TLA Line data Source code
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 : srv.bind(endpoint{address_v4::any(), 8080});
74 : srv.start();
75 : ioc.run(); // Blocks until all work completes
76 : @endcode
77 :
78 : @par Graceful Shutdown
79 : To shut down gracefully, call @ref stop then drain the io_context:
80 : @code
81 : // From a signal handler or timer callback:
82 : srv.stop();
83 :
84 : // ioc.run() returns after pending work drains.
85 : // Then from the thread that called ioc.run():
86 : srv.join(); // Wait for accept loops to finish
87 : @endcode
88 :
89 : @par Restart After Stop
90 : The server can be restarted after a complete shutdown cycle.
91 : You must drain the io_context and call @ref join before restarting:
92 : @code
93 : srv.start();
94 : ioc.run_for( 10s ); // Run for a while
95 : srv.stop(); // Signal shutdown
96 : ioc.run(); // REQUIRED: drain pending completions
97 : srv.join(); // REQUIRED: wait for accept loops
98 :
99 : // Now safe to restart
100 : srv.start();
101 : ioc.run();
102 : @endcode
103 :
104 : @par WARNING: What NOT to Do
105 : - Do NOT call @ref join from inside a worker coroutine (deadlock).
106 : - Do NOT call @ref join from a thread running `ioc.run()` (deadlock).
107 : - Do NOT call @ref start without completing @ref join after @ref stop.
108 : - Do NOT call `ioc.stop()` for graceful shutdown; use @ref stop instead.
109 :
110 : @par Example
111 : @code
112 : class my_worker : public tcp_server::worker_base
113 : {
114 : corosio::tcp_socket sock_;
115 : capy::any_executor ex_;
116 : public:
117 : my_worker(io_context& ctx)
118 : : sock_(ctx)
119 : , ex_(ctx.get_executor())
120 : {
121 : }
122 :
123 : corosio::tcp_socket& socket() override { return sock_; }
124 :
125 : void run(launcher launch) override
126 : {
127 : launch(ex_, [](corosio::tcp_socket* sock) -> capy::task<>
128 : {
129 : // handle connection using sock
130 : co_return;
131 : }(&sock_));
132 : }
133 : };
134 :
135 : auto make_workers(io_context& ctx, int n)
136 : {
137 : std::vector<std::unique_ptr<tcp_server::worker_base>> v;
138 : v.reserve(n);
139 : for(int i = 0; i < n; ++i)
140 : v.push_back(std::make_unique<my_worker>(ctx));
141 : return v;
142 : }
143 :
144 : io_context ioc;
145 : tcp_server srv(ioc, ioc.get_executor());
146 : srv.set_workers(make_workers(ioc, 100));
147 : @endcode
148 :
149 : @see worker_base, set_workers, launcher
150 : */
151 : class BOOST_COROSIO_DECL tcp_server
152 : {
153 : public:
154 : class worker_base; ///< Abstract base for connection handlers.
155 : class launcher; ///< Move-only handle to launch worker coroutines.
