include/boost/corosio/native/detail/reactor/reactor_scheduler.hpp

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reactor_scheduler.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_REACTOR_REACTOR_SCHEDULER_HPP
11		#define BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
12
13		#include <boost/corosio/detail/config.hpp>
14		#include <boost/capy/ex/execution_context.hpp>
15
16		#include <boost/corosio/detail/scheduler.hpp>
17		#include <boost/corosio/detail/scheduler_op.hpp>
18		#include <boost/corosio/detail/thread_local_ptr.hpp>
19
20		#include <atomic>
21		#include <chrono>
22		#include <coroutine>
23		#include <cstddef>
24		#include <cstdint>
25		#include <limits>
26		#include <memory>
27		#include <stdexcept>
28
29		#include <boost/corosio/detail/conditionally_enabled_mutex.hpp>
30		#include <boost/corosio/detail/conditionally_enabled_event.hpp>
31
32		namespace boost::corosio::detail {
33
34		// Forward declarations
35		class reactor_scheduler;
36		class timer_service;
37
38		/** Per-thread state for a reactor scheduler.
39
40		Each thread running a scheduler's event loop has one of these
41		on a thread-local stack. It holds a private work queue and
42		inline completion budget for speculative I/O fast paths.
43		*/
44		struct BOOST_COROSIO_SYMBOL_VISIBLE reactor_scheduler_context
45		{
46		/// Scheduler this context belongs to.
47		reactor_scheduler const* key;
48
49		/// Next context frame on this thread's stack.
50		reactor_scheduler_context* next;
51
52		/// Private work queue for reduced contention.
53		op_queue private_queue;
54
55		/// Unflushed work count for the private queue.
56		std::int64_t private_outstanding_work;
57
58		/// Remaining inline completions allowed this cycle.
59		int inline_budget;
60
61		/// Maximum inline budget (adaptive, 2-16).
62		int inline_budget_max;
63
64		/// True if no other thread absorbed queued work last cycle.
65		bool unassisted;
66
67		/// Construct a context frame linked to @a n.
68		reactor_scheduler_context(
69		reactor_scheduler const* k,
70		reactor_scheduler_context* n);
71		};
72
73		/// Thread-local context stack for reactor schedulers.
74		inline thread_local_ptr<reactor_scheduler_context> reactor_context_stack;
75
76		/// Find the context frame for a scheduler on this thread.
77		inline reactor_scheduler_context*
78	776422x	reactor_find_context(reactor_scheduler const* self) noexcept
79		{
80	776422x	for (auto* c = reactor_context_stack.get(); c != nullptr; c = c->next)
81		{
82	773306x	if (c->key == self)
83	773306x	return c;
84		}
85	3116x	return nullptr;
86		}
87
88		/// Flush private work count to global counter.
89		inline void
90	✗	reactor_flush_private_work(
91		reactor_scheduler_context* ctx,
92		std::atomic<std::int64_t>& outstanding_work) noexcept
93		{
94	✗	if (ctx && ctx->private_outstanding_work > 0)
95		{
96	✗	outstanding_work.fetch_add(
97		ctx->private_outstanding_work, std::memory_order_relaxed);
98	✗	ctx->private_outstanding_work = 0;
99		}
100	✗	}
101
102		/** Drain private queue to global queue, flushing work count first.
103
104		@return True if any ops were drained.
105		*/
106		inline bool
107	✗	reactor_drain_private_queue(
108		reactor_scheduler_context* ctx,
109		std::atomic<std::int64_t>& outstanding_work,
110		op_queue& completed_ops) noexcept
111		{
112	✗	if (!ctx \|\| ctx->private_queue.empty())
113	✗	return false;
114
115	✗	reactor_flush_private_work(ctx, outstanding_work);
116	✗	completed_ops.splice(ctx->private_queue);
117	✗	return true;
118		}
119
120		/** Non-template base for reactor-backed scheduler implementations.
121
122		Provides the complete threading model shared by epoll, kqueue,
123		and select schedulers: signal state machine, inline completion
124		budget, work counting, run/poll methods, and the do_one event
125		loop.
