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

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reactor_scheduler.hpp

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1			//
2			// Copyright (c) 2026 Steve Gerbino
3			//
4			// Distributed under the Boost Software License, Version 1.0. (See accompanying
5			// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6			//
7			// Official repository: https://github.com/cppalliance/corosio
8			//
9
10			#ifndef BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
11			#define BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
12
13			#include <boost/corosio/detail/config.hpp>
14			#include <boost/capy/ex/execution_context.hpp>
15
16			#include <boost/corosio/detail/ready_queue.hpp>
17			#include <boost/corosio/detail/scheduler.hpp>
18			#include <boost/corosio/detail/scheduler_op.hpp>
19			#include <boost/corosio/detail/thread_local_ptr.hpp>
20
21			#include <atomic>
22			#include <chrono>
23			#include <coroutine>
24			#include <cstddef>
25			#include <cstdint>
26			#include <limits>
27			#include <memory>
28			#include <stdexcept>
29
30			#include <boost/corosio/detail/conditionally_enabled_mutex.hpp>
31			#include <boost/corosio/detail/conditionally_enabled_event.hpp>
32
33			namespace boost::corosio::detail {
34
35			// Forward declarations
36			class reactor_scheduler;
37			class timer_service;
38
39			/** Per-thread state for a reactor scheduler.
40
41			Each thread running a scheduler's event loop has one of these
42			on a thread-local stack. It holds a private work queue and
43			inline completion budget for speculative I/O fast paths.
44			*/
45			struct BOOST_COROSIO_SYMBOL_VISIBLE reactor_scheduler_context
46			{
47			/// Scheduler this context belongs to.
48			reactor_scheduler const* key;
49
50			/// Next context frame on this thread's stack.
51			reactor_scheduler_context* next;
52
53			/// Private work queue for reduced contention.
54			ready_queue private_queue;
55
56			/// Unflushed work count for the private queue.
57			std::int64_t private_outstanding_work;
58
59			/// Remaining inline completions allowed this cycle.
60			int inline_budget;
61
62			/// Maximum inline budget (adaptive, 2-16).
63			int inline_budget_max;
64
65			/// True if no other thread absorbed queued work last cycle.
66			bool unassisted;
67
68			/// Construct a context frame linked to @a n.
69			reactor_scheduler_context(
70			reactor_scheduler const* k,
71			reactor_scheduler_context* n);
72			};
73
74			/// Thread-local context stack for reactor schedulers.
75			inline thread_local_ptr<reactor_scheduler_context> reactor_context_stack;
76
77			/// Find the context frame for a scheduler on this thread.
78			inline reactor_scheduler_context*
79		2800563x	reactor_find_context(reactor_scheduler const* self) noexcept
80			{
81	2/2 ✓ Branch 0 taken 2776044 times. ✓ Branch 1 taken 24519 times.	2800563x	for (auto* c = reactor_context_stack.get(); c != nullptr; c = c->next)
82			{
83	1/2 ✓ Branch 0 taken 2776044 times. ✗ Branch 1 not taken.	2776044x	if (c->key == self)
84		2776044x	return c;
85		✗	}
86		24519x	return nullptr;
87		2800563x	}
88
89			/// Flush private work count to global counter.
90			inline void
91		✗	reactor_flush_private_work(
92			reactor_scheduler_context* ctx,
93			std::atomic<std::int64_t>& outstanding_work) noexcept
94			{
95		✗	if (ctx && ctx->private_outstanding_work > 0)
96			{
97		✗	outstanding_work.fetch_add(
98		✗	ctx->private_outstanding_work, std::memory_order_relaxed);
99		✗	ctx->private_outstanding_work = 0;
100		✗	}
101		✗	}
102
103			/** Drain private queue to global queue, flushing work count first.
104
105			@return True if any ops were drained.
106			*/
107			inline bool
108		8x	reactor_drain_private_queue(
109			reactor_scheduler_context* ctx,
110			std::atomic<std::int64_t>& outstanding_work,
111			ready_queue& completed_ops) noexcept
112			{
113	2/4 ✓ Branch 0 taken 8 times. ✗ Branch 1 not taken. ✓ Branch 2 taken 8 times. ✗ Branch 3 not taken.	8x	if (!ctx \|\| ctx->private_queue.empty())
114		8x	return false;
115
116		✗	reactor_flush_private_work(ctx, outstanding_work);
117		✗	completed_ops.splice(ctx->private_queue);
118		✗	return true;
119		8x	}
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			, public capy::execution_context::service
144			{
145			public:
146			using key_type = scheduler;
147			using context_type = reactor_scheduler_context;
148			using mutex_type = conditionally_enabled_mutex;
149			using lock_type = mutex_type::scoped_lock;
150			using event_type = conditionally_enabled_event;
151
152			/// Post a coroutine for deferred execution.
153			void post(std::coroutine_handle<> h) const override;
154
155			/// Post a scheduler operation for deferred execution.
156			void post(scheduler_op* h) const override;
157
158			/// Post a continuation for deferred execution.
159			void post(capy::continuation&) const override;
160
161			/// Return true if called from a thread running this scheduler.
