include/boost/corosio/native/detail/epoll/epoll_scheduler.hpp

85.3% Lines (128/150) 100.0% List of functions (10/10)

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

epoll_scheduler.hpp

f(x) Functions (10)

Function Calls Lines Blocks

Line	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_EPOLL_EPOLL_SCHEDULER_HPP
11		#define BOOST_COROSIO_NATIVE_DETAIL_EPOLL_EPOLL_SCHEDULER_HPP
12
13		#include <boost/corosio/detail/platform.hpp>
14
15		#if BOOST_COROSIO_HAS_EPOLL
16
17		#include <boost/corosio/detail/config.hpp>
18		#include <boost/capy/ex/execution_context.hpp>
19
20		#include <boost/corosio/native/detail/reactor/reactor_scheduler.hpp>
21
22		#include <boost/corosio/native/detail/epoll/epoll_traits.hpp>
23		#include <boost/corosio/detail/timer_service.hpp>
24		#include <boost/corosio/native/detail/make_err.hpp>
25		#include <boost/corosio/native/detail/posix/posix_resolver_service.hpp>
26		#include <boost/corosio/native/detail/posix/posix_signal_service.hpp>
27		#include <boost/corosio/native/detail/posix/posix_stream_file_service.hpp>
28		#include <boost/corosio/native/detail/posix/posix_random_access_file_service.hpp>
29
30		#include <boost/corosio/detail/except.hpp>
31
32		#include <atomic>
33		#include <chrono>
34		#include <cstdint>
35		#include <mutex>
36		#include <vector>
37
38		#include <errno.h>
39		#include <sys/epoll.h>
40		#include <sys/eventfd.h>
41		#include <sys/timerfd.h>
42		#include <unistd.h>
43
44		namespace boost::corosio::detail {
45
46		/** Linux scheduler using epoll for I/O multiplexing.
47
48		This scheduler implements the scheduler interface using Linux epoll
49		for efficient I/O event notification. It uses a single reactor model
50		where one thread runs epoll_wait while other threads
51		wait on a condition variable for handler work. This design provides:
52
53		- Handler parallelism: N posted handlers can execute on N threads
54		- No thundering herd: condition_variable wakes exactly one thread
55		- IOCP parity: Behavior matches Windows I/O completion port semantics
56
57		When threads call run(), they first try to execute queued handlers.
58		If the queue is empty and no reactor is running, one thread becomes
59		the reactor and runs epoll_wait. Other threads wait on a condition
60		variable until handlers are available.
61
62		@par Thread Safety
63		All public member functions are thread-safe.
64		*/
65		class BOOST_COROSIO_DECL epoll_scheduler final : public reactor_scheduler
66		{
67		public:
68		/** Construct the scheduler.
69
70		Creates an epoll instance, eventfd for reactor interruption,
71		and timerfd for kernel-managed timer expiry.
72
73		@param ctx Reference to the owning execution_context.
74		@param concurrency_hint Hint for expected thread count (unused).
75		*/
76		epoll_scheduler(capy::execution_context& ctx, int concurrency_hint = -1);
77
78		/// Destroy the scheduler.
79		~epoll_scheduler() override;
80
81		epoll_scheduler(epoll_scheduler const&) = delete;
82		epoll_scheduler& operator=(epoll_scheduler const&) = delete;
83
84		/// Shut down the scheduler, draining pending operations.
85		void shutdown() override;
86
87		/// Apply runtime configuration, resizing the event buffer.
88		void configure_reactor(
89		unsigned max_events,
90		unsigned budget_init,
91		unsigned budget_max,
92		unsigned unassisted) override;
93
94		/** Return the epoll file descriptor.
95
96		Used by socket services to register file descriptors
97		for I/O event notification.
98
99		@return The epoll file descriptor.
100		*/
101		int epoll_fd() const noexcept
102		{
103		return epoll_fd_;
104		}
105
106		/** Register a descriptor for persistent monitoring.
