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/ready_queue.hpp>
17		#include <boost/corosio/detail/scheduler.hpp>
18		#include <boost/corosio/detail/scheduler_op.hpp>
19		#include <boost/corosio/detail/thread_local_ptr.hpp>
20
21		#include <atomic>
22		#include <chrono>
23		#include <coroutine>
24		#include <cstddef>
25		#include <cstdint>
26		#include <limits>
27		#include <memory>
28		#include <stdexcept>
29
30		#include <boost/corosio/detail/conditionally_enabled_mutex.hpp>
31		#include <boost/corosio/detail/conditionally_enabled_event.hpp>
32
33		namespace boost::corosio::detail {
34
35		// Forward declarations
36		class reactor_scheduler;
37		class timer_service;
38
39		/** Per-thread state for a reactor scheduler.
40
41		Each thread running a scheduler's event loop has one of these
42		on a thread-local stack. It holds a private work queue and
43		inline completion budget for speculative I/O fast paths.
44		*/
45		struct BOOST_COROSIO_SYMBOL_VISIBLE reactor_scheduler_context
46		{
47		/// Scheduler this context belongs to.
48		reactor_scheduler const* key;
49
50		/// Next context frame on this thread's stack.
51		reactor_scheduler_context* next;
52
53		/// Private work queue for reduced contention.
54		ready_queue private_queue;
55
56		/// Unflushed work count for the private queue.
57		std::int64_t private_outstanding_work;
58
59		/// Remaining inline completions allowed this cycle.
60		int inline_budget;
61
62		/// Maximum inline budget (adaptive, 2-16).
63		int inline_budget_max;
64
65		/// True if no other thread absorbed queued work last cycle.
66		bool unassisted;
67
68		/// Construct a context frame linked to @a n.
69		reactor_scheduler_context(
70		reactor_scheduler const* k, 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	966575x	reactor_find_context(reactor_scheduler const* self) noexcept
79		{
80	966575x	for (auto* c = reactor_context_stack.get(); c != nullptr; c = c->next)
81		{
82	941707x	if (c->key == self)
83	941707x	return c;
84		}
85	24868x	return nullptr;
86		}
87
88		/** Non-template base for reactor-backed scheduler implementations.
89
90		Provides the complete threading model shared by epoll, kqueue,
91		and select schedulers: signal state machine, inline completion
92		budget, work counting, run/poll methods, and the do_one event
93		loop.
94
95		Derived classes provide platform-specific hooks by overriding:
96		- `run_task(lock, ctx)` to run the reactor poll
97		- `interrupt_reactor()` to wake a blocked reactor
98
99		De-templated from the original CRTP design to eliminate
100		duplicate instantiations when multiple backends are compiled
101		into the same binary. Virtual dispatch for run_task (called
102		once per reactor cycle, before a blocking syscall) has
103		negligible overhead.
104
105		@par Thread Safety
106		All public member functions are thread-safe.
107		*/
108		class reactor_scheduler
109		: public scheduler
110		{
111		public:
112		using context_type = reactor_scheduler_context;
113		using mutex_type = conditionally_enabled_mutex;
114		using lock_type = mutex_type::scoped_lock;
115		using event_type = conditionally_enabled_event;
116
117		/// Post a coroutine for deferred execution.
118		void post(std::coroutine_handle<> h) const override;
119
120		/// Post a scheduler operation for deferred execution.
121		void post(scheduler_op* h) const override;
122
123		/// Post a continuation for deferred execution.
124		void post(capy::continuation&) const override;
125
126		/// Return true if called from a thread running this scheduler.
127		bool running_in_this_thread() const noexcept override;
128
129		/// Request the scheduler to stop dispatching handlers.
130		void stop() override;
131
132		/// Return true if the scheduler has been stopped.
133		bool stopped() const noexcept override;
134
135		/// Reset the stopped state so `run()` can resume.
136		void restart() override;
137
138		/// Run the event loop until no work remains.
139		std::size_t run() override;
140
141		/// Run until one handler completes or no work remains.
142		std::size_t run_one() override;
143
144		/// Run until one handler completes or @a usec elapses.
