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
32		#include <boost/corosio/detail/conditionally_enabled_mutex.hpp>
33		#include <boost/corosio/detail/conditionally_enabled_event.hpp>
34
35		namespace boost::corosio::detail {
36
37		// Forward declarations
38		class reactor_scheduler;
39
40		/** A deregistered descriptor whose owner must outlive the reactor pass
41		that may still hold it.
42
43		An event the reactor has already read from the kernel can name a
44		descriptor that another thread closes before the reactor queues it.
45		The closing thread hands over a reference instead of dropping it, so
46		the owner is neither freed nor recycled until that pass ends.
47		*/
48		struct reactor_retirable
49		{
50		// All four fields are guarded by the scheduler's mutex.
51
52		/// Next in the scheduler's retired list.
53		reactor_retirable* retired_next_ = nullptr;
54
55		/// Owner reference held until the pass ends.
56		object_ref retired_ref_;
57
58		/// Next in a settling thread's list of references to drop.
59		reactor_retirable* dropped_next_ = nullptr;
60
61		/// Owner reference waiting to be dropped outside the mutex.
62		object_ref dropped_ref_;
63
64		/// Move @p keep into a queued completion, if one is pending.
65		virtual void hand_off(object_ref& keep) noexcept = 0;
66
67		protected:
68	12288x	~reactor_retirable() = default;
69		};
70
71		/** Per-thread state for a reactor scheduler.
72
73		Each thread running a scheduler's event loop has one of these
74		on a thread-local stack. It holds a private work queue and
75		inline completion budget for speculative I/O fast paths.
76		*/
77		struct BOOST_COROSIO_SYMBOL_VISIBLE reactor_scheduler_context
78		{
79		/// Scheduler this context belongs to.
80		reactor_scheduler const* key;
81
82		/// Next context frame on this thread's stack.
83		reactor_scheduler_context* next;
84
85		/// Private work queue for reduced contention.
86		ready_queue private_queue;
87
88		/// Unflushed work count for the private queue.
89		std::int64_t private_outstanding_work;
90
91		/// Remaining inline completions allowed this cycle.
92		int inline_budget;
93
94		/// Maximum inline budget (adaptive, 2-16).
95		int inline_budget_max;
96
97		/// True if no other thread absorbed queued work last cycle.
98		bool unassisted;
99
100		/// Construct a context frame linked to @a n.
101		reactor_scheduler_context(
102		reactor_scheduler const* k, reactor_scheduler_context* n);
103		};
104
105		/// Thread-local context stack for reactor schedulers.
106		inline thread_local_ptr<reactor_scheduler_context> reactor_context_stack;
107
108		/// Find the context frame for a scheduler on this thread.
109		inline reactor_scheduler_context*
110	928398x	reactor_find_context(reactor_scheduler const* self) noexcept
111		{
112	929016x	for (auto* c = reactor_context_stack.get(); c != nullptr; c = c->next)
113		{
114	866748x	if (c->key == self)
115	866130x	return c;
116		}
117	62268x	return nullptr;
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 : public scheduler
141		{
142		public:
143		using context_type = reactor_scheduler_context;
144		using mutex_type = conditionally_enabled_mutex;
145		using lock_type = mutex_type::scoped_lock;
146		using event_type = conditionally_enabled_event;
147
148		/// Post a coroutine for deferred execution.
149		void post(std::coroutine_handle<> h) const override;
150
151		/// Post a scheduler operation for deferred execution.
152		void post(scheduler_op* h) const override;
153
154		/** Release an owner reference once no reactor pass can hold `d`.
155
156		Called after a descriptor is deregistered. If a reactor pass is
157		running, `keep` is parked on `d` until that pass ends. Then, or
158		at once if no pass is running, it moves to `d`'s queued
159		invocation if `d` is queued, and is dropped otherwise.
160
161		@param d The deregistered descriptor.
162		@param keep A reference to the descriptor's owner.
163		*/
164		void retire_descriptor(reactor_retirable& d, object_ref keep) const;
165
166		/// Post a continuation for deferred execution.