162			bool running_in_this_thread() const noexcept override;
163
164			/// Request the scheduler to stop dispatching handlers.
165			void stop() override;
166
167			/// Return true if the scheduler has been stopped.
168			bool stopped() const noexcept override;
169
170			/// Reset the stopped state so `run()` can resume.
171			void restart() override;
172
173			/// Run the event loop until no work remains.
174			std::size_t run() override;
175
176			/// Run until one handler completes or no work remains.
177			std::size_t run_one() override;
178
179			/// Run until one handler completes or @a usec elapses.
180			std::size_t wait_one(long usec) override;
181
182			/// Run ready handlers without blocking.
183			std::size_t poll() override;
184
185			/// Run at most one ready handler without blocking.
186			std::size_t poll_one() override;
187
188			/// Increment the outstanding work count.
189			void work_started() noexcept override;
190
191			/// Decrement the outstanding work count, stopping on zero.
192			void work_finished() noexcept override;
193
194			/** Reset the thread's inline completion budget.
195
196			Called at the start of each posted completion handler to
197			grant a fresh budget for speculative inline completions.
198			*/
199			void reset_inline_budget() const noexcept;
200
201			/** Consume one unit of inline budget if available.
202
203			@return True if budget was available and consumed.
204			*/
205			bool try_consume_inline_budget() const noexcept;
206
207			/** Offset a forthcoming work_finished from work_cleanup.
208
209			Called by descriptor_state when all I/O returned EAGAIN and
210			no handler will be executed. Must be called from a scheduler
211			thread.
212			*/
213			void compensating_work_started() const noexcept;
214
215			/** Drain work from thread context's private queue to global queue.
216
217			Flushes private work count to the global counter, then
218			transfers the queue under mutex protection.
219
220			@param queue The private queue to drain.
221			@param count Private work count to flush before draining.
222			*/
223			void drain_thread_queue(ready_queue& queue, std::int64_t count) const;
224
225			/** Post completed operations for deferred invocation.
226
227			If called from a thread running this scheduler, operations
228			go to the thread's private queue (fast path). Otherwise,
229			operations are added to the global queue under mutex and a
230			waiter is signaled.
231
232			@par Preconditions
233			work_started() must have been called for each operation.
234
235			@param ops Queue of operations to post.
236			*/
237			void post_deferred_completions(ready_queue& ops) const;
238
239			/** Apply runtime configuration to the scheduler.
240
241			Called by `io_context` after construction. Values that do
242			not apply to this backend are silently ignored.
243
244			@param max_events Event buffer size for epoll/kqueue.
245			@param budget_init Starting inline completion budget.
246			@param budget_max Hard ceiling on adaptive budget ramp-up.
247			@param unassisted Budget when single-threaded.
248			*/
249			virtual void configure_reactor(
250			unsigned max_events,
251			unsigned budget_init,
252			unsigned budget_max,
253			unsigned unassisted);
254
255			/// Return the configured initial inline budget.
256		3194x	unsigned inline_budget_initial() const noexcept
257			{
258		3194x	return inline_budget_initial_;
259			}
260
261			/// Return true when scheduler locking is disabled (fully-lockless tier).
262		162x	bool scheduler_locking_disabled() const noexcept override
263			{
264		162x	return scheduler_locking_disabled_;
265			}
266
267		1331x	void configure_threading(threading_config cfg) noexcept override
268			{
269		1331x	scheduler_locking_disabled_ = !cfg.scheduler_locking;
270			// reactor_io_locking takes effect at descriptor registration (see the
271			// register_descriptor overrides), not here.
272		1331x	reactor_io_locking_ = cfg.reactor_io_locking;
273		1331x	one_thread_ = cfg.one_thread;
274		1331x	mutex_.set_enabled(cfg.scheduler_locking);
275		1331x	cond_.set_enabled(cfg.scheduler_locking);
276		1331x	}
277
278			protected:
279		1331x	timer_service* timer_svc_ = nullptr;
280		1331x	bool scheduler_locking_disabled_ = false;
281		1331x	bool reactor_io_locking_ = true;
282		1331x	bool one_thread_ = false;
283
284		3993x	reactor_scheduler() = default;
285
286			/** Drain completed_ops during shutdown.
287
288			Pops all operations from the global queue and destroys them,
289			skipping the task sentinel. Signals all waiting threads.
290			Derived classes call this from their shutdown() override
291			before performing platform-specific cleanup.
292			*/
293			void shutdown_drain();
294
295			/// RAII guard that re-inserts the task sentinel after `run_task`.
296			struct task_cleanup
297			{
298			reactor_scheduler const* sched;
299			lock_type* lock;
300			context_type* ctx;
301			~task_cleanup();
302			};
303
304		1331x	mutable mutex_type mutex_{true};
305		1331x	mutable event_type cond_{true};
306			mutable ready_queue completed_ops_;
307		1331x	mutable std::atomic<std::int64_t> outstanding_work_{0};
308		1331x	std::atomic<bool> stopped_{false};
309		1331x	mutable std::atomic<bool> task_running_{false};
310		1331x	mutable bool task_interrupted_ = false;
311
312			// Runtime-configurable reactor tuning parameters.
