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	764011x	reactor_find_context(reactor_scheduler const* self) noexcept
79		{
80	764011x	for (auto* c = reactor_context_stack.get(); c != nullptr; c = c->next)
81		{
82	761027x	if (c->key == self)
83	761027x	return c;
84		}
85	2984x	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	467x	unsigned inline_budget_initial() const noexcept
253		{
254	467x	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	✗	void configure_single_threaded(bool v) noexcept
270		{
271	✗	single_threaded_ = v;
272	✗	mutex_.set_enabled(!v);
273	✗	cond_.set_enabled(!v);
274	✗	}
275
276		protected:
277		timer_service* timer_svc_ = nullptr;
278		bool single_threaded_ = false;
279
280	541x	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	467x	explicit reactor_thread_context_guard(
373		reactor_scheduler const* sched) noexcept
374	467x	: frame_(sched, reactor_context_stack.get())
375		{
376	467x	reactor_context_stack.set(&frame_);
377	467x	}
378
379		/// Destroy the guard, draining private work and popping the frame.
380	467x	~reactor_thread_context_guard() noexcept
381		{
382	467x	if (!frame_.private_queue.empty())
383	✗	frame_.key->drain_thread_queue(
384	✗	frame_.private_queue, frame_.private_outstanding_work);
385	467x	reactor_context_stack.set(frame_.next);
386	467x	}
387		};
388
389		// ---- Inline implementations ------------------------------------------------
390
391		inline
392	467x	reactor_scheduler_context::reactor_scheduler_context(
393		reactor_scheduler const* k,
394	467x	reactor_scheduler_context* n)
395	467x	: key(k)
396	467x	, next(n)
397	467x	, private_outstanding_work(0)
398	467x	, inline_budget(0)
399	467x	, inline_budget_max(
400	467x	static_cast<int>(k->inline_budget_initial()))
401	467x	, unassisted(false)
402		{
403	467x	}
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 < 1 \|\|
417	✗	budget_max > static_cast<unsigned>(std::numeric_limits<int>::max()))
418		throw std::out_of_range(
419	✗	"inline_budget_max must be in [1, INT_MAX]");
420
421		// Clamp initial and unassisted to budget_max.
422	✗	if (budget_init > budget_max)
423	✗	budget_init = budget_max;
424	✗	if (unassisted > budget_max)
425	✗	unassisted = budget_max;
426
427	✗	max_events_per_poll_ = max_events;
428	✗	inline_budget_initial_ = budget_init;
429	✗	inline_budget_max_ = budget_max;
430	✗	unassisted_budget_ = unassisted;
431	✗	}
432
433		inline void
434	97868x	reactor_scheduler::reset_inline_budget() const noexcept
435		{
436	97868x	if (auto* ctx = reactor_find_context(this))
437		{
438		// Cap when no other thread absorbed queued work
439	97868x	if (ctx->unassisted)
440		{
441	97868x	ctx->inline_budget_max =
442	97868x	static_cast<int>(unassisted_budget_);
443	97868x	ctx->inline_budget =
444	97868x	static_cast<int>(unassisted_budget_);
445	97868x	return;
446		}
447		// Ramp up when previous cycle fully consumed budget
448	✗	if (ctx->inline_budget == 0)
449	✗	ctx->inline_budget_max = (std::min)(
450	✗	ctx->inline_budget_max * 2,
451	✗	static_cast<int>(inline_budget_max_));
452	✗	else if (ctx->inline_budget < ctx->inline_budget_max)
453	✗	ctx->inline_budget_max =
454	✗	static_cast<int>(inline_budget_initial_);
455	✗	ctx->inline_budget = ctx->inline_budget_max;
456		}
457		}
458
459		inline bool
460	414956x	reactor_scheduler::try_consume_inline_budget() const noexcept
461		{
462	414956x	if (auto* ctx = reactor_find_context(this))
463		{
464	414956x	if (ctx->inline_budget > 0)
465		{
466	331992x	--ctx->inline_budget;
467	331992x	return true;
468		}
469		}
470	82964x	return false;
471		}
472
473		inline void
474	2123x	reactor_scheduler::post(std::coroutine_handle<> h) const
475		{
476		struct post_handler final : scheduler_op
477		{
