include/boost/corosio/tcp_server.hpp

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tcp_server.hpp

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1		//
2		// Copyright (c) 2026 Vinnie Falco (vinnie.falco@gmail.com)
3		//
4		// Distributed under the Boost Software License, Version 1.0. (See accompanying
5		// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6		//
7		// Official repository: https://github.com/cppalliance/corosio
8		//
9
10		#ifndef BOOST_COROSIO_TCP_SERVER_HPP
11		#define BOOST_COROSIO_TCP_SERVER_HPP
12
13		#include <boost/corosio/detail/config.hpp>
14		#include <boost/corosio/detail/except.hpp>
15		#include <boost/corosio/tcp_acceptor.hpp>
16		#include <boost/corosio/tcp_socket.hpp>
17		#include <boost/corosio/io_context.hpp>
18		#include <boost/corosio/endpoint.hpp>
19		#include <boost/capy/task.hpp>
20		#include <boost/capy/concept/execution_context.hpp>
21		#include <boost/capy/concept/io_awaitable.hpp>
22		#include <boost/capy/concept/executor.hpp>
23		#include <boost/capy/ex/any_executor.hpp>
24		#include <boost/capy/ex/frame_allocator.hpp>
25		#include <boost/capy/ex/io_env.hpp>
26		#include <boost/capy/ex/run_async.hpp>
27
28		#include <coroutine>
29		#include <memory>
30		#include <ranges>
31		#include <vector>
32
33		namespace boost::corosio {
34
35		#ifdef _MSC_VER
36		#pragma warning(push)
37		#pragma warning(disable : 4251) // class needs to have dll-interface
38		#endif
39
40		/** TCP server with pooled workers.
41
42		This class manages a pool of reusable worker objects that handle
43		incoming connections. When a connection arrives, an idle worker
44		is dispatched to handle it. After the connection completes, the
45		worker returns to the pool for reuse, avoiding allocation overhead
46		per connection.
47
48		Workers are set via @ref set_workers as a forward range of
49		pointer-like objects (e.g., `unique_ptr<worker_base>`). The server
50		takes ownership of the container via type erasure.
51
52		@par Thread Safety
53		Distinct objects: Safe.
54		Shared objects: Unsafe.
55
56		@par Lifecycle
57		The server operates in three states:
58
59		- Stopped: Initial state, or after @ref join completes.
60		- Running: After @ref start, actively accepting connections.
61		- Stopping: After @ref stop, draining active work.
62
63		State transitions:
64		@code
65		[Stopped] --start()--> [Running] --stop()--> [Stopping] --join()--> [Stopped]
66		@endcode
67
68		@par Running the Server
69		@code
70		io_context ioc;
71		tcp_server srv(ioc, ioc.get_executor());
72		srv.set_workers(make_workers(ioc, 100));
73		if (auto ec = srv.bind(endpoint{ipv4_address::any(), 8080}))
74		return;
75		srv.start();
76		ioc.run(); // Blocks until all work completes
77		@endcode
78
79		@par Graceful Shutdown
80		To shut down gracefully, call @ref stop then drain the io_context:
81		@code
82		// From a signal handler or timer callback:
83		srv.stop();
84
85		// ioc.run() returns after pending work drains.
86		// Then from the thread that called ioc.run():
87		srv.join(); // Wait for accept loops to finish
88		@endcode
89
90		@par Restart After Stop
91		The server can be restarted after a complete shutdown cycle.
92		You must drain the io_context and call @ref join before restarting:
93		@code
94		srv.start();
95		ioc.run_for( 10s ); // Run for a while
96		srv.stop(); // Signal shutdown
97		ioc.run(); // REQUIRED: drain pending completions
98		srv.join(); // REQUIRED: wait for accept loops
99
100		// Now safe to restart
101		srv.start();
102		ioc.run();
103		@endcode
104
105		@par WARNING: What NOT to Do
106		- Do NOT call @ref join from inside a worker coroutine (deadlock).
107		- Do NOT call @ref join from a thread running `ioc.run()` (deadlock).
108		- Do NOT call @ref start without completing @ref join after @ref stop.
109		- Do NOT call `ioc.stop()` for graceful shutdown; use @ref stop instead.
