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	945691x	reactor_find_context(reactor_scheduler const* self) noexcept
79		{
80	945691x	for (auto* c = reactor_context_stack.get(); c != nullptr; c = c->next)
81		{
82	939492x	if (c->key == self)
83	939492x	return c;
84		}
85	6199x	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	1x	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	1x	if (!ctx \|\| ctx->private_queue.empty())
113	1x	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	862x	unsigned inline_budget_initial() const noexcept
253		{
254	862x	return inline_budget_initial_;
255		}
256
257		/// Return true if single-threaded (lockless) mode is active.
258	159x	bool is_single_threaded() const noexcept override
259		{
260	159x	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	10x	void configure_single_threaded(bool v) noexcept override
270		{
271	10x	single_threaded_ = v;
272	10x	mutex_.set_enabled(!v);
273	10x	cond_.set_enabled(!v);
274	10x	}
275
276		protected:
277		timer_service* timer_svc_ = nullptr;
278		bool single_threaded_ = false;
279
280	1244x	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	862x	explicit reactor_thread_context_guard(
373		reactor_scheduler const* sched) noexcept
374	862x	: frame_(sched, reactor_context_stack.get())
375		{
376	862x	reactor_context_stack.set(&frame_);
377	862x	}
378
379		/// Destroy the guard, draining private work and popping the frame.
380	862x	~reactor_thread_context_guard() noexcept
381		{
382	862x	if (!frame_.private_queue.empty())
383	✗	frame_.key->drain_thread_queue(
384	✗	frame_.private_queue, frame_.private_outstanding_work);
385	862x	reactor_context_stack.set(frame_.next);
386	862x	}
387		};
388
389		// ---- Inline implementations ------------------------------------------------
390
391		inline
392	862x	reactor_scheduler_context::reactor_scheduler_context(
393		reactor_scheduler const* k,
394	862x	reactor_scheduler_context* n)
395	862x	: key(k)
396	862x	, next(n)
397	862x	, private_outstanding_work(0)
398	862x	, inline_budget(0)
399	862x	, inline_budget_max(
400	862x	static_cast<int>(k->inline_budget_initial()))
401	862x	, unassisted(false)
402		{
403	862x	}
404
405		inline void
406	16x	reactor_scheduler::configure_reactor(
407		unsigned max_events,
408		unsigned budget_init,
409		unsigned budget_max,
410		unsigned unassisted)
411		{
412	30x	if (max_events < 1 \|\|
413	14x	max_events > static_cast<unsigned>(std::numeric_limits<int>::max()))
414		throw std::out_of_range(
415	2x	"max_events_per_poll must be in [1, INT_MAX]");
416	14x	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	14x	if (budget_init > budget_max)
422	2x	budget_init = budget_max;
423	14x	if (unassisted > budget_max)
424	2x	unassisted = budget_max;
425
426	14x	max_events_per_poll_ = max_events;
427	14x	inline_budget_initial_ = budget_init;
428	14x	inline_budget_max_ = budget_max;
429	14x	unassisted_budget_ = unassisted;
430	14x	}
431
432		inline void
433	108945x	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	108945x	if (inline_budget_max_ == 0)
438	✗	return;
439	108945x	if (auto* ctx = reactor_find_context(this))
440		{
441		// Cap when no other thread absorbed queued work
442	108945x	if (ctx->unassisted)
443		{
444	108945x	ctx->inline_budget_max =
445	108945x	static_cast<int>(unassisted_budget_);
446	108945x	ctx->inline_budget =
447	108945x	static_cast<int>(unassisted_budget_);
448	108945x	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	455486x	reactor_scheduler::try_consume_inline_budget() const noexcept
465		{
466	455486x	if (inline_budget_max_ == 0)
