Index/include / boost / corosio / native / detail / select / select_scheduler.hpp

include/boost/corosio/native/detail/select/select_scheduler.hpp

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include/boost/corosio/native/detail/select/select_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_SELECT_SELECT_SCHEDULER_HPP
11 #define BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP
12
13 #include <boost/corosio/detail/platform.hpp>
14
15 #if BOOST_COROSIO_HAS_SELECT
16
17 #include <boost/corosio/detail/config.hpp>
18 #include <boost/capy/ex/execution_context.hpp>
19
20 #include <boost/corosio/native/native_scheduler.hpp>
21 #include <boost/corosio/detail/scheduler_op.hpp>
22
23 #include <boost/corosio/native/detail/select/select_op.hpp>
24 #include <boost/corosio/detail/timer_service.hpp>
25 #include <boost/corosio/detail/make_err.hpp>
26 #include <boost/corosio/native/detail/posix/posix_resolver_service.hpp>
27 #include <boost/corosio/native/detail/posix/posix_signal_service.hpp>
28
29 #include <boost/corosio/detail/except.hpp>
30 #include <boost/corosio/detail/thread_local_ptr.hpp>
31
32 #include <sys/select.h>
33 #include <sys/socket.h>
34 #include <unistd.h>
35 #include <errno.h>
36 #include <fcntl.h>
37
38 #include <algorithm>
39 #include <atomic>
40 #include <chrono>
41 #include <condition_variable>
42 #include <cstddef>
43 #include <limits>
44 #include <mutex>
45 #include <unordered_map>
46
47 namespace boost::corosio::detail {
48
49 struct select_op;
50
51 /** POSIX scheduler using select() for I/O multiplexing.
52
53 This scheduler implements the scheduler interface using the POSIX select()
54 call for I/O event notification. It uses a single reactor model
55 where one thread runs select() while other threads wait on a condition
56 variable for handler work. This design provides:
57
58 - Handler parallelism: N posted handlers can execute on N threads
59 - No thundering herd: condition_variable wakes exactly one thread
60 - Portability: Works on all POSIX systems
61
62 The design mirrors epoll_scheduler for behavioral consistency:
63 - Same single-reactor thread coordination model
64 - Same work counting semantics
65 - Same timer integration pattern
66
67 Known Limitations:
68 - FD_SETSIZE (~1024) limits maximum concurrent connections
69 - O(n) scanning: rebuilds fd_sets each iteration
70 - Level-triggered only (no edge-triggered mode)
71
72 @par Thread Safety
73 All public member functions are thread-safe.
74 */
75 class BOOST_COROSIO_DECL select_scheduler final
76 : public native_scheduler
77 , public capy::execution_context::service
78 {
79 public:
80 using key_type = scheduler;
81
82 /** Construct the scheduler.
83
84 Creates a self-pipe for reactor interruption.
85
86 @param ctx Reference to the owning execution_context.
87 @param concurrency_hint Hint for expected thread count (unused).
88 */
89 select_scheduler(capy::execution_context& ctx, int concurrency_hint = -1);
90
91 ~select_scheduler() override;
92
93 select_scheduler(select_scheduler const&) = delete;
94 select_scheduler& operator=(select_scheduler const&) = delete;
95
96 void shutdown() override;
97 void post(std::coroutine_handle<> h) const override;
98 void post(scheduler_op* h) const override;
99 bool running_in_this_thread() const noexcept override;
100 void stop() override;
101 bool stopped() const noexcept override;
102 void restart() override;
103 std::size_t run() override;
104 std::size_t run_one() override;
105 std::size_t wait_one(long usec) override;
106 std::size_t poll() override;
107 std::size_t poll_one() override;
108
109 /** Return the maximum file descriptor value supported.
110
111 Returns FD_SETSIZE - 1, the maximum fd value that can be
112 monitored by select(). Operations with fd >= FD_SETSIZE
113 will fail with EINVAL.
114
115 @return The maximum supported file descriptor value.
116 */
117 static constexpr int max_fd() noexcept
118 {
119 return FD_SETSIZE - 1;
120 }
121
122 /** Register a file descriptor for monitoring.
123
124 @param fd The file descriptor to register.
125 @param op The operation associated with this fd.
126 @param events Event mask: 1 = read, 2 = write, 3 = both.