110
111		@par Example
112		@code
113		class my_worker : public tcp_server::worker_base
114		{
115		corosio::tcp_socket sock_;
116		capy::any_executor ex_;
117		public:
118		my_worker(io_context& ctx)
119		: sock_(ctx)
120		, ex_(ctx.get_executor())
121		{
122		}
123
124		corosio::tcp_socket& socket() override { return sock_; }
125
126		void run(launcher launch) override
127		{
128		launch(ex_, [](corosio::tcp_socket* sock) -> capy::task<>
129		{
130		// handle connection using sock
131		co_return;
132		}(&sock_));
133		}
134		};
135
136		auto make_workers(io_context& ctx, int n)
137		{
138		std::vector<std::unique_ptr<tcp_server::worker_base>> v;
139		v.reserve(n);
140		for(int i = 0; i < n; ++i)
141		v.push_back(std::make_unique<my_worker>(ctx));
142		return v;
143		}
144
145		io_context ioc;
146		tcp_server srv(ioc, ioc.get_executor());
147		srv.set_workers(make_workers(ioc, 100));
148		@endcode
149
150		@see worker_base, set_workers, launcher
151		*/
152		class BOOST_COROSIO_DECL tcp_server
153		{
154		public:
155		class worker_base; ///< Abstract base for connection handlers.
156		class launcher; ///< Move-only handle to launch worker coroutines.
157
158		private:
159		struct waiter
160		{
161		waiter* next;
162		std::coroutine_handle<> h;
163		capy::continuation cont;
164		worker_base* w;
165		};
166
167		struct impl;
168
169		static impl* make_impl(capy::execution_context& ctx);
170
171		impl* impl_;
172		capy::any_executor ex_;
173		waiter* waiters_ = nullptr;
174		worker_base* idle_head_ = nullptr; // Forward list: available workers
175		worker_base* active_head_ =
176		nullptr; // Doubly linked: workers handling connections
177		worker_base* active_tail_ = nullptr; // Tail for O(1) push_back
178		std::size_t active_accepts_ = 0; // Number of active do_accept coroutines
179		std::shared_ptr<void> storage_; // Owns the worker container (type-erased)
180		bool running_ = false;
181
182		// Idle list (forward/singly linked) - push front, pop front
183	162x	void idle_push(worker_base* w) noexcept
184		{
185	162x	w->next_ = idle_head_;
186	162x	idle_head_ = w;
187	162x	}
188
189	36x	worker_base* idle_pop() noexcept
190		{
191	36x	auto* w = idle_head_;
192	36x	if (w)
193	36x	idle_head_ = w->next_;
194	36x	return w;
195		}
196
197	42x	bool idle_empty() const noexcept
198		{
199	42x	return idle_head_ == nullptr;
200		}
201
202		// Active list (doubly linked) - push back, remove anywhere
203	18x	void active_push(worker_base* w) noexcept
204		{
205	18x	w->next_ = nullptr;
206	18x	w->prev_ = active_tail_;
207	18x	if (active_tail_)
208	4x	active_tail_->next_ = w;
209		else
210	14x	active_head_ = w;
211	18x	active_tail_ = w;
212	18x	}
213
214	42x	void active_remove(worker_base* w) noexcept
215		{
216		// Skip if not in active list (e.g., after failed accept)
217	42x	if (w != active_head_ && w->prev_ == nullptr)
218	24x	return;
219	18x	if (w->prev_)
220	4x	w->prev_->next_ = w->next_;
221		else
222	14x	active_head_ = w->next_;
223	18x	if (w->next_)
224	2x	w->next_->prev_ = w->prev_;
225		else
226	16x	active_tail_ = w->prev_;
227	18x	w->prev_ = nullptr; // Mark as not in active list
228		}
229
230		template<capy::Executor Ex>
231		struct launch_wrapper
232		{
233		struct promise_type
234		{
235		Ex ex; // Executor stored directly in frame (outlives child tasks)
236		capy::io_env env_;
237
238		// For regular coroutines: first arg is executor, second is stop token
239		template<class E, class S, class... Args>
240		requires capy::Executor<std::decay_t<E>>
241		promise_type(E e, S s, Args&&...)
242		: ex(std::move(e))
243		, env_{
244		capy::executor_ref(ex), std::move(s),
245		capy::get_current_frame_allocator()}
246		{
247		}
248
249		// For lambda coroutines: first arg is closure, second is executor, third is stop token
250		template<class Closure, class E, class S, class... Args>
251		requires(!capy::Executor<std::decay_t<Closure>> &&
252		capy::Executor<std::decay_t<E>>)
253	18x	promise_type(Closure&&, E e, S s, Args&&...)