126
127		Derived classes provide platform-specific hooks by overriding:
128		- `run_task(lock, ctx)` to run the reactor poll
129		- `interrupt_reactor()` to wake a blocked reactor
130
131		De-templated from the original CRTP design to eliminate
132		duplicate instantiations when multiple backends are compiled
133		into the same binary. Virtual dispatch for run_task (called
134		once per reactor cycle, before a blocking syscall) has
135		negligible overhead.
136
137		@par Thread Safety
138		All public member functions are thread-safe.
139		*/
140		class reactor_scheduler
141		: public scheduler
142		, public capy::execution_context::service
143		{
144		public:
145		using key_type = scheduler;
146		using context_type = reactor_scheduler_context;
147		using mutex_type = conditionally_enabled_mutex;
148		using lock_type = mutex_type::scoped_lock;
149		using event_type = conditionally_enabled_event;
150
151		/// Post a coroutine for deferred execution.
152		void post(std::coroutine_handle<> h) const override;
153
154		/// Post a scheduler operation for deferred execution.
155		void post(scheduler_op* h) const override;
156
157		/// Return true if called from a thread running this scheduler.
158		bool running_in_this_thread() const noexcept override;
159
160		/// Request the scheduler to stop dispatching handlers.
161		void stop() override;
162
163		/// Return true if the scheduler has been stopped.
164		bool stopped() const noexcept override;
165
166		/// Reset the stopped state so `run()` can resume.
167		void restart() override;
168
169		/// Run the event loop until no work remains.
170		std::size_t run() override;
171
172		/// Run until one handler completes or no work remains.
173		std::size_t run_one() override;
174
175		/// Run until one handler completes or @a usec elapses.
176		std::size_t wait_one(long usec) override;
177
178		/// Run ready handlers without blocking.
179		std::size_t poll() override;
180
181		/// Run at most one ready handler without blocking.
182		std::size_t poll_one() override;
183
184		/// Increment the outstanding work count.
185		void work_started() noexcept override;
186
187		/// Decrement the outstanding work count, stopping on zero.
188		void work_finished() noexcept override;
189
190		/** Reset the thread's inline completion budget.
191
192		Called at the start of each posted completion handler to
193		grant a fresh budget for speculative inline completions.
194		*/
195		void reset_inline_budget() const noexcept;
196
197		/** Consume one unit of inline budget if available.
198
199		@return True if budget was available and consumed.
200		*/
201		bool try_consume_inline_budget() const noexcept;
202
203		/** Offset a forthcoming work_finished from work_cleanup.
204
205		Called by descriptor_state when all I/O returned EAGAIN and
206		no handler will be executed. Must be called from a scheduler
207		thread.
208		*/
209		void compensating_work_started() const noexcept;
210
211		/** Drain work from thread context's private queue to global queue.
212
213		Flushes private work count to the global counter, then
214		transfers the queue under mutex protection.
215
216		@param queue The private queue to drain.
217		@param count Private work count to flush before draining.
218		*/
219		void drain_thread_queue(op_queue& queue, std::int64_t count) const;
220
221		/** Post completed operations for deferred invocation.
222
223		If called from a thread running this scheduler, operations
224		go to the thread's private queue (fast path). Otherwise,
225		operations are added to the global queue under mutex and a
226		waiter is signaled.
227
228		@par Preconditions
229		work_started() must have been called for each operation.
230
231		@param ops Queue of operations to post.
232		*/
233		void post_deferred_completions(op_queue& ops) const;
234
235		/** Apply runtime configuration to the scheduler.
236
237		Called by `io_context` after construction. Values that do
238		not apply to this backend are silently ignored.
239
240		@param max_events Event buffer size for epoll/kqueue.
241		@param budget_init Starting inline completion budget.
242		@param budget_max Hard ceiling on adaptive budget ramp-up.
243		@param unassisted Budget when single-threaded.
244		*/
245		virtual void configure_reactor(
246		unsigned max_events,
247		unsigned budget_init,
248		unsigned budget_max,
249		unsigned unassisted);
250
251		/// Return the configured initial inline budget.
252	502x	unsigned inline_budget_initial() const noexcept
253		{
254	502x	return inline_budget_initial_;
255		}
256
257		/// Return true if single-threaded (lockless) mode is active.
258	64x	bool is_single_threaded() const noexcept
259		{
260	64x	return single_threaded_;
261		}
262
263		/** Enable or disable single-threaded (lockless) mode.
