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

74.7% Lines (286/383) 81.6% List of functions (40/49) 51.8% Branches (114/220)

[ ] prev/next file n p prev/next uncovered line

reactor_scheduler.hpp

f(x) Functions (49)

Function Calls Lines Branches Blocks

Line	Branch	Hits	Source Code
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		1436132x	reactor_find_context(reactor_scheduler const* self) noexcept
79			{
80	2/2 ✓ Branch 0 taken 1426992 times. ✓ Branch 1 taken 9140 times.	1436132x	for (auto* c = reactor_context_stack.get(); c != nullptr; c = c->next)
81			{
82	1/2 ✓ Branch 0 taken 1426992 times. ✗ Branch 1 not taken.	1426992x	if (c->key == self)
83		1426992x	return c;
84		✗	}
85		9140x	return nullptr;
86		1436132x	}
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		1990x	unsigned inline_budget_initial() const noexcept
253			{
254		1990x	return inline_budget_initial_;
255			}
256
257			/// Return true if single-threaded (lockless) mode is active.
258		66x	bool is_single_threaded() const noexcept
259			{
260		66x	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		3x	void configure_single_threaded(bool v) noexcept
270			{
271		3x	single_threaded_ = v;
272		3x	mutex_.set_enabled(!v);
273		3x	cond_.set_enabled(!v);
274		3x	}
275
276			protected:
277		743x	timer_service* timer_svc_ = nullptr;
278		743x	bool single_threaded_ = false;
279
280		2229x	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		743x	mutable mutex_type mutex_{true};
301		743x	mutable event_type cond_{true};
302			mutable op_queue completed_ops_;
303		743x	mutable std::atomic<std::int64_t> outstanding_work_{0};
304		743x	std::atomic<bool> stopped_{false};
305		743x	mutable std::atomic<bool> task_running_{false};
306		743x	mutable bool task_interrupted_ = false;
307
308			// Runtime-configurable reactor tuning parameters.
309			// Defaults match the library's built-in values.
310		743x	unsigned max_events_per_poll_ = 128;
311		743x	unsigned inline_budget_initial_ = 2;
312		743x	unsigned inline_budget_max_ = 16;
313		743x	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		743x	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		3980x	explicit reactor_thread_context_guard(
373			reactor_scheduler const* sched) noexcept
374	1/2 ✓ Branch 0 taken 1990 times. ✗ Branch 1 not taken.	1990x	: frame_(sched, reactor_context_stack.get())
375		1990x	{
376		1990x	reactor_context_stack.set(&frame_);
377		3980x	}
378
379			/// Destroy the guard, draining private work and popping the frame.
380		3980x	~reactor_thread_context_guard() noexcept
381		1990x	{
382	1/2 ✓ Branch 0 taken 1990 times. ✗ Branch 1 not taken.	1990x	if (!frame_.private_queue.empty())
383		✗	frame_.key->drain_thread_queue(
384		✗	frame_.private_queue, frame_.private_outstanding_work);
385		1990x	reactor_context_stack.set(frame_.next);
386		3980x	}
387			};
388
389			// ---- Inline implementations ------------------------------------------------
390
391			inline
392		5970x	reactor_scheduler_context::reactor_scheduler_context(
393			reactor_scheduler const* k,
394			reactor_scheduler_context* n)
395		1990x	: key(k)
396		1990x	, next(n)
397		1990x	, private_outstanding_work(0)
398		1990x	, inline_budget(0)
399		3980x	, inline_budget_max(
400		1990x	static_cast<int>(k->inline_budget_initial()))
401		1990x	, unassisted(false)
402		1990x	{
403		3980x	}
404
405			inline void
406		✗	reactor_scheduler::configure_reactor(
407			unsigned max_events,
408			unsigned budget_init,
409			unsigned budget_max,
410			unsigned unassisted)
411			{
412		✗	if (max_events < 1 \|\|
413		✗	max_events > static_cast<unsigned>(std::numeric_limits<int>::max()))
414		✗	throw std::out_of_range(
415			"max_events_per_poll must be in [1, INT_MAX]");
416		✗	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		✗	if (budget_init > budget_max)