156 :
157 : private:
158 : struct waiter
159 : {
160 : waiter* next;
161 : std::coroutine_handle<> h;
162 : worker_base* w;
163 : };
164 :
165 : struct impl;
166 :
167 : static impl* make_impl(capy::execution_context& ctx);
168 :
169 : impl* impl_;
170 : capy::any_executor ex_;
171 : waiter* waiters_ = nullptr;
172 : worker_base* idle_head_ = nullptr; // Forward list: available workers
173 : worker_base* active_head_ =
174 : nullptr; // Doubly linked: workers handling connections
175 : worker_base* active_tail_ = nullptr; // Tail for O(1) push_back
176 : std::size_t active_accepts_ = 0; // Number of active do_accept coroutines
177 : std::shared_ptr<void> storage_; // Owns the worker container (type-erased)
178 : bool running_ = false;
179 :
180 : // Idle list (forward/singly linked) - push front, pop front
181 HIT 45 : void idle_push(worker_base* w) noexcept
182 : {
183 45 : w->next_ = idle_head_;
184 45 : idle_head_ = w;
185 45 : }
186 :
187 9 : worker_base* idle_pop() noexcept
188 : {
189 9 : auto* w = idle_head_;
190 9 : if (w)
191 9 : idle_head_ = w->next_;
192 9 : return w;
193 : }
194 :
195 9 : bool idle_empty() const noexcept
196 : {
197 9 : return idle_head_ == nullptr;
198 : }
199 :
200 : // Active list (doubly linked) - push back, remove anywhere
201 3 : void active_push(worker_base* w) noexcept
202 : {
203 3 : w->next_ = nullptr;
204 3 : w->prev_ = active_tail_;
205 3 : if (active_tail_)
206 MIS 0 : active_tail_->next_ = w;
207 : else
208 HIT 3 : active_head_ = w;
209 3 : active_tail_ = w;
210 3 : }
211 :
212 9 : void active_remove(worker_base* w) noexcept
213 : {
214 : // Skip if not in active list (e.g., after failed accept)
215 9 : if (w != active_head_ && w->prev_ == nullptr)
216 6 : return;
217 3 : if (w->prev_)
218 MIS 0 : w->prev_->next_ = w->next_;
219 : else
220 HIT 3 : active_head_ = w->next_;
221 3 : if (w->next_)
222 MIS 0 : w->next_->prev_ = w->prev_;
223 : else
224 HIT 3 : active_tail_ = w->prev_;
225 3 : w->prev_ = nullptr; // Mark as not in active list
226 : }
227 :
228 : template<capy::Executor Ex>
229 : struct launch_wrapper
230 : {
231 : struct promise_type
232 : {
233 : Ex ex; // Executor stored directly in frame (outlives child tasks)
234 : capy::io_env env_;
235 :
236 : // For regular coroutines: first arg is executor, second is stop token
237 : template<class E, class S, class... Args>
238 : requires capy::Executor<std::decay_t<E>>
239 : promise_type(E e, S s, Args&&...)
240 : : ex(std::move(e))
241 : , env_{
242 : capy::executor_ref(ex), std::move(s),
243 : capy::get_current_frame_allocator()}
244 : {
245 : }
246 :
247 : // For lambda coroutines: first arg is closure, second is executor, third is stop token
248 : template<class Closure, class E, class S, class... Args>
249 : requires(!capy::Executor<std::decay_t<Closure>> &&
250 : capy::Executor<std::decay_t<E>>)
251 3 : promise_type(Closure&&, E e, S s, Args&&...)
252 3 : : ex(std::move(e))
253 3 : , env_{
254 3 : capy::executor_ref(ex), std::move(s),
255 3 : capy::get_current_frame_allocator()}
256 : {
257 3 : }
258 :
259 3 : launch_wrapper get_return_object() noexcept
260 : {
261 : return {
262 3 : std::coroutine_handle<promise_type>::from_promise(*this)};
263 : }
264 3 : std::suspend_always initial_suspend() noexcept
265 : {
266 3 : return {};
267 : }
268 3 : std::suspend_never final_suspend() noexcept
269 : {
270 3 : return {};
271 : }
272 3 : void return_void() noexcept {}
273 MIS 0 : void unhandled_exception()
274 : {
275 0 : std::terminate();
276 : }
277 :
278 : // Inject io_env for IoAwaitable
279 : template<capy::IoAwaitable Awaitable>
280 HIT 6 : auto await_transform(Awaitable&& a)
281 : {
282 : using AwaitableT = std::decay_t<Awaitable>;
283 : struct adapter
284 : {
285 : AwaitableT aw;
286 : capy::io_env const* env;
287 :
288 6 : bool await_ready()
289 : {
290 6 : return aw.await_ready();
291 : }
292 6 : decltype(auto) await_resume()
