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		3435145x	reactor_find_context(reactor_scheduler const* self) noexcept
79			{
80	2/2 ✓ Branch 0 taken 3420728 times. ✓ Branch 1 taken 14417 times.	3435145x	for (auto* c = reactor_context_stack.get(); c != nullptr; c = c->next)
81			{
82	1/2 ✓ Branch 0 taken 3420728 times. ✗ Branch 1 not taken.	3420728x	if (c->key == self)
83		3420728x	return c;
84		✗	}
85		14417x	return nullptr;
86		3435145x	}
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		2814x	unsigned inline_budget_initial() const noexcept
253			{
254		2814x	return inline_budget_initial_;
255			}
256
257			/// Return true if single-threaded (lockless) mode is active.
258		159x	bool is_single_threaded() const noexcept override
259			{
260		159x	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		10x	void configure_single_threaded(bool v) noexcept override
270			{
271		10x	single_threaded_ = v;
272		10x	mutex_.set_enabled(!v);
273		10x	cond_.set_enabled(!v);
274		10x	}
275
276			protected:
277		1321x	timer_service* timer_svc_ = nullptr;
278		1321x	bool single_threaded_ = false;
279
280		3963x	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		1321x	mutable mutex_type mutex_{true};
301		1321x	mutable event_type cond_{true};
302			mutable op_queue completed_ops_;
303		1321x	mutable std::atomic<std::int64_t> outstanding_work_{0};
304		1321x	std::atomic<bool> stopped_{false};
305		1321x	mutable std::atomic<bool> task_running_{false};
306		1321x	mutable bool task_interrupted_ = false;
307
308			// Runtime-configurable reactor tuning parameters.
309			// Defaults match the library's built-in values.
310		1321x	unsigned max_events_per_poll_ = 128;
311		1321x	unsigned inline_budget_initial_ = 2;
312		1321x	unsigned inline_budget_max_ = 16;
313		1321x	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		1321x	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		5628x	explicit reactor_thread_context_guard(
373			reactor_scheduler const* sched) noexcept
374	1/2 ✓ Branch 0 taken 2814 times. ✗ Branch 1 not taken.	2814x	: frame_(sched, reactor_context_stack.get())
375		2814x	{
376		2814x	reactor_context_stack.set(&frame_);
377		5628x	}
378
379			/// Destroy the guard, draining private work and popping the frame.
380		5628x	~reactor_thread_context_guard() noexcept
381		2814x	{
382	1/2 ✓ Branch 0 taken 2814 times. ✗ Branch 1 not taken.	2814x	if (!frame_.private_queue.empty())
383		✗	frame_.key->drain_thread_queue(
384		✗	frame_.private_queue, frame_.private_outstanding_work);
385		2814x	reactor_context_stack.set(frame_.next);
386		5628x	}
387			};
388
389			// ---- Inline implementations ------------------------------------------------
390
391			inline
392		8442x	reactor_scheduler_context::reactor_scheduler_context(
393			reactor_scheduler const* k,
394			reactor_scheduler_context* n)
395		2814x	: key(k)
396		2814x	, next(n)
397		2814x	, private_outstanding_work(0)
398		2814x	, inline_budget(0)
399		5628x	, inline_budget_max(
400		2814x	static_cast<int>(k->inline_budget_initial()))
401		2814x	, unassisted(false)
402		2814x	{
403		5628x	}
404
405			inline void
406		16x	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 14 times. ✓ Branch 1 taken 2 times.	16x	if (max_events < 1 \|\|