145		std::size_t wait_one(long usec) override;
146
147		/// Run ready handlers without blocking.
148		std::size_t poll() override;
149
150		/// Run at most one ready handler without blocking.
151		std::size_t poll_one() override;
152
153		/// Increment the outstanding work count.
154		void work_started() noexcept override;
155
156		/// Decrement the outstanding work count, stopping on zero.
157		void work_finished() noexcept override;
158
159		/** Reset the thread's inline completion budget.
160
161		Called at the start of each posted completion handler to
162		grant a fresh budget for speculative inline completions.
163		*/
164		void reset_inline_budget() const noexcept;
165
166		/** Consume one unit of inline budget if available.
167
168		@return True if budget was available and consumed.
169		*/
170		bool try_consume_inline_budget() const noexcept;
171
172		/** Offset a forthcoming work_finished from work_cleanup.
173
174		Called by descriptor_state when all I/O returned EAGAIN and
175		no handler will be executed. Must be called from a scheduler
176		thread.
177		*/
178		void compensating_work_started() const noexcept;
179
180		/** Post completed operations for deferred invocation.
181
182		If called from a thread running this scheduler, operations
183		go to the thread's private queue (fast path). Otherwise,
184		operations are added to the global queue under mutex and a
185		waiter is signaled.
186
187		@pre work_started() must have been called for each operation.
188
189		@param ops Queue of operations to post.
190		*/
191		void post_deferred_completions(ready_queue& ops) const;
192
193		/** Apply runtime configuration to the scheduler.
194
195		Called by `io_context` after construction. Values that do
196		not apply to this backend are silently ignored.
197
198		@param max_events Event buffer size for epoll/kqueue.
199		@param budget_init Starting inline completion budget.
200		@param budget_max Hard ceiling on adaptive budget ramp-up.
201		@param unassisted Budget when single-threaded.
202		*/
203		virtual void configure_reactor(
204		unsigned max_events,
205		unsigned budget_init,
206		unsigned budget_max,
207		unsigned unassisted);
208
209		/// Return the configured initial inline budget.
210	5475x	unsigned inline_budget_initial() const noexcept
211		{
212	5475x	return inline_budget_initial_;
213		}
214
215		/// Return true when scheduler locking is disabled (fully-lockless tier).
216	502x	bool scheduler_locking_disabled() const noexcept override
217		{
218	502x	return scheduler_locking_disabled_;
219		}
220
221	2243x	void configure_threading(threading_config cfg) noexcept override
222		{
223	2243x	scheduler_locking_disabled_ = !cfg.scheduler_locking;
224		// reactor_io_locking takes effect at descriptor registration (see the
225		// register_descriptor overrides), not here.
226	2243x	reactor_io_locking_ = cfg.reactor_io_locking;
227	2243x	one_thread_ = cfg.one_thread;
228	2243x	mutex_.set_enabled(cfg.scheduler_locking);
229	2243x	cond_.set_enabled(cfg.scheduler_locking);
230	2243x	}
231
232		protected:
233		timer_service* timer_svc_ = nullptr;
234		bool scheduler_locking_disabled_ = false;
235		bool reactor_io_locking_ = true;
236		bool one_thread_ = false;
237
238	2255x	reactor_scheduler() = default;
239
240		/** Drain completed_ops during shutdown.
241
242		Pops all operations from the global queue and destroys them,
243		skipping the task sentinel. Signals all waiting threads.
244		Derived classes call this from their shutdown() override
245		before performing platform-specific cleanup.
246		*/
247		void shutdown_drain();
248
249		/// RAII guard that re-inserts the task sentinel after `run_task`.
250		struct task_cleanup
251		{
252		reactor_scheduler const* sched;
253		lock_type* lock;
254		context_type& ctx;
255		~task_cleanup();
256		};
257
258		mutable mutex_type mutex_{true};
259		mutable event_type cond_{true};
260		mutable ready_queue completed_ops_;
261		mutable std::atomic<std::int64_t> outstanding_work_{0};
262		std::atomic<bool> stopped_{false};
263		mutable std::atomic<bool> task_running_{false};
264		mutable bool task_interrupted_ = false;
265
266		// Runtime-configurable reactor tuning parameters.
