\ClassLibrary2\packages\boost.1.84.0\lib\native\include\boost\multiprecision\detail\check_cpp11_config.hpp 34 Error (active) E0035 #error directive: "This library now requires a C++11 or later compiler - this message was generated as a result of BOOST_NO_CXX11_REF_QUALIFIERS being set" ClassLibrary2 C:\Users\bussly\source\repos\ClassLibrary2\packages\boost.1.84.0\lib\native\include\boost\multiprecision\detail\check_cpp11_config.hpp 58 Even I didn't make any code, just add an include boost header. Following is the scenario of what I did - Visual Studio 2022 - Create new project -> CLR Class Library(.Net Framework) - Install NuGet Package -> boost 1.84.0 - Add include boost -> #include "boost/geometry.hpp" - Build solution - Error and following is properties of my project - Platform Toolset: Visual Studio 2022(v143) - C++ Language Standard: ISO C++ 20 Standard(/std:c++20) - C Language Standard: Default(Legacy MSVC) I tried with C++ 14 and C++ 17 also, but failed. Can I get any solution for this? Thank you.

1 0

[Boost.Redis] Single Connection Concurrency Inquiry
by Samarah Uriarte 08 Jan '24

08 Jan '24

Hello, I am using the Boost Redis library to write to a local Redis server and would like to inquire about how a single connection can handle concurrent calls. I have several C++ classes that have their own Boost.Redis connections, but this is leading to ASIO-related hanging behavior that is difficult to debug. I would like to simplify the design by initializing only one connection that can be used by all of these classes instead. I know the "async_exec" method supports concurrency but I wonder if this might cause any future issues with larger workloads. Thank you in advance. Sincerely, Samarah Uriarte

1 0

Problems downloading boost on Linux
by Gonzalo Garramuño 01 Jan '24

01 Jan '24

I have tried downloading boost 1.76 on Linux from Argentina with: curl -# -L -o boost_1_76_0.zip.tmp https://boostorg.jfrog.io/artifactory/main/release/1.76.0/source/boost_1_76… and also from the boost web page. This leads to a redirect to JFrog. I tried creating an account with both Google (which led to Invalid credentials - you might not be a registered MyJFrog user. Please try again. ) and with a new account on JFrog which sent me an email requesting my company: To confirm this request, please include the license owner or any other support contact associated with your company's subscription approval in this email thread. Are the boost libraries at www.boost.org available for free or only under subscription? I found I can still download them from sourceforge, of course, but I would need to patch any dependencies that point to the older web-site. -- Gonzalo Garramuño ggarra13(a)gmail.com

