include/boost/corosio/native/detail/reactor/reactor_scheduler.hpp

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reactor_scheduler.hpp

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1			//
2			// Copyright (c) 2026 Steve Gerbino
3			//
4			// Distributed under the Boost Software License, Version 1.0. (See accompanying
5			// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6			//
7			// Official repository: https://github.com/cppalliance/corosio
8			//
9
10			#ifndef BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
11			#define BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
12
13			#include <boost/corosio/detail/config.hpp>
14			#include <boost/capy/ex/execution_context.hpp>
15
16			#include <boost/corosio/detail/scheduler.hpp>
17			#include <boost/corosio/detail/scheduler_op.hpp>
18			#include <boost/corosio/detail/thread_local_ptr.hpp>
19
20			#include <atomic>
21			#include <chrono>
22			#include <coroutine>
23			#include <cstddef>
24			#include <cstdint>
25			#include <limits>
26			#include <memory>
27			#include <stdexcept>
28
29			#include <boost/corosio/detail/conditionally_enabled_mutex.hpp>
30			#include <boost/corosio/detail/conditionally_enabled_event.hpp>
31
32			namespace boost::corosio::detail {
33
34			// Forward declarations
35			class reactor_scheduler;
36			class timer_service;
37
38			/** Per-thread state for a reactor scheduler.
39
40			Each thread running a scheduler's event loop has one of these
41			on a thread-local stack. It holds a private work queue and
42			inline completion budget for speculative I/O fast paths.
43			*/
44			struct BOOST_COROSIO_SYMBOL_VISIBLE reactor_scheduler_context
45			{
46			/// Scheduler this context belongs to.
47			reactor_scheduler const* key;
48
49			/// Next context frame on this thread's stack.
50			reactor_scheduler_context* next;
51
52			/// Private work queue for reduced contention.
53			op_queue private_queue;
54
55			/// Unflushed work count for the private queue.
56			std::int64_t private_outstanding_work;
57
58			/// Remaining inline completions allowed this cycle.
59			int inline_budget;
60
61			/// Maximum inline budget (adaptive, 2-16).
62			int inline_budget_max;
63
64			/// True if no other thread absorbed queued work last cycle.
65			bool unassisted;
66
67			/// Construct a context frame linked to @a n.
68			reactor_scheduler_context(
69			reactor_scheduler const* k,
70			reactor_scheduler_context* n);
71			};
72
73			/// Thread-local context stack for reactor schedulers.
74			inline thread_local_ptr<reactor_scheduler_context> reactor_context_stack;
75
76			/// Find the context frame for a scheduler on this thread.
77			inline reactor_scheduler_context*
78		3369144x	reactor_find_context(reactor_scheduler const* self) noexcept
79			{
80	2/2 ✓ Branch 0 taken 3356532 times. ✓ Branch 1 taken 12612 times.	3369144x	for (auto* c = reactor_context_stack.get(); c != nullptr; c = c->next)
81			{
82	1/2 ✓ Branch 0 taken 3356532 times. ✗ Branch 1 not taken.	3356532x	if (c->key == self)
83		3356532x	return c;
84		✗	}
85		12612x	return nullptr;
86		3369144x	}
87
88			/// Flush private work count to global counter.
89			inline void
90		✗	reactor_flush_private_work(
91			reactor_scheduler_context* ctx,
92			std::atomic<std::int64_t>& outstanding_work) noexcept
93			{
94		✗	if (ctx && ctx->private_outstanding_work > 0)
95			{
96		✗	outstanding_work.fetch_add(
97		✗	ctx->private_outstanding_work, std::memory_order_relaxed);
98		✗	ctx->private_outstanding_work = 0;
99		✗	}
100		✗	}
101
102			/** Drain private queue to global queue, flushing work count first.
103
104			@return True if any ops were drained.
105			*/
106			inline bool
107		✗	reactor_drain_private_queue(
108			reactor_scheduler_context* ctx,
109			std::atomic<std::int64_t>& outstanding_work,
110			op_queue& completed_ops) noexcept
111			{
112		✗	if (!ctx \|\| ctx->private_queue.empty())
113		✗	return false;
114
115		✗	reactor_flush_private_work(ctx, outstanding_work);
116		✗	completed_ops.splice(ctx->private_queue);
117		✗	return true;
118		✗	}
119
120			/** Non-template base for reactor-backed scheduler implementations.
121
122			Provides the complete threading model shared by epoll, kqueue,
123			and select schedulers: signal state machine, inline completion
124			budget, work counting, run/poll methods, and the do_one event
125			loop.
126
127			Derived classes provide platform-specific hooks by overriding:
128			- `run_task(lock, ctx)` to run the reactor poll
129			- `interrupt_reactor()` to wake a blocked reactor
130
131			De-templated from the original CRTP design to eliminate
132			duplicate instantiations when multiple backends are compiled
133			into the same binary. Virtual dispatch for run_task (called
134			once per reactor cycle, before a blocking syscall) has
135			negligible overhead.