467	✗	return false;
468	455486x	if (auto* ctx = reactor_find_context(this))
469		{
470	455486x	if (ctx->inline_budget > 0)
471		{
472	364349x	--ctx->inline_budget;
473	364349x	return true;
474		}
475		}
476	91137x	return false;
477		}
478
479		inline void
480	4355x	reactor_scheduler::post(std::coroutine_handle<> h) const
481		{
482		struct post_handler final : scheduler_op
483		{
484		std::coroutine_handle<> h_;
485
486	4355x	explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
487	8710x	~post_handler() override = default;
488
489	4343x	void operator()() override
490		{
491	4343x	auto saved = h_;
492	4343x	delete this;
493		// Ensure stores from the posting thread are visible
494		std::atomic_thread_fence(std::memory_order_acquire);
495	4343x	saved.resume();
496	4343x	}
497
498	12x	void destroy() override
499		{
500	12x	auto saved = h_;
501	12x	delete this;
502	12x	saved.destroy();
503	12x	}
504		};
505
506	4355x	auto ph = std::make_unique<post_handler>(h);
507
508	4355x	if (auto* ctx = reactor_find_context(this))
509		{
510	24x	++ctx->private_outstanding_work;
511	24x	ctx->private_queue.push(ph.release());
512	24x	return;
513		}
514
515	4331x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
516
517	4331x	lock_type lock(mutex_);
518	4331x	completed_ops_.push(ph.release());
519	4331x	wake_one_thread_and_unlock(lock);
520	4355x	}
521
522		inline void
523	109973x	reactor_scheduler::post(scheduler_op* h) const
524		{
525	109973x	if (auto* ctx = reactor_find_context(this))
526		{
527	109580x	++ctx->private_outstanding_work;
528	109580x	ctx->private_queue.push(h);
529	109580x	return;
530		}
531
532	393x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
533
534	393x	lock_type lock(mutex_);
535	393x	completed_ops_.push(h);
536	393x	wake_one_thread_and_unlock(lock);
537	393x	}
538
539		inline bool
540	2154x	reactor_scheduler::running_in_this_thread() const noexcept
541		{
542	2154x	return reactor_find_context(this) != nullptr;
543		}
544
545		inline void
546	891x	reactor_scheduler::stop()
547		{
548	891x	lock_type lock(mutex_);
549	891x	if (!stopped_.load(std::memory_order_acquire))
550		{
551	821x	stopped_.store(true, std::memory_order_release);
552	821x	signal_all(lock);
553	821x	interrupt_reactor();
554		}
555	891x	}
556
557		inline bool
558	89x	reactor_scheduler::stopped() const noexcept
559		{
560	89x	return stopped_.load(std::memory_order_acquire);
561		}
562
563		inline void
564	177x	reactor_scheduler::restart()
565		{
566	177x	stopped_.store(false, std::memory_order_release);
567	177x	}
568
569		inline std::size_t
570	835x	reactor_scheduler::run()
571		{
572	1670x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
573		{
574	57x	stop();
575	57x	return 0;
576		}
577
578	778x	reactor_thread_context_guard ctx(this);
579	778x	lock_type lock(mutex_);
580
581	778x	std::size_t n = 0;
582		for (;;)
583		{
584	397144x	if (!do_one(lock, -1, &ctx.frame_))
585	778x	break;
586	396366x	if (n != (std::numeric_limits<std::size_t>::max)())
587	396366x	++n;
588	396366x	if (!lock.owns_lock())
589	295601x	lock.lock();
590		}
591	778x	return n;
592	778x	}
593
594		inline std::size_t
595	16x	reactor_scheduler::run_one()
596		{
597	32x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
598		{
599	✗	stop();
600	✗	return 0;
601		}
602
603	16x	reactor_thread_context_guard ctx(this);
604	16x	lock_type lock(mutex_);
605	16x	return do_one(lock, -1, &ctx.frame_);
606	16x	}
607
608		inline std::size_t
609	63x	reactor_scheduler::wait_one(long usec)
610		{
611	126x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