167		void post(capy::continuation&) const override;
168
169		/// Return true if called from a thread running this scheduler.
170		bool running_in_this_thread() const noexcept override;
171
172		/// Request the scheduler to stop dispatching handlers.
173		void stop() override;
174
175		/// Return true if the scheduler has been stopped.
176		bool stopped() const noexcept override;
177
178		/// Reset the stopped state so `run()` can resume.
179		void restart() override;
180
181		/// Run the event loop until no work remains.
182		std::size_t run() override;
183
184		/// Run until one handler completes or no work remains.
185		std::size_t run_one() override;
186
187		/// Run until one handler completes or @a usec elapses.
188		std::size_t wait_one(long usec) override;
189
190		/// Run ready handlers without blocking.
191		std::size_t poll() override;
192
193		/// Run at most one ready handler without blocking.
194		std::size_t poll_one() override;
195
196		/// Increment the outstanding work count.
197		void work_started() noexcept override;
198
199		/// Decrement the outstanding work count, stopping on zero.
200		void work_finished() noexcept override;
201
202		/** Reset the thread's inline completion budget.
203
204		Called at the start of each posted completion handler to
205		grant a fresh budget for speculative inline completions.
206		*/
207		void reset_inline_budget() const noexcept;
208
209		/** Consume one unit of inline budget if available.
210
211		@return True if budget was available and consumed.
212		*/
213		bool try_consume_inline_budget() const noexcept;
214
215		/** Offset a forthcoming work_finished from work_cleanup.
216
217		Called by descriptor_state when all I/O returned EAGAIN and
218		no handler will be executed. Must be called from a scheduler
219		thread.
220		*/
221		/** Note that an op was parked outside the usual registration path.
222
223		A reactor that builds its poll set from parked ops must rebuild
224		it; one the kernel tracks needs nothing.
225		*/
226	442x	virtual void notify_reparked() const {}
227
228		void compensating_work_started() const noexcept;
229
230		/** Post an operation whose work is already counted.
231
232		The posting thread touches nothing of the scheduler after this
233		returns, unlike a @ref post followed by @ref work_finished: once
234		posted, the operation can complete and let its context be
235		destroyed.
236
237		@pre work_started() was called for @p op.
238
239		@param op The operation to post.
240		*/
241		void post_counted(scheduler_op* op) const;
242
243		/** Post completed operations for deferred invocation.
244
245		If called from a thread running this scheduler, operations
246		go to the thread's private queue (fast path). Otherwise,
247		operations are added to the global queue under mutex and a
248		waiter is signaled.
249
250		@pre work_started() must have been called for each operation.
251
252		@param ops Queue of operations to post.
253		*/
254		void post_deferred_completions(ready_queue& ops) const;
255
256		/** Apply runtime configuration to the scheduler.
257
258		Called by `io_context` after construction. Values that do
259		not apply to this backend are silently ignored.
260
261		@pre `max_events` is in [ 1, `INT_MAX` ] and `budget_max` is at
262		most `INT_MAX`; `io_context` validates both.
263
264		@param max_events Event buffer size for epoll/kqueue.
265		@param budget_init Starting inline completion budget.
266		@param budget_max Hard ceiling on adaptive budget ramp-up.
267		@param unassisted Budget when single-threaded.
268		*/
269		virtual void configure_reactor(
270		unsigned max_events,
271		unsigned budget_init,
272		unsigned budget_max,
273		unsigned unassisted);
274
275		/// Return the configured initial inline budget.
276	12743x	unsigned inline_budget_initial() const noexcept
277		{
278	12743x	return inline_budget_initial_;
279		}
280
281		/// Return true when scheduler locking is disabled (fully-lockless tier).
282	1460x	bool scheduler_locking_disabled() const noexcept override
283		{
284	1460x	return scheduler_locking_disabled_;
285		}
286
287	4498x	void configure_threading(threading_config cfg) noexcept override
288		{
289	4498x	scheduler_locking_disabled_ = !cfg.scheduler_locking;
290		// reactor_io_locking takes effect at descriptor registration (see the
291		// register_descriptor overrides), not here.
