include/boost/corosio/native/detail/posix/posix_signal_service.hpp

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posix_signal_service.hpp

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1		//
2		// Copyright (c) 2026 Steve Gerbino
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_NATIVE_DETAIL_POSIX_POSIX_SIGNAL_SERVICE_HPP
11		#define BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_SIGNAL_SERVICE_HPP
12
13		#include <boost/corosio/detail/platform.hpp>
14
15		#if BOOST_COROSIO_POSIX
16
17		#include <boost/corosio/native/detail/posix/posix_signal.hpp>
18
19		#include <boost/corosio/detail/config.hpp>
20		#include <boost/capy/ex/execution_context.hpp>
21		#include <boost/corosio/detail/scheduler.hpp>
22		#include <boost/capy/error.hpp>
23
24		#include <mutex>
25
26		#include <signal.h>
27
28		/*
29		POSIX Signal Service
30		====================
31
32		Concrete signal service implementation for POSIX backends. Manages signal
33		registrations via sigaction() and dispatches completions through the
34		scheduler. One instance per execution_context, created by
35		get_signal_service().
36
37		See the block comment further down for the full architecture overview.
38		*/
39
40		/*
41		POSIX Signal Implementation
42		===========================
43
44		This file implements signal handling for POSIX systems using sigaction().
45		The implementation supports signal flags (SA_RESTART, etc.) and integrates
46		with any POSIX-compatible scheduler via the abstract scheduler interface.
47
48		Architecture Overview
49		---------------------
50
51		Three layers manage signal registrations:
52
53		1. signal_state (global singleton)
54		- Tracks the global service list and per-signal registration counts
55		- Stores the flags used for first registration of each signal (for
56		conflict detection when multiple signal_sets register same signal)
57		- Owns the mutex that protects signal handler installation/removal
58
59		2. posix_signal_service (one per execution_context)
60		- Maintains registrations_[] table indexed by signal number
61		- Each slot is a doubly-linked list of signal_registrations for that signal
62		- Also maintains impl_list_ of all posix_signal objects it owns
63
64		3. posix_signal (one per signal_set)
65		- Owns a singly-linked list (sorted by signal number) of signal_registrations
66		- Contains the pending_op_ used for wait operations
67
68		Signal Delivery Flow
69		--------------------
70
71		1. Signal arrives -> corosio_posix_signal_handler() (must be async-signal-safe)
72		-> deliver_signal()
73
74		2. deliver_signal() iterates all posix_signal_service services:
75		- If a signal_set is waiting (impl->waiting_ == true), post the signal_op
76		to the scheduler for immediate completion
77		- Otherwise, increment reg->undelivered to queue the signal
78
79		3. When wait() is called via start_wait():
80		- First check for queued signals (undelivered > 0); if found, post
81		immediate completion without blocking
82		- Otherwise, set waiting_ = true and call work_started() to keep
83		the io_context alive
84
85		Locking Protocol
86		----------------
87
88		Two mutex levels exist (MUST acquire in this order to avoid deadlock):
89		1. signal_state::mutex - protects handler registration and service list
90		2. posix_signal_service::mutex_ - protects per-service registration tables
91
92		Async-Signal-Safety Limitation
93		------------------------------
94
95		IMPORTANT: deliver_signal() is called from signal handler context and
96		acquires mutexes. This is NOT strictly async-signal-safe per POSIX.
97		The limitation:
98		- If a signal arrives while another thread holds state->mutex or
99		service->mutex_, and that same thread receives the signal, a
100		deadlock can occur (self-deadlock on non-recursive mutex).
101
102		This design trades strict async-signal-safety for implementation simplicity.
103		In practice, deadlocks are rare because:
104		- Mutexes are held only briefly during registration changes
105		- Most programs don't modify signal sets while signals are expected
106		- The window for signal arrival during mutex hold is small
107
108		A fully async-signal-safe implementation would require lock-free data
109		structures and atomic operations throughout, significantly increasing
110		complexity.
111
112		Flag Handling
113		-------------
114
115		- Flags are abstract values in the public API (signal_set::flags_t)
116		- flags_supported() validates that requested flags are available on
117		this platform; returns false if SA_NOCLDWAIT is unavailable and
118		no_child_wait is requested
119		- to_sigaction_flags() maps validated flags to actual SA_* constants
120		- First registration of a signal establishes the flags; subsequent
121		registrations must be compatible (same flags or dont_care)
122		- Requesting unavailable flags returns operation_not_supported
123
124		Work Tracking
125		-------------
126
127		When waiting for a signal:
128		- start_wait() calls sched_->work_started() to prevent io_context::run()
129		from returning while we wait
130		- signal_op::svc is set to point to the service
131		- signal_op::operator()() calls work_finished() after resuming the coroutine
132
133		If a signal was already queued (undelivered > 0), no work tracking is needed
134		because completion is posted immediately.
