TLA Line data Source code
1 : //
2 : // Copyright (c) 2026 Vinnie Falco (vinnie.falco@gmail.com)
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 : waiter* waiters_ = nullptr;
115 : worker_base* idle_head_ = nullptr; // Forward list: available workers
116 : worker_base* active_head_ =
117 : nullptr; // Doubly linked: workers handling connections
118 : worker_base* active_tail_ = nullptr; // Tail for O(1) push_back
119 : 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 : bool running_ = false;
122 :
123 : // Idle list (forward/singly linked) - push front, pop front
124 HIT 238 : void idle_push(worker_base* w) noexcept
125 : {
126 238 : w->next_ = idle_head_;
127 238 : idle_head_ = w;
128 238 : }
129 :
130 75 : worker_base* idle_pop() noexcept
131 : {
132 75 : auto* w = idle_head_;
133 75 : if (w)
134 75 : idle_head_ = w->next_;
135 75 : return w;
136 : }
137 :
138 153 : bool idle_empty() const noexcept
139 : {
140 153 : return idle_head_ == nullptr;
141 : }
142 :
143 : // Active list (doubly linked) - push back, remove anywhere
144 88 : void active_push(worker_base* w) noexcept
145 : {
146 88 : w->next_ = nullptr;
147 88 : w->prev_ = active_tail_;
148 88 : if (active_tail_)
149 4 : active_tail_->next_ = w;
150 : else
151 84 : active_head_ = w;
152 88 : active_tail_ = w;
153 88 : }
154 :
155 153 : void active_remove(worker_base* w) noexcept
156 : {
157 : // Skip if not in active list (e.g., after failed accept)
158 153 : if (w != active_head_ && w->prev_ == nullptr)
159 65 : return;
160 88 : if (w->prev_)
161 4 : w->prev_->next_ = w->next_;
162 : else
163 84 : active_head_ = w->next_;
164 88 : if (w->next_)
165 2 : w->next_->prev_ = w->prev_;
166 : else
167 86 : active_tail_ = w->prev_;
168 88 : w->prev_ = nullptr; // Mark as not in active list
169 : }
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 88 : promise_type(Closure&&, E e, S s, Args&&...)
195 88 : : ex(std::move(e))
196 88 : , env_{
197 88 : capy::executor_ref(ex), std::move(s),
198 88 : capy::get_current_frame_allocator()}
199 : {
200 88 : }
201 :
202 88 : launch_wrapper get_return_object() noexcept
203 : {
204 : return {
205 88 : std::coroutine_handle<promise_type>::from_promise(*this)};
206 : }
207 88 : std::suspend_always initial_suspend() noexcept
208 : {
209 88 : return {};
210 : }
211 88 : std::suspend_never final_suspend() noexcept
212 : {
213 88 : return {};
214 : }
215 88 : void return_void() noexcept {}
216 MIS 0 : 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 HIT 176 : 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 :
234 176 : bool await_ready()
235 : {
236 176 : return aw.await_ready();
237 : }
238 176 : decltype(auto) await_resume()
239 : {
240 176 : return aw.await_resume();
241 : }
242 :
243 176 : auto await_suspend(std::coroutine_handle<promise_type> h)
244 : {
245 176 : return aw.await_suspend(h, env);
246 : }
247 : };
248 264 : return adapter{std::forward<Awaitable>(a), &env_};
249 88 : }
250 : };
251 :
252 : std::coroutine_handle<promise_type> h;
253 :
254 88 : launch_wrapper(std::coroutine_handle<promise_type> handle) noexcept
255 88 : : h(handle)
256 : {
257 88 : }
258 :
259 88 : ~launch_wrapper()
260 : {
261 88 : if (h)
262 MIS 0 : h.destroy();
263 HIT 88 : }
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 88 : launch_wrapper<Executor> operator()(
280 : Executor,
281 : std::stop_token,
282 : tcp_server* self,
283 : capy::task<void> t,
284 : worker_base* wp)
285 : {
286 : // Executor and stop token stored in promise via constructor
287 : co_await std::move(t);
288 : co_await self->push(*wp); // worker goes back to idle list
289 176 : }
290 : };
291 :
292 : class push_awaitable
293 : {
294 : tcp_server& self_;
295 : worker_base& w_;
296 : capy::continuation cont_;
297 :
298 : public:
299 145 : push_awaitable(tcp_server& self, worker_base& w) noexcept
300 145 : : self_(self)
301 145 : , w_(w)
302 : {
303 145 : }
304 :
305 145 : bool await_ready() const noexcept
306 : {
307 145 : return false;
308 : }
309 :
310 : std::coroutine_handle<>
311 145 : await_suspend(std::coroutine_handle<> h, capy::io_env const*) noexcept
312 : {
313 : // Symmetric transfer to server's executor
314 145 : cont_.h = h;