422		✗	budget_init = budget_max;
423		✗	if (unassisted > budget_max)
424		✗	unassisted = budget_max;
425
426		✗	max_events_per_poll_ = max_events;
427		✗	inline_budget_initial_ = budget_init;
428		✗	inline_budget_max_ = budget_max;
429		✗	unassisted_budget_ = unassisted;
430		✗	}
431
432			inline void
433		199715x	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 199715 times. ✗ Branch 1 not taken.	199715x	if (inline_budget_max_ == 0)
438		✗	return;
439	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 199715 times.	199715x	if (auto* ctx = reactor_find_context(this))
440			{
441			// Cap when no other thread absorbed queued work
442	1/2 ✓ Branch 0 taken 199715 times. ✗ Branch 1 not taken.	199715x	if (ctx->unassisted)
443			{
444		199715x	ctx->inline_budget_max =
445		199715x	static_cast<int>(unassisted_budget_);
446		199715x	ctx->inline_budget =
447		199715x	static_cast<int>(unassisted_budget_);
448		199715x	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		199715x	}
462
463			inline bool
464		762880x	reactor_scheduler::try_consume_inline_budget() const noexcept
465			{
466	1/2 ✓ Branch 0 taken 762880 times. ✗ Branch 1 not taken.	762880x	if (inline_budget_max_ == 0)
467		✗	return false;
468	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 762880 times.	762880x	if (auto* ctx = reactor_find_context(this))
469			{
470	2/2 ✓ Branch 0 taken 618919 times. ✓ Branch 1 taken 143961 times.	762880x	if (ctx->inline_budget > 0)
471			{
472		618919x	--ctx->inline_budget;
473		618919x	return true;
474			}
475		143961x	}
476		143961x	return false;
477		762880x	}
478
479			inline void
480		5200x	reactor_scheduler::post(std::coroutine_handle<> h) const
481			{
482			struct post_handler final : scheduler_op
483			{
484			std::coroutine_handle<> h_;
485
486		10398x	explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
487		10400x	~post_handler() override = default;
488
489		5191x	void operator()() override
490			{
491		5191x	auto saved = h_;
492	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 5191 times.	5191x	delete this;
493			// Ensure stores from the posting thread are visible
494		5191x	std::atomic_thread_fence(std::memory_order_acquire);
495		5191x	saved.resume();
496		5191x	}
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		5200x	auto ph = std::make_unique<post_handler>(h);
507
508	2/2 ✓ Branch 0 taken 6 times. ✓ Branch 1 taken 5194 times.	5200x	if (auto* ctx = reactor_find_context(this))
509			{
510		6x	++ctx->private_outstanding_work;
511		6x	ctx->private_queue.push(ph.release());
512		6x	return;
513			}
514
515		5194x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
516
517	1/2 ✓ Branch 0 taken 5194 times. ✗ Branch 1 not taken.	5194x	lock_type lock(mutex_);
518		5194x	completed_ops_.push(ph.release());
519	1/2 ✓ Branch 0 taken 5194 times. ✗ Branch 1 not taken.	5194x	wake_one_thread_and_unlock(lock);
520		5200x	}
521
522			inline void
523		155219x	reactor_scheduler::post(scheduler_op* h) const
524			{
525	2/2 ✓ Branch 0 taken 155045 times. ✓ Branch 1 taken 174 times.	155219x	if (auto* ctx = reactor_find_context(this))
526			{
527		155045x	++ctx->private_outstanding_work;
528		155045x	ctx->private_queue.push(h);
529		155045x	return;
530			}
531
532		174x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
533
534		174x	lock_type lock(mutex_);
535		174x	completed_ops_.push(h);
536	1/2 ✓ Branch 0 taken 174 times. ✗ Branch 1 not taken.	174x	wake_one_thread_and_unlock(lock);
537		155219x	}
538
539			inline bool
540		4174x	reactor_scheduler::running_in_this_thread() const noexcept
541			{
542		4174x	return reactor_find_context(this) != nullptr;
543			}
544
545			inline void
546		1921x	reactor_scheduler::stop()
547			{
548		1921x	lock_type lock(mutex_);