267		// Defaults match the library's built-in values.
268		unsigned max_events_per_poll_ = 128;
269		unsigned inline_budget_initial_ = 2;
270		unsigned inline_budget_max_ = 16;
271		unsigned unassisted_budget_ = 4;
272
273		/// Bit 0 of `state_`: set when the condvar should be signaled.
274		static constexpr std::size_t signaled_bit = 1;
275
276		/// Increment per waiting thread in `state_`.
277		static constexpr std::size_t waiter_increment = 2;
278		mutable std::size_t state_ = 0;
279
280		/// Sentinel op that triggers a reactor poll when dequeued.
281		struct task_op final : scheduler_op
282		{
283		// LCOV_EXCL_START: the sentinel is intercepted by pointer
284		// identity; its virtuals exist for vtable completeness.
285	−	void operator()() override {}
286	−	void destroy() override {}
287		// LCOV_EXCL_STOP
288		};
289		task_op task_op_;
290
291		/** Run the platform-specific reactor poll.
292
293		@par Postconditions
294		`lock` is owned on return, however the poll ended. An
295		implementation that unlocks around the blocking call owes the
296		caller a matching re-acquire on every path out, including the
297		errors it retries rather than reports.
298		*/
299		virtual void
300		run_task(lock_type& lock, context_type& ctx, long timeout_us) = 0;
301
302		/// Wake a blocked reactor (e.g. write to eventfd or pipe).
303		virtual void interrupt_reactor() const = 0;
304
305		private:
306		struct work_cleanup
307		{
308		reactor_scheduler* sched;
309		lock_type* lock;
310		context_type& ctx;
311		~work_cleanup();
312		};
313
314		std::size_t do_one(lock_type& lock, long timeout_us, context_type& ctx);
315
316		void signal_all(lock_type& lock) const;
317		bool maybe_unlock_and_signal_one(lock_type& lock) const;
318		bool unlock_and_signal_one(lock_type& lock) const;
319		void clear_signal() const;
320		void wait_for_signal(lock_type& lock) const;
321		void wait_for_signal_for(lock_type& lock, long timeout_us) const;
322		void wake_one_thread_and_unlock(lock_type& lock) const;
323		};
324
325		/** RAII guard that pushes/pops a scheduler context frame.
326
327		On construction, pushes a new context frame onto the
328		thread-local stack. On destruction, drains any remaining
329		private queue items to the global queue and pops the frame.
330		*/
331		struct reactor_thread_context_guard
332		{
333		/// The context frame managed by this guard.
334		reactor_scheduler_context frame_;
335
336		/// Construct the guard, pushing a frame for @a sched.
337	5475x	explicit reactor_thread_context_guard(
338		reactor_scheduler const* sched) noexcept
339	5475x	: frame_(sched, reactor_context_stack.get())
340		{
341	5475x	reactor_context_stack.set(&frame_);
342	5475x	}
343
344		/** Destroy the guard, popping the frame.
345
346		The private queue is empty here by invariant: work_cleanup and
347		task_cleanup splice it to the global queue after every handler
348		and every reactor pass.
349		*/
350	5475x	~reactor_thread_context_guard() noexcept
351		{
352	5475x	reactor_context_stack.set(frame_.next);
353	5475x	}
354		};
355
356		// ---- Inline implementations ------------------------------------------------
357
358	5475x	inline reactor_scheduler_context::reactor_scheduler_context(
359	5475x	reactor_scheduler const* k, reactor_scheduler_context* n)
360	5475x	: key(k)
361	5475x	, next(n)
362	5475x	, private_outstanding_work(0)
363	5475x	, inline_budget(0)
364	5475x	, inline_budget_max(static_cast<int>(k->inline_budget_initial()))
365	5475x	, unassisted(false)
366		{
367	5475x	}
368
369		inline void
370	44x	reactor_scheduler::configure_reactor(
371		unsigned max_events,
372		unsigned budget_init,
373		unsigned budget_max,
374		unsigned unassisted)
375		{
376	86x	if (max_events < 1 \|\|
377	42x	max_events > static_cast<unsigned>(std::numeric_limits<int>::max()))
378	2x	throw std::out_of_range("max_events_per_poll must be in [1, INT_MAX]");
379	42x	if (budget_max > static_cast<unsigned>(std::numeric_limits<int>::max()))
380	2x	throw std::out_of_range("inline_budget_max must be in [0, INT_MAX]");
381
382		// Clamp initial and unassisted to budget_max.
