Does it have a coro lock?

[nqf]

asio::mutex mutex;
	asio::co_spawn(
		pool, [&]() -> asio::awaitable<void> {
                        // Does ASIO have such a lock?
			co_await mutex.lock();
		},
		asio::detached);

[Maximsiv1410]

I join the question, are you @chriskohlhoff planning to add something like async_mutex from cppcoro? It's not about thread synchronization, but about prevention of concurrent execution of coroutines at some code points.. I believe there is no way to achieve such behavior with strands. Also there is similar async_mutex in libunifex of facebook.
Would be very useful! :)
Correct me if i'm wrong.

[nqf]

cppcoro::task<std::string> query_redis(const std::string& key) {
	std::cout << "query redis:" << key << std::endl;
	co_return std::string{"hello"};
}

asio::awaitable<void> echo(asio::ip::tcp::socket socket) {
	char data[1024];
	for (;;) {
		std::size_t n = co_await socket.async_read_some(asio::buffer(data), asio::use_awaitable);
		auto key = co_await query_redis(std::string{data});
		std::cout << "key:" << key << std::endl;
		auto w = co_await socket.async_write_some(asio::buffer(data, n), asio::use_awaitable);
	}
}


[ 50%] Building CXX object CMakeFiles/corod.dir/src/main.cpp.o
/home/xxxxx/coro/src/main.cpp: In function ‘asio::awaitable<void> echo(asio::ip::tcp::socket)’:
/home/xxxxx/coro/src/main.cpp:80:53: error: no matching function for call to ‘asio::detail::awaitable_frame<void, asio::any_io_executor>::await_transform(cppcoro::task<std::basic_string<char> >)’
   80 |    auto key = co_await query_redis(std::string{data});
      |                                                     ^
In file included from /home/xxxxx/coro/deps/.src/asio/asio/include/asio/awaitable.hpp:129,
                 from /home/xxxxx/coro/deps/.src/asio/asio/include/asio.hpp:23,
                 from /home/xxxxx/coro/src/main.cpp:15:
/home/xxxxx/coro/deps/.src/asio/asio/include/asio/impl/awaitable.hpp:161:8: note: candidate: ‘template<class T> auto asio::detail::awaitable_frame_base<Executor>::await_transform(asio::awaitable<T, Executor>) const [with T = T; Executor = asio::any_io_executor]’
  161 |   auto await_transform(awaitable<T, Executor> a) const
      |        ^~~~~~~~~~~~~~~
/home/xxxxx/coro/deps/.src/asio/asio/include/asio/impl/awaitable.hpp:161:8: note:   template argument deduction/substitution failed:
/home/xxxxx/coro/src/main.cpp:80:53: note:   ‘cppcoro::task<std::basic_string<char> >’ is not derived from ‘asio::awaitable<T, asio::any_io_executor>’
   80 |    auto key = co_await query_redis(std::string{data});
      |                                                     ^
In file included from /home/xxxxx/coro/deps/.src/asio/asio/include/asio/awaitable.hpp:129,
                 from /home/xxxxx/coro/deps/.src/asio/asio/include/asio.hpp:23,
                 from /home/xxxxx/coro/src/main.cpp:15:
/home/xxxxx/coro/deps/.src/asio/asio/include/asio/impl/awaitable.hpp:171:8: note: candidate: ‘auto asio::detail::awaitable_frame_base<Executor>::await_transform(asio::this_coro::executor_t) [with Executor = asio::any_io_executor]’
  171 |   auto await_transform(this_coro::executor_t) noexcept
      |        ^~~~~~~~~~~~~~~
/home/xxxxx/coro/deps/.src/asio/asio/include/asio/impl/awaitable.hpp:171:24: note:   no known conversion for argument 1 from ‘cppcoro::task<std::basic_string<char> >’ to ‘asio::this_coro::executor_t’
  171 |   auto await_transform(this_coro::executor_t) noexcept
      |                        ^~~~~~~~~~~~~~~~~~~~~
/home/xxxxx/coro/deps/.src/asio/asio/include/asio/impl/awaitable.hpp:197:8: note: candidate: ‘auto asio::detail::awaitable_frame_base<Executor>::await_transform(asio::this_coro::cancellation_state_t) [with Executor = asio::any_io_executor]’
  197 |   auto await_transform(this_coro::cancellation_state_t) noexcept
      |        ^~~~~~~~~~~~~~~
/home/xxxxx/coro/deps/.src/asio/asio/include/asio/impl/awaitable.hpp:197:24: note:   no known conversion for argument 1 from ‘cppcoro::task<std::basic_string<char> >’ to ‘asio::this_coro::cancellation_state_t’
  197 |   auto await_transform(this_coro::cancellation_state_t) noexcept

It doesn't seem to work with other libraries, I don't know how to deal with this situation

[microcai]

no such thing, at present ;)
but you can always re-invent your own wheel.

[yuraaka]

I reinvented it this way (maybe will be useful for someone):

class coro_strand {
  public:
      coro_strand(boost::asio::io_service& ios)
          : ios_(ios)
      {
      }

      template <typename Coroutine>
      boost::asio::awaitable<void> async_post(Coroutine&& coro) {
          co_await boost::asio::co_spawn(ios_, [&] mutable -> boost::asio::awaitable<void> {
              ++pending_;
              auto finally = make_on_exit_scope([&]() {
                  if (--pending_) {
                      schedule_next();
                  }
              });

              if (pending_ == 1) {
                  co_await coro();
              } else {
                  co_await async_defer(coro);
              }
          }, boost::asio::use_awaitable);
      }

  private:
      void schedule_next() {
          boost::asio::post(ios_, [&]() { queue_.run_one(); });
      }

      template <typename Coroutine>
      boost::asio::awaitable<void> async_defer(Coroutine&& coro) {
          if (queue_.stopped()) {
              queue_.restart();
          }

          co_await boost::asio::co_spawn(queue_, [&] mutable -> boost::asio::awaitable<void> {
              co_await boost::asio::co_spawn(ios_, [&] mutable -> boost::asio::awaitable<void> {
                  auto finally = make_on_exit_scope([&]() { schedule_next(); });
                  co_await coro();
              }, boost::asio::use_awaitable);
          }, boost::asio::use_awaitable);
      }

  private:
      boost::asio::io_service& ios_;
      boost::asio::io_service queue_;
      size_t pending_ = 0;
  };