2 2

Cobalt link error
by Josué Andrade Gomes 23 Dec '23

23 Dec '23

I'm trying to build a minimal Cobalt library sample. I'm getting link errors: Build and installed Boost with: ./bootstrap.sh --prefix=$HOME/.local ./b2 install Sample: #include <boost/cobalt.hpp> #include <iostream> boost::cobalt::main co_main(int, char *[]) { std::cout << "Hello world\n"; co_return 0; } CMakeLists.txt cmake_minimum_required(VERSION 3.20) project(coro_study) set(CMAKE_EXPORT_COMPILE_COMMANDS ON) set(CMAKE_CXX_STANDARD 20) set(CMAKE_VERBOSE_MAKEFILE ON) set(Boost_VERBOSE 1) set(Boost_DEBUG 1) find_package(Boost REQUIRED COMPONENTS system) add_executable(sample sample.cpp) target_include_directories(sample4 PRIVATE ${Boost_INCLUDE_DIRS}) target_link_libraries(sample4 PRIVATE ${Boost_LIBRARIES}) cmake output: dev ~/Projects/coroutines/x64-linux-debug $ cmake .. -- The C compiler identification is GNU 11.4.0 -- The CXX compiler identification is GNU 11.4.0 -- Detecting C compiler ABI info -- Detecting C compiler ABI info - done -- Check for working C compiler: /usr/bin/cc - skipped -- Detecting C compile features -- Detecting C compile features - done -- Detecting CXX compiler ABI info -- Detecting CXX compiler ABI info - done -- Check for working CXX compiler: /usr/bin/c++ - skipped -- Detecting CXX compile features -- Detecting CXX compile features - done -- Found Boost 1.84.0 at /home/dev/.local/lib/cmake/Boost-1.84.0 -- Requested configuration: QUIET REQUIRED COMPONENTS system -- BoostConfig: find_package(boost_headers 1.84.0 EXACT CONFIG REQUIRED QUIET HINTS /home/dev/.local/lib/cmake) -- Found boost_headers 1.84.0 at /home/dev/.local/lib/cmake/boost_headers-1.84.0 -- BoostConfig: find_package(boost_system 1.84.0 EXACT CONFIG REQUIRED QUIET HINTS /home/dev/.local/lib/cmake) -- Found boost_system 1.84.0 at /home/dev/.local/lib/cmake/boost_system-1.84.0 -- Boost toolset is gcc11 (GNU 11.4.0) -- Scanning /home/dev/.local/lib/cmake/boost_system-1.84.0/libboost_system-variant*.cmake -- Including /home/dev/.local/lib/cmake/boost_system-1.84.0/libboost_system-variant-shared.cmake -- [x] libboost_system.so.1.84.0 -- Including /home/dev/.local/lib/cmake/boost_system-1.84.0/libboost_system-variant-static.cmake -- [ ] libboost_system.a -- Adding boost_system dependencies: headers -- Found Boost: /home/dev/.local/lib/cmake/Boost-1.84.0/BoostConfig.cmake (found version "1.84.0") found components: system -- Configuring done -- Generating done -- Build files have been written to: /home/dev/Projects/coroutines/x64-linux-debug make output: dev ~/Projects/coroutines/x64-linux-debug $ make /usr/bin/cmake -S/home/dev/Projects/coroutines -B/home/dev/Projects/coroutines/x64-linux-debug --check-build-system CMakeFiles/Makefile.cmake 0 /usr/bin/cmake -E cmake_progress_start /home/dev/Projects/coroutines/x64-linux-debug/CMakeFiles /home/dev/Projects/coroutines/x64-linux-debug//CMakeFiles/progress.marks make -f CMakeFiles/Makefile2 all make[1]: Entering directory '/home/dev/Projects/coroutines/x64-linux-debug' make -f CMakeFiles/sample4.dir/build.make CMakeFiles/sample4.dir/depend make[2]: Entering directory '/home/dev/Projects/coroutines/x64-linux-debug' cd /home/dev/Projects/coroutines/x64-linux-debug && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/dev/Projects/coroutines /home/dev/Projects/coroutines /home/dev/Projects/coroutines/x64-linux-debug /home/dev/Projects/coroutines/x64-linux-debug /home/dev/Projects/coroutines/x64-linux-debug/CMakeFiles/sample4.dir/DependInfo.cmake --color= make[2]: Leaving directory '/home/dev/Projects/coroutines/x64-linux-debug' make -f CMakeFiles/sample4.dir/build.make CMakeFiles/sample4.dir/build make[2]: Entering directory '/home/dev/Projects/coroutines/x64-linux-debug' [ 50%] Building CXX object CMakeFiles/sample4.dir/sample4.cpp.o /usr/bin/c++ -DBOOST_SYSTEM_DYN_LINK -DBOOST_SYSTEM_NO_LIB -isystem /home/dev/.local/include -std=gnu++20 -MD -MT CMakeFiles/sample4.dir/sample4.cpp.o -MF CMakeFiles/sample4.dir/sample4.cpp.o.d -o CMakeFiles/sample4.dir/sample4.cpp.o -c /home/dev/Projects/coroutines/sample4.cpp [100%] Linking CXX executable sample4 /usr/bin/cmake -E cmake_link_script CMakeFiles/sample4.dir/link.txt --verbose=1 /usr/bin/c++ CMakeFiles/sample4.dir/sample4.cpp.o -o sample4 /home/dev/.local/lib/libboost_system.so.1.84.0 /usr/bin/ld: CMakeFiles/sample4.dir/sample4.cpp.o: in function `co_main(co_main(int, char**)::_Z7co_mainiPPc.Frame*) [clone .actor]': sample4.cpp:(.text+0x2a9): undefined reference to `boost::cobalt::detail::main_promise::final_suspend()' /usr/bin/ld: CMakeFiles/sample4.dir/sample4.cpp.o: in function `main::reset_res::operator()(std::pmr::memory_resource*)': sample4.cpp:(.text._ZZ4mainEN9reset_resclEPNSt3pmr15memory_resourceE[_ZZ4mainEN9reset_resclEPNSt3pmr15memory_resourceE]+0x1c): undefined reference to `boost::cobalt::this_thread::set_default_resource(std::pmr::memory_resource*)' /usr/bin/ld: CMakeFiles/sample4.dir/sample4.cpp.o: in function `main': sample4.cpp:(.text.main[main]+0x5b): undefined reference to `boost::cobalt::this_thread::set_default_resource(std::pmr::memory_resource*)' /usr/bin/ld: sample4.cpp:(.text.main[main]+0xc2): undefined reference to `boost::cobalt::detail::main_promise::run_main(boost::cobalt::main)' /usr/bin/ld: CMakeFiles/sample4.dir/sample4.cpp.o: in function `bool boost::cobalt::detail::promise_receiver<void>::awaitable::await_suspend<boost::cobalt::detail::fork::promise_type>(std::__n4861::coroutine_handle<boost::cobalt::detail::fork::promise_type>)': sample4.cpp:(.text._ZN5boost6cobalt6detail16promise_receiverIvE9awaitable13await_suspendINS1_4fork12promise_typeEEEbNSt7__n486116coroutine_handleIT_EE[_ZN5boost6cobalt6detail16promise_receiverIvE9awaitable13await_suspendINS1_4fork12promise_typeEEEbNSt7__n486116coroutine_handleIT_EE]+0x7f): undefined reference to `boost::cobalt::detail::already_awaited()' /usr/bin/ld: CMakeFiles/sample4.dir/sample4.cpp.o: in function `boost::cobalt::detail::promise_receiver<void>::awaitable::interrupt_await() &': sample4.cpp:(.text._ZNR5boost6cobalt6detail16promise_receiverIvE9awaitable15interrupt_awaitEv[_ZNR5boost6cobalt6detail16promise_receiverIvE9awaitable15interrupt_awaitEv]+0x33): undefined reference to `boost::cobalt::detail::detached_exception()' collect2: error: ld returned 1 exit status make[2]: *** [CMakeFiles/sample4.dir/build.make:101: sample4] Error 1 make[2]: Leaving directory '/home/dev/Projects/coroutines/x64-linux-debug' make[1]: *** [CMakeFiles/Makefile2:86: CMakeFiles/sample4.dir/all] Error 2 make[1]: Leaving directory '/home/dev/Projects/coroutines/x64-linux-debug' make: *** [Makefile:94: all] Error 2