383	40x	if (budget_init > budget_max)
384	16x	budget_init = budget_max;
385	40x	if (unassisted > budget_max)
386	16x	unassisted = budget_max;
387
388	40x	max_events_per_poll_ = max_events;
389	40x	inline_budget_initial_ = budget_init;
390	40x	inline_budget_max_ = budget_max;
391	40x	unassisted_budget_ = unassisted;
392	40x	}
393
394		inline void
395	93869x	reactor_scheduler::reset_inline_budget() const noexcept
396		{
397		// When budget is disabled (max==0), all paths below would no-op
398		// (inline_budget stays 0). Skip the TLS lookup entirely.
399	93869x	if (inline_budget_max_ == 0)
400	56x	return;
401	93813x	if (auto* ctx = reactor_find_context(this))
402		{
403		// Cap when no other thread absorbed queued work
404	93813x	if (ctx->unassisted)
405		{
406	93813x	ctx->inline_budget_max = static_cast<int>(unassisted_budget_);
407	93813x	ctx->inline_budget = static_cast<int>(unassisted_budget_);
408	93813x	return;
409		}
410		// Ramp up when previous cycle fully consumed budget.
411		// max(1, ...) ensures the doubling escapes zero.
412	✗	if (ctx->inline_budget == 0)
413	✗	ctx->inline_budget_max =
414	✗	(std::min)((std::max)(1, ctx->inline_budget_max) * 2,
415	✗	static_cast<int>(inline_budget_max_));
416	✗	else if (ctx->inline_budget < ctx->inline_budget_max)
417	✗	ctx->inline_budget_max = static_cast<int>(inline_budget_initial_);
418	✗	ctx->inline_budget = ctx->inline_budget_max;
419		}
420		}
421
422		inline bool
423	416148x	reactor_scheduler::try_consume_inline_budget() const noexcept
424		{
425	416148x	if (inline_budget_max_ == 0)
426	40x	return false;
427	416108x	if (auto* ctx = reactor_find_context(this))
428		{
429	416108x	if (ctx->inline_budget > 0)
430		{
431	332721x	--ctx->inline_budget;
432	332721x	return true;
433		}
434		}
435	83387x	return false;
436		}
437
438		inline void
439	3756x	reactor_scheduler::post(std::coroutine_handle<> h) const
440		{
441		struct post_handler final : scheduler_op
442		{
443		std::coroutine_handle<> h_;
444
445	3756x	explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
446	7512x	~post_handler() override = default;
447
448	3744x	void operator()() override
449		{
450	3744x	auto saved = h_;
451	3744x	delete this;
452	3744x	saved.resume();
453	3744x	}
454
455	12x	void destroy() override
456		{
457	12x	auto saved = h_;
458	12x	delete this;
459	12x	saved.destroy();
460	12x	}
461		};
462
463	3756x	auto ph = std::make_unique<post_handler>(h);
464
465	3756x	if (auto* ctx = reactor_find_context(this))
466		{
467	96x	++ctx->private_outstanding_work;
468	96x	ctx->private_queue.push(ph.release());
469	96x	return;
470		}
471
472	3660x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
473
474	3660x	lock_type lock(mutex_);
475	3660x	completed_ops_.push(ph.release());
476	3660x	wake_one_thread_and_unlock(lock);
477	3756x	}
478
479		inline void
480	103346x	reactor_scheduler::post(scheduler_op* h) const
481		{
482	103346x	if (auto* ctx = reactor_find_context(this))
483		{
484	102316x	++ctx->private_outstanding_work;
485	102316x	ctx->private_queue.push(h);
486	102316x	return;
487		}
488
489	1030x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
490
491	1030x	lock_type lock(mutex_);
492	1030x	completed_ops_.push(h);
493	1030x	wake_one_thread_and_unlock(lock);
494	1030x	}
495
496		inline void
497	25942x	reactor_scheduler::post(capy::continuation& c) const
498		{
499	25942x	if (auto* ctx = reactor_find_context(this))
500		{