293 : {
294 6 : return aw.await_resume();
295 : }
296 :
297 6 : auto await_suspend(std::coroutine_handle<promise_type> h)
298 : {
299 6 : return aw.await_suspend(h, env);
300 : }
301 : };
302 9 : return adapter{std::forward<Awaitable>(a), &env_};
303 3 : }
304 : };
305 :
306 : std::coroutine_handle<promise_type> h;
307 :
308 3 : launch_wrapper(std::coroutine_handle<promise_type> handle) noexcept
309 3 : : h(handle)
310 : {
311 3 : }
312 :
313 3 : ~launch_wrapper()
314 : {
315 3 : if (h)
316 MIS 0 : h.destroy();
317 HIT 3 : }
318 :
319 : launch_wrapper(launch_wrapper&& o) noexcept
320 : : h(std::exchange(o.h, nullptr))
321 : {
322 : }
323 :
324 : launch_wrapper(launch_wrapper const&) = delete;
325 : launch_wrapper& operator=(launch_wrapper const&) = delete;
326 : launch_wrapper& operator=(launch_wrapper&&) = delete;
327 : };
328 :
329 : // Named functor to avoid incomplete lambda type in coroutine promise
330 : template<class Executor>
331 : struct launch_coro
332 : {
333 3 : launch_wrapper<Executor> operator()(
334 : Executor,
335 : std::stop_token,
336 : tcp_server* self,
337 : capy::task<void> t,
338 : worker_base* wp)
339 : {
340 : // Executor and stop token stored in promise via constructor
341 : co_await std::move(t);
342 : co_await self->push(*wp); // worker goes back to idle list
343 6 : }
344 : };
345 :
346 : class push_awaitable
347 : {
348 : tcp_server& self_;
349 : worker_base& w_;
350 :
351 : public:
352 9 : push_awaitable(tcp_server& self, worker_base& w) noexcept
353 9 : : self_(self)
354 9 : , w_(w)
355 : {
356 9 : }
357 :
358 9 : bool await_ready() const noexcept
359 : {
360 9 : return false;
361 : }
362 :
363 : std::coroutine_handle<>
364 9 : await_suspend(std::coroutine_handle<> h, capy::io_env const*) noexcept
365 : {
366 : // Symmetric transfer to server's executor
367 9 : return self_.ex_.dispatch(h);
368 : }
369 :
370 9 : void await_resume() noexcept
371 : {
372 : // Running on server executor - safe to modify lists
373 : // Remove from active (if present), then wake waiter or add to idle
374 9 : self_.active_remove(&w_);
375 9 : if (self_.waiters_)
376 : {
377 MIS 0 : auto* wait = self_.waiters_;
378 0 : self_.waiters_ = wait->next;
379 0 : wait->w = &w_;
380 0 : self_.ex_.post(wait->h);
381 : }
382 : else
383 : {
384 HIT 9 : self_.idle_push(&w_);
385 : }
386 9 : }
387 : };
388 :
389 : class pop_awaitable
390 : {
391 : tcp_server& self_;
392 : waiter wait_;
393 :
394 : public:
395 9 : pop_awaitable(tcp_server& self) noexcept : self_(self), wait_{} {}
396 :
397 9 : bool await_ready() const noexcept
398 : {
399 9 : return !self_.idle_empty();
400 : }
401 :
402 : bool
403 MIS 0 : await_suspend(std::coroutine_handle<> h, capy::io_env const*) noexcept
404 : {
405 : // Running on server executor (do_accept runs there)
406 0 : wait_.h = h;
407 0 : wait_.w = nullptr;
408 0 : wait_.next = self_.waiters_;
409 0 : self_.waiters_ = &wait_;
410 0 : return true;
411 : }
412 :
413 HIT 9 : worker_base& await_resume() noexcept
414 : {
415 : // Running on server executor
416 9 : if (wait_.w)
417 MIS 0 : return *wait_.w; // Woken by push_awaitable
418 HIT 9 : return *self_.idle_pop();
419 : }
420 : };
421 :
422 9 : push_awaitable push(worker_base& w)
423 : {
424 9 : return push_awaitable{*this, w};
425 : }
426 :
427 : // Synchronous version for destructor/guard paths
428 : // Must be called from server executor context
429 MIS 0 : void push_sync(worker_base& w) noexcept
430 : {
431 0 : active_remove(&w);
432 0 : if (waiters_)
433 : {
434 0 : auto* wait = waiters_;
435 0 : waiters_ = wait->next;
436 0 : wait->w = &w;
437 0 : ex_.post(wait->h);
438 : }
439 : else
440 : {
441 0 : idle_push(&w);
442 : }
443 0 : }
444 :
445 HIT 9 : pop_awaitable pop()
446 : {
447 9 : return pop_awaitable{*this};
448 : }
449 :
450 : capy::task<void> do_accept(tcp_acceptor& acc);
451 :
452 : public:
453 : /** Abstract base class for connection handlers.
