TLA Line data Source code
1 : //
2 : // Copyright (c) 2026 Steve Gerbino
3 : // Copyright (c) 2026 Michael Vandeberg
4 : //
5 : // Distributed under the Boost Software License, Version 1.0. (See accompanying
6 : // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7 : //
8 : // Official repository: https://github.com/cppalliance/corosio
9 : //
10 :
11 : #ifndef BOOST_COROSIO_NATIVE_DETAIL_EPOLL_EPOLL_SCHEDULER_HPP
12 : #define BOOST_COROSIO_NATIVE_DETAIL_EPOLL_EPOLL_SCHEDULER_HPP
13 :
14 : #include <boost/corosio/detail/platform.hpp>
15 :
16 : #if BOOST_COROSIO_HAS_EPOLL
17 :
18 : #include <boost/corosio/detail/config.hpp>
19 : #include <boost/capy/ex/execution_context.hpp>
20 :
21 : #include <boost/corosio/native/detail/reactor/reactor_scheduler.hpp>
22 : #include <boost/corosio/native/detail/reactor/reactor_signal_pipe.hpp>
23 :
24 : #include <boost/corosio/native/detail/epoll/epoll_traits.hpp>
25 : #include <boost/corosio/detail/timer_service.hpp>
26 : #include <boost/corosio/native/detail/make_err.hpp>
27 : #include <boost/corosio/native/detail/posix/posix_resolver_service.hpp>
28 : #include <boost/corosio/native/detail/posix/posix_signal_service.hpp>
29 : #include <boost/corosio/native/detail/posix/posix_stream_file_service.hpp>
30 : #include <boost/corosio/native/detail/posix/posix_random_access_file_service.hpp>
31 :
32 : #include <boost/corosio/detail/except.hpp>
33 :
34 : #include <atomic>
35 : #include <chrono>
36 : #include <cstdint>
37 : #include <mutex>
38 : #include <vector>
39 :
40 : #include <errno.h>
41 : #include <sys/epoll.h>
42 : #include <sys/eventfd.h>
43 : #include <sys/timerfd.h>
44 : #include <unistd.h>
45 :
46 : namespace boost::corosio::detail {
47 :
48 : /** Linux scheduler using epoll for I/O multiplexing.
49 :
50 : This scheduler implements the scheduler interface using Linux epoll
51 : for efficient I/O event notification. It uses a single reactor model
52 : where one thread runs epoll_wait while other threads
53 : wait on a condition variable for handler work. This design provides:
54 :
55 : - Handler parallelism: N posted handlers can execute on N threads
56 : - No thundering herd: condition_variable wakes exactly one thread
57 : - IOCP parity: Behavior matches Windows I/O completion port semantics
58 :
59 : When threads call run(), they first try to execute queued handlers.
60 : If the queue is empty and no reactor is running, one thread becomes
61 : the reactor and runs epoll_wait. Other threads wait on a condition
62 : variable until handlers are available.
63 :
64 : @par Thread Safety
65 : All public member functions are thread-safe.
66 : */
67 : class BOOST_COROSIO_DECL epoll_scheduler final : public reactor_scheduler
68 : {
69 : public:
70 : /** Construct the scheduler.
71 :
72 : Creates an epoll instance, eventfd for reactor interruption,
73 : and timerfd for kernel-managed timer expiry.
74 :
75 : @param ctx Reference to the owning execution_context.
76 : @param concurrency_hint Hint for expected thread count (unused).
77 : */
78 : epoll_scheduler(capy::execution_context& ctx, int concurrency_hint = -1);
79 :
80 : /// Destroy the scheduler.
81 : ~epoll_scheduler() override;
82 :
83 : epoll_scheduler(epoll_scheduler const&) = delete;
84 : epoll_scheduler& operator=(epoll_scheduler const&) = delete;
85 :
86 : /// Shut down the scheduler, draining pending operations.
87 : void shutdown() override;
88 :
89 : /// Apply runtime configuration, resizing the event buffer.
90 : void configure_reactor(
91 : unsigned max_events,
92 : unsigned budget_init,
93 : unsigned budget_max,
94 : unsigned unassisted) override;
95 :
96 : /** Return the epoll file descriptor.
97 :
98 : Used by socket services to register file descriptors
99 : for I/O event notification.
100 :
101 : @return The epoll file descriptor.