313			// Defaults match the library's built-in values.
314		1331x	unsigned max_events_per_poll_ = 128;
315		1331x	unsigned inline_budget_initial_ = 2;
316		1331x	unsigned inline_budget_max_ = 16;
317		1331x	unsigned unassisted_budget_ = 4;
318
319			/// Bit 0 of `state_`: set when the condvar should be signaled.
320			static constexpr std::size_t signaled_bit = 1;
321
322			/// Increment per waiting thread in `state_`.
323			static constexpr std::size_t waiter_increment = 2;
324		1331x	mutable std::size_t state_ = 0;
325
326			/// Sentinel op that triggers a reactor poll when dequeued.
327			struct task_op final : scheduler_op
328			{
329		✗	void operator()() override {}
330		✗	void destroy() override {}
331			};
332			task_op task_op_;
333
334			/// Run the platform-specific reactor poll.
335			virtual void
336			run_task(lock_type& lock, context_type* ctx,
337			long timeout_us) = 0;
338
339			/// Wake a blocked reactor (e.g. write to eventfd or pipe).
340			virtual void interrupt_reactor() const = 0;
341
342			private:
343			struct work_cleanup
344			{
345			reactor_scheduler* sched;
346			lock_type* lock;
347			context_type* ctx;
348			~work_cleanup();
349			};
350
351			std::size_t do_one(
352			lock_type& lock, long timeout_us, context_type* ctx);
353
354			void signal_all(lock_type& lock) const;
355			bool maybe_unlock_and_signal_one(lock_type& lock) const;
356			bool unlock_and_signal_one(lock_type& lock) const;
357			void clear_signal() const;
358			void wait_for_signal(lock_type& lock) const;
359			void wait_for_signal_for(
360			lock_type& lock, long timeout_us) const;
361			void wake_one_thread_and_unlock(lock_type& lock) const;
362			};
363
364			/** RAII guard that pushes/pops a scheduler context frame.
365
366			On construction, pushes a new context frame onto the
367			thread-local stack. On destruction, drains any remaining
368			private queue items to the global queue and pops the frame.
369			*/
370			struct reactor_thread_context_guard
371			{
372			/// The context frame managed by this guard.
373			reactor_scheduler_context frame_;
374
375			/// Construct the guard, pushing a frame for @a sched.
376		6388x	explicit reactor_thread_context_guard(
377			reactor_scheduler const* sched) noexcept
378	1/2 ✓ Branch 0 taken 3194 times. ✗ Branch 1 not taken.	3194x	: frame_(sched, reactor_context_stack.get())
379		3194x	{
380		3194x	reactor_context_stack.set(&frame_);
381		6388x	}
382
383			/// Destroy the guard, draining private work and popping the frame.
384		6388x	~reactor_thread_context_guard() noexcept
385		3194x	{
386	1/2 ✓ Branch 0 taken 3194 times. ✗ Branch 1 not taken.	3194x	if (!frame_.private_queue.empty())
387		✗	frame_.key->drain_thread_queue(
388		✗	frame_.private_queue, frame_.private_outstanding_work);
389		3194x	reactor_context_stack.set(frame_.next);
390		6388x	}
391			};
392
393			// ---- Inline implementations ------------------------------------------------
394
395			inline
396		9582x	reactor_scheduler_context::reactor_scheduler_context(
397			reactor_scheduler const* k,
398			reactor_scheduler_context* n)
399		3194x	: key(k)
400		3194x	, next(n)
401		3194x	, private_outstanding_work(0)
402		3194x	, inline_budget(0)
403		6388x	, inline_budget_max(
404		3194x	static_cast<int>(k->inline_budget_initial()))
405		3194x	, unassisted(false)
406		3194x	{
407		6388x	}
408
409			inline void
410		25x	reactor_scheduler::configure_reactor(
411			unsigned max_events,
412			unsigned budget_init,
413			unsigned budget_max,
414			unsigned unassisted)
415			{
416	2/2 ✓ Branch 0 taken 23 times. ✓ Branch 1 taken 2 times.	25x	if (max_events < 1 \|\|
417		23x	max_events > static_cast<unsigned>(std::numeric_limits<int>::max()))
418	1/2 ✓ Branch 0 taken 2 times. ✗ Branch 1 not taken.	2x	throw std::out_of_range(
419			"max_events_per_poll must be in [1, INT_MAX]");
420	1/2 ✓ Branch 0 taken 23 times. ✗ Branch 1 not taken.	23x	if (budget_max > static_cast<unsigned>(std::numeric_limits<int>::max()))
421		✗	throw std::out_of_range(
422			"inline_budget_max must be in [0, INT_MAX]");
423
424			// Clamp initial and unassisted to budget_max.
425	2/2 ✓ Branch 0 taken 21 times. ✓ Branch 1 taken 2 times.	23x	if (budget_init > budget_max)
426		2x	budget_init = budget_max;
427	2/2 ✓ Branch 0 taken 21 times. ✓ Branch 1 taken 2 times.	23x	if (unassisted > budget_max)
428		2x	unassisted = budget_max;
429
430		23x	max_events_per_poll_ = max_events;
431		23x	inline_budget_initial_ = budget_init;
432		23x	inline_budget_max_ = budget_max;
433		23x	unassisted_budget_ = unassisted;
434		23x	}
435
436			inline void
437		310835x	reactor_scheduler::reset_inline_budget() const noexcept
438			{
439			// When budget is disabled (max==0), all paths below would no-op
440			// (inline_budget stays 0). Skip the TLS lookup entirely.