127 */
128 void register_fd(int fd, select_op* op, int events) const;
129
130 /** Unregister a file descriptor from monitoring.
131
132 @param fd The file descriptor to unregister.
133 @param events Event mask to remove: 1 = read, 2 = write, 3 = both.
134 */
135 void deregister_fd(int fd, int events) const;
136
137 void work_started() noexcept override;
138 void work_finished() noexcept override;
139
140 // Event flags for register_fd/deregister_fd
141 static constexpr int event_read = 1;
142 static constexpr int event_write = 2;
143
144 private:
145 std::size_t do_one(long timeout_us);
146 void run_reactor(std::unique_lock<std::mutex>& lock);
147 void wake_one_thread_and_unlock(std::unique_lock<std::mutex>& lock) const;
148 void interrupt_reactor() const;
149 long calculate_timeout(long requested_timeout_us) const;
150
151 // Self-pipe for interrupting select()
152 int pipe_fds_[2]; // [0]=read, [1]=write
153
154 mutable std::mutex mutex_;
155 mutable std::condition_variable wakeup_event_;
156 mutable op_queue completed_ops_;
157 mutable std::atomic<long> outstanding_work_;
158 std::atomic<bool> stopped_;
159 bool shutdown_;
160
161 // Per-fd state for tracking registered operations
162 struct fd_state
163 {
164 select_op* read_op = nullptr;
165 select_op* write_op = nullptr;
166 };
167 mutable std::unordered_map<int, fd_state> registered_fds_;
168 mutable int max_fd_ = -1;
169
170 // Single reactor thread coordination
171 mutable bool reactor_running_ = false;
172 mutable bool reactor_interrupted_ = false;
173 mutable int idle_thread_count_ = 0;
174
175 // Sentinel operation for interleaving reactor runs with handler execution.
176 // Ensures the reactor runs periodically even when handlers are continuously
177 // posted, preventing timer starvation.
178 struct task_op final : scheduler_op
179 {
180 ✗ void operator()() override {}
181 ✗ void destroy() override {}
182 };
183 task_op task_op_;
184 };
185
186 /*
187 select Scheduler - Single Reactor Model
188 =======================================
189
190 This scheduler mirrors the epoll_scheduler design but uses select() instead
191 of epoll for I/O multiplexing. The thread coordination strategy is identical:
192 one thread becomes the "reactor" while others wait on a condition variable.
193
194 Thread Model
195 ------------
196 - ONE thread runs select() at a time (the reactor thread)
197 - OTHER threads wait on wakeup_event_ (condition variable) for handlers
198 - When work is posted, exactly one waiting thread wakes via notify_one()
199
200 Key Differences from epoll
201 --------------------------
202 - Uses self-pipe instead of eventfd for interruption (more portable)
203 - fd_set rebuilding each iteration (O(n) vs O(1) for epoll)
204 - FD_SETSIZE limit (~1024 fds on most systems)
205 - Level-triggered only (no edge-triggered mode)
206
207 Self-Pipe Pattern
208 -----------------
209 To interrupt a blocking select() call (e.g., when work is posted or a timer
210 expires), we write a byte to pipe_fds_[1]. The read end pipe_fds_[0] is
211 always in the read_fds set, so select() returns immediately. We drain the
212 pipe to clear the readable state.
213
214 fd-to-op Mapping
215 ----------------
216 We use an unordered_map<int, fd_state> to track which operations are
217 registered for each fd. This allows O(1) lookup when select() returns
218 ready fds. Each fd can have at most one read op and one write op registered.