413		14x	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 14 times. ✗ Branch 1 not taken.	14x	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 12 times. ✓ Branch 1 taken 2 times.	14x	if (budget_init > budget_max)
422		2x	budget_init = budget_max;
423	2/2 ✓ Branch 0 taken 12 times. ✓ Branch 1 taken 2 times.	14x	if (unassisted > budget_max)
424		2x	unassisted = budget_max;
425
426		14x	max_events_per_poll_ = max_events;
427		14x	inline_budget_initial_ = budget_init;
428		14x	inline_budget_max_ = budget_max;
429		14x	unassisted_budget_ = unassisted;
430		14x	}
431
432			inline void
433		388577x	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 388577 times. ✗ Branch 1 not taken.	388577x	if (inline_budget_max_ == 0)
438		✗	return;
439	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 388577 times.	388577x	if (auto* ctx = reactor_find_context(this))
440			{
441			// Cap when no other thread absorbed queued work
442	1/2 ✓ Branch 0 taken 388577 times. ✗ Branch 1 not taken.	388577x	if (ctx->unassisted)
443			{
444		388577x	ctx->inline_budget_max =
445		388577x	static_cast<int>(unassisted_budget_);
446		388577x	ctx->inline_budget =
447		388577x	static_cast<int>(unassisted_budget_);
448		388577x	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		388577x	}
462
463			inline bool
464		1553450x	reactor_scheduler::try_consume_inline_budget() const noexcept
465			{
466	1/2 ✓ Branch 0 taken 1553450 times. ✗ Branch 1 not taken.	1553450x	if (inline_budget_max_ == 0)
467		✗	return false;
468	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 1553450 times.	1553450x	if (auto* ctx = reactor_find_context(this))
469			{
470	2/2 ✓ Branch 0 taken 1258446 times. ✓ Branch 1 taken 295004 times.	1553450x	if (ctx->inline_budget > 0)
471			{
472		1258446x	--ctx->inline_budget;
473		1258446x	return true;
474			}
475		295004x	}
476		295004x	return false;
477		1553450x	}
478
479			inline void
480		8464x	reactor_scheduler::post(std::coroutine_handle<> h) const
481			{
482			struct post_handler final : scheduler_op
483			{
484			std::coroutine_handle<> h_;
485
486		16928x	explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
487		16928x	~post_handler() override = default;
488
489		8452x	void operator()() override
490			{
491		8452x	auto saved = h_;
492	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 8452 times.	8452x	delete this;
493			// Ensure stores from the posting thread are visible
494		8452x	std::atomic_thread_fence(std::memory_order_acquire);
495		8452x	saved.resume();
496		8452x	}
497
498		12x	void destroy() override
499			{
500		12x	auto saved = h_;
501	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 12 times.	12x	delete this;
502		12x	saved.destroy();
503		12x	}
504			};
505
506		8464x	auto ph = std::make_unique<post_handler>(h);
507
508	2/2 ✓ Branch 0 taken 24 times. ✓ Branch 1 taken 8440 times.	8464x	if (auto* ctx = reactor_find_context(this))
509			{
510		24x	++ctx->private_outstanding_work;
511		24x	ctx->private_queue.push(ph.release());
512		24x	return;
513			}
514
515		8440x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
516
517	1/2 ✓ Branch 0 taken 8440 times. ✗ Branch 1 not taken.	8440x	lock_type lock(mutex_);
518		8440x	completed_ops_.push(ph.release());
519	1/2 ✓ Branch 0 taken 8440 times. ✗ Branch 1 not taken.	8440x	wake_one_thread_and_unlock(lock);