501	15549x	++ctx->private_outstanding_work;
502	15549x	ctx->private_queue.push(c);
503	15549x	return;
504		}
505
506	10393x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
507
508	10393x	lock_type lock(mutex_);
509	10393x	completed_ops_.push(c);
510	10393x	wake_one_thread_and_unlock(lock);
511	10393x	}
512
513		inline bool
514	10730x	reactor_scheduler::running_in_this_thread() const noexcept
515		{
516	10730x	return reactor_find_context(this) != nullptr;
517		}
518
519		inline void
520	3656x	reactor_scheduler::stop()
521		{
522	3656x	lock_type lock(mutex_);
523	3656x	if (!stopped_.load(std::memory_order_acquire))
524		{
525	2820x	stopped_.store(true, std::memory_order_release);
526	2820x	signal_all(lock);
527	2820x	interrupt_reactor();
528		}
529	3656x	}
530
531		inline bool
532	2521x	reactor_scheduler::stopped() const noexcept
533		{
534	2521x	return stopped_.load(std::memory_order_acquire);
535		}
536
537		inline void
538	1435x	reactor_scheduler::restart()
539		{
540	1435x	stopped_.store(false, std::memory_order_release);
541	1435x	}
542
543		inline std::size_t
544	2057x	reactor_scheduler::run()
545		{
546	4114x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
547		{
548	106x	stop();
549	106x	return 0;
550		}
551
552	1951x	reactor_thread_context_guard ctx(this);
553	1951x	lock_type lock(mutex_);
554
555	1951x	std::size_t n = 0;
556		for (;;)
557		{
558	455846x	if (!do_one(lock, -1, ctx.frame_))
559	1948x	break;
560	453895x	if (n != (std::numeric_limits<std::size_t>::max)())
561	453895x	++n;
562	453895x	if (!lock.owns_lock())
563	352829x	lock.lock();
564		}
565	1948x	return n;
566	1954x	}
567
568		inline std::size_t
569	112x	reactor_scheduler::run_one()
570		{
571	224x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
572		{
573	3x	stop();
574	3x	return 0;
575		}
576
577	109x	reactor_thread_context_guard ctx(this);
578	109x	lock_type lock(mutex_);
579	109x	return do_one(lock, -1, ctx.frame_);
580	109x	}
581
582		inline std::size_t
583	4130x	reactor_scheduler::wait_one(long usec)
584		{
585	8260x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
586		{
587	755x	stop();
588	755x	return 0;
589		}
590
591	3375x	reactor_thread_context_guard ctx(this);
592	3375x	lock_type lock(mutex_);
593	3375x	return do_one(lock, usec, ctx.frame_);
594	3375x	}
595
596		inline std::size_t
597	49x	reactor_scheduler::poll()
598		{
599	98x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
600		{
601	15x	stop();
602	15x	return 0;
603		}
604
605	34x	reactor_thread_context_guard ctx(this);
606	34x	lock_type lock(mutex_);
607
608	34x	std::size_t n = 0;
609		for (;;)
610		{
611	75x	if (!do_one(lock, 0, ctx.frame_))
612	34x	break;
613	41x	if (n != (std::numeric_limits<std::size_t>::max)())
614	41x	++n;
615	41x	if (!lock.owns_lock())
616	41x	lock.lock();
617		}
618	34x	return n;
619	34x	}
620
621		inline std::size_t
622	11x	reactor_scheduler::poll_one()
623		{
624	22x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
625		{
626	5x	stop();
627	5x	return 0;
628		}
629
630	6x	reactor_thread_context_guard ctx(this);
631	6x	lock_type lock(mutex_);
632	6x	return do_one(lock, 0, ctx.frame_);
633	6x	}
634
635		inline void
636	36678x	reactor_scheduler::work_started() noexcept
637		{
638	36678x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
639	36678x	}
640
641		inline void
642	68621x	reactor_scheduler::work_finished() noexcept
643		{