107
108		The fd is registered once and stays registered until explicitly
109		deregistered. Events are dispatched via reactor_descriptor_state which
110		tracks pending read/write/connect operations.
111
112		@param fd The file descriptor to register.
113		@param desc Pointer to descriptor data (stored in epoll_event.data.ptr).
114		*/
115		void register_descriptor(int fd, reactor_descriptor_state* desc) const;
116
117		/** Deregister a persistently registered descriptor.
118
119		@param fd The file descriptor to deregister.
120		*/
121		void deregister_descriptor(int fd) const;
122
123		private:
124		void
125		run_task(lock_type& lock, context_type* ctx,
126		long timeout_us) override;
127		void interrupt_reactor() const override;
128		void update_timerfd() const;
129
130		int epoll_fd_;
131		int event_fd_;
132		int timer_fd_;
133
134		// Edge-triggered eventfd state
135		mutable std::atomic<bool> eventfd_armed_{false};
136
137		// Set when the earliest timer changes; flushed before epoll_wait
138		mutable std::atomic<bool> timerfd_stale_{false};
139
140		// Event buffer sized from max_events_per_poll_ (set at construction,
141		// resized by configure_reactor via io_context_options).
142		std::vector<epoll_event> event_buffer_;
143		};
144
145	593x	inline epoll_scheduler::epoll_scheduler(capy::execution_context& ctx, int)
146	593x	: epoll_fd_(-1)
147	593x	, event_fd_(-1)
148	593x	, timer_fd_(-1)
149	1186x	, event_buffer_(max_events_per_poll_)
150		{
151	593x	epoll_fd_ = ::epoll_create1(EPOLL_CLOEXEC);
152	593x	if (epoll_fd_ < 0)
153	✗	detail::throw_system_error(make_err(errno), "epoll_create1");
154
155	593x	event_fd_ = ::eventfd(0, EFD_NONBLOCK \| EFD_CLOEXEC);
156	593x	if (event_fd_ < 0)
157		{
158	✗	int errn = errno;
159	✗	::close(epoll_fd_);
160	✗	detail::throw_system_error(make_err(errn), "eventfd");
161		}
162
163	593x	timer_fd_ = ::timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK \| TFD_CLOEXEC);
164	593x	if (timer_fd_ < 0)
165		{
166	✗	int errn = errno;
167	✗	::close(event_fd_);
168	✗	::close(epoll_fd_);
169	✗	detail::throw_system_error(make_err(errn), "timerfd_create");
170		}
171
172	593x	epoll_event ev{};
173	593x	ev.events = EPOLLIN \| EPOLLET;
174	593x	ev.data.ptr = nullptr;
175	593x	if (::epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, event_fd_, &ev) < 0)
176		{
177	✗	int errn = errno;
178	✗	::close(timer_fd_);
179	✗	::close(event_fd_);
180	✗	::close(epoll_fd_);
181	✗	detail::throw_system_error(make_err(errn), "epoll_ctl");
182		}
183
184	593x	epoll_event timer_ev{};
185	593x	timer_ev.events = EPOLLIN \| EPOLLERR;
186	593x	timer_ev.data.ptr = &timer_fd_;
187	593x	if (::epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, timer_fd_, &timer_ev) < 0)
188		{
189	✗	int errn = errno;
190	✗	::close(timer_fd_);
191	✗	::close(event_fd_);
192	✗	::close(epoll_fd_);
193	✗	detail::throw_system_error(make_err(errn), "epoll_ctl (timerfd)");
194		}
195
196	593x	timer_svc_ = &get_timer_service(ctx, *this);
197	593x	timer_svc_->set_on_earliest_changed(