136
137			@par Thread Safety
138			All public member functions are thread-safe.
139			*/
140			class reactor_scheduler
141			: public scheduler
142			, public capy::execution_context::service
143			{
144			public:
145			using key_type = scheduler;
146			using context_type = reactor_scheduler_context;
147			using mutex_type = conditionally_enabled_mutex;
148			using lock_type = mutex_type::scoped_lock;
149			using event_type = conditionally_enabled_event;
150
151			/// Post a coroutine for deferred execution.
152			void post(std::coroutine_handle<> h) const override;
153
154			/// Post a scheduler operation for deferred execution.
155			void post(scheduler_op* h) const override;
156
157			/// Return true if called from a thread running this scheduler.
158			bool running_in_this_thread() const noexcept override;
159
160			/// Request the scheduler to stop dispatching handlers.
161			void stop() override;
162
163			/// Return true if the scheduler has been stopped.
164			bool stopped() const noexcept override;
165
166			/// Reset the stopped state so `run()` can resume.
167			void restart() override;
168
169			/// Run the event loop until no work remains.
170			std::size_t run() override;
171
172			/// Run until one handler completes or no work remains.
173			std::size_t run_one() override;
174
175			/// Run until one handler completes or @a usec elapses.
176			std::size_t wait_one(long usec) override;
177
178			/// Run ready handlers without blocking.
179			std::size_t poll() override;
180
181			/// Run at most one ready handler without blocking.
182			std::size_t poll_one() override;
183
184			/// Increment the outstanding work count.
185			void work_started() noexcept override;
186
187			/// Decrement the outstanding work count, stopping on zero.
188			void work_finished() noexcept override;
189
190			/** Reset the thread's inline completion budget.
191
192			Called at the start of each posted completion handler to
193			grant a fresh budget for speculative inline completions.
194			*/
195			void reset_inline_budget() const noexcept;
196
197			/** Consume one unit of inline budget if available.
198
199			@return True if budget was available and consumed.
200			*/
201			bool try_consume_inline_budget() const noexcept;
202
203			/** Offset a forthcoming work_finished from work_cleanup.
204
205			Called by descriptor_state when all I/O returned EAGAIN and
206			no handler will be executed. Must be called from a scheduler
207			thread.
208			*/
209			void compensating_work_started() const noexcept;
210
211			/** Drain work from thread context's private queue to global queue.
212
213			Flushes private work count to the global counter, then
214			transfers the queue under mutex protection.
215
216			@param queue The private queue to drain.
217			@param count Private work count to flush before draining.
218			*/
219			void drain_thread_queue(op_queue& queue, std::int64_t count) const;
220
221			/** Post completed operations for deferred invocation.
222
223			If called from a thread running this scheduler, operations
224			go to the thread's private queue (fast path). Otherwise,
225			operations are added to the global queue under mutex and a
226			waiter is signaled.
227
228			@par Preconditions
229			work_started() must have been called for each operation.
230
231			@param ops Queue of operations to post.
232			*/
233			void post_deferred_completions(op_queue& ops) const;
234
235			/** Apply runtime configuration to the scheduler.
236
237			Called by `io_context` after construction. Values that do
238			not apply to this backend are silently ignored.
239
240			@param max_events Event buffer size for epoll/kqueue.
241			@param budget_init Starting inline completion budget.
242			@param budget_max Hard ceiling on adaptive budget ramp-up.
243			@param unassisted Budget when single-threaded.
244			*/
245			virtual void configure_reactor(
246			unsigned max_events,
247			unsigned budget_init,
248			unsigned budget_max,
249			unsigned unassisted);
250
251			/// Return the configured initial inline budget.
252		2761x	unsigned inline_budget_initial() const noexcept
253			{
254		2761x	return inline_budget_initial_;
255			}
256
257			/// Return true if single-threaded (lockless) mode is active.
258		105x	bool is_single_threaded() const noexcept
259			{
260		105x	return single_threaded_;
261			}
262
263			/** Enable or disable single-threaded (lockless) mode.
264
265			When enabled, all scheduler mutex and condition variable
266			operations become no-ops. Cross-thread post() is
267			undefined behavior.
268			*/
269		7x	void configure_single_threaded(bool v) noexcept
270			{
271		7x	single_threaded_ = v;
272		7x	mutex_.set_enabled(!v);
273		7x	cond_.set_enabled(!v);
274		7x	}
275
276			protected:
277		1092x	timer_service* timer_svc_ = nullptr;
278		1092x	bool single_threaded_ = false;
279
280		3276x	reactor_scheduler() = default;
281
282			/** Drain completed_ops during shutdown.