478		std::coroutine_handle<> h_;
479
480	2123x	explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
481	4246x	~post_handler() override = default;
482
483	2114x	void operator()() override
484		{
485	2114x	auto saved = h_;
486	2114x	delete this;
487		// Ensure stores from the posting thread are visible
488		std::atomic_thread_fence(std::memory_order_acquire);
489	2114x	saved.resume();
490	2114x	}
491
492	9x	void destroy() override
493		{
494	9x	auto saved = h_;
495	9x	delete this;
496	9x	saved.destroy();
497	9x	}
498		};
499
500	2123x	auto ph = std::make_unique<post_handler>(h);
501
502	2123x	if (auto* ctx = reactor_find_context(this))
503		{
504	6x	++ctx->private_outstanding_work;
505	6x	ctx->private_queue.push(ph.release());
506	6x	return;
507		}
508
509	2117x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
510
511	2117x	lock_type lock(mutex_);
512	2117x	completed_ops_.push(ph.release());
513	2117x	wake_one_thread_and_unlock(lock);
514	2123x	}
515
516		inline void
517	99162x	reactor_scheduler::post(scheduler_op* h) const
518		{
519	99162x	if (auto* ctx = reactor_find_context(this))
520		{
521	98990x	++ctx->private_outstanding_work;
522	98990x	ctx->private_queue.push(h);
523	98990x	return;
524		}
525
526	172x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
527
528	172x	lock_type lock(mutex_);
529	172x	completed_ops_.push(h);
530	172x	wake_one_thread_and_unlock(lock);
531	172x	}
532
533		inline bool
534	1291x	reactor_scheduler::running_in_this_thread() const noexcept
535		{
536	1291x	return reactor_find_context(this) != nullptr;
537		}
538
539		inline void
540	416x	reactor_scheduler::stop()
541		{
542	416x	lock_type lock(mutex_);
543	416x	if (!stopped_.load(std::memory_order_acquire))
544		{
545	380x	stopped_.store(true, std::memory_order_release);
546	380x	signal_all(lock);
547	380x	interrupt_reactor();
548		}
549	416x	}
550
551		inline bool
552	62x	reactor_scheduler::stopped() const noexcept
553		{
554	62x	return stopped_.load(std::memory_order_acquire);
555		}
556
557		inline void
558	91x	reactor_scheduler::restart()
559		{
560	91x	stopped_.store(false, std::memory_order_release);
561	91x	}
562
563		inline std::size_t
564	392x	reactor_scheduler::run()
565		{
566	784x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
567		{
568	26x	stop();
569	26x	return 0;
570		}
571
572	366x	reactor_thread_context_guard ctx(this);
573	366x	lock_type lock(mutex_);
574
575	366x	std::size_t n = 0;
576		for (;;)
577		{
578	264773x	if (!do_one(lock, -1, &ctx.frame_))
579	366x	break;
580	264407x	if (n != (std::numeric_limits<std::size_t>::max)())
581	264407x	++n;
582	264407x	if (!lock.owns_lock())
583	173122x	lock.lock();
584		}
585	366x	return n;
586	366x	}
587
588		inline std::size_t
589	2x	reactor_scheduler::run_one()
590		{
591	4x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
592		{
593	✗	stop();
594	✗	return 0;
595		}
596
597	2x	reactor_thread_context_guard ctx(this);
598	2x	lock_type lock(mutex_);
599	2x	return do_one(lock, -1, &ctx.frame_);
600	2x	}
601
602		inline std::size_t
603	102x	reactor_scheduler::wait_one(long usec)
604		{
605	204x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
606		{
607	10x	stop();
608	10x	return 0;
609		}
610
611	92x	reactor_thread_context_guard ctx(this);
612	92x	lock_type lock(mutex_);
613	92x	return do_one(lock, usec, &ctx.frame_);
614	92x	}
615
616		inline std::size_t
617	6x	reactor_scheduler::poll()
618		{
619	12x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
620		{
621	1x	stop();
622	1x	return 0;
623		}
624
625	5x	reactor_thread_context_guard ctx(this);
626	5x	lock_type lock(mutex_);
627
628	5x	std::size_t n = 0;
629		for (;;)
630		{
631	11x	if (!do_one(lock, 0, &ctx.frame_))
632	5x	break;
