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/corosio/detail/object_ref.hpp>
15		#include <boost/capy/ex/execution_context.hpp>
16		#include <boost/capy/ex/abandon.hpp>
17
18		#include <boost/corosio/detail/ready_queue.hpp>
19		#include <boost/corosio/detail/scheduler.hpp>
20		#include <boost/corosio/detail/scheduler_op.hpp>
21		#include <boost/corosio/detail/thread_local_ptr.hpp>
22		#include <boost/corosio/detail/timer_service.hpp>
23
24		#include <atomic>
25		#include <chrono>
26		#include <coroutine>
27		#include <cstddef>
28		#include <cstdint>
29		#include <limits>
30		#include <memory>
31		#include <stdexcept>
32
33		#include <boost/corosio/detail/conditionally_enabled_mutex.hpp>
34		#include <boost/corosio/detail/conditionally_enabled_event.hpp>
35
36		namespace boost::corosio::detail {
37
38		// Forward declarations
39		class reactor_scheduler;
40
41		/** A deregistered descriptor whose owner must outlive the reactor pass
42		that may still hold it.
43
44		An event the reactor has already read from the kernel can name a
45		descriptor that another thread closes before the reactor queues it.
46		The closing thread hands over a reference instead of dropping it, so
47		the owner is neither freed nor recycled until that pass ends.
48		*/
49		struct reactor_retirable
50		{
51		// All four fields are guarded by the scheduler's mutex.
52
53		/// Next in the scheduler's retired list.
54		reactor_retirable* retired_next_ = nullptr;
55
56		/// Owner reference held until the pass ends.
57		object_ref retired_ref_;
58
59		/// Next in a settling thread's list of references to drop.
60		reactor_retirable* dropped_next_ = nullptr;
61
62		/// Owner reference waiting to be dropped outside the mutex.
63		object_ref dropped_ref_;
64
65		/// Move @p keep into a queued completion, if one is pending.
66		virtual void hand_off(object_ref& keep) noexcept = 0;
67
68		protected:
69	11999x	~reactor_retirable() = default;
70		};
71
72		/** Per-thread state for a reactor scheduler.
73
74		Each thread running a scheduler's event loop has one of these
75		on a thread-local stack. It holds a private work queue and
76		inline completion budget for speculative I/O fast paths.
77		*/
78		struct BOOST_COROSIO_SYMBOL_VISIBLE reactor_scheduler_context
79		{
80		/// Scheduler this context belongs to.
81		reactor_scheduler const* key;
82
83		/// Next context frame on this thread's stack.
84		reactor_scheduler_context* next;
85
86		/// Private work queue for reduced contention.
87		ready_queue private_queue;
88
89		/// Unflushed work count for the private queue.
90		std::int64_t private_outstanding_work;
91
92		/// Remaining inline completions allowed this cycle.
93		int inline_budget;
94
95		/// Maximum inline budget (adaptive, 2-16).
96		int inline_budget_max;
97
98		/// True if no other thread absorbed queued work last cycle.
99		bool unassisted;
100
101		/// Construct a context frame linked to @a n.
102		reactor_scheduler_context(
103		reactor_scheduler const* k, reactor_scheduler_context* n);
104		};
105
106		/// Thread-local context stack for reactor schedulers.
107		inline thread_local_ptr<reactor_scheduler_context> reactor_context_stack;
108
109		/// Find the context frame for a scheduler on this thread.
110		inline reactor_scheduler_context*
111	1025181x	reactor_find_context(reactor_scheduler const* self) noexcept
112		{
113	1025754x	for (auto* c = reactor_context_stack.get(); c != nullptr; c = c->next)
114		{
115	962679x	if (c->key == self)
116	962106x	return c;
117		}
118	63075x	return nullptr;
119		}
120
121		/** Non-template base for reactor-backed scheduler implementations.
122
123		Provides the complete threading model shared by epoll, kqueue,
124		and select schedulers: signal state machine, inline completion
125		budget, work counting, run/poll methods, and the do_one event
126		loop.
127
128		Derived classes provide platform-specific hooks by overriding:
129		- `run_task(lock, ctx)` to run the reactor poll
130		- `interrupt_reactor()` to wake a blocked reactor
131
132		De-templated from the original CRTP design to eliminate
133		duplicate instantiations when multiple backends are compiled
134		into the same binary. Virtual dispatch for run_task (called
135		once per reactor cycle, before a blocking syscall) has
136		negligible overhead.