283
284			Pops all operations from the global queue and destroys them,
285			skipping the task sentinel. Signals all waiting threads.
286			Derived classes call this from their shutdown() override
287			before performing platform-specific cleanup.
288			*/
289			void shutdown_drain();
290
291			/// RAII guard that re-inserts the task sentinel after `run_task`.
292			struct task_cleanup
293			{
294			reactor_scheduler const* sched;
295			lock_type* lock;
296			context_type* ctx;
297			~task_cleanup();
298			};
299
300		1092x	mutable mutex_type mutex_{true};
301		1092x	mutable event_type cond_{true};
302			mutable op_queue completed_ops_;
303		1092x	mutable std::atomic<std::int64_t> outstanding_work_{0};
304		1092x	std::atomic<bool> stopped_{false};
305		1092x	mutable std::atomic<bool> task_running_{false};
306		1092x	mutable bool task_interrupted_ = false;
307
308			// Runtime-configurable reactor tuning parameters.
309			// Defaults match the library's built-in values.
310		1092x	unsigned max_events_per_poll_ = 128;
311		1092x	unsigned inline_budget_initial_ = 2;
312		1092x	unsigned inline_budget_max_ = 16;
313		1092x	unsigned unassisted_budget_ = 4;
314
315			/// Bit 0 of `state_`: set when the condvar should be signaled.
316			static constexpr std::size_t signaled_bit = 1;
317
318			/// Increment per waiting thread in `state_`.
319			static constexpr std::size_t waiter_increment = 2;
320		1092x	mutable std::size_t state_ = 0;
321
322			/// Sentinel op that triggers a reactor poll when dequeued.
323			struct task_op final : scheduler_op
324			{
325		✗	void operator()() override {}
326		✗	void destroy() override {}
327			};
328			task_op task_op_;
329
330			/// Run the platform-specific reactor poll.
331			virtual void
332			run_task(lock_type& lock, context_type* ctx,
333			long timeout_us) = 0;
334
335			/// Wake a blocked reactor (e.g. write to eventfd or pipe).
336			virtual void interrupt_reactor() const = 0;
337
338			private:
339			struct work_cleanup
340			{
341			reactor_scheduler* sched;
342			lock_type* lock;
343			context_type* ctx;
344			~work_cleanup();
345			};
346
347			std::size_t do_one(
348			lock_type& lock, long timeout_us, context_type* ctx);
349
350			void signal_all(lock_type& lock) const;
351			bool maybe_unlock_and_signal_one(lock_type& lock) const;
352			bool unlock_and_signal_one(lock_type& lock) const;
353			void clear_signal() const;
354			void wait_for_signal(lock_type& lock) const;
355			void wait_for_signal_for(
356			lock_type& lock, long timeout_us) const;
357			void wake_one_thread_and_unlock(lock_type& lock) const;
358			};
359
360			/** RAII guard that pushes/pops a scheduler context frame.
361
362			On construction, pushes a new context frame onto the
363			thread-local stack. On destruction, drains any remaining
364			private queue items to the global queue and pops the frame.
365			*/
366			struct reactor_thread_context_guard
367			{
368			/// The context frame managed by this guard.
369			reactor_scheduler_context frame_;
370
371			/// Construct the guard, pushing a frame for @a sched.
372		5522x	explicit reactor_thread_context_guard(
373			reactor_scheduler const* sched) noexcept
374	1/2 ✓ Branch 0 taken 2761 times. ✗ Branch 1 not taken.	2761x	: frame_(sched, reactor_context_stack.get())
375		2761x	{
376		2761x	reactor_context_stack.set(&frame_);
377		5522x	}
378
379			/// Destroy the guard, draining private work and popping the frame.
380		5522x	~reactor_thread_context_guard() noexcept
381		2761x	{
382	1/2 ✓ Branch 0 taken 2761 times. ✗ Branch 1 not taken.	2761x	if (!frame_.private_queue.empty())
383		✗	frame_.key->drain_thread_queue(
384		✗	frame_.private_queue, frame_.private_outstanding_work);
385		2761x	reactor_context_stack.set(frame_.next);
386		5522x	}
387			};
388
389			// ---- Inline implementations ------------------------------------------------
390
391			inline
392		8283x	reactor_scheduler_context::reactor_scheduler_context(
393			reactor_scheduler const* k,
394			reactor_scheduler_context* n)
395		2761x	: key(k)
396		2761x	, next(n)
397		2761x	, private_outstanding_work(0)
398		2761x	, inline_budget(0)
399		5522x	, inline_budget_max(
400		2761x	static_cast<int>(k->inline_budget_initial()))
401		2761x	, unassisted(false)
402		2761x	{
403		5522x	}
404
405			inline void
406		12x	reactor_scheduler::configure_reactor(
407			unsigned max_events,
408			unsigned budget_init,
409			unsigned budget_max,
410			unsigned unassisted)
411			{
412	2/2 ✓ Branch 0 taken 10 times. ✓ Branch 1 taken 2 times.	12x	if (max_events < 1 \|\|
413		10x	max_events > static_cast<unsigned>(std::numeric_limits<int>::max()))
414	1/2 ✓ Branch 0 taken 2 times. ✗ Branch 1 not taken.	2x	throw std::out_of_range(
415			"max_events_per_poll must be in [1, INT_MAX]");
416	1/2 ✓ Branch 0 taken 10 times. ✗ Branch 1 not taken.	10x	if (budget_max > static_cast<unsigned>(std::numeric_limits<int>::max()))
417		✗	throw std::out_of_range(
418			"inline_budget_max must be in [0, INT_MAX]");
419
420			// Clamp initial and unassisted to budget_max.