612		{
613	21x	stop();
614	21x	return 0;
615		}
616
617	42x	reactor_thread_context_guard ctx(this);
618	42x	lock_type lock(mutex_);
619	42x	return do_one(lock, usec, &ctx.frame_);
620	42x	}
621
622		inline std::size_t
623	28x	reactor_scheduler::poll()
624		{
625	56x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
626		{
627	6x	stop();
628	6x	return 0;
629		}
630
631	22x	reactor_thread_context_guard ctx(this);
632	22x	lock_type lock(mutex_);
633
634	22x	std::size_t n = 0;
635		for (;;)
636		{
637	64x	if (!do_one(lock, 0, &ctx.frame_))
638	22x	break;
639	42x	if (n != (std::numeric_limits<std::size_t>::max)())
640	42x	++n;
641	42x	if (!lock.owns_lock())
642	34x	lock.lock();
643		}
644	22x	return n;
645	22x	}
646
647		inline std::size_t
648	8x	reactor_scheduler::poll_one()
649		{
650	16x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
651		{
652	4x	stop();
653	4x	return 0;
654		}
655
656	4x	reactor_thread_context_guard ctx(this);
657	4x	lock_type lock(mutex_);
658	4x	return do_one(lock, 0, &ctx.frame_);
659	4x	}
660
661		inline void
662	29155x	reactor_scheduler::work_started() noexcept
663		{
664	29155x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
665	29155x	}
666
667		inline void
668	42662x	reactor_scheduler::work_finished() noexcept
669		{
670	85324x	if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
671	795x	stop();
672	42662x	}
673
674		inline void
675	264778x	reactor_scheduler::compensating_work_started() const noexcept
676		{
677	264778x	auto* ctx = reactor_find_context(this);
678	264778x	if (ctx)
679	264778x	++ctx->private_outstanding_work;
680	264778x	}
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	17382x	reactor_scheduler::post_deferred_completions(op_queue& ops) const
697		{
698	17382x	if (ops.empty())
699	17382x	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	1244x	reactor_scheduler::shutdown_drain()
714		{
715	1244x	lock_type lock(mutex_);
716
717	2678x	while (auto* h = completed_ops_.pop())
718		{
719	1434x	if (h == &task_op_)
720	1244x	continue;
721	190x	lock.unlock();
722	190x	h->destroy();
723	190x	lock.lock();
724	1434x	}
725
726	1244x	signal_all(lock);
727	1244x	}
728
729		inline void
730	2065x	reactor_scheduler::signal_all(lock_type&) const
731		{
732	2065x	state_ \|= signaled_bit;
733	2065x	cond_.notify_all();
734	2065x	}
735
736		inline bool
737	4724x	reactor_scheduler::maybe_unlock_and_signal_one(
738		lock_type& lock) const
739		{
740	4724x	state_ \|= signaled_bit;
741	4724x	if (state_ > signaled_bit)
742		{
743	✗	lock.unlock();
744	✗	cond_.notify_one();
745	✗	return true;
746		}
747	4724x	return false;
748		}
749
750		inline bool
751	448808x	reactor_scheduler::unlock_and_signal_one(
752		lock_type& lock) const
753		{
754	448808x	state_ \|= signaled_bit;
755	448808x	bool have_waiters = state_ > signaled_bit;
756	448808x	lock.unlock();
757	448808x	if (have_waiters)
758	✗	cond_.notify_one();
759	448808x	return have_waiters;
760		}
761
762		inline void
763	1x	reactor_scheduler::clear_signal() const
764		{
765	1x	state_ &= ~signaled_bit;
766	1x	}
767
768		inline void
769	1x	reactor_scheduler::wait_for_signal(
770		lock_type& lock) const
771		{
772	2x	while ((state_ & signaled_bit) == 0)
773		{
774	1x	state_ += waiter_increment;
775	1x	cond_.wait(lock);
776	1x	state_ -= waiter_increment;
777		}
778	1x	}
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	4724x	reactor_scheduler::wake_one_thread_and_unlock(
794		lock_type& lock) const
795		{
796	4724x	if (maybe_unlock_and_signal_one(lock))
797	✗	return;
798