441	1/2 ✓ Branch 0 taken 310835 times. ✗ Branch 1 not taken.	310835x	if (inline_budget_max_ == 0)
442		✗	return;
443	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 310835 times.	310835x	if (auto* ctx = reactor_find_context(this))
444			{
445			// Cap when no other thread absorbed queued work
446	1/2 ✓ Branch 0 taken 310835 times. ✗ Branch 1 not taken.	310835x	if (ctx->unassisted)
447			{
448		310835x	ctx->inline_budget_max =
449		310835x	static_cast<int>(unassisted_budget_);
450		310835x	ctx->inline_budget =
451		310835x	static_cast<int>(unassisted_budget_);
452		310835x	return;
453			}
454			// Ramp up when previous cycle fully consumed budget.
455			// max(1, ...) ensures the doubling escapes zero.
456		✗	if (ctx->inline_budget == 0)
457		✗	ctx->inline_budget_max = (std::min)(
458		✗	(std::max)(1, ctx->inline_budget_max) * 2,
459		✗	static_cast<int>(inline_budget_max_));
460		✗	else if (ctx->inline_budget < ctx->inline_budget_max)
461		✗	ctx->inline_budget_max =
462		✗	static_cast<int>(inline_budget_initial_);
463		✗	ctx->inline_budget = ctx->inline_budget_max;
464		✗	}
465		310835x	}
466
467			inline bool
468		1142736x	reactor_scheduler::try_consume_inline_budget() const noexcept
469			{
470	1/2 ✓ Branch 0 taken 1142736 times. ✗ Branch 1 not taken.	1142736x	if (inline_budget_max_ == 0)
471		✗	return false;
472	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 1142736 times.	1142736x	if (auto* ctx = reactor_find_context(this))
473			{
474	2/2 ✓ Branch 0 taken 930030 times. ✓ Branch 1 taken 212706 times.	1142736x	if (ctx->inline_budget > 0)
475			{
476		930030x	--ctx->inline_budget;
477		930030x	return true;
478			}
479		212706x	}
480		212706x	return false;
481		1142736x	}
482
483			inline void
484		3684x	reactor_scheduler::post(std::coroutine_handle<> h) const
485			{
486			struct post_handler final : scheduler_op
487			{
488			std::coroutine_handle<> h_;
489
490		7359x	explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
491		7359x	~post_handler() override = default;
492
493		3666x	void operator()() override
494			{
495		3666x	auto saved = h_;
496	2/2 ✓ Branch 0 taken 1 time. ✓ Branch 1 taken 3667 times.	3666x	delete this;
497		3668x	saved.resume();
498		3668x	}
499
500		12x	void destroy() override
501			{
502		12x	auto saved = h_;
503	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 12 times.	12x	delete this;
504		12x	saved.destroy();
505		12x	}
506			};
507
508		3684x	auto ph = std::make_unique<post_handler>(h);
509
510	2/2 ✓ Branch 0 taken 26 times. ✓ Branch 1 taken 3658 times.	3684x	if (auto* ctx = reactor_find_context(this))
511			{
512		26x	++ctx->private_outstanding_work;
513		26x	ctx->private_queue.push(ph.release());
514		26x	return;
515			}
516
517		3658x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
518
519	1/2 ✓ Branch 0 taken 3658 times. ✗ Branch 1 not taken.	3658x	lock_type lock(mutex_);
520		3658x	completed_ops_.push(ph.release());
521	1/2 ✓ Branch 0 taken 3658 times. ✗ Branch 1 not taken.	3658x	wake_one_thread_and_unlock(lock);
522		3684x	}
523
524			inline void
525		222591x	reactor_scheduler::post(scheduler_op* h) const
526			{
527	2/2 ✓ Branch 0 taken 222203 times. ✓ Branch 1 taken 388 times.	222591x	if (auto* ctx = reactor_find_context(this))
528			{
529		222203x	++ctx->private_outstanding_work;
530		222203x	ctx->private_queue.push(h);
531		222203x	return;
532			}
533
534		388x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
535
536		388x	lock_type lock(mutex_);
537		388x	completed_ops_.push(h);
538	1/2 ✓ Branch 0 taken 388 times. ✗ Branch 1 not taken.	388x	wake_one_thread_and_unlock(lock);
539		222591x	}
540
541			inline void
542		19523x	reactor_scheduler::post(capy::continuation& c) const
543			{
544	2/2 ✓ Branch 0 taken 9282 times. ✓ Branch 1 taken 10241 times.	19523x	if (auto* ctx = reactor_find_context(this))
545			{
546		9282x	++ctx->private_outstanding_work;
547		9282x	ctx->private_queue.push(c);
548		9282x	return;
549			}
550
551		10241x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
