include/boost/corosio/tcp_server.hpp

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tcp_server.hpp

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