264
265		When enabled, all scheduler mutex and condition variable
266		operations become no-ops. Cross-thread post() is
267		undefined behavior.
268		*/
269	1x	void configure_single_threaded(bool v) noexcept
270		{
271	1x	single_threaded_ = v;
272	1x	mutex_.set_enabled(!v);
273	1x	cond_.set_enabled(!v);
274	1x	}
275
276		protected:
277		timer_service* timer_svc_ = nullptr;
278		bool single_threaded_ = false;
279
280	605x	reactor_scheduler() = default;
281
282		/** Drain completed_ops during shutdown.
283
284		Pops all operations from the global queue and destroys them,
285		skipping the task sentinel. Signals all waiting threads.
286		Derived classes call this from their shutdown() override
287		before performing platform-specific cleanup.
288		*/
289		void shutdown_drain();
290
291		/// RAII guard that re-inserts the task sentinel after `run_task`.
292		struct task_cleanup
293		{
294		reactor_scheduler const* sched;
295		lock_type* lock;
296		context_type* ctx;
297		~task_cleanup();
298		};
299
300		mutable mutex_type mutex_{true};
301		mutable event_type cond_{true};
302		mutable op_queue completed_ops_;
303		mutable std::atomic<std::int64_t> outstanding_work_{0};
304		std::atomic<bool> stopped_{false};
305		mutable std::atomic<bool> task_running_{false};
306		mutable bool task_interrupted_ = false;
307
308		// Runtime-configurable reactor tuning parameters.
309		// Defaults match the library's built-in values.
310		unsigned max_events_per_poll_ = 128;
311		unsigned inline_budget_initial_ = 2;
312		unsigned inline_budget_max_ = 16;
313		unsigned unassisted_budget_ = 4;
314
315		/// Bit 0 of `state_`: set when the condvar should be signaled.
316		static constexpr std::size_t signaled_bit = 1;
317
318		/// Increment per waiting thread in `state_`.
319		static constexpr std::size_t waiter_increment = 2;
320		mutable std::size_t state_ = 0;
321
322		/// Sentinel op that triggers a reactor poll when dequeued.
323		struct task_op final : scheduler_op
324		{
325	✗	void operator()() override {}
326	✗	void destroy() override {}
327		};
328		task_op task_op_;
329
330		/// Run the platform-specific reactor poll.
331		virtual void
332		run_task(lock_type& lock, context_type* ctx,
333		long timeout_us) = 0;
334
335		/// Wake a blocked reactor (e.g. write to eventfd or pipe).
336		virtual void interrupt_reactor() const = 0;
337
338		private:
339		struct work_cleanup
340		{
341		reactor_scheduler* sched;
342		lock_type* lock;
343		context_type* ctx;
344		~work_cleanup();
345		};
346
347		std::size_t do_one(
348		lock_type& lock, long timeout_us, context_type* ctx);
349
350		void signal_all(lock_type& lock) const;
351		bool maybe_unlock_and_signal_one(lock_type& lock) const;
352		bool unlock_and_signal_one(lock_type& lock) const;
353		void clear_signal() const;
354		void wait_for_signal(lock_type& lock) const;
355		void wait_for_signal_for(
356		lock_type& lock, long timeout_us) const;
357		void wake_one_thread_and_unlock(lock_type& lock) const;
358		};
359
360		/** RAII guard that pushes/pops a scheduler context frame.
361
362		On construction, pushes a new context frame onto the
363		thread-local stack. On destruction, drains any remaining
364		private queue items to the global queue and pops the frame.
365		*/
366		struct reactor_thread_context_guard
367		{
368		/// The context frame managed by this guard.
369		reactor_scheduler_context frame_;
370
371		/// Construct the guard, pushing a frame for @a sched.
372	502x	explicit reactor_thread_context_guard(
373		reactor_scheduler const* sched) noexcept
374	502x	: frame_(sched, reactor_context_stack.get())
375		{
376	502x	reactor_context_stack.set(&frame_);
377	502x	}
378
379		/// Destroy the guard, draining private work and popping the frame.