219 */
220
221 namespace select {
222
223 struct BOOST_COROSIO_SYMBOL_VISIBLE scheduler_context
224 {
225 select_scheduler const* key;
226 scheduler_context* next;
227 };
228
229 inline thread_local_ptr<scheduler_context> context_stack;
230
231 struct thread_context_guard
232 {
233 scheduler_context frame_;
234
235 135 explicit thread_context_guard(select_scheduler const* ctx) noexcept
236 135 : frame_{ctx, context_stack.get()}
237 {
238 135 context_stack.set(&frame_);
239 135 }
240
241 135 ~thread_context_guard() noexcept
242 {
243 135 context_stack.set(frame_.next);
244 135 }
245 };
246
247 struct work_guard
248 {
249 select_scheduler* self;
250 142059 ~work_guard()
251 {
252 142059 self->work_finished();
253 142059 }
254 };
255
256 } // namespace select
257
258 154 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
259 154 : pipe_fds_{-1, -1}
260 154 , outstanding_work_(0)
261 154 , stopped_(false)
262 154 , shutdown_(false)
263 154 , max_fd_(-1)
264 154 , reactor_running_(false)
265 154 , reactor_interrupted_(false)
266 308 , idle_thread_count_(0)
267 {
268 // Create self-pipe for interrupting select()
269 154 if (::pipe(pipe_fds_) < 0)
270 ✗ detail::throw_system_error(make_err(errno), "pipe");
271
272 // Set both ends to non-blocking and close-on-exec
273 462 for (int i = 0; i < 2; ++i)
274 {
275 308 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
276 308 if (flags == -1)
277 {
278 ✗ int errn = errno;
279 ✗ ::close(pipe_fds_[0]);
280 ✗ ::close(pipe_fds_[1]);
281 ✗ detail::throw_system_error(make_err(errn), "fcntl F_GETFL");
282 }
283 308 if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1)
284 {
285 ✗ int errn = errno;
286 ✗ ::close(pipe_fds_[0]);
287 ✗ ::close(pipe_fds_[1]);
288 ✗ detail::throw_system_error(make_err(errn), "fcntl F_SETFL");
289 }
290 308 if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1)
291 {
292 ✗ int errn = errno;
293 ✗ ::close(pipe_fds_[0]);
294 ✗ ::close(pipe_fds_[1]);
295 ✗ detail::throw_system_error(make_err(errn), "fcntl F_SETFD");
296 }
297 }
298
299 154 timer_svc_ = &get_timer_service(ctx, *this);
300 154 timer_svc_->set_on_earliest_changed(
301 3036 timer_service::callback(this, [](void* p) {
302 2882 static_cast<select_scheduler*>(p)->interrupt_reactor();
303 2882 }));
304
305 // Initialize resolver service
306 154 get_resolver_service(ctx, *this);
307
308 // Initialize signal service
309 154 get_signal_service(ctx, *this);
310
311 // Push task sentinel to interleave reactor runs with handler execution
312 154 completed_ops_.push(&task_op_);
313 154 }
314
315 308 inline select_scheduler::~select_scheduler()
316 {
317 154 if (pipe_fds_[0] >= 0)
318 154 ::close(pipe_fds_[0]);
319 154 if (pipe_fds_[1] >= 0)
320 154 ::close(pipe_fds_[1]);
321 308 }
322
323 inline void
324 154 select_scheduler::shutdown()
325 {
326 {
327 154 std::unique_lock lock(mutex_);
328 154 shutdown_ = true;
329
330 308 while (auto* h = completed_ops_.pop())
331 {
332 154 if (h == &task_op_)
333 154 continue;
334 ✗ lock.unlock();
335 ✗ h->destroy();
336 ✗ lock.lock();
337 154 }
338 154 }
339
340 154 outstanding_work_.store(0, std::memory_order_release);
341
342 154 if (pipe_fds_[1] >= 0)
343 154 interrupt_reactor();
344
345 154 wakeup_event_.notify_all();
346 154 }
347
348 inline void
349 3251 select_scheduler::post(std::coroutine_handle<> h) const
350 {
351 struct post_handler final : scheduler_op
352 {
353 std::coroutine_handle<> h_;
354
355 3251 explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
356
357 6502 ~post_handler() override = default;
358
359 3251 void operator()() override
360 {
361 3251 auto h = h_;
362 3251 delete this;
363 3251 h.resume();
364 3251 }
365
366 ✗ void destroy() override
367 {
368 ✗ delete this;
369 ✗ }
370 };
371
372 3251 auto ph = std::make_unique<post_handler>(h);
373 3251 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
374
375 3251 std::unique_lock lock(mutex_);