137
138		@par Thread Safety
139		All public member functions are thread-safe.
140		*/
141		class reactor_scheduler
142		: public scheduler
143		{
144		public:
145		using context_type = reactor_scheduler_context;
146		using mutex_type = conditionally_enabled_mutex;
147		using lock_type = mutex_type::scoped_lock;
148		using event_type = conditionally_enabled_event;
149
150		/// Post a coroutine for deferred execution.
151		void post(std::coroutine_handle<> h) const override;
152
153		/// Post a scheduler operation for deferred execution.
154		void post(scheduler_op* h) const override;
155
156		/** Release an owner reference once no reactor pass can hold `d`.
157
158		Called after a descriptor is deregistered. If a reactor pass is
159		running, `keep` is parked on `d` until that pass ends. Then, or
160		at once if no pass is running, it moves to `d`'s queued
161		invocation if `d` is queued, and is dropped otherwise.
162
163		@param d The deregistered descriptor.
164		@param keep A reference to the descriptor's owner.
165		*/
166		void retire_descriptor(reactor_retirable& d, object_ref keep) const;
167
168		/// Post a continuation for deferred execution.
169		void post(capy::continuation&) const override;
170
171		/// Return true if called from a thread running this scheduler.
172		bool running_in_this_thread() const noexcept override;
173
174		/// Request the scheduler to stop dispatching handlers.
175		void stop() override;
176
177		/// Return true if the scheduler has been stopped.
178		bool stopped() const noexcept override;
179
180		/// Reset the stopped state so `run()` can resume.
181		void restart() override;
182
183		/// Run the event loop until no work remains.
184		std::size_t run() override;
185
186		/// Run until one handler completes or no work remains.
187		std::size_t run_one() override;
188
189		/// Run until one handler completes or @a usec elapses.
190		std::size_t wait_one(long usec) override;
191
192		/// Run ready handlers without blocking.
193		std::size_t poll() override;
194
195		/// Run at most one ready handler without blocking.
196		std::size_t poll_one() override;
197
198		/// Increment the outstanding work count.
199		void work_started() noexcept override;
200
201		/// Decrement the outstanding work count, stopping on zero.
202		void work_finished() noexcept override;
203
204		/** Reset the thread's inline completion budget.
205
206		Called at the start of each posted completion handler to
207		grant a fresh budget for speculative inline completions.
208		*/
209		void reset_inline_budget() const noexcept;
210
211		/** Consume one unit of inline budget if available.
212
213		@return True if budget was available and consumed.
214		*/
215		bool try_consume_inline_budget() const noexcept;
216
217		/** Offset a forthcoming work_finished from work_cleanup.
218
219		Called by descriptor_state when all I/O returned EAGAIN and
220		no handler will be executed. Must be called from a scheduler
221		thread.
222		*/
223		/** Note that an op was parked outside the usual registration path.
224
225		A reactor that builds its poll set from parked ops must rebuild
226		it; one the kernel tracks needs nothing.
227		*/
228	458x	virtual void notify_reparked() const {}
229
230		void compensating_work_started() const noexcept;
231
232		/** Post an operation whose work is already counted.
233
234		The posting thread touches nothing of the scheduler after this
235		returns, unlike a @ref post followed by @ref work_finished: once
236		posted, the operation can complete and let its context be
237		destroyed.
238
239		@pre work_started() was called for @p op.
240
241		@param op The operation to post.
242		*/
243		void post_counted(scheduler_op* op) const;
244
245		/** Post completed operations for deferred invocation.
246
247		If called from a thread running this scheduler, operations
248		go to the thread's private queue (fast path). Otherwise,
249		operations are added to the global queue under mutex and a
250		waiter is signaled.
251
252		@pre work_started() must have been called for each operation.
253
254		@param ops Queue of operations to post.
255		*/
256		void post_deferred_completions(ready_queue& ops) const;
257
258		/** Apply runtime configuration to the scheduler.
259
260		Called by `io_context` after construction. Values that do
261		not apply to this backend are silently ignored.
262
263		@param max_events Event buffer size for epoll/kqueue.
264		@param budget_init Starting inline completion budget.
265		@param budget_max Hard ceiling on adaptive budget ramp-up.
266		@param unassisted Budget when single-threaded.
267		*/
268		virtual void configure_reactor(
269		unsigned max_events,
270		unsigned budget_init,
271		unsigned budget_max,
272		unsigned unassisted);
273
274		/// Return the configured initial inline budget.
275	13155x	unsigned inline_budget_initial() const noexcept
276		{
277	13155x	return inline_budget_initial_;
278		}
279
280		/// Return true when scheduler locking is disabled (fully-lockless tier).