380	502x	~reactor_thread_context_guard() noexcept
381		{
382	502x	if (!frame_.private_queue.empty())
383	✗	frame_.key->drain_thread_queue(
384	✗	frame_.private_queue, frame_.private_outstanding_work);
385	502x	reactor_context_stack.set(frame_.next);
386	502x	}
387		};
388
389		// ---- Inline implementations ------------------------------------------------
390
391		inline
392	502x	reactor_scheduler_context::reactor_scheduler_context(
393		reactor_scheduler const* k,
394	502x	reactor_scheduler_context* n)
395	502x	: key(k)
396	502x	, next(n)
397	502x	, private_outstanding_work(0)
398	502x	, inline_budget(0)
399	502x	, inline_budget_max(
400	502x	static_cast<int>(k->inline_budget_initial()))
401	502x	, unassisted(false)
402		{
403	502x	}
404
405		inline void
406	✗	reactor_scheduler::configure_reactor(
407		unsigned max_events,
408		unsigned budget_init,
409		unsigned budget_max,
410		unsigned unassisted)
411		{
412	✗	if (max_events < 1 \|\|
413	✗	max_events > static_cast<unsigned>(std::numeric_limits<int>::max()))
414		throw std::out_of_range(
415	✗	"max_events_per_poll must be in [1, INT_MAX]");
416	✗	if (budget_max > static_cast<unsigned>(std::numeric_limits<int>::max()))
417		throw std::out_of_range(
418	✗	"inline_budget_max must be in [0, INT_MAX]");
419
420		// Clamp initial and unassisted to budget_max.
421	✗	if (budget_init > budget_max)
422	✗	budget_init = budget_max;
423	✗	if (unassisted > budget_max)
424	✗	unassisted = budget_max;
425
426	✗	max_events_per_poll_ = max_events;
427	✗	inline_budget_initial_ = budget_init;
428	✗	inline_budget_max_ = budget_max;
429	✗	unassisted_budget_ = unassisted;
430	✗	}
431
432		inline void
433	101098x	reactor_scheduler::reset_inline_budget() const noexcept
434		{
435		// When budget is disabled (max==0), all paths below would no-op
436		// (inline_budget stays 0). Skip the TLS lookup entirely.
437	101098x	if (inline_budget_max_ == 0)
438	✗	return;
439	101098x	if (auto* ctx = reactor_find_context(this))
440		{
441		// Cap when no other thread absorbed queued work
442	101098x	if (ctx->unassisted)
443		{
444	101098x	ctx->inline_budget_max =
445	101098x	static_cast<int>(unassisted_budget_);
446	101098x	ctx->inline_budget =
447	101098x	static_cast<int>(unassisted_budget_);
448	101098x	return;
449		}
450		// Ramp up when previous cycle fully consumed budget.
451		// max(1, ...) ensures the doubling escapes zero.
452	✗	if (ctx->inline_budget == 0)
453	✗	ctx->inline_budget_max = (std::min)(
454	✗	(std::max)(1, ctx->inline_budget_max) * 2,
455	✗	static_cast<int>(inline_budget_max_));
456	✗	else if (ctx->inline_budget < ctx->inline_budget_max)
457	✗	ctx->inline_budget_max =
458	✗	static_cast<int>(inline_budget_initial_);
459	✗	ctx->inline_budget = ctx->inline_budget_max;
460		}
461		}
462
463		inline bool
464	424684x	reactor_scheduler::try_consume_inline_budget() const noexcept
465		{
466	424684x	if (inline_budget_max_ == 0)
467	✗	return false;
468	424684x	if (auto* ctx = reactor_find_context(this))
469		{
470	424684x	if (ctx->inline_budget > 0)
471		{
472	339755x	--ctx->inline_budget;
473	339755x	return true;
474		}
475		}
476	84929x	return false;
477		}
478
479		inline void
480	2189x	reactor_scheduler::post(std::coroutine_handle<> h) const
481		{
482		struct post_handler final : scheduler_op
483		{
484		std::coroutine_handle<> h_;
485
486	2189x	explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
487	4378x	~post_handler() override = default;
488
489	2180x	void operator()() override
490		{
491	2180x	auto saved = h_;
492	2180x	delete this;
493		// Ensure stores from the posting thread are visible