376 3251 completed_ops_.push(ph.release());
377 3251 wake_one_thread_and_unlock(lock);
378 3251 }
379
380 inline void
381 133324 select_scheduler::post(scheduler_op* h) const
382 {
383 133324 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
384
385 133324 std::unique_lock lock(mutex_);
386 133324 completed_ops_.push(h);
387 133324 wake_one_thread_and_unlock(lock);
388 133324 }
389
390 inline bool
391 577 select_scheduler::running_in_this_thread() const noexcept
392 {
393 577 for (auto* c = select::context_stack.get(); c != nullptr; c = c->next)
394 364 if (c->key == this)
395 364 return true;
396 213 return false;
397 }
398
399 inline void
400 114 select_scheduler::stop()
401 {
402 114 bool expected = false;
403 114 if (stopped_.compare_exchange_strong(
404 expected, true, std::memory_order_release,
405 std::memory_order_relaxed))
406 {
407 // Wake all threads so they notice stopped_ and exit
408 {
409 114 std::lock_guard lock(mutex_);
410 114 wakeup_event_.notify_all();
411 114 }
412 114 interrupt_reactor();
413 }
414 114 }
415
416 inline bool
417 3 select_scheduler::stopped() const noexcept
418 {
419 3 return stopped_.load(std::memory_order_acquire);
420 }
421
422 inline void
423 38 select_scheduler::restart()
424 {
425 38 stopped_.store(false, std::memory_order_release);
426 38 }
427
428 inline std::size_t
429 111 select_scheduler::run()
430 {
431 111 if (stopped_.load(std::memory_order_acquire))
432 ✗ return 0;
433
434 222 if (outstanding_work_.load(std::memory_order_acquire) == 0)
435 {
436 ✗ stop();
437 ✗ return 0;
438 }
439
440 111 select::thread_context_guard ctx(this);
441
442 111 std::size_t n = 0;
443 142146 while (do_one(-1))
444 142035 if (n != (std::numeric_limits<std::size_t>::max)())
445 142035 ++n;
446 111 return n;
447 111 }
448
449 inline std::size_t
450 ✗ select_scheduler::run_one()
451 {
452 ✗ if (stopped_.load(std::memory_order_acquire))
453 ✗ return 0;
454
455 ✗ if (outstanding_work_.load(std::memory_order_acquire) == 0)
456 {
457 ✗ stop();
458 ✗ return 0;
459 }
460
461 ✗ select::thread_context_guard ctx(this);
462 ✗ return do_one(-1);
463 ✗ }
464
465 inline std::size_t
466 27 select_scheduler::wait_one(long usec)
467 {
468 27 if (stopped_.load(std::memory_order_acquire))
469 3 return 0;
470
471 48 if (outstanding_work_.load(std::memory_order_acquire) == 0)
472 {
473 ✗ stop();
474 ✗ return 0;
475 }
476
477 24 select::thread_context_guard ctx(this);
478 24 return do_one(usec);
479 24 }
480
481 inline std::size_t
482 ✗ select_scheduler::poll()
483 {
484 ✗ if (stopped_.load(std::memory_order_acquire))
485 ✗ return 0;
486
487 ✗ if (outstanding_work_.load(std::memory_order_acquire) == 0)
488 {
489 ✗ stop();
490 ✗ return 0;
491 }
492
493 ✗ select::thread_context_guard ctx(this);
494
495 ✗ std::size_t n = 0;
496 ✗ while (do_one(0))
497 ✗ if (n != (std::numeric_limits<std::size_t>::max)())
498 ✗ ++n;
499 ✗ return n;
500 ✗ }
501
502 inline std::size_t
503 ✗ select_scheduler::poll_one()
504 {
505 ✗ if (stopped_.load(std::memory_order_acquire))
506 ✗ return 0;
507
508 ✗ if (outstanding_work_.load(std::memory_order_acquire) == 0)
509 {
510 ✗ stop();
511 ✗ return 0;
512 }
513
514 ✗ select::thread_context_guard ctx(this);
515 ✗ return do_one(0);
516 ✗ }
517
518 inline void
519 5644 select_scheduler::register_fd(int fd, select_op* op, int events) const
520 {
521 // Validate fd is within select() limits
522 5644 if (fd < 0 || fd >= FD_SETSIZE)
523 ✗ detail::throw_system_error(make_err(EINVAL), "select: fd out of range");
524
525 {
526 5644 std::lock_guard lock(mutex_);
527
528 5644 auto& state = registered_fds_[fd];
529 5644 if (events & event_read)
530 2961 state.read_op = op;
531 5644 if (events & event_write)
532 2683 state.write_op = op;
533
534 5644 if (fd > max_fd_)
535 249 max_fd_ = fd;
536 5644 }
537
538 // Wake the reactor so a thread blocked in select() rebuilds its fd_sets
539 // with the newly registered fd.