135		*/
136
137		namespace boost::corosio {
138
139		namespace detail {
140
141		/** Signal service for POSIX backends.
142
143		Manages signal registrations via sigaction() and dispatches signal
144		completions through the scheduler. One instance per execution_context.
145		*/
146		class BOOST_COROSIO_DECL posix_signal_service final
147		: public capy::execution_context::service
148		, public io_object::io_service
149		{
150		public:
151		using key_type = posix_signal_service;
152
153		posix_signal_service(capy::execution_context& ctx, scheduler& sched);
154		~posix_signal_service() override;
155
156		posix_signal_service(posix_signal_service const&) = delete;
157		posix_signal_service& operator=(posix_signal_service const&) = delete;
158
159		io_object::implementation* construct() override;
160
161	88x	void destroy(io_object::implementation* p) override
162		{
163	88x	auto& impl = static_cast<posix_signal&>(*p);
164	88x	[[maybe_unused]] auto n = impl.clear();
165	88x	impl.cancel();
166	88x	destroy_impl(impl);
167	88x	}
168
169		void shutdown() override;
170
171		void destroy_impl(posix_signal& impl);
172
173		std::error_code add_signal(
174		posix_signal& impl, int signal_number, signal_set::flags_t flags);
175
176		std::error_code remove_signal(posix_signal& impl, int signal_number);
177
178		std::error_code clear_signals(posix_signal& impl);
179
180		void cancel_wait(posix_signal& impl);
181		void start_wait(posix_signal& impl, signal_op* op);
182
183		static void deliver_signal(int signal_number);
184
185		void work_started() noexcept;
186		void work_finished() noexcept;
187		void post(signal_op* op);
188
189		private:
190		static void add_service(posix_signal_service* service);
191		static void remove_service(posix_signal_service* service);
192
193		scheduler* sched_;
194		std::mutex mutex_;
195		intrusive_list<posix_signal> impl_list_;
196
197		// Per-signal registration table
198		signal_registration* registrations_[max_signal_number];
199
200		// Registration counts for each signal
201		std::size_t registration_count_[max_signal_number];
202
203		// Linked list of all posix_signal_service services for signal delivery
204		posix_signal_service* next_ = nullptr;
205		posix_signal_service* prev_ = nullptr;
206		};
207
208		/** Get or create the signal service for the given context.
209
210		This function is called by the concrete scheduler during initialization
211		to create the signal service with a reference to itself.
212
213		@param ctx Reference to the owning execution_context.
214		@param sched Reference to the scheduler for posting completions.
215		@return Reference to the signal service.
216		*/
217		posix_signal_service&
218		get_signal_service(capy::execution_context& ctx, scheduler& sched);
219
220		} // namespace detail
221
222		} // namespace boost::corosio
223
224		// ---------------------------------------------------------------------------
225		// Inline implementation
226		// ---------------------------------------------------------------------------
227
228		namespace boost::corosio {
229
230		namespace detail {
231
232		namespace posix_signal_detail {
233
234		struct signal_state
235		{
236		std::mutex mutex;
237		posix_signal_service* service_list = nullptr;
238		std::size_t registration_count[max_signal_number] = {};
239		signal_set::flags_t registered_flags[max_signal_number] = {};
240		};
241
242		BOOST_COROSIO_DECL signal_state* get_signal_state();
243
244		// Check if requested flags are supported on this platform.
245		// Returns true if all flags are supported, false otherwise.
246		inline bool
247	94x	flags_supported([[maybe_unused]] signal_set::flags_t flags)
248		{
249		#ifndef SA_NOCLDWAIT
250		if (flags & signal_set::no_child_wait)
251		return false;
252		#endif
253	94x	return true;
254		}
255
256		// Map abstract flags to sigaction() flags.
257		// Caller must ensure flags_supported() returns true first.