3 4

Handshake Error 10009
by Jens Kallup 23 Dec '23

23 Dec '23

Hello, I tried use the boost::asio to create a SSL-Server, but I fail. The Code I used is attached to this Text. acceptor_ and context_ give me true result, but the start_accept() methode give me a Handshake-Error: 10009 (invalid descriptor handle). How can I avoid this, and how can I fix the Code in the right point ? Thanks for reading paule32 // ----------------------------------------------------------------- // File: BoostServer.cc // Author: (c) 2023 Jens Kallup - paule32 // All rights reserved // // only for education, and non-profit usage ! // ----------------------------------------------------------------- # include <stdio.h> # include <stdlib.h> # include <sys/types.h> # include <iostream> # include <string> # include <functional> # include <thread> # include <memory> # include <boost/asio.hpp> # include <boost/asio/ssl.hpp> using namespace boost::asio; using namespace std; // ----------------------------------------------------------------- // @brief namespace name for Version 1.0.0 of our project ... // ----------------------------------------------------------------- namespace dBaseRelease { std::string ApplicationExeName; // ----------------------------------------------------------------- // @brief This member handle the exception message text that is use // to "try catch" exception's during the runtime of the // application. // // @param std::string& message - The e.what() message. // @return nothing // // @since dBaseRelease // @author paule32 // ----------------------------------------------------------------- void handle_exception(const std::string& message) { std::string error_message; for (int len = 0; len < message.length(); ++len) { if (message[len] == '[') break; error_message.push_back(message[len]); } std::cerr << "Exception " << error_message << std::endl; } class SSLServer: public std::enable_shared_from_this<SSLServer> { public: SSLServer(io_service& service, uint16_t port): acceptor_(service, ip::tcp::endpoint(ip::tcp::v4(), port)), context_ (ssl::context::tlsv12) { context_.set_options( ssl::context::default_workarounds | ssl::context::sslv2 | ssl::context::sslv3 | ssl::context::tlsv12); if (isAcceptorInitialized() && isContextInitialized ()) { std::cout << "acceptor ok" << std::endl; std::cout << "context ok" << std::endl; start_accept(); } else { std::cout << "server init error" << std::endl; } } private: void start_accept() { ssl_socket_ = std::make_shared<ssl::stream<ip::tcp::socket> >(acceptor_.get_executor(), context_); // ---------------------------------- // Starte den asynchronen Handshake // ---------------------------------- ssl_socket_->async_handshake(ssl::stream_base::server, [this](const boost::system::error_code& error) { if (!error) { // ----------------------------------- // Wenn der Handshake erfolgreich ist, // akzeptiere die Verbindung // ----------------------------------- if (ssl_socket_ && ssl_socket_->lowest_layer().is_open()) { std::cout << "SSL-Handshake erfolgreich und verbunden." << std::endl; acceptor_.async_accept(ssl_socket_->lowest_layer(), [this](const boost::system::error_code& accept_error) { if (!accept_error) { handle_client(); } else { std::cerr << "Accept error: " << accept_error.message() << std::endl; } }); } else { std::cerr << "SSL-Handshake erfolgreich, aber Verbindung nicht geöffnet." << std::endl; } } else { std::cerr << "Handshake error: " << error.message() << " (" << error.value() << ")" << std::endl; } }); } void handle_client() { // ------------------------------------ // Lese/Schreibe Daten mit ssl_socket_ // ------------------------------------ boost::asio::async_read_until(*ssl_socket_, buffer_, '\n', [this](const boost::system::error_code& read_error, std::size_t bytes_transferred) { if (!read_error) { std::istream is(&buffer_); std::string received_data; std::getline(is, received_data); std::cout << "Received data from client: " << received_data << std::endl; // ----------------------------------------- // Hier kannst du auf die empfangenen Daten // reagieren und die Antwort vorbereiten // ----------------------------------------- std::string response = "Hello from the server!\n"; // ----------------------------------------- // Sende die Antwort an den Client // ----------------------------------------- boost::asio::async_write(*ssl_socket_, boost::asio::buffer(response), [this](const boost::system::error_code& write_error, std::size_t) { if (!write_error) { // ----------------------------- // Schließe die Verbindung // ----------------------------- ssl_socket_->lowest_layer().close(); // ----------------------------- // Starte die nächste Akzeptanz // ----------------------------- start_accept(); } else { std::cerr << "Write error: " << write_error.message() << std::endl; } }); } else { std::cerr << "Read error: " << read_error.message() << std::endl; } }); } // ------------------------------------------------ // Überprüfung, ob der Acceptor initialisiert wurde // ------------------------------------------------ bool isAcceptorInitialized() const { return acceptor_.is_open(); } // ------------------------------------------------ // Überprüfung, ob der Context initialisiert wurde // ------------------------------------------------ bool isContextInitialized() { try { // ---------------------------------- // load certificate, and private key // ---------------------------------- context_.use_certificate_chain_file("server.crt.pem"); context_.use_private_key_file("server.key.pem", ssl::context::pem); return true; } catch (const boost::system::system_error& e) { handle_exception(e.what()); return false; } } private: ip::tcp::acceptor acceptor_; ssl::context context_; std::shared_ptr<ssl::stream<ip::tcp::socket>> ssl_socket_; boost::asio::streambuf buffer_; }; } // namespace: dBaseRelease int main(int argc, char **argv) { using namespace dBaseRelease; try { ApplicationExeName = argv[0]; io_service service; std::shared_ptr<SSLServer> server = std::make_shared<SSLServer>(service, 12345); service.run(); } catch (const std::exception& e) { std::cerr << "Exception: " << e.what() << std::endl; return EXIT_FAILURE; } return EXIT_SUCCESS; } -- Diese E-Mail wurde von Avast-Antivirussoftware auf Viren geprüft. www.avast.com