552
553		10241x	lock_type lock(mutex_);
554		10241x	completed_ops_.push(c);
555	1/2 ✓ Branch 0 taken 10241 times. ✗ Branch 1 not taken.	10241x	wake_one_thread_and_unlock(lock);
556		19523x	}
557
558			inline bool
559		10701x	reactor_scheduler::running_in_this_thread() const noexcept
560			{
561		10701x	return reactor_find_context(this) != nullptr;
562			}
563
564			inline void
565		3178x	reactor_scheduler::stop()
566			{
567		3178x	lock_type lock(mutex_);
568	2/2 ✓ Branch 0 taken 60 times. ✓ Branch 1 taken 3118 times.	3178x	if (!stopped_.load(std::memory_order_acquire))
569			{
570		3118x	stopped_.store(true, std::memory_order_release);
571	1/2 ✓ Branch 0 taken 3118 times. ✗ Branch 1 not taken.	3118x	signal_all(lock);
572	1/2 ✓ Branch 0 taken 3118 times. ✗ Branch 1 not taken.	3118x	interrupt_reactor();
573		3118x	}
574		3178x	}
575
576			inline bool
577		90x	reactor_scheduler::stopped() const noexcept
578			{
579		90x	return stopped_.load(std::memory_order_acquire);
580			}
581
582			inline void
583		2353x	reactor_scheduler::restart()
584			{
585		2353x	stopped_.store(false, std::memory_order_release);
586		2353x	}
587
588			inline std::size_t
589		3186x	reactor_scheduler::run()
590			{
591	2/2 ✓ Branch 0 taken 3134 times. ✓ Branch 1 taken 52 times.	3186x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
592			{
593		52x	stop();
594		52x	return 0;
595			}
596
597		3134x	reactor_thread_context_guard ctx(this);
598	1/2 ✓ Branch 0 taken 3134 times. ✗ Branch 1 not taken.	3134x	lock_type lock(mutex_);
599
600		3134x	std::size_t n = 0;
601		1436521x	for (;;)
602			{
603	4/4 ✓ Branch 0 taken 1436498 times. ✓ Branch 1 taken 23 times. ✓ Branch 2 taken 1433388 times. ✓ Branch 3 taken 3110 times.	1436521x	if (!do_one(lock, -1, &ctx.frame_))
604		3110x	break;
605	2/2 ✓ Branch 0 taken 12 times. ✓ Branch 1 taken 1433376 times.	1433388x	if (n != (std::numeric_limits<std::size_t>::max)())
606		1433376x	++n;
607	2/2 ✓ Branch 0 taken 1208165 times. ✓ Branch 1 taken 225199 times.	1433388x	if (!lock.owns_lock())
608	2/2 ✓ Branch 0 taken 1208188 times. ✓ Branch 1 taken 23 times.	1208165x	lock.lock();
609			}
610		3110x	return n;
611		3208x	}
612
613			inline std::size_t
614		22x	reactor_scheduler::run_one()
615			{
616	1/2 ✓ Branch 0 taken 22 times. ✗ Branch 1 not taken.	22x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
617			{
618		✗	stop();
619		✗	return 0;
620			}
621
622		22x	reactor_thread_context_guard ctx(this);
623	1/2 ✓ Branch 0 taken 22 times. ✗ Branch 1 not taken.	22x	lock_type lock(mutex_);
624	1/2 ✓ Branch 0 taken 22 times. ✗ Branch 1 not taken.	22x	return do_one(lock, -1, &ctx.frame_);
625		22x	}
626
627			inline std::size_t
628		62x	reactor_scheduler::wait_one(long usec)
629			{
630	2/2 ✓ Branch 0 taken 42 times. ✓ Branch 1 taken 20 times.	62x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
631			{
632		20x	stop();
633		20x	return 0;
634			}
635
636		42x	reactor_thread_context_guard ctx(this);
637	1/2 ✓ Branch 0 taken 42 times. ✗ Branch 1 not taken.	42x	lock_type lock(mutex_);
638	1/2 ✓ Branch 0 taken 42 times. ✗ Branch 1 not taken.	42x	return do_one(lock, usec, &ctx.frame_);
639		62x	}
640
641			inline std::size_t
642		18x	reactor_scheduler::poll()
643			{
644	2/2 ✓ Branch 0 taken 16 times. ✓ Branch 1 taken 2 times.	18x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
645			{
646		2x	stop();
647		2x	return 0;
648			}
649
650		16x	reactor_thread_context_guard ctx(this);
651	1/2 ✓ Branch 0 taken 16 times. ✗ Branch 1 not taken.	16x	lock_type lock(mutex_);
652
653		16x	std::size_t n = 0;
654		50x	for (;;)
655			{
656	3/4 ✓ Branch 0 taken 50 times. ✗ Branch 1 not taken. ✓ Branch 2 taken 34 times. ✓ Branch 3 taken 16 times.	50x	if (!do_one(lock, 0, &ctx.frame_))
657		16x	break;
658	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 34 times.	34x	if (n != (std::numeric_limits<std::size_t>::max)())
659		34x	++n;
660	1/2 ✓ Branch 0 taken 34 times. ✗ Branch 1 not taken.	34x	if (!lock.owns_lock())