633	6x	if (n != (std::numeric_limits<std::size_t>::max)())
634	6x	++n;
635	6x	if (!lock.owns_lock())
636	6x	lock.lock();
637		}
638	5x	return n;
639	5x	}
640
641		inline std::size_t
642	4x	reactor_scheduler::poll_one()
643		{
644	8x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
645		{
646	2x	stop();
647	2x	return 0;
648		}
649
650	2x	reactor_thread_context_guard ctx(this);
651	2x	lock_type lock(mutex_);
652	2x	return do_one(lock, 0, &ctx.frame_);
653	2x	}
654
655		inline void
656	24098x	reactor_scheduler::work_started() noexcept
657		{
658	24098x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
659	24098x	}
660
661		inline void
662	34059x	reactor_scheduler::work_finished() noexcept
663		{
664	68118x	if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
665	372x	stop();
666	34059x	}
667
668		inline void
669	148611x	reactor_scheduler::compensating_work_started() const noexcept
670		{
671	148611x	auto* ctx = reactor_find_context(this);
672	148611x	if (ctx)
673	148611x	++ctx->private_outstanding_work;
674	148611x	}
675
676		inline void
677	✗	reactor_scheduler::drain_thread_queue(
678		op_queue& queue, std::int64_t count) const
679		{
680	✗	if (count > 0)
681	✗	outstanding_work_.fetch_add(count, std::memory_order_relaxed);
682
683	✗	lock_type lock(mutex_);
684	✗	completed_ops_.splice(queue);
685	✗	if (count > 0)
686	✗	maybe_unlock_and_signal_one(lock);
687	✗	}
688
689		inline void
690	14589x	reactor_scheduler::post_deferred_completions(op_queue& ops) const
691		{
692	14589x	if (ops.empty())
693	14589x	return;
694
695	✗	if (auto* ctx = reactor_find_context(this))
696		{
697	✗	ctx->private_queue.splice(ops);
698	✗	return;
699		}
700
701	✗	lock_type lock(mutex_);
702	✗	completed_ops_.splice(ops);
703	✗	wake_one_thread_and_unlock(lock);
704	✗	}
705
706		inline void
707	541x	reactor_scheduler::shutdown_drain()
708		{
709	541x	lock_type lock(mutex_);
710
711	1171x	while (auto* h = completed_ops_.pop())
712		{
713	630x	if (h == &task_op_)
714	541x	continue;
715	89x	lock.unlock();
716	89x	h->destroy();
717	89x	lock.lock();
718	630x	}
719
720	541x	signal_all(lock);
721	541x	}
722
723		inline void
724	921x	reactor_scheduler::signal_all(lock_type&) const
725		{
726	921x	state_ \|= signaled_bit;
727	921x	cond_.notify_all();
728	921x	}
729
730		inline bool
731	2289x	reactor_scheduler::maybe_unlock_and_signal_one(
732		lock_type& lock) const
733		{
734	2289x	state_ \|= signaled_bit;
735	2289x	if (state_ > signaled_bit)
736		{
737	✗	lock.unlock();
738	✗	cond_.notify_one();
739	✗	return true;
740		}
741	2289x	return false;
742		}
743
744		inline bool
745	311585x	reactor_scheduler::unlock_and_signal_one(
746		lock_type& lock) const
747		{
748	311585x	state_ \|= signaled_bit;
749	311585x	bool have_waiters = state_ > signaled_bit;
750	311585x	lock.unlock();
751	311585x	if (have_waiters)
752	✗	cond_.notify_one();
753	311585x	return have_waiters;
754		}
755
756		inline void
757	✗	reactor_scheduler::clear_signal() const
758		{
759	✗	state_ &= ~signaled_bit;
760	✗	}
761
762		inline void
763	✗	reactor_scheduler::wait_for_signal(
764		lock_type& lock) const
765		{
766	✗	while ((state_ & signaled_bit) == 0)
767		{
768	✗	state_ += waiter_increment;
769	✗	cond_.wait(lock);
770	✗	state_ -= waiter_increment;
771		}
772	✗	}
773
774		inline void
775	✗	reactor_scheduler::wait_for_signal_for(
776		lock_type& lock, long timeout_us) const
777		{
778	✗	if ((state_ & signaled_bit) == 0)
779		{
780	✗	state_ += waiter_increment;
781	✗	cond_.wait_for(lock, std::chrono::microseconds(timeout_us));
782	✗	state_ -= waiter_increment;
783		}
784	✗	}
785
786		inline void
787	2289x	reactor_scheduler::wake_one_thread_and_unlock(
788		lock_type& lock) const
789		{
790	2289x	if (maybe_unlock_and_signal_one(lock))