520		8464x	}
521
522			inline void
523		309880x	reactor_scheduler::post(scheduler_op* h) const
524			{
525	2/2 ✓ Branch 0 taken 309487 times. ✓ Branch 1 taken 393 times.	309880x	if (auto* ctx = reactor_find_context(this))
526			{
527		309487x	++ctx->private_outstanding_work;
528		309487x	ctx->private_queue.push(h);
529		309487x	return;
530			}
531
532		393x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
533
534		393x	lock_type lock(mutex_);
535		393x	completed_ops_.push(h);
536	1/2 ✓ Branch 0 taken 393 times. ✗ Branch 1 not taken.	393x	wake_one_thread_and_unlock(lock);
537		309880x	}
538
539			inline bool
540		6055x	reactor_scheduler::running_in_this_thread() const noexcept
541			{
542		6055x	return reactor_find_context(this) != nullptr;
543			}
544
545			inline void
546		2808x	reactor_scheduler::stop()
547			{
548		2808x	lock_type lock(mutex_);
549	2/2 ✓ Branch 0 taken 52 times. ✓ Branch 1 taken 2756 times.	2808x	if (!stopped_.load(std::memory_order_acquire))
550			{
551		2756x	stopped_.store(true, std::memory_order_release);
552	1/2 ✓ Branch 0 taken 2756 times. ✗ Branch 1 not taken.	2756x	signal_all(lock);
553	1/2 ✓ Branch 0 taken 2756 times. ✗ Branch 1 not taken.	2756x	interrupt_reactor();
554		2756x	}
555		2808x	}
556
557			inline bool
558		88x	reactor_scheduler::stopped() const noexcept
559			{
560		88x	return stopped_.load(std::memory_order_acquire);
561			}
562
563			inline void
564		2050x	reactor_scheduler::restart()
565			{
566		2050x	stopped_.store(false, std::memory_order_release);
567		2050x	}
568
569			inline std::size_t
570		2774x	reactor_scheduler::run()
571			{
572	2/2 ✓ Branch 0 taken 2734 times. ✓ Branch 1 taken 40 times.	2774x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
573			{
574		40x	stop();
575		40x	return 0;
576			}
577
578		2734x	reactor_thread_context_guard ctx(this);
579	1/2 ✓ Branch 0 taken 2734 times. ✗ Branch 1 not taken.	2734x	lock_type lock(mutex_);
580
581		2734x	std::size_t n = 0;
582		1582391x	for (;;)
583			{
584	4/4 ✓ Branch 0 taken 1582388 times. ✓ Branch 1 taken 3 times. ✓ Branch 2 taken 1579658 times. ✓ Branch 3 taken 2730 times.	1582391x	if (!do_one(lock, -1, &ctx.frame_))
585		2730x	break;
586	2/2 ✓ Branch 0 taken 2 times. ✓ Branch 1 taken 1579656 times.	1579658x	if (n != (std::numeric_limits<std::size_t>::max)())
587		1579656x	++n;
588	2/2 ✓ Branch 0 taken 1276341 times. ✓ Branch 1 taken 303313 times.	1579658x	if (!lock.owns_lock())
589	2/2 ✓ Branch 0 taken 1276344 times. ✓ Branch 1 taken 3 times.	1276341x	lock.lock();
590			}
591		2730x	return n;
592		2776x	}
593
594			inline std::size_t
595		16x	reactor_scheduler::run_one()
596			{
597	1/2 ✓ Branch 0 taken 16 times. ✗ Branch 1 not taken.	16x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
598			{
599		✗	stop();
600		✗	return 0;
601			}
602
603		16x	reactor_thread_context_guard ctx(this);
604	1/2 ✓ Branch 0 taken 16 times. ✗ Branch 1 not taken.	16x	lock_type lock(mutex_);
605	1/2 ✓ Branch 0 taken 16 times. ✗ Branch 1 not taken.	16x	return do_one(lock, -1, &ctx.frame_);
606		16x	}
607
608			inline std::size_t
609		62x	reactor_scheduler::wait_one(long usec)
610			{
611	2/2 ✓ Branch 0 taken 42 times. ✓ Branch 1 taken 20 times.	62x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