258		inline int
259	76x	to_sigaction_flags(signal_set::flags_t flags)
260		{
261	76x	int sa_flags = 0;
262	76x	if (flags & signal_set::restart)
263	18x	sa_flags \|= SA_RESTART;
264	76x	if (flags & signal_set::no_child_stop)
265	✗	sa_flags \|= SA_NOCLDSTOP;
266		#ifdef SA_NOCLDWAIT
267	76x	if (flags & signal_set::no_child_wait)
268	✗	sa_flags \|= SA_NOCLDWAIT;
269		#endif
270	76x	if (flags & signal_set::no_defer)
271	2x	sa_flags \|= SA_NODEFER;
272	76x	if (flags & signal_set::reset_handler)
273	✗	sa_flags \|= SA_RESETHAND;
274	76x	return sa_flags;
275		}
276
277		// Check if two flag values are compatible
278		inline bool
279	18x	flags_compatible(signal_set::flags_t existing, signal_set::flags_t requested)
280		{
281		// dont_care is always compatible
282	34x	if ((existing & signal_set::dont_care) \|\|
283	16x	(requested & signal_set::dont_care))
284	6x	return true;
285
286		// Mask out dont_care bit for comparison
287	12x	constexpr auto mask = ~signal_set::dont_care;
288	12x	return (existing & mask) == (requested & mask);
289		}
290
291		// C signal handler - must be async-signal-safe
292		inline void
293	20x	corosio_posix_signal_handler(int signal_number)
294		{
295	20x	posix_signal_service::deliver_signal(signal_number);
296		// Note: With sigaction(), the handler persists automatically
297		// (unlike some signal() implementations that reset to SIG_DFL)
298	20x	}
299
300		} // namespace posix_signal_detail
301
302		// signal_op implementation
303
304		inline void
305	22x	signal_op::operator()()
306		{
307	22x	if (ec_out)
308	22x	*ec_out = {};
309	22x	if (signal_out)
310	22x	*signal_out = signal_number;
311
312		// Capture svc before resuming (coro may destroy us)
313	22x	auto* service = svc;
314	22x	svc = nullptr;
315
316	22x	cont_op.cont.h = h;
317	22x	d.post(cont_op.cont);
318
319		// Balance the work_started() from start_wait
320	22x	if (service)
321	12x	service->work_finished();
322	22x	}
323
324		inline void
325	✗	signal_op::destroy()
326		{
327		// No-op: signal_op is embedded in posix_signal
328	✗	}
329
330		// posix_signal implementation
331
332	88x	inline posix_signal::posix_signal(posix_signal_service& svc) noexcept
333	88x	: svc_(svc)
334		{
335	88x	}
336
337		inline std::coroutine_handle<>
338	26x	posix_signal::wait(
339		std::coroutine_handle<> h,
340		capy::executor_ref d,
341		std::stop_token token,
342		std::error_code* ec,
343		int* signal_out)
344		{
345	26x	pending_op_.h = h;
346	26x	pending_op_.d = d;
347	26x	pending_op_.ec_out = ec;
348	26x	pending_op_.signal_out = signal_out;
349	26x	pending_op_.signal_number = 0;
350
351	26x	if (token.stop_requested())
352		{
353	✗	if (ec)
354	✗	*ec = make_error_code(capy::error::canceled);
355	✗	if (signal_out)
356	✗	*signal_out = 0;
357	✗	pending_op_.cont_op.cont.h = h;
358	✗	d.post(pending_op_.cont_op.cont);
359		// completion is always posted to scheduler queue, never inline.
360	✗	return std::noop_coroutine();
361		}
362
363	26x	svc_.start_wait(*this, &pending_op_);
364		// completion is always posted to scheduler queue, never inline.