540 5644 interrupt_reactor();
541 5644 }
542
543 inline void
544 5598 select_scheduler::deregister_fd(int fd, int events) const
545 {
546 5598 std::lock_guard lock(mutex_);
547
548 5598 auto it = registered_fds_.find(fd);
549 5598 if (it == registered_fds_.end())
550 5438 return;
551
552 160 if (events & event_read)
553 160 it->second.read_op = nullptr;
554 160 if (events & event_write)
555 ✗ it->second.write_op = nullptr;
556
557 // Remove entry if both are null
558 160 if (!it->second.read_op && !it->second.write_op)
559 {
560 160 registered_fds_.erase(it);
561
562 // Recalculate max_fd_ if needed
563 160 if (fd == max_fd_)
564 {
565 159 max_fd_ = pipe_fds_[0]; // At minimum, the pipe read end
566 159 for (auto& [registered_fd, state] : registered_fds_)
567 {
568 ✗ if (registered_fd > max_fd_)
569 ✗ max_fd_ = registered_fd;
570 }
571 }
572 }
573 5598 }
574
575 inline void
576 9126 select_scheduler::work_started() noexcept
577 {
578 9126 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
579 9126 }
580
581 inline void
582 145701 select_scheduler::work_finished() noexcept
583 {
584 291402 if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
585 114 stop();
586 145701 }
587
588 inline void
589 11667 select_scheduler::interrupt_reactor() const
590 {
591 11667 char byte = 1;
592 11667 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
593 11667 }
594
595 inline void
596 136575 select_scheduler::wake_one_thread_and_unlock(
597 std::unique_lock<std::mutex>& lock) const
598 {
599 136575 if (idle_thread_count_ > 0)
600 {
601 // Idle worker exists - wake it via condvar
602 ✗ wakeup_event_.notify_one();
603 ✗ lock.unlock();
604 }
605 136575 else if (reactor_running_ && !reactor_interrupted_)
606 {
607 // No idle workers but reactor is running - interrupt it
608 2873 reactor_interrupted_ = true;
609 2873 lock.unlock();
610 2873 interrupt_reactor();
611 }
612 else
613 {
614 // No one to wake
615 133702 lock.unlock();
616 }
617 136575 }
618
619 inline long
620 8119 select_scheduler::calculate_timeout(long requested_timeout_us) const
621 {
622 8119 if (requested_timeout_us == 0)
623 ✗ return 0;
624
625 8119 auto nearest = timer_svc_->nearest_expiry();
626 8119 if (nearest == timer_service::time_point::max())
627 46 return requested_timeout_us;
628
629 8073 auto now = std::chrono::steady_clock::now();
630 8073 if (nearest <= now)
631 236 return 0;
632
633 auto timer_timeout_us =
634 7837 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
635 7837 .count();
636
637 // Clamp to [0, LONG_MAX] to prevent truncation on 32-bit long platforms
638 7837 constexpr auto long_max =
639 static_cast<long long>((std::numeric_limits<long>::max)());
640 auto capped_timer_us =
641 7837 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
642 7837 static_cast<long long>(0)),
643 7837 long_max);
644
645 7837 if (requested_timeout_us < 0)
646 7837 return static_cast<long>(capped_timer_us);
647
648 // requested_timeout_us is already long, so min() result fits in long
649 return static_cast<long>(
650 ✗ (std::min)(static_cast<long long>(requested_timeout_us),
651 ✗ capped_timer_us));
652 }
653
654 inline void
655 78615 select_scheduler::run_reactor(std::unique_lock<std::mutex>& lock)
656 {
657 // Calculate timeout considering timers, use 0 if interrupted
658 long effective_timeout_us =
659 78615 reactor_interrupted_ ? 0 : calculate_timeout(-1);
660
661 // Build fd_sets from registered_fds_
662 fd_set read_fds, write_fds, except_fds;
663 1336455 FD_ZERO(&read_fds);
664 1336455 FD_ZERO(&write_fds);
665 1336455 FD_ZERO(&except_fds);
666