454 :
455 : Derive from this class to implement custom connection handling.
456 : Each worker owns a socket and is reused across multiple
457 : connections to avoid per-connection allocation.
458 :
459 : @see tcp_server, launcher
460 : */
461 : class BOOST_COROSIO_DECL worker_base
462 : {
463 : // Ordered largest to smallest for optimal packing
464 : std::stop_source stop_; // ~16 bytes
465 : worker_base* next_ = nullptr; // 8 bytes - used by idle and active lists
466 : worker_base* prev_ = nullptr; // 8 bytes - used only by active list
467 :
468 : friend class tcp_server;
469 :
470 : public:
471 : /// Destroy the worker.
472 36 : virtual ~worker_base() = default;
473 :
474 : /** Handle an accepted connection.
475 :
476 : Called when this worker is dispatched to handle a new
477 : connection. The implementation must invoke the launcher
478 : exactly once to start the handling coroutine.
479 :
480 : @param launch Handle to launch the connection coroutine.
481 : */
482 : virtual void run(launcher launch) = 0;
483 :
484 : /// Return the socket used for connections.
485 : virtual corosio::tcp_socket& socket() = 0;
486 : };
487 :
488 : /** Move-only handle to launch a worker coroutine.
489 :
490 : Passed to @ref worker_base::run to start the connection-handling
491 : coroutine. The launcher ensures the worker returns to the idle
492 : pool when the coroutine completes or if launching fails.
493 :
494 : The launcher must be invoked exactly once via `operator()`.
495 : If destroyed without invoking, the worker is returned to the
496 : idle pool automatically.
497 :
498 : @see worker_base::run
499 : */
500 : class BOOST_COROSIO_DECL launcher
501 : {
502 : tcp_server* srv_;
503 : worker_base* w_;
504 :
505 : friend class tcp_server;
506 :
507 3 : launcher(tcp_server& srv, worker_base& w) noexcept : srv_(&srv), w_(&w)
508 : {
509 3 : }
510 :
511 : public:
512 : /// Return the worker to the pool if not launched.
513 3 : ~launcher()
514 : {
515 3 : if (w_)
516 MIS 0 : srv_->push_sync(*w_);
517 HIT 3 : }
518 :
519 : launcher(launcher&& o) noexcept
520 : : srv_(o.srv_)
521 : , w_(std::exchange(o.w_, nullptr))
522 : {
523 : }
524 : launcher(launcher const&) = delete;
525 : launcher& operator=(launcher const&) = delete;
526 : launcher& operator=(launcher&&) = delete;
527 :
528 : /** Launch the connection-handling coroutine.
529 :
530 : Starts the given coroutine on the specified executor. When
531 : the coroutine completes, the worker is automatically returned
532 : to the idle pool.
533 :
534 : @param ex The executor to run the coroutine on.
535 : @param task The coroutine to execute.
536 :
537 : @throws std::logic_error If this launcher was already invoked.