254	18x	: ex(std::move(e))
255	18x	, env_{
256	18x	capy::executor_ref(ex), std::move(s),
257	18x	capy::get_current_frame_allocator()}
258		{
259	18x	}
260
261	18x	launch_wrapper get_return_object() noexcept
262		{
263		return {
264	18x	std::coroutine_handle<promise_type>::from_promise(*this)};
265		}
266	18x	std::suspend_always initial_suspend() noexcept
267		{
268	18x	return {};
269		}
270	18x	std::suspend_never final_suspend() noexcept
271		{
272	18x	return {};
273		}
274	18x	void return_void() noexcept {}
275	✗	void unhandled_exception()
276		{
277	✗	std::terminate();
278		}
279
280		// Inject io_env for IoAwaitable
281		template<capy::IoAwaitable Awaitable>
282	36x	auto await_transform(Awaitable&& a)
283		{
284		using AwaitableT = std::decay_t<Awaitable>;
285		struct adapter
286		{
287		AwaitableT aw;
288		capy::io_env const* env;
289
290		bool await_ready()
291		{
292		return aw.await_ready();
293		}
294		decltype(auto) await_resume()
295		{
296		return aw.await_resume();
297		}
298
299		auto await_suspend(std::coroutine_handle<promise_type> h)
300		{
301		return aw.await_suspend(h, env);
302		}
303		};
304	54x	return adapter{std::forward<Awaitable>(a), &env_};
305	18x	}
306		};
307
308		std::coroutine_handle<promise_type> h;
309
310	18x	launch_wrapper(std::coroutine_handle<promise_type> handle) noexcept
311	18x	: h(handle)
312		{
313	18x	}
314
315	18x	~launch_wrapper()
316		{
317	18x	if (h)
318	✗	h.destroy();
319	18x	}
320
321		launch_wrapper(launch_wrapper&& o) noexcept
322		: h(std::exchange(o.h, nullptr))
323		{
324		}
325
326		launch_wrapper(launch_wrapper const&) = delete;
327		launch_wrapper& operator=(launch_wrapper const&) = delete;
328		launch_wrapper& operator=(launch_wrapper&&) = delete;
329		};
330
331		// Named functor to avoid incomplete lambda type in coroutine promise
332		template<class Executor>
333		struct launch_coro
334		{
335	18x	launch_wrapper<Executor> operator()(
336		Executor,
337		std::stop_token,
338		tcp_server* self,
339		capy::task<void> t,
340		worker_base* wp)
341		{
342		// Executor and stop token stored in promise via constructor
343		co_await std::move(t);
344		co_await self->push(*wp); // worker goes back to idle list
345	36x	}
346		};
347
348		class push_awaitable
349		{
350		tcp_server& self_;
351		worker_base& w_;
352		capy::continuation cont_;
353
354		public:
355	38x	push_awaitable(tcp_server& self, worker_base& w) noexcept
356	38x	: self_(self)
357	38x	, w_(w)
358		{
359	38x	}
360
361	38x	bool await_ready() const noexcept
362		{
363	38x	return false;
364		}
365
366		std::coroutine_handle<>
367	38x	await_suspend(std::coroutine_handle<> h, capy::io_env const*) noexcept
368		{
369		// Symmetric transfer to server's executor
370	38x	cont_.h = h;
371	38x	return self_.ex_.dispatch(cont_);
372		}
373
374	38x	void await_resume() noexcept
375		{
376		// Running on server executor - safe to modify lists
377		// Remove from active (if present), then wake waiter or add to idle
378	38x	self_.active_remove(&w_);
379	38x	if (self_.waiters_)
380		{
381	6x	auto* wait = self_.waiters_;
382	6x	self_.waiters_ = wait->next;
383	6x	wait->w = &w_;
384	6x	wait->cont.h = wait->h;
385	6x	self_.ex_.post(wait->cont);
386		}
387		else
388		{
389	32x	self_.idle_push(&w_);
390		}
391	38x	}
392		};
393
394		class pop_awaitable
395		{
396		tcp_server& self_;
397		waiter wait_;
398
399		public:
400	42x	pop_awaitable(tcp_server& self) noexcept : self_(self), wait_{} {}
401
402	42x	bool await_ready() const noexcept
403		{
404	42x	return !self_.idle_empty();
405		}
406
407		bool
408	6x	await_suspend(std::coroutine_handle<> h, capy::io_env const*) noexcept
409		{
410		// Running on server executor (do_accept runs there)