281	1448x	bool scheduler_locking_disabled() const noexcept override
282		{
283	1448x	return scheduler_locking_disabled_;
284		}
285
286	4413x	void configure_threading(threading_config cfg) noexcept override
287		{
288	4413x	scheduler_locking_disabled_ = !cfg.scheduler_locking;
289		// reactor_io_locking takes effect at descriptor registration (see the
290		// register_descriptor overrides), not here.
291	4413x	reactor_io_locking_ = cfg.reactor_io_locking;
292	4413x	one_thread_ = cfg.one_thread;
293	4413x	mutex_.set_enabled(cfg.scheduler_locking);
294	4413x	cond_.set_enabled(cfg.scheduler_locking);
295	4413x	}
296
297		protected:
298		timer_service* timer_svc_ = nullptr;
299		bool scheduler_locking_disabled_ = false;
300		bool reactor_io_locking_ = true;
301		bool one_thread_ = false;
302
303	4425x	reactor_scheduler() = default;
304
305		/// Destroy, destroying whatever was posted after the drain.
306		~reactor_scheduler() override;
307
308		/** Drain completed_ops during shutdown.
309
310		Pops all operations from the global queue and destroys them,
311		skipping the task sentinel. Signals all waiting threads.
312		Derived classes call this from their shutdown() override
313		before performing platform-specific cleanup.
314		*/
315		void shutdown_drain();
316
317		/// Destroy every queued operation without running it.
318		void destroy_queued(lock_type& lock) noexcept;
319
320		/// RAII guard that re-inserts the task sentinel after `run_task`.
321		struct task_cleanup
322		{
323		reactor_scheduler const* sched;
324		lock_type* lock;
325		context_type& ctx;
326		~task_cleanup();
327		};
328
329		mutable mutex_type mutex_{true};
330		mutable event_type cond_{true};
331		mutable ready_queue completed_ops_;
332		mutable std::atomic<std::int64_t> outstanding_work_{0};
333		std::atomic<bool> stopped_{false};
334		mutable std::atomic<bool> task_running_{false};
335		mutable bool task_interrupted_ = false;
336
337		// Descriptors retired during the running reactor pass (guarded by
338		// mutex_).
339		mutable reactor_retirable* retired_ = nullptr;
340
341		/// Settle every descriptor retired before the current pass ended.
342		/// @pre `lock` holds `mutex_`; it is held again on return.
343		void settle_retired(lock_type& lock) const;
344
345		// Runtime-configurable reactor tuning parameters.
346		// Defaults match the library's built-in values.
347		unsigned max_events_per_poll_ = 128;
348		unsigned inline_budget_initial_ = 2;
349		unsigned inline_budget_max_ = 16;
350		unsigned unassisted_budget_ = 4;
351
352		/// Bit 0 of `state_`: set when the condvar should be signaled.
353		static constexpr std::size_t signaled_bit = 1;
354
355		/// Increment per waiting thread in `state_`.
356		static constexpr std::size_t waiter_increment = 2;
357		mutable std::size_t state_ = 0;
358
359		/// Sentinel op that triggers a reactor poll when dequeued.
360		struct task_op final : scheduler_op
361		{
362		// LCOV_EXCL_START: the sentinel is intercepted by pointer
363		// identity; its virtuals exist for vtable completeness.
364	−	void operator()() override {}
365	−	void destroy() override {}
366		// LCOV_EXCL_STOP
367		};
368		task_op task_op_;
369
370		/** Run the platform-specific reactor poll.
371
372		@par Postconditions
373		`lock` is owned on return, however the poll ended. An
374		implementation that unlocks around the blocking call owes the
375		caller a matching re-acquire on every path out, including the
376		errors it retries rather than reports.
377		*/
378		virtual void
379		run_task(lock_type& lock, context_type& ctx, long timeout_us) = 0;
380
381		/// Wake a blocked reactor (e.g. write to eventfd or pipe).
382		virtual void interrupt_reactor() const = 0;
383
384		private:
385		struct work_cleanup
386		{
387		reactor_scheduler* sched;
388		lock_type* lock;
389		context_type& ctx;
390		~work_cleanup();
391		};
392
393		std::size_t do_one(lock_type& lock, long timeout_us, context_type& ctx);
394
395		void signal_all(lock_type& lock) const;
396		bool maybe_unlock_and_signal_one(lock_type& lock) const;
397		bool unlock_and_signal_one(lock_type& lock) const;
398		void clear_signal() const;
399		void wait_for_signal(lock_type& lock) const;
400		void wait_for_signal_for(lock_type& lock, long timeout_us) const;
401		void wake_one_thread_and_unlock(lock_type& lock) const;
402		};
403
404		/** RAII guard that pushes/pops a scheduler context frame.