538 : */
539 : template<class Executor>
540 3 : void operator()(Executor const& ex, capy::task<void> task)
541 : {
542 3 : if (!w_)
543 MIS 0 : detail::throw_logic_error(); // launcher already invoked
544 :
545 HIT 3 : auto* w = std::exchange(w_, nullptr);
546 :
547 : // Worker is being dispatched - add to active list
548 3 : srv_->active_push(w);
549 :
550 : // Return worker to pool if coroutine setup throws
551 : struct guard_t
552 : {
553 : tcp_server* srv;
554 : worker_base* w;
555 3 : ~guard_t()
556 : {
557 3 : if (w)
558 MIS 0 : srv->push_sync(*w);
559 HIT 3 : }
560 3 : } guard{srv_, w};
561 :
562 : // Reset worker's stop source for this connection
563 3 : w->stop_ = {};
564 3 : auto st = w->stop_.get_token();
565 :
566 3 : auto wrapper =
567 3 : launch_coro<Executor>{}(ex, st, srv_, std::move(task), w);
568 :
569 : // Executor and stop token stored in promise via constructor
570 3 : ex.post(std::exchange(wrapper.h, nullptr)); // Release before post
571 3 : guard.w = nullptr; // Success - dismiss guard
572 3 : }
573 : };
574 :
575 : /** Construct a TCP server.
576 :
577 : @tparam Ctx Execution context type satisfying ExecutionContext.
578 : @tparam Ex Executor type satisfying Executor.
579 :
580 : @param ctx The execution context for socket operations.
581 : @param ex The executor for dispatching coroutines.
582 :
583 : @par Example
584 : @code
585 : tcp_server srv(ctx, ctx.get_executor());
586 : srv.set_workers(make_workers(ctx, 100));
587 : srv.bind(endpoint{...});
588 : srv.start();
589 : @endcode
590 : */
591 : template<capy::ExecutionContext Ctx, capy::Executor Ex>
592 9 : tcp_server(Ctx& ctx, Ex ex) : impl_(make_impl(ctx))
593 9 : , ex_(std::move(ex))
594 : {
595 9 : }
596 :
597 : public:
598 : ~tcp_server();
599 : tcp_server(tcp_server const&) = delete;
600 : tcp_server& operator=(tcp_server const&) = delete;
601 : tcp_server(tcp_server&& o) noexcept;
602 : tcp_server& operator=(tcp_server&& o) noexcept;
603 :
604 : /** Bind to a local endpoint.
605 :
606 : Creates an acceptor listening on the specified endpoint.
607 : Multiple endpoints can be bound by calling this method
608 : multiple times before @ref start.
609 :
610 : @param ep The local endpoint to bind to.
611 :
612 : @return The error code if binding fails.
613 : */
614 : std::error_code bind(endpoint ep);
615 :
616 : /** Set the worker pool.
617 :
618 : Replaces any existing workers with the given range. Any
619 : previous workers are released and the idle/active lists
620 : are cleared before populating with new workers.
621 :
622 : @tparam Range Forward range of pointer-like objects to worker_base.
623 :
624 : @param workers Range of workers to manage. Each element must
625 : support `std::to_address()` yielding `worker_base*`.
626 :
627 : @par Example
628 : @code
629 : std::vector<std::unique_ptr<my_worker>> workers;
630 : for(int i = 0; i < 100; ++i)
631 : workers.push_back(std::make_unique<my_worker>(ctx));
632 : srv.set_workers(std::move(workers));
633 : @endcode
634 : */
635 : template<std::ranges::forward_range Range>
636 : requires std::convertible_to<
637 : decltype(std::to_address(
638 : std::declval<std::ranges::range_value_t<Range>&>())),
639 : worker_base*>
640 9 : void set_workers(Range&& workers)
641 : {
642 : // Clear existing state
643 9 : storage_.reset();
644 9 : idle_head_ = nullptr;
645 9 : active_head_ = nullptr;
646 9 : active_tail_ = nullptr;
647 :
648 : // Take ownership and populate idle list
649 : using StorageType = std::decay_t<Range>;
650 9 : auto* p = new StorageType(std::forward<Range>(workers));
651 9 : storage_ = std::shared_ptr<void>(
652 9 : p, [](void* ptr) { delete static_cast<StorageType*>(ptr); });
653 45 : for (auto&& elem : *static_cast<StorageType*>(p))
654 36 : idle_push(std::to_address(elem));
655 9 : }
656 :
657 : /** Start accepting connections.
658 :
659 : Launches accept loops for all bound endpoints. Incoming
660 : connections are dispatched to idle workers from the pool.