411	6x	wait_.h = h;
412	6x	wait_.w = nullptr;
413	6x	wait_.next = self_.waiters_;
414	6x	self_.waiters_ = &wait_;
415	6x	return true;
416		}
417
418	42x	worker_base& await_resume() noexcept
419		{
420		// Running on server executor
421	42x	if (wait_.w)
422	6x	return *wait_.w; // Woken by push_awaitable
423	36x	return *self_.idle_pop();
424		}
425		};
426
427	38x	push_awaitable push(worker_base& w)
428		{
429	38x	return push_awaitable{*this, w};
430		}
431
432		// Synchronous version for destructor/guard paths
433		// Must be called from server executor context
434	4x	void push_sync(worker_base& w) noexcept
435		{
436	4x	active_remove(&w);
437	4x	if (waiters_)
438		{
439	✗	auto* wait = waiters_;
440	✗	waiters_ = wait->next;
441	✗	wait->w = &w;
442	✗	wait->cont.h = wait->h;
443	✗	ex_.post(wait->cont);
444		}
445		else
446		{
447	4x	idle_push(&w);
448		}
449	4x	}
450
451	42x	pop_awaitable pop()
452		{
453	42x	return pop_awaitable{*this};
454		}
455
456		capy::task<void> do_accept(tcp_acceptor& acc);
457
458		public:
459		/** Abstract base class for connection handlers.
460
461		Derive from this class to implement custom connection handling.
462		Each worker owns a socket and is reused across multiple
463		connections to avoid per-connection allocation.
464
465		@see tcp_server, launcher
466		*/
467		class BOOST_COROSIO_DECL worker_base
468		{
469		// Ordered largest to smallest for optimal packing
470		std::stop_source stop_; // ~16 bytes
471		worker_base* next_ = nullptr; // 8 bytes - used by idle and active lists
472		worker_base* prev_ = nullptr; // 8 bytes - used only by active list
473
474		friend class tcp_server;
475
476		public:
477		/// Construct a worker.
478		worker_base();
479
480		/// Destroy the worker.
481		virtual ~worker_base();
482
483		/** Handle an accepted connection.
484
485		Called when this worker is dispatched to handle a new
486		connection. The implementation must invoke the launcher
487		exactly once to start the handling coroutine.
488
489		@param launch Handle to launch the connection coroutine.
490		*/
491		virtual void run(launcher launch) = 0;
492
493		/// Return the socket used for connections.
494		virtual corosio::tcp_socket& socket() = 0;
495		};
496
497		/** Move-only handle to launch a worker coroutine.
498
499		Passed to @ref worker_base::run to start the connection-handling
500		coroutine. The launcher ensures the worker returns to the idle
501		pool when the coroutine completes or if launching fails.
502
503		The launcher must be invoked exactly once via `operator()`.
504		If destroyed without invoking, the worker is returned to the
505		idle pool automatically.
506
507		@see worker_base::run
508		*/
509		class BOOST_COROSIO_DECL launcher
510		{
511		tcp_server* srv_;
512		worker_base* w_;
513
514		friend class tcp_server;
515
516	22x	launcher(tcp_server& srv, worker_base& w) noexcept : srv_(&srv), w_(&w)
517		{
518	22x	}
519
520		public:
521		/// Return the worker to the pool if not launched.
522	22x	~launcher()
523		{
524	22x	if (w_)
525	4x	srv_->push_sync(*w_);
526	22x	}
527
528		launcher(launcher&& o) noexcept
529		: srv_(o.srv_)
530		, w_(std::exchange(o.w_, nullptr))
531		{
532		}
533		launcher(launcher const&) = delete;
534		launcher& operator=(launcher const&) = delete;
535		launcher& operator=(launcher&&) = delete;
536
537		/** Launch the connection-handling coroutine.
538
539		Starts the given coroutine on the specified executor. When
540		the coroutine completes, the worker is automatically returned
541		to the idle pool.
542
543		@param ex The executor to run the coroutine on.
544		@param task The coroutine to execute.
545
546		@throws std::logic_error If this launcher was already invoked.