292	4498x	reactor_io_locking_ = cfg.reactor_io_locking;
293	4498x	one_thread_ = cfg.one_thread;
294	4498x	mutex_.set_enabled(cfg.scheduler_locking);
295	4498x	cond_.set_enabled(cfg.scheduler_locking);
296	4498x	}
297
298		protected:
299		bool scheduler_locking_disabled_ = false;
300		bool reactor_io_locking_ = true;
301		bool one_thread_ = false;
302
303	4514x	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		/// Wake the reactor whenever the earliest timer changes.
385		void on_timer_service_attached(timer_service& svc) override;
386
387		private:
388		struct work_cleanup
389		{
390		reactor_scheduler* sched;
391		lock_type* lock;
392		context_type& ctx;
393		~work_cleanup();
394		};
395
396		std::size_t do_one(lock_type& lock, long timeout_us, context_type& ctx);
397
398		void signal_all(lock_type& lock) const;
399		bool maybe_unlock_and_signal_one(lock_type& lock) const;
400		bool unlock_and_signal_one(lock_type& lock) const;
401		void clear_signal() const;
402		void wait_for_signal(lock_type& lock) const;
403		void wait_for_signal_for(lock_type& lock, long timeout_us) const;
404		void wake_one_thread_and_unlock(lock_type& lock) const;
405		};
406
407		/** RAII guard that pushes/pops a scheduler context frame.
408
409		On construction, pushes a new context frame onto the
410		thread-local stack. On destruction, drains any remaining
411		private queue items to the global queue and pops the frame.
412		*/
413		struct reactor_thread_context_guard
414		{
415		/// The context frame managed by this guard.
416		reactor_scheduler_context frame_;
417
418		/// Marks the scheduler innermost for the executor's fast check.
419		running_scheduler_guard running_;
420
421		/// Construct the guard, pushing a frame for @a sched.
422	12743x	explicit reactor_thread_context_guard(
423		reactor_scheduler const* sched) noexcept
424	12743x	: frame_(sched, reactor_context_stack.get())
425	12743x	, running_(sched)
426		{
427	12743x	reactor_context_stack.set(&frame_);
428	12743x	}
429
430		/** Destroy the guard, popping the frame.
431
432		The private queue is empty here by invariant: work_cleanup and
433		task_cleanup splice it to the global queue after every handler
434		and every reactor pass.
435		*/
436	12743x	~reactor_thread_context_guard() noexcept
437		{
438	12743x	reactor_context_stack.set(frame_.next);
439	12743x	}
440		};
441
442		// ---- Inline implementations ------------------------------------------------
443
444	12743x	inline reactor_scheduler_context::reactor_scheduler_context(
445	12743x	reactor_scheduler const* k, reactor_scheduler_context* n)
446	12743x	: key(k)
447	12743x	, next(n)
448	12743x	, private_outstanding_work(0)
449	12743x	, inline_budget(0)
450	12743x	, inline_budget_max(static_cast<int>(k->inline_budget_initial()))
451	12743x	, unassisted(false)
452		{
453	12743x	}
454
455		inline void
456	50x	reactor_scheduler::configure_reactor(
457		unsigned max_events,
458		unsigned budget_init,
459		unsigned budget_max,
460		unsigned unassisted)
461		{
462	50x	BOOST_COROSIO_ASSERT(
463		max_events >= 1 &&
464		max_events <= static_cast<unsigned>((std::numeric_limits<int>::max)()));
465	50x	BOOST_COROSIO_ASSERT(
466		budget_max <= static_cast<unsigned>((std::numeric_limits<int>::max)()));
467
468		// Clamp initial and unassisted to budget_max.
469	50x	if (budget_init > budget_max)
470	20x	budget_init = budget_max;
471	50x	if (unassisted > budget_max)
472	20x	unassisted = budget_max;
473
474	50x	max_events_per_poll_ = max_events;
475	50x	inline_budget_initial_ = budget_init;
476	50x	inline_budget_max_ = budget_max;
477	50x	unassisted_budget_ = unassisted;
478	50x	}
479
480		inline void
481	100333x	reactor_scheduler::reset_inline_budget() const noexcept
482		{
483		// When budget is disabled (max==0), all paths below would no-op
484		// (inline_budget stays 0). Skip the TLS lookup entirely.