644	137242x	if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
645	2757x	stop();
646	68621x	}
647
648		inline void
649	312878x	reactor_scheduler::compensating_work_started() const noexcept
650		{
651	312878x	auto* ctx = reactor_find_context(this);
652	312878x	if (ctx)
653	312878x	++ctx->private_outstanding_work;
654	312878x	}
655
656		inline void
657	9874x	reactor_scheduler::post_deferred_completions(ready_queue& ops) const
658		{
659	9874x	if (ops.empty())
660	9874x	return;
661
662	2x	if (auto* ctx = reactor_find_context(this))
663		{
664	2x	ctx->private_queue.splice(ops);
665	2x	return;
666		}
667
668	✗	lock_type lock(mutex_);
669	✗	completed_ops_.splice(ops);
670	✗	wake_one_thread_and_unlock(lock);
671	✗	}
672
673		inline void
674	2243x	reactor_scheduler::shutdown_drain()
675		{
676	2243x	lock_type lock(mutex_);
677
678	4863x	while (auto e = completed_ops_.pop())
679		{
680	2620x	if (ready_is_continuation(e))
681		{
682	8x	lock.unlock();
683	8x	if (auto h = ready_as_cont(e)->h)
684	8x	h.destroy();
685	8x	lock.lock();
686		}
687		else
688		{
689	2612x	auto* op = ready_as_op(e);
690	2612x	if (op == &task_op_)
691	2240x	continue;
692	372x	lock.unlock();
693	372x	op->destroy();
694	372x	lock.lock();
695		}
696	2620x	}
697
698	2243x	signal_all(lock);
699	2243x	}
700
701		inline void
702	5063x	reactor_scheduler::signal_all(lock_type&) const
703		{
704	5063x	state_ \|= signaled_bit;
705	5063x	cond_.notify_all();
706	5063x	}
707
708		inline bool
709	15083x	reactor_scheduler::maybe_unlock_and_signal_one(lock_type& lock) const
710		{
711	15083x	state_ \|= signaled_bit;
712	15083x	if (state_ > signaled_bit)
713		{
714	9x	lock.unlock();
715	9x	cond_.notify_one();
716	9x	return true;
717		}
718	15074x	return false;
719		}
720
721		inline bool
722	510167x	reactor_scheduler::unlock_and_signal_one(lock_type& lock) const
723		{
724	510167x	state_ \|= signaled_bit;
725	510167x	bool have_waiters = state_ > signaled_bit;
726	510167x	lock.unlock();
727	510167x	if (have_waiters)
728	6x	cond_.notify_one();
729	510167x	return have_waiters;
730		}
731
732		inline void
733	20x	reactor_scheduler::clear_signal() const
734		{
735	20x	state_ &= ~signaled_bit;
736	20x	}
737
738		inline void
739	6x	reactor_scheduler::wait_for_signal(lock_type& lock) const
740		{
741	14x	while ((state_ & signaled_bit) == 0)
742		{
743	8x	state_ += waiter_increment;
744	8x	cond_.wait(lock);
745	8x	state_ -= waiter_increment;
746		}
747	6x	}
748
749		inline void
750	14x	reactor_scheduler::wait_for_signal_for(lock_type& lock, long timeout_us) const
751		{
752	14x	if ((state_ & signaled_bit) == 0)
753		{
754	14x	state_ += waiter_increment;
755	14x	cond_.wait_for(lock, std::chrono::microseconds(timeout_us));
756	14x	state_ -= waiter_increment;
757		}
758	14x	}
759
760		inline void
761	15083x	reactor_scheduler::wake_one_thread_and_unlock(lock_type& lock) const
762		{
763	15083x	if (maybe_unlock_and_signal_one(lock))
764	9x	return;
765
766	15074x	if (task_running_.load(std::memory_order_relaxed) && !task_interrupted_)
767		{
768	874x	task_interrupted_ = true;
769	874x	lock.unlock();
770	874x	interrupt_reactor();
771		}
772		else
773		{
774	14200x	lock.unlock();
775		}
776		}
777
778	455714x	inline reactor_scheduler::work_cleanup::~work_cleanup()
779		{
780	455714x	std::int64_t produced = ctx.private_outstanding_work;
781	455714x	if (produced > 1)
782	344x	sched->outstanding_work_.fetch_add(
783		produced - 1, std::memory_order_relaxed);