494		std::atomic_thread_fence(std::memory_order_acquire);
495	2180x	saved.resume();
496	2180x	}
497
498	9x	void destroy() override
499		{
500	9x	auto saved = h_;
501	9x	delete this;
502	9x	saved.destroy();
503	9x	}
504		};
505
506	2189x	auto ph = std::make_unique<post_handler>(h);
507
508	2189x	if (auto* ctx = reactor_find_context(this))
509		{
510	6x	++ctx->private_outstanding_work;
511	6x	ctx->private_queue.push(ph.release());
512	6x	return;
513		}
514
515	2183x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
516
517	2183x	lock_type lock(mutex_);
518	2183x	completed_ops_.push(ph.release());
519	2183x	wake_one_thread_and_unlock(lock);
520	2189x	}
521
522		inline void
523	102369x	reactor_scheduler::post(scheduler_op* h) const
524		{
525	102369x	if (auto* ctx = reactor_find_context(this))
526		{
527	102197x	++ctx->private_outstanding_work;
528	102197x	ctx->private_queue.push(h);
529	102197x	return;
530		}
531
532	172x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
533
534	172x	lock_type lock(mutex_);
535	172x	completed_ops_.push(h);
536	172x	wake_one_thread_and_unlock(lock);
537	172x	}
538
539		inline bool
540	1359x	reactor_scheduler::running_in_this_thread() const noexcept
541		{
542	1359x	return reactor_find_context(this) != nullptr;
543		}
544
545		inline void
546	461x	reactor_scheduler::stop()
547		{
548	461x	lock_type lock(mutex_);
549	461x	if (!stopped_.load(std::memory_order_acquire))
550		{
551	420x	stopped_.store(true, std::memory_order_release);
552	420x	signal_all(lock);
553	420x	interrupt_reactor();
554		}
555	461x	}
556
557		inline bool
558	62x	reactor_scheduler::stopped() const noexcept
559		{
560	62x	return stopped_.load(std::memory_order_acquire);
561		}
562
563		inline void
564	111x	reactor_scheduler::restart()
565		{
566	111x	stopped_.store(false, std::memory_order_release);
567	111x	}
568
569		inline std::size_t
570	432x	reactor_scheduler::run()
571		{
572	864x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
573		{
574	31x	stop();
575	31x	return 0;
576		}
577
578	401x	reactor_thread_context_guard ctx(this);
579	401x	lock_type lock(mutex_);
580
581	401x	std::size_t n = 0;
582		for (;;)
583		{
584	265456x	if (!do_one(lock, -1, &ctx.frame_))
585	401x	break;
586	265055x	if (n != (std::numeric_limits<std::size_t>::max)())
587	265055x	++n;
588	265055x	if (!lock.owns_lock())
589	171183x	lock.lock();
590		}
591	401x	return n;
592	401x	}
593
594		inline std::size_t
595	2x	reactor_scheduler::run_one()
596		{
597	4x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
598		{
599	✗	stop();
600	✗	return 0;
601		}
602
603	2x	reactor_thread_context_guard ctx(this);
604	2x	lock_type lock(mutex_);
605	2x	return do_one(lock, -1, &ctx.frame_);
606	2x	}
607
608		inline std::size_t
609	102x	reactor_scheduler::wait_one(long usec)
610		{
611	204x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
612		{
613	10x	stop();
614	10x	return 0;
615		}
616
617	92x	reactor_thread_context_guard ctx(this);
618	92x	lock_type lock(mutex_);
619	92x	return do_one(lock, usec, &ctx.frame_);
620	92x	}
621
622		inline std::size_t
623	6x	reactor_scheduler::poll()
624		{
625	12x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
626		{
627	1x	stop();
628	1x	return 0;
629		}
630
631	5x	reactor_thread_context_guard ctx(this);
632	5x	lock_type lock(mutex_);
633
634	5x	std::size_t n = 0;
635		for (;;)
636		{
637	11x	if (!do_one(lock, 0, &ctx.frame_))
638	5x	break;
639	6x	if (n != (std::numeric_limits<std::size_t>::max)())
640	6x	++n;
641	6x	if (!lock.owns_lock())
642	6x	lock.lock();
643		}
644	5x	return n;
645	5x	}
646
647		inline std::size_t
648	4x	reactor_scheduler::poll_one()
649		{