485	100333x	if (inline_budget_max_ == 0)
486	58x	return;
487	100275x	if (auto* ctx = reactor_find_context(this))
488		{
489		// Cap when no other thread absorbed queued work
490	100275x	if (ctx->unassisted)
491		{
492	99564x	ctx->inline_budget_max = static_cast<int>(unassisted_budget_);
493	99564x	ctx->inline_budget = static_cast<int>(unassisted_budget_);
494	99564x	return;
495		}
496		// Ramp up when previous cycle fully consumed budget.
497		// max(1, ...) ensures the doubling escapes zero.
498		// Doubled in a wider type: the cap may be as large as INT_MAX.
499	711x	if (ctx->inline_budget == 0)
500		{
501		long long const doubled =
502	232x	2LL * (std::max)(1, ctx->inline_budget_max);
503	232x	long long const cap = inline_budget_max_;
504	232x	ctx->inline_budget_max = static_cast<int>((std::min)(doubled, cap));
505		}
506	479x	else if (ctx->inline_budget < ctx->inline_budget_max)
507		{
508	152x	ctx->inline_budget_max = static_cast<int>(inline_budget_initial_);
509		}
510	711x	ctx->inline_budget = ctx->inline_budget_max;
511		}
512		}
513
514		inline bool
515	420255x	reactor_scheduler::try_consume_inline_budget() const noexcept
516		{
517	420255x	if (inline_budget_max_ == 0)
518	44x	return false;
519	420211x	if (auto* ctx = reactor_find_context(this))
520		{
521	420167x	if (ctx->inline_budget > 0)
522		{
523	335885x	--ctx->inline_budget;
524	335885x	return true;
525		}
526		}
527	84326x	return false;
528		}
529
530		inline void
531	3672x	reactor_scheduler::post(std::coroutine_handle<> h) const
532		{
533		struct post_handler final : scheduler_op
534		{
535		std::coroutine_handle<> h_;
536
537	3672x	explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
538	7344x	~post_handler() override = default;
539
540	3656x	void operator()() override
541		{
542	3656x	auto saved = h_;
543	3656x	delete this;
544	3656x	saved.resume();
545	3656x	}
546
547	16x	void destroy() override
548		{
549		// A bare handle carries no owner to unwind from: it is
550		// destroyed directly.
551	16x	auto saved = h_;
552	16x	delete this;
553	16x	saved.destroy();
554	16x	}
555		};
556
557	3672x	auto ph = std::make_unique<post_handler>(h);
558
559	3672x	if (auto* ctx = reactor_find_context(this))
560		{
561	8x	++ctx->private_outstanding_work;
562	8x	ctx->private_queue.push(ph.release());
563	8x	return;
564		}
565
566	3664x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
567
568	3664x	lock_type lock(mutex_);
569	3664x	completed_ops_.push(ph.release());
570	3664x	wake_one_thread_and_unlock(lock);
571	3672x	}
572
573		inline void
574	109179x	reactor_scheduler::post(scheduler_op* h) const
575		{
576	109179x	if (auto* ctx = reactor_find_context(this))
577		{
578	107294x	++ctx->private_outstanding_work;
579	107294x	ctx->private_queue.push(h);
580	107294x	return;
581		}
582
583	1885x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
584
585	1885x	lock_type lock(mutex_);
586	1885x	completed_ops_.push(h);
587	1885x	wake_one_thread_and_unlock(lock);
588	1885x	}
589
590		inline void
591	236244x	reactor_scheduler::post(capy::continuation& c) const
592		{
593	236244x	if (auto* ctx = reactor_find_context(this))
594		{
595	204385x	++ctx->private_outstanding_work;
596	204385x	ctx->private_queue.push(c);
597	204385x	return;
598		}
599
600	31859x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
601
602	31859x	lock_type lock(mutex_);
603	31859x	completed_ops_.push(c);