784	455370x	else if (produced < 1)
785	41887x	sched->work_finished();
786	455714x	ctx.private_outstanding_work = 0;
787
788	455714x	if (!ctx.private_queue.empty())
789		{
790	101268x	lock->lock();
791	101268x	sched->completed_ops_.splice(ctx.private_queue);
792		}
793	455714x	}
794
795	343439x	inline reactor_scheduler::task_cleanup::~task_cleanup()
796		{
797	343439x	if (ctx.private_outstanding_work > 0)
798		{
799	9820x	sched->outstanding_work_.fetch_add(
800	9820x	ctx.private_outstanding_work, std::memory_order_relaxed);
801	9820x	ctx.private_outstanding_work = 0;
802		}
803
804	343439x	if (!ctx.private_queue.empty())
805		{
806	9820x	if (!lock->owns_lock())
807	✗	lock->lock();
808	9820x	sched->completed_ops_.splice(ctx.private_queue);
809		}
810	343439x	}
811
812		inline std::size_t
813	459411x	reactor_scheduler::do_one(lock_type& lock, long timeout_us, context_type& ctx)
814		{
815		for (;;)
816		{
817	801157x	if (stopped_.load(std::memory_order_acquire))
818	1951x	return 0;
819
820	799206x	std::uintptr_t e = completed_ops_.pop();
821	799206x	scheduler_op* op = ready_is_continuation(e) ? nullptr : ready_as_op(e);
822
823		// Handle reactor sentinel — time to poll for I/O
824	799206x	if (op == &task_op_)
825		{
826	343472x	bool more_handlers = !completed_ops_.empty();
827
828	632446x	if (!more_handlers &&
829	577948x	(outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
830		timeout_us == 0))
831		{
832	33x	completed_ops_.push(&task_op_);
833	33x	return 0;
834		}
835
836	343439x	long task_timeout_us = more_handlers ? 0 : timeout_us;
837	343439x	task_interrupted_ = task_timeout_us == 0;
838	343439x	task_running_.store(true, std::memory_order_release);
839
840		// Wake a peer to take the pending handlers while this thread
841		// polls the reactor; skipped when one_thread_ (no peer exists).
842	343439x	if (more_handlers && !one_thread_)
843	54491x	unlock_and_signal_one(lock);
844
845		try
846		{
847	343439x	run_task(lock, ctx, task_timeout_us);
848		}
849	3x	catch (...)
850		{
851	3x	task_running_.store(false, std::memory_order_relaxed);
852	3x	throw;
853	3x	}
854
855	343436x	task_running_.store(false, std::memory_order_relaxed);
856	343436x	completed_ops_.push(&task_op_);
857	343436x	if (timeout_us > 0)
858	1710x	return 0;
859	341726x	continue;
860	341726x	}
861
862		// Handle ready entry (op or continuation)
863	455734x	if (e != 0)
864		{
865	455714x	bool more = !completed_ops_.empty();
866
867	455714x	if (more && !one_thread_)
868		{
869		// Wake a peer for the remaining work; unassisted if none
870		// was parked to take it.
871	455676x	ctx.unassisted = !unlock_and_signal_one(lock);
872		}
873		else
874		{
875		// No peer to wake (one_thread_, or nothing more queued).
876	38x	ctx.unassisted = more;
877	38x	lock.unlock();
878		}
879
880	455714x	[[maybe_unused]] work_cleanup on_exit{this, &lock, ctx};
881
882	455714x	if (ready_is_continuation(e))
883	25934x	ready_as_cont(e)->h.resume();
884		else
885	429780x	(*op)();
886	455714x	return 1;
887	455714x	}
888
889	40x	if (outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
890		timeout_us == 0)
891	✗	return 0;
892
893	20x	clear_signal();
894	20x	if (timeout_us < 0)
895	6x	wait_for_signal(lock);
896		else
897	14x	wait_for_signal_for(lock, timeout_us);
898	341746x	}
899		}
900
901		} // namespace boost::corosio::detail
902
903		#endif // BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
904