661	1/2 ✓ Branch 0 taken 34 times. ✗ Branch 1 not taken.	34x	lock.lock();
662			}
663		16x	return n;
664		18x	}
665
666			inline std::size_t
667		8x	reactor_scheduler::poll_one()
668			{
669	2/2 ✓ Branch 0 taken 4 times. ✓ Branch 1 taken 4 times.	8x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
670			{
671		4x	stop();
672		4x	return 0;
673			}
674
675		4x	reactor_thread_context_guard ctx(this);
676	1/2 ✓ Branch 0 taken 4 times. ✗ Branch 1 not taken.	4x	lock_type lock(mutex_);
677	1/2 ✓ Branch 0 taken 4 times. ✗ Branch 1 not taken.	4x	return do_one(lock, 0, &ctx.frame_);
678		8x	}
679
680			inline void
681		117720x	reactor_scheduler::work_started() noexcept
682			{
683		117720x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
684		117720x	}
685
686			inline void
687		138502x	reactor_scheduler::work_finished() noexcept
688			{
689	2/2 ✓ Branch 0 taken 135408 times. ✓ Branch 1 taken 3094 times.	138502x	if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
690	1/2 ✓ Branch 0 taken 3094 times. ✗ Branch 1 not taken.	3094x	stop();
691		138502x	}
692
693			inline void
694		1090499x	reactor_scheduler::compensating_work_started() const noexcept
695			{
696		1090499x	auto* ctx = reactor_find_context(this);
697	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 1090499 times.	1090499x	if (ctx)
698		1090499x	++ctx->private_outstanding_work;
699		1090499x	}
700
701			inline void
702		✗	reactor_scheduler::drain_thread_queue(
703			ready_queue& queue, std::int64_t count) const
704			{
705		✗	if (count > 0)
706		✗	outstanding_work_.fetch_add(count, std::memory_order_relaxed);
707
708		✗	lock_type lock(mutex_);
709		✗	completed_ops_.splice(queue);
710		✗	if (count > 0)
711		✗	maybe_unlock_and_signal_one(lock);
712		✗	}
713
714			inline void
715		97200x	reactor_scheduler::post_deferred_completions(ready_queue& ops) const
716			{
717	2/2 ✓ Branch 0 taken 97199 times. ✓ Branch 1 taken 1 time.	97200x	if (ops.empty())
718		97199x	return;
719
720	1/2 ✓ Branch 0 taken 1 time. ✗ Branch 1 not taken.	1x	if (auto* ctx = reactor_find_context(this))
721			{
722		1x	ctx->private_queue.splice(ops);
723		1x	return;
724			}
725
726		✗	lock_type lock(mutex_);
727		✗	completed_ops_.splice(ops);
728		✗	wake_one_thread_and_unlock(lock);
729		97200x	}
730
731			inline void
732		1331x	reactor_scheduler::shutdown_drain()
733			{
734		1331x	lock_type lock(mutex_);
735
736	2/2 ✓ Branch 0 taken 1331 times. ✓ Branch 1 taken 1543 times.	2874x	while (auto e = completed_ops_.pop())
737			{
738	2/2 ✓ Branch 0 taken 4 times. ✓ Branch 1 taken 1539 times.	1543x	if (ready_is_continuation(e))
739			{
740	1/2 ✓ Branch 0 taken 4 times. ✗ Branch 1 not taken.	4x	lock.unlock();
741	1/2 ✓ Branch 0 taken 4 times. ✗ Branch 1 not taken.	4x	if (auto h = ready_as_cont(e)->h)
742	1/2 ✓ Branch 0 taken 4 times. ✗ Branch 1 not taken.	4x	h.destroy();
743	1/2 ✓ Branch 0 taken 4 times. ✗ Branch 1 not taken.	4x	lock.lock();
744		4x	}
745			else
746			{
747		1539x	auto* op = ready_as_op(e);
748	2/2 ✓ Branch 0 taken 208 times. ✓ Branch 1 taken 1331 times.	1539x	if (op == &task_op_)
749		1331x	continue;
750	1/2 ✓ Branch 0 taken 208 times. ✗ Branch 1 not taken.	208x	lock.unlock();
751	1/2 ✓ Branch 0 taken 208 times. ✗ Branch 1 not taken.	208x	op->destroy();
752	1/2 ✓ Branch 0 taken 208 times. ✗ Branch 1 not taken.	208x	lock.lock();
753			}
754			}
755
756	1/2 ✓ Branch 0 taken 1331 times. ✗ Branch 1 not taken.	1331x	signal_all(lock);
757		1331x	}
758
759			inline void
760		4449x	reactor_scheduler::signal_all(lock_type&) const
761			{
762		4449x	state_ \|= signaled_bit;
763		4449x	cond_.notify_all();
764		4449x	}
765
766			inline bool
767		14289x	reactor_scheduler::maybe_unlock_and_signal_one(
768			lock_type& lock) const
769			{
770		14289x	state_ \|= signaled_bit;
771	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 14289 times.	14289x	if (state_ > signaled_bit)
772			{
773		✗	lock.unlock();
774		✗	cond_.notify_one();
775		✗	return true;
776			}
777		14289x	return false;
778		14289x	}
779