547		*/
548		template<class Executor>
549	20x	void operator()(Executor const& ex, capy::task<void> task)
550		{
551	20x	if (!w_)
552	2x	detail::throw_logic_error(); // launcher already invoked
553
554	18x	auto* w = std::exchange(w_, nullptr);
555
556		// Worker is being dispatched - add to active list
557	18x	srv_->active_push(w);
558
559		// Return worker to pool if coroutine setup throws
560		struct guard_t
561		{
562		tcp_server* srv;
563		worker_base* w;
564	18x	~guard_t()
565		{
566	18x	if (w)
567	✗	srv->push_sync(*w);
568	18x	}
569	18x	} guard{srv_, w};
570
571		// Reset worker's stop source for this connection
572	18x	w->stop_ = {};
573	18x	auto st = w->stop_.get_token();
574
575	18x	auto wrapper =
576	18x	launch_coro<Executor>{}(ex, st, srv_, std::move(task), w);
577
578		// Executor and stop token stored in promise via constructor
579	18x	ex.post(std::exchange(wrapper.h, nullptr)); // Release before post
580	18x	guard.w = nullptr; // Success - dismiss guard
581	18x	}
582		};
583
584		/** Construct a TCP server.
585
586		@tparam Ctx Execution context type satisfying ExecutionContext.
587		@tparam Ex Executor type satisfying Executor.
588
589		@param ctx The execution context for socket operations.
590		@param ex The executor for dispatching coroutines.
591
592		@par Example
593		@code
594		tcp_server srv(ctx, ctx.get_executor());
595		srv.set_workers(make_workers(ctx, 100));
596		if (auto ec = srv.bind(endpoint{...}))
597		return;
598		srv.start();
599		@endcode
600		*/
601		template<capy::ExecutionContext Ctx, capy::Executor Ex>
602	36x	tcp_server(Ctx& ctx, Ex ex) : impl_(make_impl(ctx))
603	36x	, ex_(std::move(ex))
604		{
605	36x	}
606
607		public:
608		/// Destroy the server, stopping all accept loops.
609		~tcp_server();
610
611		tcp_server(tcp_server const&) = delete;
612		tcp_server& operator=(tcp_server const&) = delete;
613
614		/** Move construct from another server.
615
616		@param o The source server. After the move, @p o is
617		in a valid but unspecified state.
618		*/
619		tcp_server(tcp_server&& o) noexcept;
620
621		/** Move assign from another server.
622
623		@param o The source server. After the move, @p o is
624		in a valid but unspecified state.
625
626		@return `*this`.
627		*/
628		tcp_server& operator=(tcp_server&& o) noexcept;
629
630		/** Bind to a local endpoint.
631
632		Creates an acceptor listening on the specified endpoint.
633		Multiple endpoints can be bound by calling this method
634		multiple times before @ref start.
635
636		@param ep The local endpoint to bind to.
637
638		@return The error code if binding fails.
639		*/
640		[[nodiscard]] std::error_code bind(endpoint ep);
641
642		/** Set the worker pool.
643
644		Replaces any existing workers with the given range. Any
645		previous workers are released and the idle/active lists
646		are cleared before populating with new workers.
647
648		@tparam Range Forward range of pointer-like objects to worker_base.
649
650		@param workers Range of workers to manage. Each element must
651		support `std::to_address()` yielding `worker_base*`.
652
653		@par Example
654		@code
655		std::vector<std::unique_ptr<my_worker>> workers;
656		for(int i = 0; i < 100; ++i)
657		workers.push_back(std::make_unique<my_worker>(ctx));
658		srv.set_workers(std::move(workers));
659		@endcode
660		*/
661		template<std::ranges::forward_range Range>
662		requires std::convertible_to<
663		decltype(std::to_address(
664		std::declval<std::ranges::range_value_t<Range>&>())),
665		worker_base*>
666	36x	void set_workers(Range&& workers)
667		{
668		// Clear existing state
669	36x	storage_.reset();
670	36x	idle_head_ = nullptr;
671	36x	active_head_ = nullptr;
672	36x	active_tail_ = nullptr;
673
674		// Take ownership and populate idle list
675		using StorageType = std::decay_t<Range>;
676	36x	auto* p = new StorageType(std::forward<Range>(workers));
677	36x	storage_ = std::shared_ptr<void>(
678	36x	p, [](void* ptr) { delete static_cast<StorageType*>(ptr); });
679	162x	for (auto&& elem : static_cast<StorageType>(p))
680	126x	idle_push(std::to_address(elem));
681	36x	}
682
683		/** Start accepting connections.