421	2/2 ✓ Branch 0 taken 8 times. ✓ Branch 1 taken 2 times.	10x	if (budget_init > budget_max)
422		2x	budget_init = budget_max;
423	2/2 ✓ Branch 0 taken 8 times. ✓ Branch 1 taken 2 times.	10x	if (unassisted > budget_max)
424		2x	unassisted = budget_max;
425
426		10x	max_events_per_poll_ = max_events;
427		10x	inline_budget_initial_ = budget_init;
428		10x	inline_budget_max_ = budget_max;
429		10x	unassisted_budget_ = unassisted;
430		10x	}
431
432			inline void
433		372353x	reactor_scheduler::reset_inline_budget() const noexcept
434			{
435			// When budget is disabled (max==0), all paths below would no-op
436			// (inline_budget stays 0). Skip the TLS lookup entirely.
437	1/2 ✓ Branch 0 taken 372353 times. ✗ Branch 1 not taken.	372353x	if (inline_budget_max_ == 0)
438		✗	return;
439	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 372353 times.	372353x	if (auto* ctx = reactor_find_context(this))
440			{
441			// Cap when no other thread absorbed queued work
442	1/2 ✓ Branch 0 taken 372353 times. ✗ Branch 1 not taken.	372353x	if (ctx->unassisted)
443			{
444		372353x	ctx->inline_budget_max =
445		372353x	static_cast<int>(unassisted_budget_);
446		372353x	ctx->inline_budget =
447		372353x	static_cast<int>(unassisted_budget_);
448		372353x	return;
449			}
450			// Ramp up when previous cycle fully consumed budget.
451			// max(1, ...) ensures the doubling escapes zero.
452		✗	if (ctx->inline_budget == 0)
453		✗	ctx->inline_budget_max = (std::min)(
454		✗	(std::max)(1, ctx->inline_budget_max) * 2,
455		✗	static_cast<int>(inline_budget_max_));
456		✗	else if (ctx->inline_budget < ctx->inline_budget_max)
457		✗	ctx->inline_budget_max =
458		✗	static_cast<int>(inline_budget_initial_);
459		✗	ctx->inline_budget = ctx->inline_budget_max;
460		✗	}
461		372353x	}
462
463			inline bool
464		1514281x	reactor_scheduler::try_consume_inline_budget() const noexcept
465			{
466	1/2 ✓ Branch 0 taken 1514281 times. ✗ Branch 1 not taken.	1514281x	if (inline_budget_max_ == 0)
467		✗	return false;
468	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 1514281 times.	1514281x	if (auto* ctx = reactor_find_context(this))
469			{
470	2/2 ✓ Branch 0 taken 1227724 times. ✓ Branch 1 taken 286557 times.	1514281x	if (ctx->inline_budget > 0)
471			{
472		1227724x	--ctx->inline_budget;
473		1227724x	return true;
474			}
475		286557x	}
476		286557x	return false;
477		1514281x	}
478
479			inline void
480		6923x	reactor_scheduler::post(std::coroutine_handle<> h) const
481			{
482			struct post_handler final : scheduler_op
483			{
484			std::coroutine_handle<> h_;
485
486		13846x	explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
487		13846x	~post_handler() override = default;
488
489		6914x	void operator()() override
490			{
491		6914x	auto saved = h_;
492	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 6914 times.	6914x	delete this;
493			// Ensure stores from the posting thread are visible
494		6914x	std::atomic_thread_fence(std::memory_order_acquire);
495		6914x	saved.resume();
496		6914x	}
497
498		9x	void destroy() override
499			{
500		9x	auto saved = h_;
501	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 9 times.	9x	delete this;
502		9x	saved.destroy();
503		9x	}
504			};
505
506		6923x	auto ph = std::make_unique<post_handler>(h);
507
508	2/2 ✓ Branch 0 taken 12 times. ✓ Branch 1 taken 6911 times.	6923x	if (auto* ctx = reactor_find_context(this))
509			{
510		12x	++ctx->private_outstanding_work;
511		12x	ctx->private_queue.push(ph.release());
512		12x	return;
513			}
514
515		6911x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
516
517	1/2 ✓ Branch 0 taken 6911 times. ✗ Branch 1 not taken.	6911x	lock_type lock(mutex_);