1 0

Abwesenheitsnachricht: Re: Cobalt link error
by Sören Textor 23 Dec '23

23 Dec '23

Derzeit bin ich nicht im Hause Ihre E-Mail wird nicht weitergeleitet. In dringenden Fällen bitte support(a)ditec-gmbh.de oder Telefonhotline +49-6221-31698-110 oder die Zentrale +49-6221-31698-0 kontaktieren. Mit freundlichen Grüßen Dr. Sören Textor ----------------------------------------------- DiTEC Dr. Siegfried Kahlich & Dierk Langer GmbH Im Breitspiel 19 | 69126 Heidelberg | Germany Handelsregister | Mannheim | HRB 341229 Dieses Dokument ist vertraulich zu behandeln. Die Weitergabe, sowie Vervielfältigung, Verwertung und Mitteilung seines Inhalts ist nur mit unserer ausdrücklichen Genehmigung gestattet. Alle Rechte vorbehalten, insbesondere für den Fall der Schutzrechtsanmeldung. This document has to be treated confidentially. Its contents are not to be passed on, duplicated, exploited or disclosed without our express permission. All rights reserved, especially the right to apply for protective rights.

1 0

Boost Asio Multicast
by Georg Gast 17 Dec '23

17 Dec '23

Hi there, I wrote an application that is to a good part based on https://www.boost.org/doc/libs/1_83_0/doc/html/boost_asio/example/cpp11/mul… https://www.boost.org/doc/libs/1_83_0/doc/html/boost_asio/example/cpp11/mul… It worked OK on my laptop as the packages arrived in my vm and my host. As we tried it on real machines the packages did not arrive. (all windows machines). With *netsh interface ip show joins* I could see on my laptop that the join was on the ethernet card. On the real machines it choose "the wrong" network card. I tried with "outbound_interface" to change it but didn't work... It's all ipv4. Can or should I use a static route to get the packages into the right net segment? Bye Georg

2 1

[Boost.Asio] Asynchronous queue?
by accelerator0099 15 Dec '23

15 Dec '23

Consider the producer-consumer model: producer -+- consumer1 +- consumer2 +- consumer3 +- consumer4 +- consumer5 The producer periodly push items into a queue, and those consumers wait on that queue for items It's easy to implement in a synchronous, multi-threaded environment: the producer just locks the queue and push into it, and notify one consumer through a condition variable. Consumers waiting on that condition variable will be woken one by one, popping items and consume them How to do those in a asynchronous environment? Consumers async_pop() on that queue, posting their completion tokens into the executor. When there are items available, the executor notify one consumer by calling its completion token Is it right? How do the producer tell the executor "The asynchronous operation is done, You should call that completion token"? My implemention of a possible async queue (based on timers): #include <boost/asio.hpp> #include <deque> #include <iostream> using namespace std::literals; namespace io = boost::asio; using io::awaitable; auto& uawait = io::use_awaitable; template<class D> awaitable<void> delay(const D& dur) { io::steady_timer tm{ co_await io::this_coro::executor }; tm.expires_after(dur); co_await tm.async_wait(uawait); } template<class T> class aqueue { std::deque<T> mq; public: using reference = T&; using const_reference = const T&; size_t size() const noexcept { return mq.size(); } bool empty() const noexcept { return mq.empty(); } awaitable<T> async_pop() { while (empty()) { co_await delay(1ms); } auto t = std::move(mq.front()); mq.pop_front(); co_return t; } awaitable<void> async_push(T t) { mq.push_back(std::move(t)); co_return; } }; class consumer { public: const int id; aqueue<int>& queue; consumer(int _i, aqueue<int>& _q) : id{ _i }, queue{ _q } {} awaitable<void> operator()() { std::cout << "Consumer " << id << " started\n"; auto i = co_await queue.async_pop(); std::cout << "Consumer " << id << " got " << i << '\n'; } }; int main() { io::io_context ctx; aqueue<int> aq; auto producer = [&]() -> awaitable<void> { std::cout << "Producer started\n"; for (int i{}; i != 5; ++i) { co_await delay(1s); co_await aq.async_push(i); } }; io::co_spawn(ctx, producer, io::detached); for (int i{}; i != 5; ++i) io::co_spawn(ctx, consumer{ i, aq }, io::detached); std::cout << "RUN\n"; ctx.run(); return 0; } Is it a proper way to do so using timers? I think there should be a better way

3 2