549	2/2 ✓ Branch 0 taken 28 times. ✓ Branch 1 taken 1893 times.	1921x	if (!stopped_.load(std::memory_order_acquire))
550			{
551		1893x	stopped_.store(true, std::memory_order_release);
552	1/2 ✓ Branch 0 taken 1893 times. ✗ Branch 1 not taken.	1893x	signal_all(lock);
553	1/2 ✓ Branch 0 taken 1893 times. ✗ Branch 1 not taken.	1893x	interrupt_reactor();
554		1893x	}
555		1921x	}
556
557			inline bool
558		72x	reactor_scheduler::stopped() const noexcept
559			{
560		72x	return stopped_.load(std::memory_order_acquire);
561			}
562
563			inline void
564		1502x	reactor_scheduler::restart()
565			{
566		1502x	stopped_.store(false, std::memory_order_release);
567		1502x	}
568
569			inline std::size_t
570		1899x	reactor_scheduler::run()
571			{
572	2/2 ✓ Branch 0 taken 1883 times. ✓ Branch 1 taken 16 times.	1899x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
573			{
574		16x	stop();
575		16x	return 0;
576			}
577
578		1883x	reactor_thread_context_guard ctx(this);
579	1/2 ✓ Branch 0 taken 1883 times. ✗ Branch 1 not taken.	1883x	lock_type lock(mutex_);
580
581		1883x	std::size_t n = 0;
582		526328x	for (;;)
583			{
584	4/4 ✓ Branch 0 taken 526326 times. ✓ Branch 1 taken 2 times. ✓ Branch 2 taken 524443 times. ✓ Branch 3 taken 1883 times.	526328x	if (!do_one(lock, -1, &ctx.frame_))
585		1883x	break;
586	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 524443 times.	524443x	if (n != (std::numeric_limits<std::size_t>::max)())
587		524443x	++n;
588	2/2 ✓ Branch 0 taken 374212 times. ✓ Branch 1 taken 150231 times.	524443x	if (!lock.owns_lock())
589	2/2 ✓ Branch 0 taken 374214 times. ✓ Branch 1 taken 2 times.	374212x	lock.lock();
590			}
591		1883x	return n;
592		1903x	}
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		108x	reactor_scheduler::wait_one(long usec)
610			{
611	2/2 ✓ Branch 0 taken 96 times. ✓ Branch 1 taken 12 times.	108x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
612			{
613		12x	stop();
614		12x	return 0;
615			}
616
617		96x	reactor_thread_context_guard ctx(this);
618	1/2 ✓ Branch 0 taken 96 times. ✗ Branch 1 not taken.	96x	lock_type lock(mutex_);
619	1/2 ✓ Branch 0 taken 96 times. ✗ Branch 1 not taken.	96x	return do_one(lock, usec, &ctx.frame_);
620		108x	}
621
622			inline std::size_t
623		8x	reactor_scheduler::poll()
624			{
625	2/2 ✓ Branch 0 taken 7 times. ✓ Branch 1 taken 1 time.	8x	if (outstanding_work_.load(std::memory_order_acquire) == 0)
626			{
627		1x	stop();
628		1x	return 0;
629			}
630
631		7x	reactor_thread_context_guard ctx(this);
632	1/2 ✓ Branch 0 taken 7 times. ✗ Branch 1 not taken.	7x	lock_type lock(mutex_);
633
634		7x	std::size_t n = 0;
635		15x	for (;;)
636			{
637	3/4 ✓ Branch 0 taken 15 times. ✗ Branch 1 not taken. ✓ Branch 2 taken 8 times. ✓ Branch 3 taken 7 times.	15x	if (!do_one(lock, 0, &ctx.frame_))
638		7x	break;
639	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 8 times.	8x	if (n != (std::numeric_limits<std::size_t>::max)())
640		8x	++n;
641	1/2 ✓ Branch 0 taken 8 times. ✗ Branch 1 not taken.	8x	if (!lock.owns_lock())
642	1/2 ✓ Branch 0 taken 8 times. ✗ Branch 1 not taken.	8x	lock.lock();
643			}
644		7x	return n;
645		8x	}
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		65273x	reactor_scheduler::work_started() noexcept
663			{
664		65273x	outstanding_work_.fetch_add(1, std::memory_order_relaxed);
665		65273x	}
666
667			inline void
668		75420x	reactor_scheduler::work_finished() noexcept
669			{
670	2/2 ✓ Branch 0 taken 73537 times. ✓ Branch 1 taken 1883 times.	75420x	if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
671	1/2 ✓ Branch 0 taken 1883 times. ✗ Branch 1 not taken.	1883x	stop();
672		75420x	}
673
674			inline void
675		308944x	reactor_scheduler::compensating_work_started() const noexcept
676			{
677		308944x	auto* ctx = reactor_find_context(this);