518		6911x	completed_ops_.push(ph.release());
519	1/2 ✓ Branch 0 taken 6911 times. ✗ Branch 1 not taken.	6911x	wake_one_thread_and_unlock(lock);
520		6923x	}
521
522			inline void
523		299811x	reactor_scheduler::post(scheduler_op* h) const
524			{
525	2/2 ✓ Branch 0 taken 299589 times. ✓ Branch 1 taken 222 times.	299811x	if (auto* ctx = reactor_find_context(this))
526			{
527		299589x	++ctx->private_outstanding_work;
528		299589x	ctx->private_queue.push(h);
529		299589x	return;
530			}
531
532		222x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
533
534		222x	lock_type lock(mutex_);
535		222x	completed_ops_.push(h);
536	1/2 ✓ Branch 0 taken 222 times. ✗ Branch 1 not taken.	222x	wake_one_thread_and_unlock(lock);
537		299811x	}
538
539			inline bool
540		5907x	reactor_scheduler::running_in_this_thread() const noexcept
541			{
542		5907x	return reactor_find_context(this) != nullptr;
543			}
544
545			inline void
546		2760x	reactor_scheduler::stop()
547			{
548		2760x	lock_type lock(mutex_);
549	2/2 ✓ Branch 0 taken 28 times. ✓ Branch 1 taken 2732 times.	2760x	if (!stopped_.load(std::memory_order_acquire))
550			{
551		2732x	stopped_.store(true, std::memory_order_release);
552	1/2 ✓ Branch 0 taken 2732 times. ✗ Branch 1 not taken.	2732x	signal_all(lock);
553	1/2 ✓ Branch 0 taken 2732 times. ✗ Branch 1 not taken.	2732x	interrupt_reactor();
554		2732x	}
555		2760x	}
556
557			inline bool
558		56x	reactor_scheduler::stopped() const noexcept
559			{
560		56x	return stopped_.load(std::memory_order_acquire);
561			}
562
563			inline void
564		2163x	reactor_scheduler::restart()
565			{
566		2163x	stopped_.store(false, std::memory_order_release);
567		2163x	}
568
569			inline std::size_t
570		2730x	reactor_scheduler::run()
571			{
572	2/2 ✓ Branch 0 taken 2712 times. ✓ Branch 1 taken 18 times.	2730x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
573			{
574		18x	stop();
575		18x	return 0;
576			}
577
578		2712x	reactor_thread_context_guard ctx(this);
579	1/2 ✓ Branch 0 taken 2712 times. ✗ Branch 1 not taken.	2712x	lock_type lock(mutex_);
580
581		2712x	std::size_t n = 0;
582		1564165x	for (;;)
583			{
584	4/4 ✓ Branch 0 taken 1564164 times. ✓ Branch 1 taken 1 time. ✓ Branch 2 taken 1561452 times. ✓ Branch 3 taken 2712 times.	1564165x	if (!do_one(lock, -1, &ctx.frame_))
585		2712x	break;
586	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 1561452 times.	1561452x	if (n != (std::numeric_limits<std::size_t>::max)())
587		1561452x	++n;
588	2/2 ✓ Branch 0 taken 1267293 times. ✓ Branch 1 taken 294159 times.	1561452x	if (!lock.owns_lock())
589	2/2 ✓ Branch 0 taken 1267294 times. ✓ Branch 1 taken 1 time.	1267293x	lock.lock();
590			}
591		2712x	return n;
592		2732x	}
593
594			inline std::size_t
595		2x	reactor_scheduler::run_one()
596			{
597	1/2 ✓ Branch 0 taken 2 times. ✗ Branch 1 not taken.	2x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
598			{
599		✗	stop();
600		✗	return 0;
601			}
602
603		2x	reactor_thread_context_guard ctx(this);
604	1/2 ✓ Branch 0 taken 2 times. ✗ Branch 1 not taken.	2x	lock_type lock(mutex_);
605	1/2 ✓ Branch 0 taken 2 times. ✗ Branch 1 not taken.	2x	return do_one(lock, -1, &ctx.frame_);
606		2x	}
607
608			inline std::size_t
609		37x	reactor_scheduler::wait_one(long usec)
610			{
611	2/2 ✓ Branch 0 taken 24 times. ✓ Branch 1 taken 13 times.	37x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
612			{
613		13x	stop();
614		13x	return 0;
615			}
616
617		24x	reactor_thread_context_guard ctx(this);
618	1/2 ✓ Branch 0 taken 24 times. ✗ Branch 1 not taken.	24x	lock_type lock(mutex_);
619	1/2 ✓ Branch 0 taken 24 times. ✗ Branch 1 not taken.	24x	return do_one(lock, usec, &ctx.frame_);
620		37x	}
621
622			inline std::size_t