365	26x	return std::noop_coroutine();
366		}
367
368		inline std::error_code
369	96x	posix_signal::add(int signal_number, signal_set::flags_t flags)
370		{
371	96x	return svc_.add_signal(*this, signal_number, flags);
372		}
373
374		inline std::error_code
375	4x	posix_signal::remove(int signal_number)
376		{
377	4x	return svc_.remove_signal(*this, signal_number);
378		}
379
380		inline std::error_code
381	92x	posix_signal::clear()
382		{
383	92x	return svc_.clear_signals(*this);
384		}
385
386		inline void
387	100x	posix_signal::cancel()
388		{
389	100x	svc_.cancel_wait(*this);
390	100x	}
391
392		// posix_signal_service implementation
393
394	515x	inline posix_signal_service::posix_signal_service(
395	515x	capy::execution_context&, scheduler& sched)
396	515x	: sched_(&sched)
397		{
398	33475x	for (int i = 0; i < max_signal_number; ++i)
399		{
400	32960x	registrations_[i] = nullptr;
401	32960x	registration_count_[i] = 0;
402		}
403	515x	add_service(this);
404	515x	}
405
406	1030x	inline posix_signal_service::~posix_signal_service()
407		{
408	515x	remove_service(this);
409	1030x	}
410
411		inline void
412	515x	posix_signal_service::shutdown()
413		{
414	515x	std::lock_guard lock(mutex_);
415
416	515x	for (auto* impl = impl_list_.pop_front(); impl != nullptr;
417	✗	impl = impl_list_.pop_front())
418		{
419	✗	while (auto* reg = impl->signals_)
420		{
421	✗	impl->signals_ = reg->next_in_set;
422	✗	delete reg;
423	✗	}
424	✗	delete impl;
425		}
426	515x	}
427
428		inline io_object::implementation*
429	88x	posix_signal_service::construct()
430		{
431	88x	auto* impl = new posix_signal(*this);
432
433		{
434	88x	std::lock_guard lock(mutex_);
435	88x	impl_list_.push_back(impl);
436	88x	}
437
438	88x	return impl;
439		}
440
441		inline void
442	88x	posix_signal_service::destroy_impl(posix_signal& impl)
443		{
444		{
445	88x	std::lock_guard lock(mutex_);
446	88x	impl_list_.remove(&impl);
447	88x	}
448
449	88x	delete &impl;
450	88x	}
451
452		inline std::error_code
453	96x	posix_signal_service::add_signal(
454		posix_signal& impl, int signal_number, signal_set::flags_t flags)
455		{
456	96x	if (signal_number < 0 \|\| signal_number >= max_signal_number)
457	2x	return make_error_code(std::errc::invalid_argument);
458
459		// Validate that requested flags are supported on this platform
460		// (e.g., SA_NOCLDWAIT may not be available on all POSIX systems)
461	94x	if (!posix_signal_detail::flags_supported(flags))
462	✗	return make_error_code(std::errc::operation_not_supported);
463
464		posix_signal_detail::signal_state* state =
465	94x	posix_signal_detail::get_signal_state();
466	94x	std::lock_guard state_lock(state->mutex);
467	94x	std::lock_guard lock(mutex_);
468
469		// Find insertion point (list is sorted by signal number)
470	94x	signal_registration** insertion_point = &impl.signals_;
471	94x	signal_registration* reg = impl.signals_;
472	104x	while (reg && reg->signal_number < signal_number)
473		{
474	10x	insertion_point = &reg->next_in_set;
475	10x	reg = reg->next_in_set;
476		}
477
478		// Already registered in this set - check flag compatibility
479		// (same signal_set adding same signal twice with different flags)
480	94x	if (reg && reg->signal_number == signal_number)
481		{
482	10x	if (!posix_signal_detail::flags_compatible(reg->flags, flags))
483	2x	return make_error_code(std::errc::invalid_argument);
484	8x	return {};
485		}
486
487		// Check flag compatibility with global registration
488		// (different signal_set already registered this signal with different flags)
489	84x	if (state->registration_count[signal_number] > 0)
490		{
491	8x	if (!posix_signal_detail::flags_compatible(
492		state->registered_flags[signal_number], flags))
493	2x	return make_error_code(std::errc::invalid_argument);
494		}
495
496	82x	auto* new_reg = new signal_registration;
497	82x	new_reg->signal_number = signal_number;
498	82x	new_reg->flags = flags;
499	82x	new_reg->owner = &impl;
500	82x	new_reg->undelivered = 0;
501
502		// Install signal handler on first global registration
503	82x	if (state->registration_count[signal_number] == 0)
504		{
505	76x	struct sigaction sa = {};
506	76x	sa.sa_handler = posix_signal_detail::corosio_posix_signal_handler;
507	76x	sigemptyset(&sa.sa_mask);