684
685		Launches accept loops for all bound endpoints. Incoming
686		connections are dispatched to idle workers from the pool.
687
688		Calling `start()` on an already-running server has no effect.
689
690		@par Preconditions
691		- At least one endpoint bound via @ref bind.
692		- Workers provided via @ref set_workers.
693		- If restarting, @ref join must have completed first.
694
695		@par Effects
696		Creates one accept coroutine per bound endpoint. Each coroutine
697		runs on the server's executor, waiting for connections and
698		dispatching them to idle workers.
699
700		@par Restart Sequence
701		To restart after stopping, complete the full shutdown cycle:
702		@code
703		srv.start();
704		ioc.run_for( 1s );
705		srv.stop(); // 1. Signal shutdown
706		ioc.run(); // 2. Drain remaining completions
707		srv.join(); // 3. Wait for accept loops
708
709		// Now safe to restart
710		srv.start();
711		ioc.run();
712		@endcode
713
714		@par Thread Safety
715		Not thread safe.
716
717		@throws std::logic_error If a previous session has not been
718		joined (accept loops still active).
719		*/
720		void start();
721
722		/** Return the local endpoint for the i-th bound port.
723
724		@param index Zero-based index into the list of bound ports.
725
726		@return The local endpoint, or a default-constructed endpoint
727		if @p index is out of range or the acceptor is not open.
728		*/
729		endpoint local_endpoint(std::size_t index = 0) const noexcept;
730
731		/** Stop accepting connections.
732
733		Requests the accept loops' stop token and requests cancellation
734		of active workers via their stop tokens. The acceptors are not
735		closed; a suspended accept completes once more before its loop
736		observes the stop token and ends.
737
738		This function returns immediately; it does not wait for workers
739		to finish. Pending I/O operations complete asynchronously.
740
741		Calling `stop()` on a non-running server has no effect.
742
743		@par Effects
744		- Requests stop on the accept loops' stop token. The acceptors
745		are not closed; a pending accept completes once more before
746		the accept loop ends.
747		- Requests stop on each active worker's stop token.
748		- Workers observing their stop token should exit promptly.
749
750		@par Postconditions
751		No new connections will be accepted. Active workers continue
752		until they observe their stop token or complete naturally.
753
754		@par What Happens Next
755		After calling `stop()`:
756		1. Let `ioc.run()` return (drains pending completions).
757		2. Call @ref join to wait for accept loops to finish.
758		3. Only then is it safe to restart or destroy the server.
759
760		@par Thread Safety
761		Not thread safe.
762
763		@see join, start
764		*/
765		void stop();
766
767		/** Block until all accept loops complete.
768
769		Blocks the calling thread until all accept coroutines launched
770		by @ref start have finished executing. This synchronizes the
771		shutdown sequence, ensuring the server is fully stopped before
772		restarting or destroying it.
773
774		@par Preconditions
775		@ref stop has been called and `ioc.run()` has returned.
776
777		@par Postconditions
778		All accept loops have completed. The server is in the stopped
779		state and may be restarted via @ref start.
780
781		@par Example (Correct Usage)
782		@code
783		// main thread
784		srv.start();
785		ioc.run(); // Blocks until work completes
786		srv.join(); // Safe: called after ioc.run() returns
787		@endcode
788
789		@par WARNING: Deadlock Scenarios
790		Calling `join()` from the wrong context causes deadlock:
791
792		@code
793		// WRONG: calling join() from inside a worker coroutine
794		void run( launcher launch ) override
795		{
796		launch( ex, [this]() -> capy::task<>
797		{
798		srv_.join(); // DEADLOCK: blocks the executor
799		co_return;
800		}());
801		}
802
803		// WRONG: calling join() while ioc.run() is still active
804		std::thread t( [&]{ ioc.run(); } );
805		srv.stop();
806		srv.join(); // DEADLOCK: ioc.run() still running in thread t
807		@endcode
808
809		@par Thread Safety
810		May be called from any thread, but will deadlock if called
811		from within the io_context event loop or from a worker coroutine.
812
813		@see stop, start
814		*/
815		void join();
816
817		private:
818		capy::task<> do_stop();
819		};
820
821		#ifdef _MSC_VER
822		#pragma warning(pop)
823		#endif
824
825		} // namespace boost::corosio
826
827		#endif
828