102 : */
103 : int epoll_fd() const noexcept
104 : {
105 : return epoll_fd_;
106 : }
107 :
108 : /** Register a descriptor for persistent monitoring.
109 :
110 : The fd is registered once and stays registered until explicitly
111 : deregistered. Events are dispatched via reactor_descriptor_state which
112 : tracks pending read/write/connect operations.
113 :
114 : @param fd The file descriptor to register.
115 : @param desc Pointer to descriptor data (stored in epoll_event.data.ptr).
116 :
117 : @return The error if registration fails, otherwise a default
118 : constructed error code.
119 : */
120 : std::error_code
121 : register_descriptor(int fd, reactor_descriptor_state* desc) const;
122 :
123 : /** Deregister a persistently registered descriptor.
124 :
125 : @param fd The file descriptor to deregister.
126 : */
127 : void deregister_descriptor(int fd) const;
128 :
129 : /// Watch the read end of the POSIX signal self-pipe (see scheduler.hpp).
130 : [[nodiscard]] std::error_code
131 HIT 51 : register_signal_reader(int read_fd) override
132 : {
133 51 : return register_descriptor(read_fd, signal_pipe_reader_.arm());
134 : }
135 :
136 : private:
137 : void
138 : run_task(lock_type& lock, context_type* ctx,
139 : long timeout_us) override;
140 : void interrupt_reactor() const override;
141 : void update_timerfd() const;
142 :
143 : int epoll_fd_;
144 : int event_fd_;
145 : int timer_fd_;
146 :
147 : // Watches the global signal self-pipe's read end (armed lazily by
148 : // register_signal_reader on the first signal registration).
149 : reactor_signal_pipe_reader signal_pipe_reader_;
150 :
151 : // Edge-triggered eventfd state
152 : mutable std::atomic<bool> eventfd_armed_{false};
153 :
154 : // Set when the earliest timer changes; flushed before epoll_wait
155 : mutable std::atomic<bool> timerfd_stale_{false};
156 :
157 : // Event buffer sized from max_events_per_poll_ (set at construction,
158 : // resized by configure_reactor via io_context_options).
159 : std::vector<epoll_event> event_buffer_;
160 : };
161 :
162 902 : inline epoll_scheduler::epoll_scheduler(capy::execution_context& ctx, int)
163 902 : : epoll_fd_(-1)
164 902 : , event_fd_(-1)
165 902 : , timer_fd_(-1)
166 1804 : , event_buffer_(max_events_per_poll_)
167 : {
168 902 : epoll_fd_ = ::epoll_create1(EPOLL_CLOEXEC);
169 902 : if (epoll_fd_ < 0)
170 MIS 0 : detail::throw_system_error(make_err(errno), "epoll_create1");
171 :
172 HIT 902 : event_fd_ = ::eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
173 902 : if (event_fd_ < 0)
174 : {
175 MIS 0 : int errn = errno;
176 0 : ::close(epoll_fd_);
177 0 : detail::throw_system_error(make_err(errn), "eventfd");
178 : }
179 :
180 HIT 902 : timer_fd_ = ::timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK | TFD_CLOEXEC);
181 902 : if (timer_fd_ < 0)
182 : {
183 MIS 0 : int errn = errno;
184 0 : ::close(event_fd_);
185 0 : ::close(epoll_fd_);
186 0 : detail::throw_system_error(make_err(errn), "timerfd_create");
187 : }
188 :
189 HIT 902 : epoll_event ev{};
190 902 : ev.events = EPOLLIN | EPOLLET;
191 902 : ev.data.ptr = nullptr;
192 902 : if (::epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, event_fd_, &ev) < 0)
193 : {
194 MIS 0 : int errn = errno;
195 0 : ::close(timer_fd_);
196 0 : ::close(event_fd_);
197 0 : ::close(epoll_fd_);
198 0 : detail::throw_system_error(make_err(errn), "epoll_ctl");
199 : }
200 :
201 HIT 902 : epoll_event timer_ev{};