623		26x	reactor_scheduler::poll()
624			{
625	2/2 ✓ Branch 0 taken 21 times. ✓ Branch 1 taken 5 times.	26x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
626			{
627		5x	stop();
628		5x	return 0;
629			}
630
631		21x	reactor_thread_context_guard ctx(this);
632	1/2 ✓ Branch 0 taken 21 times. ✗ Branch 1 not taken.	21x	lock_type lock(mutex_);
633
634		21x	std::size_t n = 0;
635		61x	for (;;)
636			{
637	3/4 ✓ Branch 0 taken 61 times. ✗ Branch 1 not taken. ✓ Branch 2 taken 40 times. ✓ Branch 3 taken 21 times.	61x	if (!do_one(lock, 0, &ctx.frame_))
638		21x	break;
639	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 40 times.	40x	if (n != (std::numeric_limits<std::size_t>::max)())
640		40x	++n;
641	2/2 ✓ Branch 0 taken 32 times. ✓ Branch 1 taken 8 times.	40x	if (!lock.owns_lock())
642	1/2 ✓ Branch 0 taken 32 times. ✗ Branch 1 not taken.	32x	lock.lock();
643			}
644		21x	return n;
645		26x	}
646
647			inline std::size_t
648		4x	reactor_scheduler::poll_one()
649			{
650	2/2 ✓ Branch 0 taken 2 times. ✓ Branch 1 taken 2 times.	4x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
651			{
652		2x	stop();
653		2x	return 0;
654			}
655
656		2x	reactor_thread_context_guard ctx(this);
657	1/2 ✓ Branch 0 taken 2 times. ✗ Branch 1 not taken.	2x	lock_type lock(mutex_);
658	1/2 ✓ Branch 0 taken 2 times. ✗ Branch 1 not taken.	2x	return do_one(lock, 0, &ctx.frame_);
659		4x	}
660
661			inline void
662		97897x	reactor_scheduler::work_started() noexcept
663			{
664		97897x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
665		97897x	}
666
667			inline void
668		110445x	reactor_scheduler::work_finished() noexcept
669			{
670	2/2 ✓ Branch 0 taken 107730 times. ✓ Branch 1 taken 2715 times.	110445x	if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
671	1/2 ✓ Branch 0 taken 2715 times. ✗ Branch 1 not taken.	2715x	stop();
672		110445x	}
673
674			inline void
675		1169869x	reactor_scheduler::compensating_work_started() const noexcept
676			{
677		1169869x	auto* ctx = reactor_find_context(this);
678	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 1169869 times.	1169869x	if (ctx)
679		1169869x	++ctx->private_outstanding_work;
680		1169869x	}
681
682			inline void
683		✗	reactor_scheduler::drain_thread_queue(
684			op_queue& queue, std::int64_t count) const
685			{
686		✗	if (count > 0)
687		✗	outstanding_work_.fetch_add(count, std::memory_order_relaxed);
688
689		✗	lock_type lock(mutex_);
690		✗	completed_ops_.splice(queue);
691		✗	if (count > 0)
692		✗	maybe_unlock_and_signal_one(lock);
693		✗	}
694
695			inline void
696		84925x	reactor_scheduler::post_deferred_completions(op_queue& ops) const
697			{
698	2/2 ✓ Branch 0 taken 84924 times. ✓ Branch 1 taken 1 time.	84925x	if (ops.empty())
699		84924x	return;
700
701	1/2 ✓ Branch 0 taken 1 time. ✗ Branch 1 not taken.	1x	if (auto* ctx = reactor_find_context(this))
702			{
703		1x	ctx->private_queue.splice(ops);
704		1x	return;
705			}
706
707		✗	lock_type lock(mutex_);
708		✗	completed_ops_.splice(ops);
709		✗	wake_one_thread_and_unlock(lock);
710		84925x	}
711
712			inline void
713		1092x	reactor_scheduler::shutdown_drain()
714			{
715		1092x	lock_type lock(mutex_);
716
717	2/2 ✓ Branch 0 taken 1092 times. ✓ Branch 1 taken 1248 times.	2340x	while (auto* h = completed_ops_.pop())
718			{
719	2/2 ✓ Branch 0 taken 156 times. ✓ Branch 1 taken 1092 times.	1248x	if (h == &task_op_)
720		1092x	continue;
721	1/2 ✓ Branch 0 taken 156 times. ✗ Branch 1 not taken.	156x	lock.unlock();
722	1/2 ✓ Branch 0 taken 156 times. ✗ Branch 1 not taken.	156x	h->destroy();
723	1/2 ✓ Branch 0 taken 156 times. ✗ Branch 1 not taken.	156x	lock.lock();
724			}
725
726	1/2 ✓ Branch 0 taken 1092 times. ✗ Branch 1 not taken.	1092x	signal_all(lock);