405
406		On construction, pushes a new context frame onto the
407		thread-local stack. On destruction, drains any remaining
408		private queue items to the global queue and pops the frame.
409		*/
410		struct reactor_thread_context_guard
411		{
412		/// The context frame managed by this guard.
413		reactor_scheduler_context frame_;
414
415		/// Marks the scheduler innermost for the executor's fast check.
416		running_scheduler_guard running_;
417
418		/// Construct the guard, pushing a frame for @a sched.
419	13155x	explicit reactor_thread_context_guard(
420		reactor_scheduler const* sched) noexcept
421	13155x	: frame_(sched, reactor_context_stack.get())
422	13155x	, running_(sched)
423		{
424	13155x	reactor_context_stack.set(&frame_);
425	13155x	}
426
427		/** Destroy the guard, popping the frame.
428
429		The private queue is empty here by invariant: work_cleanup and
430		task_cleanup splice it to the global queue after every handler
431		and every reactor pass.
432		*/
433	13155x	~reactor_thread_context_guard() noexcept
434		{
435	13155x	reactor_context_stack.set(frame_.next);
436	13155x	}
437		};
438
439		// ---- Inline implementations ------------------------------------------------
440
441	13155x	inline reactor_scheduler_context::reactor_scheduler_context(
442	13155x	reactor_scheduler const* k, reactor_scheduler_context* n)
443	13155x	: key(k)
444	13155x	, next(n)
445	13155x	, private_outstanding_work(0)
446	13155x	, inline_budget(0)
447	13155x	, inline_budget_max(static_cast<int>(k->inline_budget_initial()))
448	13155x	, unassisted(false)
449		{
450	13155x	}
451
452		inline void
453	54x	reactor_scheduler::configure_reactor(
454		unsigned max_events,
455		unsigned budget_init,
456		unsigned budget_max,
457		unsigned unassisted)
458		{
459	106x	if (max_events < 1 \|\|
460	52x	max_events > static_cast<unsigned>(std::numeric_limits<int>::max()))
461	2x	throw std::out_of_range("max_events_per_poll must be in [1, INT_MAX]");
462	52x	if (budget_max > static_cast<unsigned>(std::numeric_limits<int>::max()))
463	2x	throw std::out_of_range("inline_budget_max must be in [0, INT_MAX]");
464
465		// Clamp initial and unassisted to budget_max.
466	50x	if (budget_init > budget_max)
467	20x	budget_init = budget_max;
468	50x	if (unassisted > budget_max)
469	20x	unassisted = budget_max;
470
471	50x	max_events_per_poll_ = max_events;
472	50x	inline_budget_initial_ = budget_init;
473	50x	inline_budget_max_ = budget_max;
474	50x	unassisted_budget_ = unassisted;
475	50x	}
476
477		inline void
478	111330x	reactor_scheduler::reset_inline_budget() const noexcept
479		{
480		// When budget is disabled (max==0), all paths below would no-op
481		// (inline_budget stays 0). Skip the TLS lookup entirely.
482	111330x	if (inline_budget_max_ == 0)
483	58x	return;
484	111272x	if (auto* ctx = reactor_find_context(this))
485		{
486		// Cap when no other thread absorbed queued work
487	111272x	if (ctx->unassisted)
488		{
489	110162x	ctx->inline_budget_max = static_cast<int>(unassisted_budget_);
490	110162x	ctx->inline_budget = static_cast<int>(unassisted_budget_);
491	110162x	return;
492		}
493		// Ramp up when previous cycle fully consumed budget.
494		// max(1, ...) ensures the doubling escapes zero.
495	1110x	if (ctx->inline_budget == 0)
496	330x	ctx->inline_budget_max =
497	330x	(std::min)((std::max)(1, ctx->inline_budget_max) * 2,
498	660x	static_cast<int>(inline_budget_max_));
499	780x	else if (ctx->inline_budget < ctx->inline_budget_max)
500	245x	ctx->inline_budget_max = static_cast<int>(inline_budget_initial_);
501	1110x	ctx->inline_budget = ctx->inline_budget_max;
502		}
503		}
504
505		inline bool
506	472848x	reactor_scheduler::try_consume_inline_budget() const noexcept
507		{
508	472848x	if (inline_budget_max_ == 0)
509	44x	return false;
510	472804x	if (auto* ctx = reactor_find_context(this))
511		{
512	472786x	if (ctx->inline_budget > 0)
513		{
514	377932x	--ctx->inline_budget;
515	377932x	return true;
516		}
517		}
518	94872x	return false;
519		}
520
521		inline void
522	3672x	reactor_scheduler::post(std::coroutine_handle<> h) const
523		{
524		struct post_handler final : scheduler_op
525		{
526		std::coroutine_handle<> h_;
527
528	3672x	explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
529	7344x	~post_handler() override = default;
530
531	3656x	void operator()() override
532		{
533	3656x	auto saved = h_;
534	3656x	delete this;
535	3656x	saved.resume();
536	3656x	}
537
538	16x	void destroy() override
539		{
540		// A bare handle carries no owner to unwind from: it is
541		// destroyed directly.