612			{
613		20x	stop();
614		20x	return 0;
615			}
616
617		42x	reactor_thread_context_guard ctx(this);
618	1/2 ✓ Branch 0 taken 42 times. ✗ Branch 1 not taken.	42x	lock_type lock(mutex_);
619	1/2 ✓ Branch 0 taken 42 times. ✗ Branch 1 not taken.	42x	return do_one(lock, usec, &ctx.frame_);
620		62x	}
621
622			inline std::size_t
623		28x	reactor_scheduler::poll()
624			{
625	2/2 ✓ Branch 0 taken 22 times. ✓ Branch 1 taken 6 times.	28x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
626			{
627		6x	stop();
628		6x	return 0;
629			}
630
631		22x	reactor_thread_context_guard ctx(this);
632	1/2 ✓ Branch 0 taken 22 times. ✗ Branch 1 not taken.	22x	lock_type lock(mutex_);
633
634		22x	std::size_t n = 0;
635		64x	for (;;)
636			{
637	3/4 ✓ Branch 0 taken 64 times. ✗ Branch 1 not taken. ✓ Branch 2 taken 42 times. ✓ Branch 3 taken 22 times.	64x	if (!do_one(lock, 0, &ctx.frame_))
638		22x	break;
639	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 42 times.	42x	if (n != (std::numeric_limits<std::size_t>::max)())
640		42x	++n;
641	2/2 ✓ Branch 0 taken 34 times. ✓ Branch 1 taken 8 times.	42x	if (!lock.owns_lock())
642	1/2 ✓ Branch 0 taken 34 times. ✗ Branch 1 not taken.	34x	lock.lock();
643			}
644		22x	return n;
645		28x	}
646
647			inline std::size_t
648		8x	reactor_scheduler::poll_one()
649			{
650	2/2 ✓ Branch 0 taken 4 times. ✓ Branch 1 taken 4 times.	8x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
651			{
652		4x	stop();
653		4x	return 0;
654			}
655
656		4x	reactor_thread_context_guard ctx(this);
657	1/2 ✓ Branch 0 taken 4 times. ✗ Branch 1 not taken.	4x	lock_type lock(mutex_);
658	1/2 ✓ Branch 0 taken 4 times. ✗ Branch 1 not taken.	4x	return do_one(lock, 0, &ctx.frame_);
659		8x	}
660
661			inline void
662		106694x	reactor_scheduler::work_started() noexcept
663			{
664		106694x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
665		106694x	}
666
667			inline void
668		121668x	reactor_scheduler::work_finished() noexcept
669			{
670	2/2 ✓ Branch 0 taken 118938 times. ✓ Branch 1 taken 2730 times.	121668x	if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
671	1/2 ✓ Branch 0 taken 2730 times. ✗ Branch 1 not taken.	2730x	stop();
672		121668x	}
673
674			inline void
675		1168718x	reactor_scheduler::compensating_work_started() const noexcept
676			{
677		1168718x	auto* ctx = reactor_find_context(this);
678	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 1168718 times.	1168718x	if (ctx)
679		1168718x	++ctx->private_outstanding_work;
680		1168718x	}
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		92716x	reactor_scheduler::post_deferred_completions(op_queue& ops) const
697			{
698	2/2 ✓ Branch 0 taken 92715 times. ✓ Branch 1 taken 1 time.	92716x	if (ops.empty())
699		92715x	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		92716x	}
711
712			inline void
713		1321x	reactor_scheduler::shutdown_drain()
714			{
715		1321x	lock_type lock(mutex_);
716
717	2/2 ✓ Branch 0 taken 1321 times. ✓ Branch 1 taken 1517 times.	2838x	while (auto* h = completed_ops_.pop())
718			{
719	2/2 ✓ Branch 0 taken 196 times. ✓ Branch 1 taken 1321 times.	1517x	if (h == &task_op_)
720		1321x	continue;
721	1/2 ✓ Branch 0 taken 196 times. ✗ Branch 1 not taken.	196x	lock.unlock();