604	31859x	wake_one_thread_and_unlock(lock);
605	31859x	}
606
607		inline bool
608	23432x	reactor_scheduler::running_in_this_thread() const noexcept
609		{
610	23432x	return reactor_find_context(this) != nullptr;
611		}
612
613		inline void
614	8002x	reactor_scheduler::stop()
615		{
616	8002x	lock_type lock(mutex_);
617	8002x	if (!stopped_.load(std::memory_order_acquire))
618		{
619	6988x	stopped_.store(true, std::memory_order_release);
620	6988x	signal_all(lock);
621	6988x	interrupt_reactor();
622		}
623	8002x	}
624
625		inline bool
626	3540x	reactor_scheduler::stopped() const noexcept
627		{
628	3540x	return stopped_.load(std::memory_order_acquire);
629		}
630
631		inline void
632	5360x	reactor_scheduler::restart()
633		{
634	5360x	stopped_.store(false, std::memory_order_release);
635	5360x	}
636
637		inline std::size_t
638	6157x	reactor_scheduler::run()
639		{
640	12314x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
641		{
642	220x	stop();
643	220x	return 0;
644		}
645
646	5937x	reactor_thread_context_guard ctx(this);
647	5937x	lock_type lock(mutex_);
648
649	5937x	std::size_t n = 0;
650		for (;;)
651		{
652	385241x	if (!do_one(lock, -1, ctx.frame_))
653	5934x	break;
654	379304x	if (n != (std::numeric_limits<std::size_t>::max)())
655	379304x	++n;
656	379304x	if (!lock.owns_lock())
657	86511x	lock.lock();
658		}
659	5934x	return n;
660	5940x	}
661
662		inline std::size_t
663	128x	reactor_scheduler::run_one()
664		{
665	256x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
666		{
667	3x	stop();
668	3x	return 0;
669		}
670
671	125x	reactor_thread_context_guard ctx(this);
672	125x	lock_type lock(mutex_);
673	125x	return do_one(lock, -1, ctx.frame_);
674	125x	}
675
676		inline std::size_t
677	6135x	reactor_scheduler::wait_one(long usec)
678		{
679	12270x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
680		{
681	818x	stop();
682	818x	return 0;
683		}
684
685	5317x	reactor_thread_context_guard ctx(this);
686	5317x	lock_type lock(mutex_);
687	5317x	return do_one(lock, usec, ctx.frame_);
688	5317x	}
689
690		inline std::size_t
691	1339x	reactor_scheduler::poll()
692		{
693	2678x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
694		{
695	30x	stop();
696	30x	return 0;
697		}
698
699	1309x	reactor_thread_context_guard ctx(this);
700	1309x	lock_type lock(mutex_);
701
702	1309x	std::size_t n = 0;
703		for (;;)
704		{
705	9315x	if (!do_one(lock, 0, ctx.frame_))
706	1309x	break;
707	8006x	if (n != (std::numeric_limits<std::size_t>::max)())
708	8006x	++n;
709	8006x	if (!lock.owns_lock())
710	8004x	lock.lock();
711		}
712	1309x	return n;
713	1309x	}
714
715		inline std::size_t
716	60x	reactor_scheduler::poll_one()
717		{
718	120x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
719		{
720	5x	stop();
721	5x	return 0;
722		}
723
724	55x	reactor_thread_context_guard ctx(this);
725	55x	lock_type lock(mutex_);
726	55x	return do_one(lock, 0, ctx.frame_);
727	55x	}
728
729		inline void
730	66627x	reactor_scheduler::work_started() noexcept
731		{
732	66627x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
733	66627x	}
734
735		inline void
736	111519x	reactor_scheduler::work_finished() noexcept
737		{
738	223038x	if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
739	6861x	stop();
740	111519x	}
741
742		inline void
743	33397x	reactor_scheduler::compensating_work_started() const noexcept
744		{