542	16x	auto saved = h_;
543	16x	delete this;
544	16x	saved.destroy();
545	16x	}
546		};
547
548	3672x	auto ph = std::make_unique<post_handler>(h);
549
550	3672x	if (auto* ctx = reactor_find_context(this))
551		{
552	8x	++ctx->private_outstanding_work;
553	8x	ctx->private_queue.push(ph.release());
554	8x	return;
555		}
556
557	3664x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
558
559	3664x	lock_type lock(mutex_);
560	3664x	completed_ops_.push(ph.release());
561	3664x	wake_one_thread_and_unlock(lock);
562	3672x	}
563
564		inline void
565	119742x	reactor_scheduler::post(scheduler_op* h) const
566		{
567	119742x	if (auto* ctx = reactor_find_context(this))
568		{
569	117685x	++ctx->private_outstanding_work;
570	117685x	ctx->private_queue.push(h);
571	117685x	return;
572		}
573
574	2057x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
575
576	2057x	lock_type lock(mutex_);
577	2057x	completed_ops_.push(h);
578	2057x	wake_one_thread_and_unlock(lock);
579	2057x	}
580
581		inline void
582	252861x	reactor_scheduler::post(capy::continuation& c) const
583		{
584	252861x	if (auto* ctx = reactor_find_context(this))
585		{
586	220651x	++ctx->private_outstanding_work;
587	220651x	ctx->private_queue.push(c);
588	220651x	return;
589		}
590
591	32210x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
592
593	32210x	lock_type lock(mutex_);
594	32210x	completed_ops_.push(c);
595	32210x	wake_one_thread_and_unlock(lock);
596	32210x	}
597
598		inline bool
599	23757x	reactor_scheduler::running_in_this_thread() const noexcept
600		{
601	23757x	return reactor_find_context(this) != nullptr;
602		}
603
604		inline void
605	8364x	reactor_scheduler::stop()
606		{
607	8364x	lock_type lock(mutex_);
608	8364x	if (!stopped_.load(std::memory_order_acquire))
609		{
610	7368x	stopped_.store(true, std::memory_order_release);
611	7368x	signal_all(lock);
612	7368x	interrupt_reactor();
613		}
614	8364x	}
615
616		inline bool
617	3552x	reactor_scheduler::stopped() const noexcept
618		{
619	3552x	return stopped_.load(std::memory_order_acquire);
620		}
621
622		inline void
623	5766x	reactor_scheduler::restart()
624		{
625	5766x	stopped_.store(false, std::memory_order_release);
626	5766x	}
627
628		inline std::size_t
629	6542x	reactor_scheduler::run()
630		{
631	13084x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
632		{
633	238x	stop();
634	238x	return 0;
635		}
636
637	6304x	reactor_thread_context_guard ctx(this);
638	6304x	lock_type lock(mutex_);
639
640	6304x	std::size_t n = 0;
641		for (;;)
642		{
643	418815x	if (!do_one(lock, -1, ctx.frame_))
644	6301x	break;
645	412511x	if (n != (std::numeric_limits<std::size_t>::max)())
646	412511x	++n;
647	412511x	if (!lock.owns_lock())
648	93067x	lock.lock();
649		}
650	6301x	return n;
651	6307x	}
652
653		inline std::size_t
654	130x	reactor_scheduler::run_one()
655		{
656	260x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
657		{
658	3x	stop();
659	3x	return 0;
660		}
661
662	127x	reactor_thread_context_guard ctx(this);
663	127x	lock_type lock(mutex_);
664	127x	return do_one(lock, -1, ctx.frame_);
665	127x	}
666
667		inline std::size_t
668	6158x	reactor_scheduler::wait_one(long usec)
669		{
670	12316x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
671		{
672	785x	stop();
673	785x	return 0;
674		}
675
676	5373x	reactor_thread_context_guard ctx(this);
677	5373x	lock_type lock(mutex_);
678	5373x	return do_one(lock, usec, ctx.frame_);
679	5373x	}
680
681		inline std::size_t
682	1327x	reactor_scheduler::poll()