727		1092x	}
728
729			inline void
730		3824x	reactor_scheduler::signal_all(lock_type&) const
731			{
732		3824x	state_ \|= signaled_bit;
733		3824x	cond_.notify_all();
734		3824x	}
735
736			inline bool
737		7133x	reactor_scheduler::maybe_unlock_and_signal_one(
738			lock_type& lock) const
739			{
740		7133x	state_ \|= signaled_bit;
741	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 7133 times.	7133x	if (state_ > signaled_bit)
742			{
743		✗	lock.unlock();
744		✗	cond_.notify_one();
745		✗	return true;
746			}
747		7133x	return false;
748		7133x	}
749
750			inline bool
751		1626708x	reactor_scheduler::unlock_and_signal_one(
752			lock_type& lock) const
753			{
754		1626708x	state_ \|= signaled_bit;
755		1626708x	bool have_waiters = state_ > signaled_bit;
756		1626708x	lock.unlock();
757	1/2 ✓ Branch 0 taken 1626708 times. ✗ Branch 1 not taken.	1626708x	if (have_waiters)
758		✗	cond_.notify_one();
759		1626708x	return have_waiters;
760			}
761
762			inline void
763		✗	reactor_scheduler::clear_signal() const
764			{
765		✗	state_ &= ~signaled_bit;
766		✗	}
767
768			inline void
769		✗	reactor_scheduler::wait_for_signal(
770			lock_type& lock) const
771			{
772		✗	while ((state_ & signaled_bit) == 0)
773			{
774		✗	state_ += waiter_increment;
775		✗	cond_.wait(lock);
776		✗	state_ -= waiter_increment;
777			}
778		✗	}
779
780			inline void
781		✗	reactor_scheduler::wait_for_signal_for(
782			lock_type& lock, long timeout_us) const
783			{
784		✗	if ((state_ & signaled_bit) == 0)
785			{
786		✗	state_ += waiter_increment;
787		✗	cond_.wait_for(lock, std::chrono::microseconds(timeout_us));
788		✗	state_ -= waiter_increment;
789		✗	}
790		✗	}
791
792			inline void
793		7133x	reactor_scheduler::wake_one_thread_and_unlock(
794			lock_type& lock) const
795			{
796	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 7133 times.	7133x	if (maybe_unlock_and_signal_one(lock))
797		✗	return;
798
799	4/4 ✓ Branch 0 taken 169 times. ✓ Branch 1 taken 6964 times. ✓ Branch 2 taken 88 times. ✓ Branch 3 taken 81 times.	7133x	if (task_running_.load(std::memory_order_relaxed) && !task_interrupted_)
800			{
801		81x	task_interrupted_ = true;
802		81x	lock.unlock();
803		81x	interrupt_reactor();
804		81x	}
805			else
806			{
807		7052x	lock.unlock();
808			}
809		7133x	}
810
811		3123020x	inline reactor_scheduler::work_cleanup::~work_cleanup()
812		1561510x	{
813	1/2 ✓ Branch 0 taken 1561510 times. ✗ Branch 1 not taken.	1561510x	if (ctx)
814			{
815		1561510x	std::int64_t produced = ctx->private_outstanding_work;
816	2/2 ✓ Branch 0 taken 12 times. ✓ Branch 1 taken 1561498 times.	1561510x	if (produced > 1)
817		24x	sched->outstanding_work_.fetch_add(
818		12x	produced - 1, std::memory_order_relaxed);
819	2/2 ✓ Branch 0 taken 1464023 times. ✓ Branch 1 taken 97475 times.	1561498x	else if (produced < 1)
820		97475x	sched->work_finished();
821		1561510x	ctx->private_outstanding_work = 0;
822
823	2/2 ✓ Branch 0 taken 1267343 times. ✓ Branch 1 taken 294167 times.	1561510x	if (!ctx->private_queue.empty())
824			{
825	1/2 ✓ Branch 0 taken 294167 times. ✗ Branch 1 not taken.	294167x	lock->lock();
826		294167x	sched->completed_ops_.splice(ctx->private_queue);
827		294167x	}
828		1561510x	}
829			else
830			{
831		✗	sched->work_finished();
832			}
833		3123020x	}
834
835		2370846x	inline reactor_scheduler::task_cleanup::~task_cleanup()
836		1185423x	{
837	1/2 ✓ Branch 0 taken 1185423 times. ✗ Branch 1 not taken.	1185423x	if (!ctx)
838		✗	return;
839
840	2/2 ✓ Branch 0 taken 1180016 times. ✓ Branch 1 taken 5407 times.	1185423x	if (ctx->private_outstanding_work > 0)
841			{
842		10814x	sched->outstanding_work_.fetch_add(
843		5407x	ctx->private_outstanding_work, std::memory_order_relaxed);