198	3045x	timer_service::callback(this, [](void* p) {
199	2452x	auto* self = static_cast<epoll_scheduler*>(p);
200	2452x	self->timerfd_stale_.store(true, std::memory_order_release);
201	2452x	self->interrupt_reactor();
202	2452x	}));
203
204	593x	get_resolver_service(ctx, *this);
205	593x	get_signal_service(ctx, *this);
206	593x	get_stream_file_service(ctx, *this);
207	593x	get_random_access_file_service(ctx, *this);
208
209	593x	completed_ops_.push(&task_op_);
210	593x	}
211
212	1186x	inline epoll_scheduler::~epoll_scheduler()
213		{
214	593x	if (timer_fd_ >= 0)
215	593x	::close(timer_fd_);
216	593x	if (event_fd_ >= 0)
217	593x	::close(event_fd_);
218	593x	if (epoll_fd_ >= 0)
219	593x	::close(epoll_fd_);
220	1186x	}
221
222		inline void
223	593x	epoll_scheduler::shutdown()
224		{
225	593x	shutdown_drain();
226
227	593x	if (event_fd_ >= 0)
228	593x	interrupt_reactor();
229	593x	}
230
231		inline void
232	8x	epoll_scheduler::configure_reactor(
233		unsigned max_events,
234		unsigned budget_init,
235		unsigned budget_max,
236		unsigned unassisted)
237		{
238	8x	reactor_scheduler::configure_reactor(
239		max_events, budget_init, budget_max, unassisted);
240	7x	event_buffer_.resize(max_events_per_poll_);
241	7x	}
242
243		inline void
244	4786x	epoll_scheduler::register_descriptor(int fd, reactor_descriptor_state* desc) const
245		{
246	4786x	epoll_event ev{};
247	4786x	ev.events = EPOLLIN \| EPOLLOUT \| EPOLLET \| EPOLLERR \| EPOLLHUP;
248	4786x	ev.data.ptr = desc;
249
250	4786x	if (::epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, fd, &ev) < 0)
251	✗	detail::throw_system_error(make_err(errno), "epoll_ctl (register)");
252
253	4786x	desc->registered_events = ev.events;
254	4786x	desc->fd = fd;
255	4786x	desc->scheduler_ = this;
256	4786x	desc->mutex.set_enabled(!single_threaded_);
257	4786x	desc->ready_events_.store(0, std::memory_order_relaxed);
258
259	4786x	conditionally_enabled_mutex::scoped_lock lock(desc->mutex);
260	4786x	desc->impl_ref_.reset();
261	4786x	desc->read_ready = false;
262	4786x	desc->write_ready = false;
263	4786x	}
264
265		inline void
266	4786x	epoll_scheduler::deregister_descriptor(int fd) const
267		{
268	4786x	::epoll_ctl(epoll_fd_, EPOLL_CTL_DEL, fd, nullptr);
269	4786x	}
270
271		inline void
272	3514x	epoll_scheduler::interrupt_reactor() const
273		{
274	3514x	bool expected = false;
275	3514x	if (eventfd_armed_.compare_exchange_strong(
276		expected, true, std::memory_order_release,
277		std::memory_order_relaxed))
278		{
279	3161x	std::uint64_t val = 1;
280	3161x	[[maybe_unused]] auto r = ::write(event_fd_, &val, sizeof(val));
281		}
282	3514x	}
283
284		inline void
285	4860x	epoll_scheduler::update_timerfd() const
286		{
287	4860x	auto nearest = timer_svc_->nearest_expiry();
288
289	4860x	itimerspec ts{};
290	4860x	int flags = 0;
291
292	4860x	if (nearest == timer_service::time_point::max())
293		{
294		// No timers — disarm by setting to 0 (relative)
295		}
296		else
297		{
298	4763x	auto now = std::chrono::steady_clock::now();
299	4763x	if (nearest <= now)
300		{