683		{
684	2654x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
685		{
686	29x	stop();
687	29x	return 0;
688		}
689
690	1298x	reactor_thread_context_guard ctx(this);
691	1298x	lock_type lock(mutex_);
692
693	1298x	std::size_t n = 0;
694		for (;;)
695		{
696	9275x	if (!do_one(lock, 0, ctx.frame_))
697	1298x	break;
698	7977x	if (n != (std::numeric_limits<std::size_t>::max)())
699	7977x	++n;
700	7977x	if (!lock.owns_lock())
701	7975x	lock.lock();
702		}
703	1298x	return n;
704	1298x	}
705
706		inline std::size_t
707	58x	reactor_scheduler::poll_one()
708		{
709	116x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
710		{
711	5x	stop();
712	5x	return 0;
713		}
714
715	53x	reactor_thread_context_guard ctx(this);
716	53x	lock_type lock(mutex_);
717	53x	return do_one(lock, 0, ctx.frame_);
718	53x	}
719
720		inline void
721	67648x	reactor_scheduler::work_started() noexcept
722		{
723	67648x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
724	67648x	}
725
726		inline void
727	113181x	reactor_scheduler::work_finished() noexcept
728		{
729	226362x	if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
730	7239x	stop();
731	113181x	}
732
733		inline void
734	39099x	reactor_scheduler::compensating_work_started() const noexcept
735		{
736	39099x	auto* ctx = reactor_find_context(this);
737	39099x	if (ctx)
738	39097x	++ctx->private_outstanding_work;
739	39099x	}
740
741		inline void
742	1972x	reactor_scheduler::post_counted(scheduler_op* op) const
743		{
744	1972x	if (auto* ctx = reactor_find_context(this))
745		{
746	605x	ctx->private_queue.push(op);
747	605x	return;
748		}
749
750	1367x	lock_type lock(mutex_);
751	1367x	completed_ops_.push(op);
752	1367x	wake_one_thread_and_unlock(lock);
753	1367x	}
754
755		inline void
756	16057x	reactor_scheduler::post_deferred_completions(ready_queue& ops) const
757		{
758	16057x	if (ops.empty())
759	16057x	return;
760
761	2x	if (auto* ctx = reactor_find_context(this))
762		{
763	2x	ctx->private_queue.splice(ops);
764	2x	return;
765		}
766
767	✗	lock_type lock(mutex_);
768	✗	completed_ops_.splice(ops);
769	✗	wake_one_thread_and_unlock(lock);
770	✗	}
771
772		inline void
773	22999x	reactor_scheduler::retire_descriptor(
774		reactor_retirable& d, object_ref keep) const
775		{
776	22999x	lock_type lock(mutex_);
777	22999x	if (!task_running_.load(std::memory_order_relaxed))
778		{
779		// No pass can hold an event, but an earlier one may have
780		// queued d.
781	17625x	d.hand_off(keep);
782	17625x	return;
783		}
784		// Already parked for this pass: the held reference suffices.
785	5374x	if (d.retired_ref_)
786	7x	return;
787	5367x	d.retired_ref_ = std::move(keep);
788	5367x	d.retired_next_ = retired_;
789	5367x	retired_ = &d;
790	22999x	}
791
792		inline void
793	369989x	reactor_scheduler::settle_retired(lock_type& lock) const
794		{
795		// Handed off under the lock, since a later pass may retire the same
796		// descriptor again as soon as it is released. A reference that is
797		// not handed off may be the owner's last, and its release recycles
798		// through the pool mutex, so it is dropped with the lock released.
799	369989x	reactor_retirable* dropped = nullptr;
800	375356x	while (auto* d = retired_)
801		{
802	5367x	retired_ = d->retired_next_;
803	5367x	d->retired_next_ = nullptr;
804	5367x	auto keep = std::move(d->retired_ref_);
805	5367x	d->hand_off(keep);
806		// A drop already pending keeps the owner alive, so this one
807		// cannot be the last and is released here.