722	1/2 ✓ Branch 0 taken 196 times. ✗ Branch 1 not taken.	196x	h->destroy();
723	1/2 ✓ Branch 0 taken 196 times. ✗ Branch 1 not taken.	196x	lock.lock();
724			}
725
726	1/2 ✓ Branch 0 taken 1321 times. ✗ Branch 1 not taken.	1321x	signal_all(lock);
727		1321x	}
728
729			inline void
730		4077x	reactor_scheduler::signal_all(lock_type&) const
731			{
732		4077x	state_ \|= signaled_bit;
733		4077x	cond_.notify_all();
734		4077x	}
735
736			inline bool
737		8833x	reactor_scheduler::maybe_unlock_and_signal_one(
738			lock_type& lock) const
739			{
740		8833x	state_ \|= signaled_bit;
741	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 8833 times.	8833x	if (state_ > signaled_bit)
742			{
743		✗	lock.unlock();
744		✗	cond_.notify_one();
745		✗	return true;
746			}
747		8833x	return false;
748		8833x	}
749
750			inline bool
751		1639573x	reactor_scheduler::unlock_and_signal_one(
752			lock_type& lock) const
753			{
754		1639573x	state_ \|= signaled_bit;
755		1639573x	bool have_waiters = state_ > signaled_bit;
756		1639573x	lock.unlock();
757	1/2 ✓ Branch 0 taken 1639573 times. ✗ Branch 1 not taken.	1639573x	if (have_waiters)
758		✗	cond_.notify_one();
759		1639573x	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		8833x	reactor_scheduler::wake_one_thread_and_unlock(
794			lock_type& lock) const
795			{
796	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 8833 times.	8833x	if (maybe_unlock_and_signal_one(lock))
797		✗	return;
798
799	4/4 ✓ Branch 0 taken 271 times. ✓ Branch 1 taken 8562 times. ✓ Branch 2 taken 155 times. ✓ Branch 3 taken 116 times.	8833x	if (task_running_.load(std::memory_order_relaxed) && !task_interrupted_)
800			{
801		116x	task_interrupted_ = true;
802		116x	lock.unlock();
803		116x	interrupt_reactor();
804		116x	}
805			else
806			{
807		8717x	lock.unlock();
808			}
809		8833x	}
810
811		3159486x	inline reactor_scheduler::work_cleanup::~work_cleanup()
812		1579743x	{
813	1/2 ✓ Branch 0 taken 1579743 times. ✗ Branch 1 not taken.	1579743x	if (ctx)
814			{
815		1579743x	std::int64_t produced = ctx->private_outstanding_work;
816	2/2 ✓ Branch 0 taken 13 times. ✓ Branch 1 taken 1579730 times.	1579743x	if (produced > 1)
817		26x	sched->outstanding_work_.fetch_add(
818		13x	produced - 1, std::memory_order_relaxed);
819	2/2 ✓ Branch 0 taken 1472026 times. ✓ Branch 1 taken 107704 times.	1579730x	else if (produced < 1)
820		107704x	sched->work_finished();
821		1579743x	ctx->private_outstanding_work = 0;
822
823	2/2 ✓ Branch 0 taken 1276422 times. ✓ Branch 1 taken 303321 times.	1579743x	if (!ctx->private_queue.empty())
824			{
825	1/2 ✓ Branch 0 taken 303321 times. ✗ Branch 1 not taken.	303321x	lock->lock();
826		303321x	sched->completed_ops_.splice(ctx->private_queue);
827		303321x	}
828		1579743x	}
829			else
830			{
831		✗	sched->work_finished();
832			}
833		3159486x	}
834
835		2375568x	inline reactor_scheduler::task_cleanup::~task_cleanup()
836		1187784x	{
837	1/2 ✓ Branch 0 taken 1187784 times. ✗ Branch 1 not taken.	1187784x	if (!ctx)
838		✗	return;
839
840	2/2 ✓ Branch 0 taken 1181622 times. ✓ Branch 1 taken 6162 times.	1187784x	if (ctx->private_outstanding_work > 0)
841			{
842		12324x	sched->outstanding_work_.fetch_add(
843		6162x	ctx->private_outstanding_work, std::memory_order_relaxed);
844		6162x	ctx->private_outstanding_work = 0;