661 :
662 : Calling `start()` on an already-running server has no effect.
663 :
664 : @par Preconditions
665 : - At least one endpoint bound via @ref bind.
666 : - Workers provided to the constructor.
667 : - If restarting, @ref join must have completed first.
668 :
669 : @par Effects
670 : Creates one accept coroutine per bound endpoint. Each coroutine
671 : runs on the server's executor, waiting for connections and
672 : dispatching them to idle workers.
673 :
674 : @par Restart Sequence
675 : To restart after stopping, complete the full shutdown cycle:
676 : @code
677 : srv.start();
678 : ioc.run_for( 1s );
679 : srv.stop(); // 1. Signal shutdown
680 : ioc.run(); // 2. Drain remaining completions
681 : srv.join(); // 3. Wait for accept loops
682 :
683 : // Now safe to restart
684 : srv.start();
685 : ioc.run();
686 : @endcode
687 :
688 : @par Thread Safety
689 : Not thread safe.
690 :
691 : @throws std::logic_error If a previous session has not been
692 : joined (accept loops still active).
693 : */
694 : void start();
695 :
696 : /** Stop accepting connections.
697 :
698 : Signals all listening ports to stop accepting new connections
699 : and requests cancellation of active workers via their stop tokens.
700 :
701 : This function returns immediately; it does not wait for workers
702 : to finish. Pending I/O operations complete asynchronously.
703 :
704 : Calling `stop()` on a non-running server has no effect.
705 :
706 : @par Effects
707 : - Closes all acceptors (pending accepts complete with error).
708 : - Requests stop on each active worker's stop token.
709 : - Workers observing their stop token should exit promptly.
710 :
711 : @par Postconditions
712 : No new connections will be accepted. Active workers continue
713 : until they observe their stop token or complete naturally.
714 :
715 : @par What Happens Next
716 : After calling `stop()`:
717 : 1. Let `ioc.run()` return (drains pending completions).
718 : 2. Call @ref join to wait for accept loops to finish.
719 : 3. Only then is it safe to restart or destroy the server.
720 :
721 : @par Thread Safety
722 : Not thread safe.
723 :
724 : @see join, start
725 : */
726 : void stop();
727 :
728 : /** Block until all accept loops complete.
729 :
730 : Blocks the calling thread until all accept coroutines launched
731 : by @ref start have finished executing. This synchronizes the
732 : shutdown sequence, ensuring the server is fully stopped before
733 : restarting or destroying it.
734 :
735 : @par Preconditions
736 : @ref stop has been called and `ioc.run()` has returned.
737 :
738 : @par Postconditions
739 : All accept loops have completed. The server is in the stopped
740 : state and may be restarted via @ref start.
741 :
742 : @par Example (Correct Usage)
743 : @code
744 : // main thread
745 : srv.start();
746 : ioc.run(); // Blocks until work completes
747 : srv.join(); // Safe: called after ioc.run() returns
748 : @endcode
749 :
750 : @par WARNING: Deadlock Scenarios
751 : Calling `join()` from the wrong context causes deadlock:
752 :
753 : @code
754 : // WRONG: calling join() from inside a worker coroutine
755 : void run( launcher launch ) override
756 : {
757 : launch( ex, [this]() -> capy::task<>
758 : {
759 : srv_.join(); // DEADLOCK: blocks the executor
760 : co_return;
761 : }());
762 : }
763 :
764 : // WRONG: calling join() while ioc.run() is still active
765 : std::thread t( [&]{ ioc.run(); } );
766 : srv.stop();
767 : srv.join(); // DEADLOCK: ioc.run() still running in thread t
768 : @endcode
769 :
770 : @par Thread Safety
771 : May be called from any thread, but will deadlock if called
772 : from within the io_context event loop or from a worker coroutine.
773 :
774 : @see stop, start
775 : */
776 : void join();
777 :
778 : private:
779 : capy::task<> do_stop();
780 : };
781 :
782 : #ifdef _MSC_VER
783 : #pragma warning(pop)
784 : #endif
785 :
786 : } // namespace boost::corosio
787 :
788 : #endif
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