808	5367x	if (!keep \|\| d->dropped_ref_)
809	511x	continue;
810	4856x	d->dropped_ref_ = std::move(keep);
811	4856x	d->dropped_next_ = dropped;
812	4856x	dropped = d;
813	10734x	}
814	374845x	while (auto* d = dropped)
815		{
816	4856x	dropped = d->dropped_next_;
817	4856x	d->dropped_next_ = nullptr;
818	4856x	auto keep = std::move(d->dropped_ref_);
819	4856x	lock.unlock();
820	4856x	keep.reset();
821	4856x	lock.lock();
822	4856x	}
823	369989x	}
824
825		inline void
826	4413x	reactor_scheduler::shutdown_drain()
827		{
828		// This scheduler's constructor registered the timer service, so
829		// the context shuts it down later; its waiters' frames must be
830		// destroyed before the drain, which then destroys whatever their
831		// destructors post. The context's own call later finds no waiter.
832	4413x	if (timer_svc_)
833	4413x	timer_svc_->shutdown();
834
835	4413x	wait_cancels_posting();
836
837	4413x	lock_type lock(mutex_);
838	4413x	settle_retired(lock);
839	4413x	destroy_queued(lock);
840	4413x	signal_all(lock);
841	4413x	}
842
843	4425x	inline reactor_scheduler::~reactor_scheduler()
844		{
845		// Service destructors run after the drain and may still post.
846	4425x	lock_type lock(mutex_);
847	4425x	destroy_queued(lock);
848	4425x	}
849
850		inline void
851	8838x	reactor_scheduler::destroy_queued(lock_type& lock) noexcept
852		{
853	22593x	while (auto e = completed_ops_.pop())
854		{
855	13755x	if (ready_is_continuation(e))
856		{
857	7808x	lock.unlock();
858	7808x	if (auto* c = ready_as_cont(e); c->h)
859	7808x	capy::abandon(*c);
860	7808x	lock.lock();
861		}
862		else
863		{
864	5947x	auto* op = ready_as_op(e);
865	5947x	if (op == &task_op_)
866	4410x	continue;
867	1537x	lock.unlock();
868	1537x	op->destroy();
869	1537x	lock.lock();
870		}
871	13755x	}
872	8838x	}
873
874		inline void
875	11781x	reactor_scheduler::signal_all(lock_type&) const
876		{
877	11781x	state_ \|= signaled_bit;
878	11781x	cond_.notify_all();
879	11781x	}
880
881		inline bool
882	39298x	reactor_scheduler::maybe_unlock_and_signal_one(lock_type& lock) const
883		{
884	39298x	state_ \|= signaled_bit;
885	39298x	if (state_ > signaled_bit)
886		{
887		// Signalled before unlocking: a post from another context's
888		// thread may be the last touch of this scheduler before the
889		// posted work runs, finishes and lets it be destroyed.
890	215x	cond_.notify_one();
891	215x	lock.unlock();
892	215x	return true;
893		}
894	39083x	return false;
895		}
896
897		inline bool
898	686818x	reactor_scheduler::unlock_and_signal_one(lock_type& lock) const
899		{
900	686818x	state_ \|= signaled_bit;
901	686818x	bool have_waiters = state_ > signaled_bit;
902	686818x	lock.unlock();
903	686818x	if (have_waiters)
904	4769x	cond_.notify_one();
905	686818x	return have_waiters;
906		}
907
908		inline void
909	841x	reactor_scheduler::clear_signal() const
910		{
911	841x	state_ &= ~signaled_bit;
912	841x	}
913
914		inline void
915	831x	reactor_scheduler::wait_for_signal(lock_type& lock) const
916		{
917	1747x	while ((state_ & signaled_bit) == 0)
918		{
919	916x	state_ += waiter_increment;
920	916x	cond_.wait(lock);
921	916x	state_ -= waiter_increment;
922		}
923	831x	}
924
925		inline void
926	10x	reactor_scheduler::wait_for_signal_for(lock_type& lock, long timeout_us) const
927		{
928	10x	if ((state_ & signaled_bit) == 0)
929		{
930	10x	state_ += waiter_increment;
931	10x	cond_.wait_for(lock, std::chrono::microseconds(timeout_us));
932	10x	state_ -= waiter_increment;
933		}
934	10x	}
935
936		inline void
937	39298x	reactor_scheduler::wake_one_thread_and_unlock(lock_type& lock) const
938		{
939	39298x	if (maybe_unlock_and_signal_one(lock))
940	215x	return;
941
942	39083x	if (task_running_.load(std::memory_order_relaxed) && !task_interrupted_)
943		{
944	1614x	task_interrupted_ = true;
945		// Under the lock, for the same reason as the signal above.