301		// Use 1ns instead of 0 — zero disarms the timerfd
302	484x	ts.it_value.tv_nsec = 1;
303		}
304		else
305		{
306	4279x	auto nsec = std::chrono::duration_cast<std::chrono::nanoseconds>(
307	4279x	nearest - now)
308	4279x	.count();
309	4279x	ts.it_value.tv_sec = nsec / 1000000000;
310	4279x	ts.it_value.tv_nsec = nsec % 1000000000;
311	4279x	if (ts.it_value.tv_sec == 0 && ts.it_value.tv_nsec == 0)
312	✗	ts.it_value.tv_nsec = 1;
313		}
314		}
315
316	4860x	if (::timerfd_settime(timer_fd_, flags, &ts, nullptr) < 0)
317	✗	detail::throw_system_error(make_err(errno), "timerfd_settime");
318	4860x	}
319
320		inline void
321	26515x	epoll_scheduler::run_task(
322		lock_type& lock, context_type* ctx, long timeout_us)
323		{
324		int timeout_ms;
325	26515x	if (task_interrupted_)
326	20649x	timeout_ms = 0;
327	5866x	else if (timeout_us < 0)
328	5862x	timeout_ms = -1;
329		else
330	4x	timeout_ms = static_cast<int>((timeout_us + 999) / 1000);
331
332	26515x	if (lock.owns_lock())
333	5866x	lock.unlock();
334
335	26515x	task_cleanup on_exit{this, &lock, ctx};
336
337		// Flush deferred timerfd programming before blocking
338	26515x	if (timerfd_stale_.exchange(false, std::memory_order_acquire))
339	2428x	update_timerfd();
340
341	26515x	int nfds = ::epoll_wait(
342		epoll_fd_, event_buffer_.data(),
343	26515x	static_cast<int>(event_buffer_.size()), timeout_ms);
344
345	26515x	if (nfds < 0 && errno != EINTR)
346	✗	detail::throw_system_error(make_err(errno), "epoll_wait");
347
348	26515x	bool check_timers = false;
349	26515x	op_queue local_ops;
350
351	63245x	for (int i = 0; i < nfds; ++i)
352		{
353	36730x	if (event_buffer_[i].data.ptr == nullptr)
354		{
355		std::uint64_t val;
356		// NOLINTNEXTLINE(clang-analyzer-unix.BlockInCriticalSection)
357	2568x	[[maybe_unused]] auto r = ::read(event_fd_, &val, sizeof(val));
358	2568x	eventfd_armed_.store(false, std::memory_order_relaxed);
359	2568x	continue;
360	2568x	}
361
362	34162x	if (event_buffer_[i].data.ptr == &timer_fd_)
363		{
364		std::uint64_t expirations;
365		// NOLINTNEXTLINE(clang-analyzer-unix.BlockInCriticalSection)
366		[[maybe_unused]] auto r =
367	2432x	::read(timer_fd_, &expirations, sizeof(expirations));
368	2432x	check_timers = true;
369	2432x	continue;
370	2432x	}
371
372		auto* desc =
373	31730x	static_cast<reactor_descriptor_state*>(event_buffer_[i].data.ptr);
374	31730x	desc->add_ready_events(event_buffer_[i].events);
375
376	31730x	bool expected = false;
377	31730x	if (desc->is_enqueued_.compare_exchange_strong(
378		expected, true, std::memory_order_release,
379		std::memory_order_relaxed))
380		{
381	31730x	local_ops.push(desc);
382		}
383		}
384
385	26515x	if (check_timers)
386		{
387	2432x	timer_svc_->process_expired();
388	2432x	update_timerfd();
389		}
390
391	26515x	lock.lock();
392
393	26515x	if (!local_ops.empty())
394	20093x	completed_ops_.splice(local_ops);
395	26515x	}
396
397		} // namespace boost::corosio::detail
398
399		#endif // BOOST_COROSIO_HAS_EPOLL
400
401		#endif // BOOST_COROSIO_NATIVE_DETAIL_EPOLL_EPOLL_SCHEDULER_HPP
402