508	76x	sa.sa_flags = posix_signal_detail::to_sigaction_flags(flags);
509
510	76x	if (::sigaction(signal_number, &sa, nullptr) < 0)
511		{
512	✗	delete new_reg;
513	✗	return make_error_code(std::errc::invalid_argument);
514		}
515
516		// Store the flags used for first registration
517	76x	state->registered_flags[signal_number] = flags;
518		}
519
520	82x	new_reg->next_in_set = reg;
521	82x	*insertion_point = new_reg;
522
523	82x	new_reg->next_in_table = registrations_[signal_number];
524	82x	new_reg->prev_in_table = nullptr;
525	82x	if (registrations_[signal_number])
526	6x	registrations_[signal_number]->prev_in_table = new_reg;
527	82x	registrations_[signal_number] = new_reg;
528
529	82x	++state->registration_count[signal_number];
530	82x	++registration_count_[signal_number];
531
532	82x	return {};
533	94x	}
534
535		inline std::error_code
536	4x	posix_signal_service::remove_signal(posix_signal& impl, int signal_number)
537		{
538	4x	if (signal_number < 0 \|\| signal_number >= max_signal_number)
539	✗	return make_error_code(std::errc::invalid_argument);
540
541		posix_signal_detail::signal_state* state =
542	4x	posix_signal_detail::get_signal_state();
543	4x	std::lock_guard state_lock(state->mutex);
544	4x	std::lock_guard lock(mutex_);
545
546	4x	signal_registration** deletion_point = &impl.signals_;
547	4x	signal_registration* reg = impl.signals_;
548	4x	while (reg && reg->signal_number < signal_number)
549		{
550	✗	deletion_point = &reg->next_in_set;
551	✗	reg = reg->next_in_set;
552		}
553
554	4x	if (!reg \|\| reg->signal_number != signal_number)
555	2x	return {};
556
557		// Restore default handler on last global unregistration
558	2x	if (state->registration_count[signal_number] == 1)
559		{
560	2x	struct sigaction sa = {};
561	2x	sa.sa_handler = SIG_DFL;
562	2x	sigemptyset(&sa.sa_mask);
563	2x	sa.sa_flags = 0;
564
565	2x	if (::sigaction(signal_number, &sa, nullptr) < 0)
566	✗	return make_error_code(std::errc::invalid_argument);
567
568		// Clear stored flags
569	2x	state->registered_flags[signal_number] = signal_set::none;
570		}
571
572	2x	*deletion_point = reg->next_in_set;
573
574	2x	if (registrations_[signal_number] == reg)
575	2x	registrations_[signal_number] = reg->next_in_table;
576	2x	if (reg->prev_in_table)
577	✗	reg->prev_in_table->next_in_table = reg->next_in_table;
578	2x	if (reg->next_in_table)
579	✗	reg->next_in_table->prev_in_table = reg->prev_in_table;
580
581	2x	--state->registration_count[signal_number];
582	2x	--registration_count_[signal_number];
583
584	2x	delete reg;
585	2x	return {};
586	4x	}
587
588		inline std::error_code
589	92x	posix_signal_service::clear_signals(posix_signal& impl)
590		{
591		posix_signal_detail::signal_state* state =
592	92x	posix_signal_detail::get_signal_state();
593	92x	std::lock_guard state_lock(state->mutex);
594	92x	std::lock_guard lock(mutex_);
595
596	92x	std::error_code first_error;
597
598	172x	while (signal_registration* reg = impl.signals_)
599		{
600	80x	int signal_number = reg->signal_number;
601
602	80x	if (state->registration_count[signal_number] == 1)
603		{
604	74x	struct sigaction sa = {};
605	74x	sa.sa_handler = SIG_DFL;
606	74x	sigemptyset(&sa.sa_mask);
607	74x	sa.sa_flags = 0;
608
609	74x	if (::sigaction(signal_number, &sa, nullptr) < 0 && !first_error)
610	✗	first_error = make_error_code(std::errc::invalid_argument);
611
612		// Clear stored flags
613	74x	state->registered_flags[signal_number] = signal_set::none;
614		}
615
616	80x	impl.signals_ = reg->next_in_set;
617
618	80x	if (registrations_[signal_number] == reg)
619	80x	registrations_[signal_number] = reg->next_in_table;
620	80x	if (reg->prev_in_table)
621	✗	reg->prev_in_table->next_in_table = reg->next_in_table;
622	80x	if (reg->next_in_table)
623	6x	reg->next_in_table->prev_in_table = reg->prev_in_table;
624
625	80x	--state->registration_count[signal_number];
626	80x	--registration_count_[signal_number];
627
628	80x	delete reg;
629	80x	}
630
631	92x	if (first_error)
632	✗	return first_error;
633	92x	return {};
634	92x	}
635
636		inline void
637	100x	posix_signal_service::cancel_wait(posix_signal& impl)
638		{
639	100x	bool was_waiting = false;
640	100x	signal_op* op = nullptr;
641
642		{