745	33397x	auto* ctx = reactor_find_context(this);
746	33397x	if (ctx)
747	33395x	++ctx->private_outstanding_work;
748	33397x	}
749
750		inline void
751	1986x	reactor_scheduler::post_counted(scheduler_op* op) const
752		{
753	1986x	if (auto* ctx = reactor_find_context(this))
754		{
755	604x	ctx->private_queue.push(op);
756	604x	return;
757		}
758
759	1382x	lock_type lock(mutex_);
760	1382x	completed_ops_.push(op);
761	1382x	wake_one_thread_and_unlock(lock);
762	1382x	}
763
764		inline void
765	15708x	reactor_scheduler::post_deferred_completions(ready_queue& ops) const
766		{
767	15708x	if (ops.empty())
768	15708x	return;
769
770	2x	if (auto* ctx = reactor_find_context(this))
771		{
772	2x	ctx->private_queue.splice(ops);
773	2x	return;
774		}
775
776	✗	lock_type lock(mutex_);
777	✗	completed_ops_.splice(ops);
778	✗	wake_one_thread_and_unlock(lock);
779	✗	}
780
781		inline void
782	22638x	reactor_scheduler::retire_descriptor(
783		reactor_retirable& d, object_ref keep) const
784		{
785	22638x	lock_type lock(mutex_);
786	22638x	if (!task_running_.load(std::memory_order_relaxed))
787		{
788		// No pass can hold an event, but an earlier one may have
789		// queued d.
790	17322x	d.hand_off(keep);
791	17322x	return;
792		}
793		// Already parked for this pass: the held reference suffices.
794	5316x	if (d.retired_ref_)
795	126x	return;
796	5190x	d.retired_ref_ = std::move(keep);
797	5190x	d.retired_next_ = retired_;
798	5190x	retired_ = &d;
799	22638x	}
800
801		inline void
802	303677x	reactor_scheduler::settle_retired(lock_type& lock) const
803		{
804		// Handed off under the lock, since a later pass may retire the same
805		// descriptor again as soon as it is released. A reference that is
806		// not handed off may be the owner's last, and its release recycles
807		// through the pool mutex, so it is dropped with the lock released.
808	303677x	reactor_retirable* dropped = nullptr;
809	308867x	while (auto* d = retired_)
810		{
811	5190x	retired_ = d->retired_next_;
812	5190x	d->retired_next_ = nullptr;
813	5190x	auto keep = std::move(d->retired_ref_);
814	5190x	d->hand_off(keep);
815		// A drop already pending keeps the owner alive, so this one
816		// cannot be the last and is released here.
817	5190x	if (!keep \|\| d->dropped_ref_)
818	346x	continue;
819	4844x	d->dropped_ref_ = std::move(keep);
820	4844x	d->dropped_next_ = dropped;
821	4844x	dropped = d;
822	10380x	}
823	308521x	while (auto* d = dropped)
824		{
825	4844x	dropped = d->dropped_next_;
826	4844x	d->dropped_next_ = nullptr;
827	4844x	auto keep = std::move(d->dropped_ref_);
828	4844x	lock.unlock();
829	4844x	keep.reset();
830	4844x	lock.lock();
831	4844x	}
832	303677x	}
833
834		inline void
835	391x	reactor_scheduler::on_timer_service_attached(timer_service& svc)
836		{
837	391x	svc.set_on_earliest_changed(timer_service::callback(this, [](void* p) {
838	3089x	static_cast<reactor_scheduler*>(p)->interrupt_reactor();
839	3089x	}));
840	391x	}
841
842		inline void
843	4498x	reactor_scheduler::shutdown_drain()
844		{
845	4498x	wait_cancels_posting();
846
847	4498x	lock_type lock(mutex_);
848	4498x	settle_retired(lock);
849	4498x	destroy_queued(lock);
850	4498x	signal_all(lock);
851	4498x	}
852
853	4514x	inline reactor_scheduler::~reactor_scheduler()
854		{
855		// Services give up their work in shutdown(), but anything posted
856		// after the drain, such as from a destructor, is still destroyed.