780			inline bool
781		1487119x	reactor_scheduler::unlock_and_signal_one(
782			lock_type& lock) const
783			{
784		1487119x	state_ \|= signaled_bit;
785		1487119x	bool have_waiters = state_ > signaled_bit;
786		1487119x	lock.unlock();
787	2/2 ✓ Branch 0 taken 1487114 times. ✓ Branch 1 taken 5 times.	1487119x	if (have_waiters)
788		5x	cond_.notify_one();
789		1487119x	return have_waiters;
790			}
791
792			inline void
793		7x	reactor_scheduler::clear_signal() const
794			{
795		7x	state_ &= ~signaled_bit;
796		7x	}
797
798			inline void
799		7x	reactor_scheduler::wait_for_signal(
800			lock_type& lock) const
801			{
802	2/2 ✓ Branch 0 taken 8 times. ✓ Branch 1 taken 7 times.	15x	while ((state_ & signaled_bit) == 0)
803			{
804		8x	state_ += waiter_increment;
805		8x	cond_.wait(lock);
806		8x	state_ -= waiter_increment;
807			}
808		7x	}
809
810			inline void
811		✗	reactor_scheduler::wait_for_signal_for(
812			lock_type& lock, long timeout_us) const
813			{
814		✗	if ((state_ & signaled_bit) == 0)
815			{
816		✗	state_ += waiter_increment;
817		✗	cond_.wait_for(lock, std::chrono::microseconds(timeout_us));
818		✗	state_ -= waiter_increment;
819		✗	}
820		✗	}
821
822			inline void
823		14289x	reactor_scheduler::wake_one_thread_and_unlock(
824			lock_type& lock) const
825			{
826	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 14289 times.	14289x	if (maybe_unlock_and_signal_one(lock))
827		✗	return;
828
829	4/4 ✓ Branch 0 taken 206 times. ✓ Branch 1 taken 14083 times. ✓ Branch 2 taken 90 times. ✓ Branch 3 taken 116 times.	14289x	if (task_running_.load(std::memory_order_relaxed) && !task_interrupted_)
830			{
831		116x	task_interrupted_ = true;
832		116x	lock.unlock();
833		116x	interrupt_reactor();
834		116x	}
835			else
836			{
837		14173x	lock.unlock();
838			}
839		14289x	}
840
841		2866914x	inline reactor_scheduler::work_cleanup::~work_cleanup()
842		1433446x	{
843	1/2 ✓ Branch 0 taken 1433468 times. ✗ Branch 1 not taken.	1433468x	if (ctx)
844			{
845		1433468x	std::int64_t produced = ctx->private_outstanding_work;
846	2/2 ✓ Branch 0 taken 306 times. ✓ Branch 1 taken 1433162 times.	1433468x	if (produced > 1)
847		612x	sched->outstanding_work_.fetch_add(
848		306x	produced - 1, std::memory_order_relaxed);
849	2/2 ✓ Branch 0 taken 1315109 times. ✓ Branch 1 taken 118053 times.	1433162x	else if (produced < 1)
850		118053x	sched->work_finished();
851		1433468x	ctx->private_outstanding_work = 0;
852
853	2/2 ✓ Branch 0 taken 1208269 times. ✓ Branch 1 taken 225199 times.	1433468x	if (!ctx->private_queue.empty())
854			{
855	1/2 ✓ Branch 0 taken 225199 times. ✗ Branch 1 not taken.	225199x	lock->lock();
856		225199x	sched->completed_ops_.splice(ctx->private_queue);
857		225199x	}
858		1433468x	}
859			else
860			{
861		✗	sched->work_finished();
862			}
863		2866914x	}
864
865		2255968x	inline reactor_scheduler::task_cleanup::~task_cleanup()
866		1127984x	{
867	1/2 ✓ Branch 0 taken 1127984 times. ✗ Branch 1 not taken.	1127984x	if (!ctx)
868		✗	return;
869
870	2/2 ✓ Branch 0 taken 1121689 times. ✓ Branch 1 taken 6295 times.	1127984x	if (ctx->private_outstanding_work > 0)
871			{
872		12590x	sched->outstanding_work_.fetch_add(
873		6295x	ctx->private_outstanding_work, std::memory_order_relaxed);
874		6295x	ctx->private_outstanding_work = 0;
875		6295x	}
876
877	2/2 ✓ Branch 0 taken 1121689 times. ✓ Branch 1 taken 6295 times.	1127984x	if (!ctx->private_queue.empty())
878			{
879	1/2 ✓ Branch 0 taken 6295 times. ✗ Branch 1 not taken.	6295x	if (!lock->owns_lock())
880		✗	lock->lock();
881		6295x	sched->completed_ops_.splice(ctx->private_queue);
882		6295x	}
883		2255968x	}
884
885			inline std::size_t
886		1436597x	reactor_scheduler::do_one(
887			lock_type& lock, long timeout_us, context_type* ctx)
888			{
889		1436604x	for (;;)
890			{
891	2/2 ✓ Branch 0 taken 2561458 times. ✓ Branch 1 taken 3112 times.	2564570x	if (stopped_.load(std::memory_order_acquire))
892		3112x	return 0;
893
894		2561458x	std::uintptr_t e = completed_ops_.pop();