650	8x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
651		{
652	2x	stop();
653	2x	return 0;
654		}
655
656	2x	reactor_thread_context_guard ctx(this);
657	2x	lock_type lock(mutex_);
658	2x	return do_one(lock, 0, &ctx.frame_);
659	2x	}
660
661		inline void
662	26051x	reactor_scheduler::work_started() noexcept
663		{
664	26051x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
665	26051x	}
666
667		inline void
668	36698x	reactor_scheduler::work_finished() noexcept
669		{
670	73396x	if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
671	412x	stop();
672	36698x	}
673
674		inline void
675	144723x	reactor_scheduler::compensating_work_started() const noexcept
676		{
677	144723x	auto* ctx = reactor_find_context(this);
678	144723x	if (ctx)
679	144723x	++ctx->private_outstanding_work;
680	144723x	}
681
682		inline void
683	✗	reactor_scheduler::drain_thread_queue(
684		op_queue& queue, std::int64_t count) const
685		{
686	✗	if (count > 0)
687	✗	outstanding_work_.fetch_add(count, std::memory_order_relaxed);
688
689	✗	lock_type lock(mutex_);
690	✗	completed_ops_.splice(queue);
691	✗	if (count > 0)
692	✗	maybe_unlock_and_signal_one(lock);
693	✗	}
694
695		inline void
696	15852x	reactor_scheduler::post_deferred_completions(op_queue& ops) const
697		{
698	15852x	if (ops.empty())
699	15852x	return;
700
701	✗	if (auto* ctx = reactor_find_context(this))
702		{
703	✗	ctx->private_queue.splice(ops);
704	✗	return;
705		}
706
707	✗	lock_type lock(mutex_);
708	✗	completed_ops_.splice(ops);
709	✗	wake_one_thread_and_unlock(lock);
710	✗	}
711
712		inline void
713	605x	reactor_scheduler::shutdown_drain()
714		{
715	605x	lock_type lock(mutex_);
716
717	1315x	while (auto* h = completed_ops_.pop())
718		{
719	710x	if (h == &task_op_)
720	605x	continue;
721	105x	lock.unlock();
722	105x	h->destroy();
723	105x	lock.lock();
724	710x	}
725
726	605x	signal_all(lock);
727	605x	}
728
729		inline void
730	1025x	reactor_scheduler::signal_all(lock_type&) const
731		{
732	1025x	state_ \|= signaled_bit;
733	1025x	cond_.notify_all();
734	1025x	}
735
736		inline bool
737	2355x	reactor_scheduler::maybe_unlock_and_signal_one(
738		lock_type& lock) const
739		{
740	2355x	state_ \|= signaled_bit;
741	2355x	if (state_ > signaled_bit)
742		{
743	✗	lock.unlock();
744	✗	cond_.notify_one();
745	✗	return true;
746		}
747	2355x	return false;
748		}
749
750		inline bool
751	314908x	reactor_scheduler::unlock_and_signal_one(
752		lock_type& lock) const
753		{
754	314908x	state_ \|= signaled_bit;
755	314908x	bool have_waiters = state_ > signaled_bit;
756	314908x	lock.unlock();
757	314908x	if (have_waiters)
758	✗	cond_.notify_one();
759	314908x	return have_waiters;
760		}
761
762		inline void
763	✗	reactor_scheduler::clear_signal() const
764		{
765	✗	state_ &= ~signaled_bit;
766	✗	}
767
768		inline void
769	✗	reactor_scheduler::wait_for_signal(
770		lock_type& lock) const
771		{
772	✗	while ((state_ & signaled_bit) == 0)
773		{
774	✗	state_ += waiter_increment;
775	✗	cond_.wait(lock);
776	✗	state_ -= waiter_increment;
777		}
778	✗	}
779
780		inline void
781	✗	reactor_scheduler::wait_for_signal_for(
782		lock_type& lock, long timeout_us) const
783		{
784	✗	if ((state_ & signaled_bit) == 0)
785		{
786	✗	state_ += waiter_increment;
787	✗	cond_.wait_for(lock, std::chrono::microseconds(timeout_us));
788	✗	state_ -= waiter_increment;
789		}
790	✗	}
791
792		inline void
793	2355x	reactor_scheduler::wake_one_thread_and_unlock(
794		lock_type& lock) const
795		{
796	2355x	if (maybe_unlock_and_signal_one(lock))
797	✗	return;
798
799	2355x	if (task_running_.load(std::memory_order_relaxed) && !task_interrupted_)