643	100x	std::lock_guard lock(mutex_);
644	100x	if (impl.waiting_)
645		{
646	4x	was_waiting = true;
647	4x	impl.waiting_ = false;
648	4x	op = &impl.pending_op_;
649		}
650	100x	}
651
652	100x	if (was_waiting)
653		{
654	4x	if (op->ec_out)
655	4x	*op->ec_out = make_error_code(capy::error::canceled);
656	4x	if (op->signal_out)
657	4x	*op->signal_out = 0;
658	4x	op->cont_op.cont.h = op->h;
659	4x	op->d.post(op->cont_op.cont);
660	4x	sched_->work_finished();
661		}
662	100x	}
663
664		inline void
665	26x	posix_signal_service::start_wait(posix_signal& impl, signal_op* op)
666		{
667		{
668	26x	std::lock_guard lock(mutex_);
669
670		// Check for queued signals first (signal arrived before wait started)
671	26x	signal_registration* reg = impl.signals_;
672	44x	while (reg)
673		{
674	28x	if (reg->undelivered > 0)
675		{
676	10x	--reg->undelivered;
677	10x	op->signal_number = reg->signal_number;
678		// svc=nullptr: no work_finished needed since we never called work_started
679	10x	op->svc = nullptr;
680	10x	sched_->post(op);
681	10x	return;
682		}
683	18x	reg = reg->next_in_set;
684		}
685
686		// No queued signals - wait for delivery
687	16x	impl.waiting_ = true;
688		// svc=this: signal_op::operator() will call work_finished() to balance this
689	16x	op->svc = this;
690	16x	sched_->work_started();
691	26x	}
692		}
693
694		inline void
695	20x	posix_signal_service::deliver_signal(int signal_number)
696		{
697	20x	if (signal_number < 0 \|\| signal_number >= max_signal_number)
698	✗	return;
699
700		posix_signal_detail::signal_state* state =
701	20x	posix_signal_detail::get_signal_state();
702	20x	std::lock_guard lock(state->mutex);
703
704	20x	posix_signal_service* service = state->service_list;
705	40x	while (service)
706		{
707	20x	std::lock_guard svc_lock(service->mutex_);
708
709	20x	signal_registration* reg = service->registrations_[signal_number];
710	42x	while (reg)
711		{
712	22x	posix_signal* impl = static_cast<posix_signal*>(reg->owner);
713
714	22x	if (impl->waiting_)
715		{
716	12x	impl->waiting_ = false;
717	12x	impl->pending_op_.signal_number = signal_number;
718	12x	service->post(&impl->pending_op_);
719		}
720		else
721		{
722	10x	++reg->undelivered;
723		}
724
725	22x	reg = reg->next_in_table;
726		}
727
728	20x	service = service->next_;
729	20x	}
730	20x	}
731
732		inline void
733		posix_signal_service::work_started() noexcept
734		{
735		sched_->work_started();
736		}
737
738		inline void
739	12x	posix_signal_service::work_finished() noexcept
740		{
741	12x	sched_->work_finished();
742	12x	}
743
744		inline void
745	12x	posix_signal_service::post(signal_op* op)
746		{
747	12x	sched_->post(op);
748	12x	}
749
750		inline void
751	515x	posix_signal_service::add_service(posix_signal_service* service)
752		{
753		posix_signal_detail::signal_state* state =
754	515x	posix_signal_detail::get_signal_state();
755	515x	std::lock_guard lock(state->mutex);
756
757	515x	service->next_ = state->service_list;
758	515x	service->prev_ = nullptr;
759	515x	if (state->service_list)
760	5x	state->service_list->prev_ = service;
761	515x	state->service_list = service;
762	515x	}
763
764		inline void
765	515x	posix_signal_service::remove_service(posix_signal_service* service)
766		{
767		posix_signal_detail::signal_state* state =
768	515x	posix_signal_detail::get_signal_state();
769	515x	std::lock_guard lock(state->mutex);
770
771	515x	if (service->next_ \|\| service->prev_ \|\| state->service_list == service)
772		{
773	515x	if (state->service_list == service)
774	515x	state->service_list = service->next_;
775	515x	if (service->prev_)
776	✗	service->prev_->next_ = service->next_;
777	515x	if (service->next_)
778	5x	service->next_->prev_ = service->prev_;
779	515x	service->next_ = nullptr;
780	515x	service->prev_ = nullptr;
781		}
782	515x	}
783
784		// get_signal_service - factory function
785
786		inline posix_signal_service&
787	515x	get_signal_service(capy::execution_context& ctx, scheduler& sched)
788		{
789	515x	return ctx.make_service<posix_signal_service>(sched);
790		}
791
792		} // namespace detail
793		} // namespace boost::corosio
794
795		#endif // BOOST_COROSIO_POSIX
796
797		#endif // BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_SIGNAL_SERVICE_HPP
798