799	4724x	if (task_running_.load(std::memory_order_relaxed) && !task_interrupted_)
800		{
801	116x	task_interrupted_ = true;
802	116x	lock.unlock();
803	116x	interrupt_reactor();
804		}
805		else
806		{
807	4608x	lock.unlock();
808		}
809		}
810
811	396452x	inline reactor_scheduler::work_cleanup::~work_cleanup()
812		{
813	396452x	if (ctx)
814		{
815	396452x	std::int64_t produced = ctx->private_outstanding_work;
816	396452x	if (produced > 1)
817	14x	sched->outstanding_work_.fetch_add(
818		produced - 1, std::memory_order_relaxed);
819	396438x	else if (produced < 1)
820	30901x	sched->work_finished();
821	396452x	ctx->private_outstanding_work = 0;
822
823	396452x	if (!ctx->private_queue.empty())
824		{
825	100773x	lock->lock();
826	100773x	sched->completed_ops_.splice(ctx->private_queue);
827		}
828		}
829		else
830		{
831	✗	sched->work_finished();
832		}
833	396452x	}
834
835	599346x	inline reactor_scheduler::task_cleanup::~task_cleanup()
836		{
837	299673x	if (!ctx)
838	✗	return;
839
840	299673x	if (ctx->private_outstanding_work > 0)
841		{
842	8806x	sched->outstanding_work_.fetch_add(
843	8806x	ctx->private_outstanding_work, std::memory_order_relaxed);
844	8806x	ctx->private_outstanding_work = 0;
845		}
846
847	299673x	if (!ctx->private_queue.empty())
848		{
849	8806x	if (!lock->owns_lock())
850	✗	lock->lock();
851	8806x	sched->completed_ops_.splice(ctx->private_queue);
852		}
853	299673x	}
854
855		inline std::size_t
856	397270x	reactor_scheduler::do_one(
857		lock_type& lock, long timeout_us, context_type* ctx)
858		{
859		for (;;)
860		{
861	696927x	if (stopped_.load(std::memory_order_acquire))
862	785x	return 0;
863
864	696142x	scheduler_op* op = completed_ops_.pop();
865
866		// Handle reactor sentinel — time to poll for I/O
867	696142x	if (op == &task_op_)
868		{
869		bool more_handlers =
870	299689x	!completed_ops_.empty() \|\| (ctx && !ctx->private_queue.empty());
871
872	547022x	if (!more_handlers &&
873	494666x	(outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
874		timeout_us == 0))
875		{
876	16x	completed_ops_.push(&task_op_);
877	16x	return 0;
878		}
879
880	299673x	long task_timeout_us = more_handlers ? 0 : timeout_us;
881	299673x	task_interrupted_ = task_timeout_us == 0;
882	299673x	task_running_.store(true, std::memory_order_release);
883
884	299673x	if (more_handlers)
885	52356x	unlock_and_signal_one(lock);
886
887		try
888		{
889	299673x	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	299673x	task_running_.store(false, std::memory_order_relaxed);
898	299673x	completed_ops_.push(&task_op_);
899	299673x	if (timeout_us > 0)
900	17x	return 0;
901	299656x	continue;
902	299656x	}
903
904		// Handle operation
905	396453x	if (op != nullptr)
906		{
907	396452x	bool more = !completed_ops_.empty();
908
909	396452x	if (more)
910	396452x	ctx->unassisted = !unlock_and_signal_one(lock);
911		else
912		{
913	✗	ctx->unassisted = false;
914	✗	lock.unlock();
915		}
916
917	396452x	work_cleanup on_exit{this, &lock, ctx};
918		(void)on_exit;
919
920	396452x	(*op)();
921	396452x	return 1;
922	396452x	}
923
924		// Try private queue before blocking
925	1x	if (reactor_drain_private_queue(ctx, outstanding_work_, completed_ops_))
926	✗	continue;
927
928	2x	if (outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
929		timeout_us == 0)
930	✗	return 0;
931
932	1x	clear_signal();
933	1x	if (timeout_us < 0)
934	1x	wait_for_signal(lock);
935		else
936	✗	wait_for_signal_for(lock, timeout_us);
937	299657x	}
938		}
939
940		} // namespace boost::corosio::detail
941
942		#endif // BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
943