678	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 308944 times.	308944x	if (ctx)
679		308944x	++ctx->private_outstanding_work;
680		308944x	}
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		55164x	reactor_scheduler::post_deferred_completions(op_queue& ops) const
697			{
698	1/2 ✓ Branch 0 taken 55164 times. ✗ Branch 1 not taken.	55164x	if (ops.empty())
699		55164x	return;
700
701		✗	if (auto* ctx = reactor_find_context(this))
702			{
703		✗	ctx->private_queue.splice(ops);
704		✗	return;
705			}
706
707		✗	lock_type lock(mutex_);
708		✗	completed_ops_.splice(ops);
709		✗	wake_one_thread_and_unlock(lock);
710		55164x	}
711
712			inline void
713		743x	reactor_scheduler::shutdown_drain()
714			{
715		743x	lock_type lock(mutex_);
716
717	2/2 ✓ Branch 0 taken 743 times. ✓ Branch 1 taken 865 times.	1608x	while (auto* h = completed_ops_.pop())
718			{
719	2/2 ✓ Branch 0 taken 122 times. ✓ Branch 1 taken 743 times.	865x	if (h == &task_op_)
720		743x	continue;
721	1/2 ✓ Branch 0 taken 122 times. ✗ Branch 1 not taken.	122x	lock.unlock();
722	1/2 ✓ Branch 0 taken 122 times. ✗ Branch 1 not taken.	122x	h->destroy();
723	1/2 ✓ Branch 0 taken 122 times. ✗ Branch 1 not taken.	122x	lock.lock();
724			}
725
726	1/2 ✓ Branch 0 taken 743 times. ✗ Branch 1 not taken.	743x	signal_all(lock);
727		743x	}
728
729			inline void
730		2636x	reactor_scheduler::signal_all(lock_type&) const
731			{
732		2636x	state_ \|= signaled_bit;
733		2636x	cond_.notify_all();
734		2636x	}
735
736			inline bool
737		5368x	reactor_scheduler::maybe_unlock_and_signal_one(
738			lock_type& lock) const
739			{
740		5368x	state_ \|= signaled_bit;
741	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 5368 times.	5368x	if (state_ > signaled_bit)
742			{
743		✗	lock.unlock();
744		✗	cond_.notify_one();
745		✗	return true;
746			}
747		5368x	return false;
748		5368x	}
749
750			inline bool
751		560995x	reactor_scheduler::unlock_and_signal_one(
752			lock_type& lock) const
753			{
754		560995x	state_ \|= signaled_bit;
755		560995x	bool have_waiters = state_ > signaled_bit;
756		560995x	lock.unlock();
757	1/2 ✓ Branch 0 taken 560995 times. ✗ Branch 1 not taken.	560995x	if (have_waiters)
758		✗	cond_.notify_one();
759		560995x	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		5368x	reactor_scheduler::wake_one_thread_and_unlock(
794			lock_type& lock) const
795			{
796	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 5368 times.	5368x	if (maybe_unlock_and_signal_one(lock))
797		✗	return;
798
799	4/4 ✓ Branch 0 taken 110 times. ✓ Branch 1 taken 5258 times. ✓ Branch 2 taken 49 times. ✓ Branch 3 taken 61 times.	5368x	if (task_running_.load(std::memory_order_relaxed) && !task_interrupted_)
800			{
801		61x	task_interrupted_ = true;
802		61x	lock.unlock();
803		61x	interrupt_reactor();
804		61x	}
805			else
806			{
807		5307x	lock.unlock();
808			}
809		5368x	}
810
811		1049018x	inline reactor_scheduler::work_cleanup::~work_cleanup()
812		524508x	{
813	1/2 ✓ Branch 0 taken 524510 times. ✗ Branch 1 not taken.	524510x	if (ctx)
814			{
815		524510x	std::int64_t produced = ctx->private_outstanding_work;
816	2/2 ✓ Branch 0 taken 16 times. ✓ Branch 1 taken 524494 times.	524510x	if (produced > 1)
817		32x	sched->outstanding_work_.fetch_add(
818		16x	produced - 1, std::memory_order_relaxed);
819	2/2 ✓ Branch 0 taken 459184 times. ✓ Branch 1 taken 65310 times.	524494x	else if (produced < 1)
820		65310x	sched->work_finished();
821		524510x	ctx->private_outstanding_work = 0;
822
823	2/2 ✓ Branch 0 taken 374257 times. ✓ Branch 1 taken 150253 times.	524510x	if (!ctx->private_queue.empty())
824			{
825	1/2 ✓ Branch 0 taken 150253 times. ✗ Branch 1 not taken.	150253x	lock->lock();
826		150253x	sched->completed_ops_.splice(ctx->private_queue);