202 902 : timer_ev.events = EPOLLIN | EPOLLERR;
203 902 : timer_ev.data.ptr = &timer_fd_;
204 902 : if (::epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, timer_fd_, &timer_ev) < 0)
205 : {
206 MIS 0 : int errn = errno;
207 0 : ::close(timer_fd_);
208 0 : ::close(event_fd_);
209 0 : ::close(epoll_fd_);
210 0 : detail::throw_system_error(make_err(errn), "epoll_ctl (timerfd)");
211 : }
212 :
213 HIT 902 : timer_svc_ = &get_timer_service(ctx, *this);
214 902 : timer_svc_->set_on_earliest_changed(
215 5467 : timer_service::callback(this, [](void* p) {
216 4565 : auto* self = static_cast<epoll_scheduler*>(p);
217 4565 : self->timerfd_stale_.store(true, std::memory_order_release);
218 4565 : self->interrupt_reactor();
219 4565 : }));
220 :
221 902 : get_resolver_service(ctx, *this);
222 902 : get_signal_service(ctx, *this);
223 902 : get_stream_file_service(ctx, *this);
224 902 : get_random_access_file_service(ctx, *this);
225 :
226 902 : completed_ops_.push(&task_op_);
227 902 : }
228 :
229 1804 : inline epoll_scheduler::~epoll_scheduler()
230 : {
231 902 : if (timer_fd_ >= 0)
232 902 : ::close(timer_fd_);
233 902 : if (event_fd_ >= 0)
234 902 : ::close(event_fd_);
235 902 : if (epoll_fd_ >= 0)
236 902 : ::close(epoll_fd_);
237 1804 : }
238 :
239 : inline void
240 902 : epoll_scheduler::shutdown()
241 : {
242 902 : shutdown_drain();
243 :
244 902 : if (event_fd_ >= 0)
245 902 : interrupt_reactor();
246 902 : }
247 :
248 : inline void
249 19 : epoll_scheduler::configure_reactor(
250 : unsigned max_events,
251 : unsigned budget_init,
252 : unsigned budget_max,
253 : unsigned unassisted)
254 : {
255 19 : reactor_scheduler::configure_reactor(
256 : max_events, budget_init, budget_max, unassisted);
257 18 : event_buffer_.resize(max_events_per_poll_);
258 18 : }
259 :
260 : inline std::error_code
261 8085 : epoll_scheduler::register_descriptor(int fd, reactor_descriptor_state* desc) const
262 : {
263 8085 : epoll_event ev{};
264 8085 : ev.events = EPOLLIN | EPOLLOUT | EPOLLET | EPOLLERR | EPOLLHUP;
265 8085 : ev.data.ptr = desc;
266 :
267 8085 : if (::epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, fd, &ev) < 0)
268 1 : return make_err(errno);
269 :
270 8084 : desc->registered_events = ev.events;
271 8084 : desc->fd = fd;
272 8084 : desc->scheduler_ = this;
273 8084 : desc->mutex.set_enabled(reactor_io_locking_);
274 8084 : desc->ready_events_.store(0, std::memory_order_relaxed);
275 :
276 8084 : conditionally_enabled_mutex::scoped_lock lock(desc->mutex);
277 8084 : desc->impl_ref_.reset();
278 8084 : desc->read_ready = false;
279 8084 : desc->write_ready = false;
280 8084 : return {};
281 8084 : }
282 :
283 : inline void
284 8033 : epoll_scheduler::deregister_descriptor(int fd) const
285 : {
286 8033 : ::epoll_ctl(epoll_fd_, EPOLL_CTL_DEL, fd, nullptr);
287 8033 : }
288 :
289 : inline void
290 6296 : epoll_scheduler::interrupt_reactor() const
291 : {
292 6296 : bool expected = false;
293 6296 : if (eventfd_armed_.compare_exchange_strong(
294 : expected, true, std::memory_order_release,
295 : std::memory_order_relaxed))
296 : {
297 5058 : std::uint64_t val = 1;
298 5058 : [[maybe_unused]] auto r = ::write(event_fd_, &val, sizeof(val));
299 : }
300 6296 : }
301 :
302 : inline void
303 7779 : epoll_scheduler::update_timerfd() const
304 : {
305 7779 : auto nearest = timer_svc_->nearest_expiry();
306 :
307 7779 : itimerspec ts{};
308 7779 : int flags = 0;
309 :