315 145 : return self_.ex_.dispatch(cont_);
316 : }
317 :
318 145 : 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
322 145 : self_.active_remove(&w_);
323 145 : if (self_.waiters_)
324 : {
325 76 : auto* wait = self_.waiters_;
326 76 : self_.waiters_ = wait->next;
327 76 : wait->w = &w_;
328 76 : wait->cont.h = wait->h;
329 76 : self_.ex_.post(wait->cont);
330 : }
331 : else
332 : {
333 69 : self_.idle_push(&w_);
334 : }
335 145 : }
336 : };
337 :
338 : class pop_awaitable
339 : {
340 : tcp_server& self_;
341 : waiter wait_;
342 :
343 : public:
344 153 : pop_awaitable(tcp_server& self) noexcept : self_(self), wait_{} {}
345 :
346 153 : bool await_ready() const noexcept
347 : {
348 153 : return !self_.idle_empty();
349 : }
350 :
351 : bool
352 78 : await_suspend(std::coroutine_handle<> h, capy::io_env const*) noexcept
353 : {
354 : // Running on server executor (do_accept runs there)
355 78 : wait_.h = h;
356 78 : wait_.w = nullptr;
357 78 : wait_.next = self_.waiters_;
358 78 : self_.waiters_ = &wait_;
359 78 : return true;
360 : }
361 :
362 153 : worker_base& await_resume() noexcept
363 : {
364 : // Running on server executor
365 153 : if (wait_.w)
366 78 : return *wait_.w; // Woken by push_awaitable
367 75 : return *self_.idle_pop();
368 : }
369 : };
370 :
371 145 : push_awaitable push(worker_base& w)
372 : {
373 145 : return push_awaitable{*this, w};
374 : }
375 :
376 : // Synchronous version for destructor/guard paths
377 : // Must be called from server executor context
378 8 : void push_sync(worker_base& w) noexcept
379 : {
380 8 : active_remove(&w);
381 8 : if (waiters_)
382 : {
383 2 : auto* wait = waiters_;
384 2 : waiters_ = wait->next;
385 2 : wait->w = &w;
386 2 : wait->cont.h = wait->h;
387 2 : ex_.post(wait->cont);
388 : }
389 : else
390 : {
391 6 : idle_push(&w);
392 : }
393 8 : }
394 :
395 153 : pop_awaitable pop()
396 : {
397 153 : 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 96 : launcher(tcp_server& srv, worker_base& w) noexcept : srv_(&srv), w_(&w)
461 : {
462 96 : }
463 :
464 : public:
465 : /// Return the worker to the pool if not launched.
466 98 : ~launcher()
467 : {
468 98 : if (w_)
469 8 : srv_->push_sync(*w_);
470 98 : }
471 :
472 2 : launcher(launcher&& o) noexcept
473 2 : : srv_(o.srv_)
474 2 : , w_(std::exchange(o.w_, nullptr))
475 : {
476 2 : }
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 90 : void operator()(Executor const& ex, capy::task<void> task)
494 : {
495 90 : if (!w_)
496 2 : detail::throw_logic_error(); // launcher already invoked
497 :
498 88 : auto* w = std::exchange(w_, nullptr);
499 :
500 : // Worker is being dispatched - add to active list
501 88 : 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 88 : ~guard_t()
509 : {
510 88 : if (w)
511 MIS 0 : srv->push_sync(*w);
512 HIT 88 : }
513 88 : } guard{srv_, w};
514 :
515 : // Reset worker's stop source for this connection
516 88 : w->stop_ = {};
517 88 : auto st = w->stop_.get_token();
518 :
519 88 : auto wrapper =
520 88 : launch_coro<Executor>{}(ex, st, srv_, std::move(task), w);
521 :
522 : // Executor and stop token stored in promise via constructor
523 88 : ex.post(std::exchange(wrapper.h, nullptr)); // Release before post
524 88 : guard.w = nullptr; // Success - dismiss guard
525 88 : }
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 73 : tcp_server(Ctx& ctx, Ex ex) : impl_(make_impl(ctx))
541 73 : , ex_(std::move(ex))
542 : {
543 73 : }
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 73 : void set_workers(Range&& workers)
600 : {
601 : // Clear existing state
602 73 : storage_.reset();
603 73 : idle_head_ = nullptr;
604 73 : active_head_ = nullptr;
605 73 : active_tail_ = nullptr;
606 :
607 : // Take ownership and populate idle list
608 : using StorageType = std::decay_t<Range>;
609 73 : auto* p = new StorageType(std::forward<Range>(workers));
610 73 : storage_ = std::shared_ptr<void>(
611 73 : p, [](void* ptr) { delete static_cast<StorageType*>(ptr); });
612 236 : for (auto&& elem : *static_cast<StorageType*>(p))
613 163 : idle_push(std::to_address(elem));
614 73 : }
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
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