895	2/2 ✓ Branch 0 taken 19502 times. ✓ Branch 1 taken 2541956 times.	2561458x	scheduler_op* op = ready_is_continuation(e) ? nullptr : ready_as_op(e);
896
897			// Handle reactor sentinel — time to poll for I/O
898	2/2 ✓ Branch 0 taken 1433461 times. ✓ Branch 1 taken 1127997 times.	2561458x	if (op == &task_op_)
899			{
900		1127997x	bool more_handlers =
901	3/4 ✓ Branch 0 taken 53683 times. ✓ Branch 1 taken 1074314 times. ✗ Branch 2 not taken. ✓ Branch 3 taken 1074314 times.	1127997x	!completed_ops_.empty() \|\| (ctx && !ctx->private_queue.empty());
902
903	4/4 ✓ Branch 0 taken 1074314 times. ✓ Branch 1 taken 53683 times. ✓ Branch 2 taken 1074301 times. ✓ Branch 3 taken 12 times.	2202310x	if (!more_handlers &&
904	2/2 ✓ Branch 0 taken 1074313 times. ✓ Branch 1 taken 1 time.	1074314x	(outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
905		1074313x	timeout_us == 0))
906			{
907		13x	completed_ops_.push(&task_op_);
908		13x	return 0;
909			}
910
911	2/2 ✓ Branch 0 taken 53683 times. ✓ Branch 1 taken 1074301 times.	1127984x	long task_timeout_us = more_handlers ? 0 : timeout_us;
912		1127984x	task_interrupted_ = task_timeout_us == 0;
913		1127984x	task_running_.store(true, std::memory_order_release);
914
915			// Wake a peer to take the pending handlers while this thread
916			// polls the reactor; skipped when one_thread_ (no peer exists).
917	4/4 ✓ Branch 0 taken 53683 times. ✓ Branch 1 taken 1074301 times. ✓ Branch 2 taken 7 times. ✓ Branch 3 taken 53676 times.	1127984x	if (more_handlers && !one_thread_)
918		53676x	unlock_and_signal_one(lock);
919
920			try
921			{
922	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 1127984 times.	1127984x	run_task(lock, ctx, task_timeout_us);
923		1127984x	}
924			catch (...)
925			{
926		✗	task_running_.store(false, std::memory_order_relaxed);
927		✗	throw;
928		✗	}
929
930		1127984x	task_running_.store(false, std::memory_order_relaxed);
931		1127984x	completed_ops_.push(&task_op_);
932	2/2 ✓ Branch 0 taken 18 times. ✓ Branch 1 taken 1127966 times.	1127984x	if (timeout_us > 0)
933		18x	return 0;
934		1127966x	continue;
935			}
936
937			// Handle ready entry (op or continuation)
938	2/2 ✓ Branch 0 taken 8 times. ✓ Branch 1 taken 1433453 times.	1433461x	if (e != 0)
939			{
940		1433453x	bool more = !completed_ops_.empty();
941
942	4/4 ✓ Branch 0 taken 1433451 times. ✓ Branch 1 taken 2 times. ✓ Branch 2 taken 8 times. ✓ Branch 3 taken 1433443 times.	1433453x	if (more && !one_thread_)
943			{
944			// Wake a peer for the remaining work; unassisted if none
945			// was parked to take it.
946		1433443x	ctx->unassisted = !unlock_and_signal_one(lock);
947		1433443x	}
948			else
949			{
950			// No peer to wake (one_thread_, or nothing more queued).
951		10x	ctx->unassisted = more;
952		10x	lock.unlock();
953			}
954
955		1433453x	work_cleanup on_exit{this, &lock, ctx};
956			(void)on_exit;
957
958	2/2 ✓ Branch 0 taken 1413946 times. ✓ Branch 1 taken 19507 times.	1433453x	if (ready_is_continuation(e))
959	2/2 ✓ Branch 0 taken 19504 times. ✓ Branch 1 taken 3 times.	19507x	ready_as_cont(e)->h.resume();
960			else
961	2/2 ✓ Branch 0 taken 1413949 times. ✓ Branch 1 taken 3 times.	1413946x	(*op)();
962		1433453x	return 1;
963		1433459x	}
964
965			// Try private queue before blocking
966	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 8 times.	8x	if (reactor_drain_private_queue(ctx, outstanding_work_, completed_ops_))
967		✗	continue;
968
969	3/4 ✓ Branch 0 taken 7 times. ✓ Branch 1 taken 1 time. ✗ Branch 2 not taken. ✓ Branch 3 taken 7 times.	8x	if (outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
970		7x	timeout_us == 0)
971		1x	return 0;
972
973		7x	clear_signal();
974	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 7 times.	7x	if (timeout_us < 0)
975		7x	wait_for_signal(lock);
976			else
977		✗	wait_for_signal_for(lock, timeout_us);
978			}
979		1436603x	}
980
981			} // namespace boost::corosio::detail
982
983			#endif // BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
984