845		6162x	}
846
847	2/2 ✓ Branch 0 taken 1181622 times. ✓ Branch 1 taken 6162 times.	1187784x	if (!ctx->private_queue.empty())
848			{
849	1/2 ✓ Branch 0 taken 6162 times. ✗ Branch 1 not taken.	6162x	if (!lock->owns_lock())
850		✗	lock->lock();
851		6162x	sched->completed_ops_.splice(ctx->private_queue);
852		6162x	}
853		2375568x	}
854
855			inline std::size_t
856		1582513x	reactor_scheduler::do_one(
857			lock_type& lock, long timeout_us, context_type* ctx)
858			{
859		1582513x	for (;;)
860			{
861	2/2 ✓ Branch 0 taken 2767542 times. ✓ Branch 1 taken 2737 times.	2770279x	if (stopped_.load(std::memory_order_acquire))
862		2737x	return 0;
863
864		2767542x	scheduler_op* op = completed_ops_.pop();
865
866			// Handle reactor sentinel — time to poll for I/O
867	2/2 ✓ Branch 0 taken 1579743 times. ✓ Branch 1 taken 1187799 times.	2767542x	if (op == &task_op_)
868			{
869		1187799x	bool more_handlers =
870	3/4 ✓ Branch 0 taken 59835 times. ✓ Branch 1 taken 1127964 times. ✗ Branch 2 not taken. ✓ Branch 3 taken 1127964 times.	1187799x	!completed_ops_.empty() \|\| (ctx && !ctx->private_queue.empty());
871
872	4/4 ✓ Branch 0 taken 1127964 times. ✓ Branch 1 taken 59835 times. ✓ Branch 2 taken 1127949 times. ✓ Branch 3 taken 14 times.	2315762x	if (!more_handlers &&
873	2/2 ✓ Branch 0 taken 1127963 times. ✓ Branch 1 taken 1 time.	1127964x	(outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
874		1127963x	timeout_us == 0))
875			{
876		15x	completed_ops_.push(&task_op_);
877		15x	return 0;
878			}
879
880	2/2 ✓ Branch 0 taken 59835 times. ✓ Branch 1 taken 1127949 times.	1187784x	long task_timeout_us = more_handlers ? 0 : timeout_us;
881		1187784x	task_interrupted_ = task_timeout_us == 0;
882		1187784x	task_running_.store(true, std::memory_order_release);
883
884	2/2 ✓ Branch 0 taken 1127949 times. ✓ Branch 1 taken 59835 times.	1187784x	if (more_handlers)
885		59835x	unlock_and_signal_one(lock);
886
887			try
888			{
889	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 1187784 times.	1187784x	run_task(lock, ctx, task_timeout_us);
890		1187784x	}
891			catch (...)
892			{
893		✗	task_running_.store(false, std::memory_order_relaxed);
894		✗	throw;
895		✗	}
896
897		1187784x	task_running_.store(false, std::memory_order_relaxed);
898		1187784x	completed_ops_.push(&task_op_);
899	2/2 ✓ Branch 0 taken 18 times. ✓ Branch 1 taken 1187766 times.	1187784x	if (timeout_us > 0)
900		18x	return 0;
901		1187766x	continue;
902			}
903
904			// Handle operation
905	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 1579743 times.	1579743x	if (op != nullptr)
906			{
907		1579743x	bool more = !completed_ops_.empty();
908
909	2/2 ✓ Branch 0 taken 1579738 times. ✓ Branch 1 taken 5 times.	1579743x	if (more)
910		1579738x	ctx->unassisted = !unlock_and_signal_one(lock);
911			else
912			{
913		5x	ctx->unassisted = false;
914		5x	lock.unlock();
915			}
916
917		1579743x	work_cleanup on_exit{this, &lock, ctx};
918			(void)on_exit;
919
920	1/2 ✓ Branch 0 taken 1579743 times. ✗ Branch 1 not taken.	1579743x	(*op)();
921		1579743x	return 1;
922		1579743x	}
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		1582513x	}
939
940			} // namespace boost::corosio::detail
941
942			#endif // BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
943