844		5407x	ctx->private_outstanding_work = 0;
845		5407x	}
846
847	2/2 ✓ Branch 0 taken 1180016 times. ✓ Branch 1 taken 5407 times.	1185423x	if (!ctx->private_queue.empty())
848			{
849	1/2 ✓ Branch 0 taken 5407 times. ✗ Branch 1 not taken.	5407x	if (!lock->owns_lock())
850		✗	lock->lock();
851		5407x	sched->completed_ops_.splice(ctx->private_queue);
852		5407x	}
853		2370846x	}
854
855			inline std::size_t
856		1564254x	reactor_scheduler::do_one(
857			lock_type& lock, long timeout_us, context_type* ctx)
858			{
859		1564254x	for (;;)
860			{
861	2/2 ✓ Branch 0 taken 2746947 times. ✓ Branch 1 taken 2719 times.	2749666x	if (stopped_.load(std::memory_order_acquire))
862		2719x	return 0;
863
864		2746947x	scheduler_op* op = completed_ops_.pop();
865
866			// Handle reactor sentinel — time to poll for I/O
867	2/2 ✓ Branch 0 taken 1561510 times. ✓ Branch 1 taken 1185437 times.	2746947x	if (op == &task_op_)
868			{
869		1185437x	bool more_handlers =
870	3/4 ✓ Branch 0 taken 65209 times. ✓ Branch 1 taken 1120228 times. ✗ Branch 2 not taken. ✓ Branch 3 taken 1120228 times.	1185437x	!completed_ops_.empty() \|\| (ctx && !ctx->private_queue.empty());
871
872	4/4 ✓ Branch 0 taken 1120228 times. ✓ Branch 1 taken 65209 times. ✓ Branch 2 taken 1120214 times. ✓ Branch 3 taken 14 times.	2305665x	if (!more_handlers &&
873	1/2 ✓ Branch 0 taken 1120228 times. ✗ Branch 1 not taken.	1120228x	(outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
874		1120228x	timeout_us == 0))
875			{
876		14x	completed_ops_.push(&task_op_);
877		14x	return 0;
878			}
879
880	2/2 ✓ Branch 0 taken 65209 times. ✓ Branch 1 taken 1120214 times.	1185423x	long task_timeout_us = more_handlers ? 0 : timeout_us;
881		1185423x	task_interrupted_ = task_timeout_us == 0;
882		1185423x	task_running_.store(true, std::memory_order_release);
883
884	2/2 ✓ Branch 0 taken 1120214 times. ✓ Branch 1 taken 65209 times.	1185423x	if (more_handlers)
885		65209x	unlock_and_signal_one(lock);
886
887			try
888			{
889	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 1185423 times.	1185423x	run_task(lock, ctx, task_timeout_us);
890		1185423x	}
891			catch (...)
892			{
893		✗	task_running_.store(false, std::memory_order_relaxed);
894		✗	throw;
895		✗	}
896
897		1185423x	task_running_.store(false, std::memory_order_relaxed);
898		1185423x	completed_ops_.push(&task_op_);
899	2/2 ✓ Branch 0 taken 11 times. ✓ Branch 1 taken 1185412 times.	1185423x	if (timeout_us > 0)
900		11x	return 0;
901		1185412x	continue;
902			}
903
904			// Handle operation
905	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 1561510 times.	1561510x	if (op != nullptr)
906			{
907		1561510x	bool more = !completed_ops_.empty();
908
909	2/2 ✓ Branch 0 taken 1561499 times. ✓ Branch 1 taken 11 times.	1561510x	if (more)
910		1561499x	ctx->unassisted = !unlock_and_signal_one(lock);
911			else
912			{
913		11x	ctx->unassisted = false;
914		11x	lock.unlock();
915			}
916
917		1561510x	work_cleanup on_exit{this, &lock, ctx};
918			(void)on_exit;
919
920	1/2 ✓ Branch 0 taken 1561510 times. ✗ Branch 1 not taken.	1561510x	(*op)();
921		1561510x	return 1;
922		1561510x	}
923
924			// Try private queue before blocking
925		✗	if (reactor_drain_private_queue(ctx, outstanding_work_, completed_ops_))
926		✗	continue;
927
928		✗	if (outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
929		✗	timeout_us == 0)
930		✗	return 0;
931
932		✗	clear_signal();
933		✗	if (timeout_us < 0)
934		✗	wait_for_signal(lock);
935			else
936		✗	wait_for_signal_for(lock, timeout_us);
937			}
938		1564254x	}
939
940			} // namespace boost::corosio::detail
941
942			#endif // BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
943