946	1614x	interrupt_reactor();
947	1614x	lock.unlock();
948		}
949		else
950		{
951	37469x	lock.unlock();
952		}
953		}
954
955	423346x	inline reactor_scheduler::work_cleanup::~work_cleanup()
956		{
957	423346x	std::int64_t produced = ctx.private_outstanding_work;
958	423346x	if (produced > 1)
959	1011x	sched->outstanding_work_.fetch_add(
960		produced - 1, std::memory_order_relaxed);
961	422335x	else if (produced < 1)
962	65834x	sched->work_finished();
963	423346x	ctx.private_outstanding_work = 0;
964
965	423346x	if (!ctx.private_queue.empty())
966		{
967	319757x	lock->lock();
968	319757x	sched->completed_ops_.splice(ctx.private_queue);
969		}
970	423346x	}
971
972	365579x	inline reactor_scheduler::task_cleanup::~task_cleanup()
973		{
974	365579x	if (ctx.private_outstanding_work > 0)
975		{
976	10592x	sched->outstanding_work_.fetch_add(
977	10592x	ctx.private_outstanding_work, std::memory_order_relaxed);
978	10592x	ctx.private_outstanding_work = 0;
979		}
980
981	365579x	if (!ctx.private_queue.empty())
982		{
983	10592x	if (!lock->owns_lock())
984	✗	lock->lock();
985	10592x	sched->completed_ops_.splice(ctx.private_queue);
986		}
987	365579x	}
988
989		inline std::size_t
990	433643x	reactor_scheduler::do_one(lock_type& lock, long timeout_us, context_type& ctx)
991		{
992		for (;;)
993		{
994	797367x	if (stopped_.load(std::memory_order_acquire))
995	6470x	return 0;
996
997	790897x	std::uintptr_t e = completed_ops_.pop();
998	790897x	scheduler_op* op = ready_is_continuation(e) ? nullptr : ready_as_op(e);
999
1000		// Handle reactor sentinel — time to poll for I/O
1001	790897x	if (op == &task_op_)
1002		{
1003	366710x	bool more_handlers = !completed_ops_.empty();
1004
1005	468053x	if (!more_handlers &&
1006	202686x	(outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
1007		timeout_us == 0))
1008		{
1009	1131x	completed_ops_.push(&task_op_);
1010	1131x	return 0;
1011		}
1012
1013	365579x	long task_timeout_us = more_handlers ? 0 : timeout_us;
1014	365579x	task_interrupted_ = task_timeout_us == 0;
1015	365579x	task_running_.store(true, std::memory_order_release);
1016
1017		// Wake a peer to take the pending handlers while this thread
1018		// polls the reactor; skipped when one_thread_ (no peer exists).
1019	365579x	if (more_handlers && !one_thread_)
1020	265356x	unlock_and_signal_one(lock);
1021
1022		try
1023		{
1024	365579x	run_task(lock, ctx, task_timeout_us);
1025		}
1026	3x	catch (...)
1027		{
1028	3x	task_running_.store(false, std::memory_order_relaxed);
1029	3x	throw;
1030	3x	}
1031
1032	365576x	task_running_.store(false, std::memory_order_relaxed);
1033	365576x	completed_ops_.push(&task_op_);
1034	365576x	settle_retired(lock);
1035	365576x	if (timeout_us > 0)
1036	2693x	return 0;
1037	362883x	continue;
1038	362883x	}
1039
1040		// Handle ready entry (op or continuation)
1041	424187x	if (e != 0)
1042		{
1043	423346x	bool more = !completed_ops_.empty();
1044
1045	423346x	if (more && !one_thread_)
1046		{
1047		// Wake a peer for the remaining work; unassisted if none
1048		// was parked to take it.
1049	421462x	ctx.unassisted = !unlock_and_signal_one(lock);
1050		}
1051		else
1052		{
1053		// No peer to wake (one_thread_, or nothing more queued).
1054	1884x	ctx.unassisted = more;
1055	1884x	lock.unlock();
1056		}
1057
1058	423346x	[[maybe_unused]] work_cleanup on_exit{this, &lock, ctx};
1059
1060	423346x	if (ready_is_continuation(e))
1061	245053x	ready_as_cont(e)->h.resume();
1062		else
1063	178293x	(*op)();
1064	423346x	return 1;
1065	423346x	}
1066
1067	1682x	if (outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
1068		timeout_us == 0)
1069	✗	return 0;
1070
1071	841x	clear_signal();
1072	841x	if (timeout_us < 0)
1073	831x	wait_for_signal(lock);
1074		else
1075	10x	wait_for_signal_for(lock, timeout_us);
1076	363724x	}
1077		}
1078
1079		} // namespace boost::corosio::detail
1080
1081		#endif // BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
1082