310 7779 : if (nearest == timer_service::time_point::max())
311 : {
312 : // No timers — disarm by setting to 0 (relative)
313 : }
314 : else
315 : {
316 7602 : auto now = std::chrono::steady_clock::now();
317 7602 : if (nearest <= now)
318 : {
319 : // Use 1ns instead of 0 — zero disarms the timerfd
320 896 : ts.it_value.tv_nsec = 1;
321 : }
322 : else
323 : {
324 6706 : auto nsec = std::chrono::duration_cast<std::chrono::nanoseconds>(
325 6706 : nearest - now)
326 6706 : .count();
327 6706 : ts.it_value.tv_sec = nsec / 1000000000;
328 6706 : ts.it_value.tv_nsec = nsec % 1000000000;
329 6706 : if (ts.it_value.tv_sec == 0 && ts.it_value.tv_nsec == 0)
330 MIS 0 : ts.it_value.tv_nsec = 1;
331 : }
332 : }
333 :
334 HIT 7779 : if (::timerfd_settime(timer_fd_, flags, &ts, nullptr) < 0)
335 MIS 0 : detail::throw_system_error(make_err(errno), "timerfd_settime");
336 HIT 7779 : }
337 :
338 : inline void
339 49383 : epoll_scheduler::run_task(
340 : lock_type& lock, context_type* ctx, long timeout_us)
341 : {
342 : int timeout_ms;
343 49383 : if (task_interrupted_)
344 38744 : timeout_ms = 0;
345 10639 : else if (timeout_us < 0)
346 10636 : timeout_ms = -1;
347 : else
348 3 : timeout_ms = static_cast<int>((timeout_us + 999) / 1000);
349 :
350 49383 : if (lock.owns_lock())
351 10641 : lock.unlock();
352 :
353 49383 : task_cleanup on_exit{this, &lock, ctx};
354 :
355 : // Flush deferred timerfd programming before blocking
356 49383 : if (timerfd_stale_.exchange(false, std::memory_order_acquire))
357 3897 : update_timerfd();
358 :
359 49383 : int nfds = ::epoll_wait(
360 : epoll_fd_, event_buffer_.data(),
361 49383 : static_cast<int>(event_buffer_.size()), timeout_ms);
362 :
363 49383 : if (nfds < 0 && errno != EINTR)
364 MIS 0 : detail::throw_system_error(make_err(errno), "epoll_wait");
365 :
366 HIT 49383 : bool check_timers = false;
367 49383 : ready_queue local_ops;
368 :
369 113995 : for (int i = 0; i < nfds; ++i)
370 : {
371 64612 : if (event_buffer_[i].data.ptr == nullptr)
372 : {
373 : std::uint64_t val;
374 : // NOLINTNEXTLINE(clang-analyzer-unix.BlockInCriticalSection)
375 4156 : [[maybe_unused]] auto r = ::read(event_fd_, &val, sizeof(val));
376 4156 : eventfd_armed_.store(false, std::memory_order_relaxed);
377 4156 : continue;
378 4156 : }
379 :
380 60456 : if (event_buffer_[i].data.ptr == &timer_fd_)
381 : {
382 : std::uint64_t expirations;
383 : // NOLINTNEXTLINE(clang-analyzer-unix.BlockInCriticalSection)
384 : [[maybe_unused]] auto r =
385 3882 : ::read(timer_fd_, &expirations, sizeof(expirations));
386 3882 : check_timers = true;
387 3882 : continue;
388 3882 : }
389 :
390 : auto* desc =
391 56574 : static_cast<reactor_descriptor_state*>(event_buffer_[i].data.ptr);
392 56574 : desc->add_ready_events(event_buffer_[i].events);
393 :
394 56574 : bool expected = false;
395 56574 : if (desc->is_enqueued_.compare_exchange_strong(
396 : expected, true, std::memory_order_release,
397 : std::memory_order_relaxed))
398 : {
399 56574 : local_ops.push(desc);
400 : }
401 : }
402 :
403 49383 : if (check_timers)
404 : {
405 3882 : timer_svc_->process_expired();
406 3882 : update_timerfd();
407 : }
408 :
409 49383 : lock.lock();
410 :
411 49383 : completed_ops_.splice(local_ops);
412 49383 : }
413 :
414 : } // namespace boost::corosio::detail
415 :
416 : #endif // BOOST_COROSIO_HAS_EPOLL
417 :
418 : #endif // BOOST_COROSIO_NATIVE_DETAIL_EPOLL_EPOLL_SCHEDULER_HPP
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