857	4514x	lock_type lock(mutex_);
858	4514x	destroy_queued(lock);
859	4514x	}
860
861		inline void
862	9012x	reactor_scheduler::destroy_queued(lock_type& lock) noexcept
863		{
864	22891x	while (auto e = completed_ops_.pop())
865		{
866	13879x	if (ready_is_continuation(e))
867		{
868	7843x	lock.unlock();
869	7843x	if (auto* c = ready_as_cont(e); c->h)
870	7843x	capy::abandon(*c);
871	7843x	lock.lock();
872		}
873		else
874		{
875	6036x	auto* op = ready_as_op(e);
876	6036x	if (op == &task_op_)
877	4495x	continue;
878	1541x	lock.unlock();
879	1541x	op->destroy();
880	1541x	lock.lock();
881		}
882	13879x	}
883	9012x	}
884
885		inline void
886	11486x	reactor_scheduler::signal_all(lock_type&) const
887		{
888	11486x	state_ \|= signaled_bit;
889	11486x	cond_.notify_all();
890	11486x	}
891
892		inline bool
893	38790x	reactor_scheduler::maybe_unlock_and_signal_one(lock_type& lock) const
894		{
895	38790x	state_ \|= signaled_bit;
896	38790x	if (state_ > signaled_bit)
897		{
898		// Signalled before unlocking: a post from another context's
899		// thread may be the last touch of this scheduler before the
900		// posted work runs, finishes and lets it be destroyed.
901	216x	cond_.notify_one();
902	216x	lock.unlock();
903	216x	return true;
904		}
905	38574x	return false;
906		}
907
908		inline bool
909	640000x	reactor_scheduler::unlock_and_signal_one(lock_type& lock) const
910		{
911	640000x	state_ \|= signaled_bit;
912	640000x	bool have_waiters = state_ > signaled_bit;
913	640000x	lock.unlock();
914	640000x	if (have_waiters)
915	3134x	cond_.notify_one();
916	640000x	return have_waiters;
917		}
918
919		inline void
920	809x	reactor_scheduler::clear_signal() const
921		{
922	809x	state_ &= ~signaled_bit;
923	809x	}
924
925		inline void
926	797x	reactor_scheduler::wait_for_signal(lock_type& lock) const
927		{
928	1672x	while ((state_ & signaled_bit) == 0)
929		{
930	875x	state_ += waiter_increment;
931	875x	cond_.wait(lock);
932	875x	state_ -= waiter_increment;
933		}
934	797x	}
935
936		inline void
937	12x	reactor_scheduler::wait_for_signal_for(lock_type& lock, long timeout_us) const
938		{
939	12x	if ((state_ & signaled_bit) == 0)
940		{
941	12x	state_ += waiter_increment;
942	12x	cond_.wait_for(lock, std::chrono::microseconds(timeout_us));
943	12x	state_ -= waiter_increment;
944		}
945	12x	}
946
947		inline void
948	38790x	reactor_scheduler::wake_one_thread_and_unlock(lock_type& lock) const
949		{
950	38790x	if (maybe_unlock_and_signal_one(lock))
951	216x	return;
952
953	38574x	if (task_running_.load(std::memory_order_relaxed) && !task_interrupted_)
954		{
955	1639x	task_interrupted_ = true;
956		// Under the lock, for the same reason as the signal above.