827		150253x	}
828		524510x	}
829			else
830			{
831		✗	sched->work_finished();
832			}
833		1049018x	}
834
835		657080x	inline reactor_scheduler::task_cleanup::~task_cleanup()
836		328540x	{
837	1/2 ✓ Branch 0 taken 328540 times. ✗ Branch 1 not taken.	328540x	if (!ctx)
838		✗	return;
839
840	2/2 ✓ Branch 0 taken 323774 times. ✓ Branch 1 taken 4766 times.	328540x	if (ctx->private_outstanding_work > 0)
841			{
842		9532x	sched->outstanding_work_.fetch_add(
843		4766x	ctx->private_outstanding_work, std::memory_order_relaxed);
844		4766x	ctx->private_outstanding_work = 0;
845		4766x	}
846
847	2/2 ✓ Branch 0 taken 323774 times. ✓ Branch 1 taken 4766 times.	328540x	if (!ctx->private_queue.empty())
848			{
849	1/2 ✓ Branch 0 taken 4766 times. ✗ Branch 1 not taken.	4766x	if (!lock->owns_lock())
850		✗	lock->lock();
851		4766x	sched->completed_ops_.splice(ctx->private_queue);
852		4766x	}
853		657080x	}
854
855			inline std::size_t
856		526443x	reactor_scheduler::do_one(
857			lock_type& lock, long timeout_us, context_type* ctx)
858			{
859		526443x	for (;;)
860			{
861	2/2 ✓ Branch 0 taken 853054 times. ✓ Branch 1 taken 1886 times.	854940x	if (stopped_.load(std::memory_order_acquire))
862		1886x	return 0;
863
864		853054x	scheduler_op* op = completed_ops_.pop();
865
866			// Handle reactor sentinel — time to poll for I/O
867	2/2 ✓ Branch 0 taken 524510 times. ✓ Branch 1 taken 328544 times.	853054x	if (op == &task_op_)
868			{
869		328544x	bool more_handlers =
870	3/4 ✓ Branch 0 taken 36491 times. ✓ Branch 1 taken 292053 times. ✗ Branch 2 not taken. ✓ Branch 3 taken 292053 times.	328544x	!completed_ops_.empty() \|\| (ctx && !ctx->private_queue.empty());
871
872	4/4 ✓ Branch 0 taken 292053 times. ✓ Branch 1 taken 36491 times. ✓ Branch 2 taken 292049 times. ✓ Branch 3 taken 4 times.	620597x	if (!more_handlers &&
873	1/2 ✓ Branch 0 taken 292053 times. ✗ Branch 1 not taken.	292053x	(outstanding_work_.load(std::memory_order_acquire) == 0 \|\|
874		292053x	timeout_us == 0))
875			{
876		4x	completed_ops_.push(&task_op_);
877		4x	return 0;
878			}
879
880	2/2 ✓ Branch 0 taken 36491 times. ✓ Branch 1 taken 292049 times.	328540x	long task_timeout_us = more_handlers ? 0 : timeout_us;
881		328540x	task_interrupted_ = task_timeout_us == 0;
882		328540x	task_running_.store(true, std::memory_order_release);
883
884	2/2 ✓ Branch 0 taken 292049 times. ✓ Branch 1 taken 36491 times.	328540x	if (more_handlers)
885		36491x	unlock_and_signal_one(lock);
886
887			try
888			{
889	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 328540 times.	328540x	run_task(lock, ctx, task_timeout_us);
890		328540x	}
891			catch (...)
892			{
893		✗	task_running_.store(false, std::memory_order_relaxed);
894		✗	throw;
895		✗	}
896
897		328540x	task_running_.store(false, std::memory_order_relaxed);
898		328540x	completed_ops_.push(&task_op_);
899	2/2 ✓ Branch 0 taken 43 times. ✓ Branch 1 taken 328497 times.	328540x	if (timeout_us > 0)
900		43x	return 0;
901		328497x	continue;
902			}
903
904			// Handle operation
905	1/2 ✗ Branch 0 not taken. ✓ Branch 1 taken 524510 times.	524510x	if (op != nullptr)
906			{
907		524510x	bool more = !completed_ops_.empty();
908
909	2/2 ✓ Branch 0 taken 524504 times. ✓ Branch 1 taken 6 times.	524510x	if (more)
910		524504x	ctx->unassisted = !unlock_and_signal_one(lock);
911			else
912			{
913		6x	ctx->unassisted = false;
914		6x	lock.unlock();
915			}
916
917		524510x	work_cleanup on_exit{this, &lock, ctx};
918			(void)on_exit;
919
920	1/2 ✓ Branch 0 taken 524510 times. ✗ Branch 1 not taken.	524510x	(*op)();
921		524510x	return 1;
922		524510x	}
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		526443x	}
939
940			} // namespace boost::corosio::detail
941
942			#endif // BOOST_COROSIO_NATIVE_DETAIL_REACTOR_REACTOR_SCHEDULER_HPP
943