791	✗	return;
792
793	2289x	if (task_running_.load(std::memory_order_relaxed) && !task_interrupted_)
794		{
795	51x	task_interrupted_ = true;
796	51x	lock.unlock();
797	51x	interrupt_reactor();
798		}
799		else
800		{
801	2238x	lock.unlock();
802		}
803		}
804
805	264468x	inline reactor_scheduler::work_cleanup::~work_cleanup()
806		{
807	264468x	if (ctx)
808		{
809	264468x	std::int64_t produced = ctx->private_outstanding_work;
810	264468x	if (produced > 1)
811	15x	sched->outstanding_work_.fetch_add(
812		produced - 1, std::memory_order_relaxed);
813	264453x	else if (produced < 1)
814	24550x	sched->work_finished();
815	264468x	ctx->private_outstanding_work = 0;
816
817	264468x	if (!ctx->private_queue.empty())
818		{
819	91307x	lock->lock();
820	91307x	sched->completed_ops_.splice(ctx->private_queue);
821		}
822		}
823		else
824		{
825	✗	sched->work_finished();
826		}
827	264468x	}
828
829	357584x	inline reactor_scheduler::task_cleanup::~task_cleanup()
830		{
831	178792x	if (!ctx)
832	✗	return;
833
834	178792x	if (ctx->private_outstanding_work > 0)
835		{
836	7662x	sched->outstanding_work_.fetch_add(
837	7662x	ctx->private_outstanding_work, std::memory_order_relaxed);
838	7662x	ctx->private_outstanding_work = 0;
839		}
840
841	178792x	if (!ctx->private_queue.empty())
842		{
843	7662x	if (!lock->owns_lock())
844	✗	lock->lock();
845	7662x	sched->completed_ops_.splice(ctx->private_queue);
846		}
847	178792x	}
848
849		inline std::size_t
850	264880x	reactor_scheduler::do_one(
851		lock_type& lock, long timeout_us, context_type* ctx)
852		{
853		for (;;)
854		{
855	443631x	if (stopped_.load(std::memory_order_acquire))
856	366x	return 0;
857
858	443265x	scheduler_op* op = completed_ops_.pop();
859
860		// Handle reactor sentinel — time to poll for I/O
861	443265x	if (op == &task_op_)
862		{
863		bool more_handlers =
864	178797x	!completed_ops_.empty() \|\| (ctx && !ctx->private_queue.empty());
865
866	310477x	if (!more_handlers &&
867	263360x	(outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
868		timeout_us == 0))
869		{
870	5x	completed_ops_.push(&task_op_);
871	5x	return 0;
872		}
873
874	178792x	long task_timeout_us = more_handlers ? 0 : timeout_us;
875	178792x	task_interrupted_ = task_timeout_us == 0;
876	178792x	task_running_.store(true, std::memory_order_release);
877
878	178792x	if (more_handlers)
879	47117x	unlock_and_signal_one(lock);
880
881		try
882		{
883	178792x	run_task(lock, ctx, task_timeout_us);
884		}
885	✗	catch (...)
886		{
887	✗	task_running_.store(false, std::memory_order_relaxed);
888	✗	throw;
889	✗	}
890
891	178792x	task_running_.store(false, std::memory_order_relaxed);
892	178792x	completed_ops_.push(&task_op_);
893	178792x	if (timeout_us > 0)
894	41x	return 0;
895	178751x	continue;
896	178751x	}
897
898		// Handle operation
899	264468x	if (op != nullptr)
900		{
901	264468x	bool more = !completed_ops_.empty();
902
903	264468x	if (more)
904	264468x	ctx->unassisted = !unlock_and_signal_one(lock);
905		else
906		{
907	✗	ctx->unassisted = false;
908	✗	lock.unlock();
909		}
910
911	264468x	work_cleanup on_exit{this, &lock, ctx};
912		(void)on_exit;
913
914	264468x	(*op)();
915	264468x	return 1;
916	264468x	}
917
918		// Try private queue before blocking
919	✗	if (reactor_drain_private_queue(ctx, outstanding_work_, completed_ops_))
920	✗	continue;
921
922	✗	if (outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
923		timeout_us == 0)
924	✗	return 0;
925
926	✗	clear_signal();
927	✗	if (timeout_us < 0)
928	✗	wait_for_signal(lock);
929		else
930	✗	wait_for_signal_for(lock, timeout_us);
931	178751x	}
932		}
933
934		} // namespace boost::corosio::detail
935
936		#endif // BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
937