957	1639x	interrupt_reactor();
958	1639x	lock.unlock();
959		}
960		else
961		{
962	36935x	lock.unlock();
963		}
964		}
965
966	390157x	inline reactor_scheduler::work_cleanup::~work_cleanup()
967		{
968	390157x	std::int64_t produced = ctx.private_outstanding_work;
969	390157x	if (produced > 1)
970	939x	sched->outstanding_work_.fetch_add(
971		produced - 1, std::memory_order_relaxed);
972	389218x	else if (produced < 1)
973	64930x	sched->work_finished();
974	390157x	ctx.private_outstanding_work = 0;
975
976	390157x	if (!ctx.private_queue.empty())
977		{
978	293149x	lock->lock();
979	293149x	sched->completed_ops_.splice(ctx.private_queue);
980		}
981	390157x	}
982
983	299182x	inline reactor_scheduler::task_cleanup::~task_cleanup()
984		{
985	299182x	if (ctx.private_outstanding_work > 0)
986		{
987	9498x	sched->outstanding_work_.fetch_add(
988	9498x	ctx.private_outstanding_work, std::memory_order_relaxed);
989	9498x	ctx.private_outstanding_work = 0;
990		}
991
992	299182x	if (!ctx.private_queue.empty())
993		{
994	9498x	if (!lock->owns_lock())
995	✗	lock->lock();
996	9498x	sched->completed_ops_.splice(ctx.private_queue);
997		}
998	299182x	}
999
1000		inline std::size_t
1001	400053x	reactor_scheduler::do_one(lock_type& lock, long timeout_us, context_type& ctx)
1002		{
1003		for (;;)
1004		{
1005	697393x	if (stopped_.load(std::memory_order_acquire))
1006	6110x	return 0;
1007
1008	691283x	auto const e = completed_ops_.pop();
1009	691283x	scheduler_op* op = ready_is_continuation(e) ? nullptr : ready_as_op(e);
1010
1011		// Handle reactor sentinel — time to poll for I/O
1012	691283x	if (op == &task_op_)
1013		{
1014	300317x	bool more_handlers = !completed_ops_.empty();
1015
1016	348870x	if (!more_handlers &&
1017	97106x	(outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
1018		timeout_us == 0))
1019		{
1020	1135x	completed_ops_.push(&task_op_);
1021	1135x	return 0;
1022		}
1023
1024	299182x	long task_timeout_us = more_handlers ? 0 : timeout_us;
1025	299182x	task_interrupted_ = task_timeout_us == 0;
1026	299182x	task_running_.store(true, std::memory_order_release);
1027
1028		// Wake a peer to take the pending handlers while this thread
1029		// polls the reactor; skipped when one_thread_ (no peer exists).
1030	299182x	if (more_handlers && !one_thread_)
1031	251753x	unlock_and_signal_one(lock);
1032
1033		try
1034		{
1035	299182x	run_task(lock, ctx, task_timeout_us);
1036		}
1037	3x	catch (...)
1038		{
1039	3x	task_running_.store(false, std::memory_order_relaxed);
1040	3x	throw;
1041	3x	}
1042
1043	299179x	task_running_.store(false, std::memory_order_relaxed);
1044	299179x	completed_ops_.push(&task_op_);
1045	299179x	settle_retired(lock);
1046	299179x	if (timeout_us > 0)
1047	2648x	return 0;
1048	296531x	continue;
1049	296531x	}
1050
1051		// Handle ready entry (op or continuation)
1052	390966x	if (e != nullptr)
1053		{
1054	390157x	bool more = !completed_ops_.empty();
1055
1056	390157x	if (more && !one_thread_)
1057		{
1058		// Wake a peer for the remaining work; unassisted if none
1059		// was parked to take it.
1060	388247x	ctx.unassisted = !unlock_and_signal_one(lock);
1061		}
1062		else
1063		{
1064		// No peer to wake (one_thread_, or nothing more queued).
1065	1910x	ctx.unassisted = more;
1066	1910x	lock.unlock();
1067		}
1068
1069	390157x	[[maybe_unused]] work_cleanup on_exit{this, &lock, ctx};
1070
1071	390157x	if (ready_is_continuation(e))
1072	228401x	ready_as_cont(e)->h.resume();
1073		else
1074	161756x	(*op)();
1075	390157x	return 1;
1076	390157x	}
1077
1078	1618x	if (outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
1079		timeout_us == 0)
1080	✗	return 0;
1081
1082	809x	clear_signal();
1083	809x	if (timeout_us < 0)
1084	797x	wait_for_signal(lock);
1085		else
1086	12x	wait_for_signal_for(lock, timeout_us);
1087	297340x	}
1088		}
1089
1090		} // namespace boost::corosio::detail
1091
1092		#endif // BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
1093