800		{
801	52x	task_interrupted_ = true;
802	52x	lock.unlock();
803	52x	interrupt_reactor();
804		}
805		else
806		{
807	2303x	lock.unlock();
808		}
809		}
810
811	265116x	inline reactor_scheduler::work_cleanup::~work_cleanup()
812		{
813	265116x	if (ctx)
814		{
815	265116x	std::int64_t produced = ctx->private_outstanding_work;
816	265116x	if (produced > 1)
817	15x	sched->outstanding_work_.fetch_add(
818		produced - 1, std::memory_order_relaxed);
819	265101x	else if (produced < 1)
820	26499x	sched->work_finished();
821	265116x	ctx->private_outstanding_work = 0;
822
823	265116x	if (!ctx->private_queue.empty())
824		{
825	93894x	lock->lock();
826	93894x	sched->completed_ops_.splice(ctx->private_queue);
827		}
828		}
829		else
830		{
831	✗	sched->work_finished();
832		}
833	265116x	}
834
835	360808x	inline reactor_scheduler::task_cleanup::~task_cleanup()
836		{
837	180404x	if (!ctx)
838	✗	return;
839
840	180404x	if (ctx->private_outstanding_work > 0)
841		{
842	8282x	sched->outstanding_work_.fetch_add(
843	8282x	ctx->private_outstanding_work, std::memory_order_relaxed);
844	8282x	ctx->private_outstanding_work = 0;
845		}
846
847	180404x	if (!ctx->private_queue.empty())
848		{
849	8282x	if (!lock->owns_lock())
850	✗	lock->lock();
851	8282x	sched->completed_ops_.splice(ctx->private_queue);
852		}
853	180404x	}
854
855		inline std::size_t
856	265563x	reactor_scheduler::do_one(
857		lock_type& lock, long timeout_us, context_type* ctx)
858		{
859		for (;;)
860		{
861	445926x	if (stopped_.load(std::memory_order_acquire))
862	402x	return 0;
863
864	445524x	scheduler_op* op = completed_ops_.pop();
865
866		// Handle reactor sentinel — time to poll for I/O
867	445524x	if (op == &task_op_)
868		{
869		bool more_handlers =
870	180408x	!completed_ops_.empty() \|\| (ctx && !ctx->private_queue.empty());
871
872	311024x	if (!more_handlers &&
873	261232x	(outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
874		timeout_us == 0))
875		{
876	4x	completed_ops_.push(&task_op_);
877	4x	return 0;
878		}
879
880	180404x	long task_timeout_us = more_handlers ? 0 : timeout_us;
881	180404x	task_interrupted_ = task_timeout_us == 0;
882	180404x	task_running_.store(true, std::memory_order_release);
883
884	180404x	if (more_handlers)
885	49792x	unlock_and_signal_one(lock);
886
887		try
888		{
889	180404x	run_task(lock, ctx, task_timeout_us);
890		}
891	✗	catch (...)
892		{
893	✗	task_running_.store(false, std::memory_order_relaxed);
894	✗	throw;
895	✗	}
896
897	180404x	task_running_.store(false, std::memory_order_relaxed);
898	180404x	completed_ops_.push(&task_op_);
899	180404x	if (timeout_us > 0)
900	41x	return 0;
901	180363x	continue;
902	180363x	}
903
904		// Handle operation
905	265116x	if (op != nullptr)
906		{
907	265116x	bool more = !completed_ops_.empty();
908
909	265116x	if (more)
910	265116x	ctx->unassisted = !unlock_and_signal_one(lock);
911		else
912		{
913	✗	ctx->unassisted = false;
914	✗	lock.unlock();
915		}
916
917	265116x	work_cleanup on_exit{this, &lock, ctx};
918		(void)on_exit;
919
920	265116x	(*op)();
921	265116x	return 1;
922	265116x	}
923
924		// Try private queue before blocking
925	✗	if (reactor_drain_private_queue(ctx, outstanding_work_, completed_ops_))
926	✗	continue;
927
928	✗	if (outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
929		timeout_us == 0)
930	✗	return 0;
931
932	✗	clear_signal();
933	✗	if (timeout_us < 0)
934	✗	wait_for_signal(lock);
935		else
936	✗	wait_for_signal_for(lock, timeout_us);
937	180363x	}
938		}
939
940		} // namespace boost::corosio::detail
941
942		#endif // BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
943