667 // Always include the interrupt pipe
668 78615 FD_SET(pipe_fds_[0], &read_fds);
669 78615 int nfds = pipe_fds_[0];
670
671 // Add registered fds
672 91822 for (auto& [fd, state] : registered_fds_)
673 {
674 13207 if (state.read_op)
675 10524 FD_SET(fd, &read_fds);
676 13207 if (state.write_op)
677 {
678 2683 FD_SET(fd, &write_fds);
679 // Also monitor for errors on connect operations
680 2683 FD_SET(fd, &except_fds);
681 }
682 13207 if (fd > nfds)
683 10528 nfds = fd;
684 }
685
686 // Convert timeout to timeval
687 struct timeval tv;
688 78615 struct timeval* tv_ptr = nullptr;
689 78615 if (effective_timeout_us >= 0)
690 {
691 78569 tv.tv_sec = effective_timeout_us / 1000000;
692 78569 tv.tv_usec = effective_timeout_us % 1000000;
693 78569 tv_ptr = &tv;
694 }
695
696 78615 lock.unlock();
697
698 78615 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr);
699 78615 int saved_errno = errno;
700
701 // Process timers outside the lock
702 78615 timer_svc_->process_expired();
703
704 78615 if (ready < 0 && saved_errno != EINTR)
705 ✗ detail::throw_system_error(make_err(saved_errno), "select");
706
707 // Re-acquire lock before modifying completed_ops_
708 78615 lock.lock();
709
710 // Drain the interrupt pipe if readable
711 78615 if (ready > 0 && FD_ISSET(pipe_fds_[0], &read_fds))
712 {
713 char buf[256];
714 16962 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
715 {
716 }
717 }
718
719 // Process I/O completions
720 78615 int completions_queued = 0;
721 78615 if (ready > 0)
722 {
723 // Iterate over registered fds (copy keys to avoid iterator invalidation)
724 8481 std::vector<int> fds_to_check;
725 8481 fds_to_check.reserve(registered_fds_.size());
726 19053 for (auto& [fd, state] : registered_fds_)
727 10572 fds_to_check.push_back(fd);
728
729 19053 for (int fd : fds_to_check)
730 {
731 10572 auto it = registered_fds_.find(fd);
732 10572 if (it == registered_fds_.end())
733 ✗ continue;
734
735 10572 auto& state = it->second;
736
737 // Check for errors (especially for connect operations)
738 10572 bool has_error = FD_ISSET(fd, &except_fds);
739
740 // Process read readiness
741 10572 if (state.read_op && (FD_ISSET(fd, &read_fds) || has_error))
742 {
743 2801 auto* op = state.read_op;
744 // Claim the op by exchanging to unregistered. Both registering and
745 // registered states mean the op is ours to complete.
746 2801 auto prev = op->registered.exchange(
747 select_registration_state::unregistered,
748 std::memory_order_acq_rel);
749 2801 if (prev != select_registration_state::unregistered)
750 {
751 2801 state.read_op = nullptr;
752
753 2801 if (has_error)
754 {
755 ✗ int errn = 0;
756 ✗ socklen_t len = sizeof(errn);
757 ✗ if (::getsockopt(
758 ✗ fd, SOL_SOCKET, SO_ERROR, &errn, &len) < 0)
759 ✗ errn = errno;
760 ✗ if (errn == 0)
761 ✗ errn = EIO;
762 ✗ op->complete(errn, 0);
763 }
764 else
765 {
766 2801 op->perform_io();
767 }
768
769 2801 completed_ops_.push(op);
770 2801 ++completions_queued;
771 }
772 }
773
774 // Process write readiness
775 10572 if (state.write_op && (FD_ISSET(fd, &write_fds) || has_error))
776 {
777 2683 auto* op = state.write_op;
778 // Claim the op by exchanging to unregistered. Both registering and
779 // registered states mean the op is ours to complete.
780 2683 auto prev = op->registered.exchange(
781 select_registration_state::unregistered,
782 std::memory_order_acq_rel);
783 2683 if (prev != select_registration_state::unregistered)
784 {
785 2683 state.write_op = nullptr;
786
787 2683 if (has_error)
788 {
789 ✗ int errn = 0;
790 ✗ socklen_t len = sizeof(errn);
791 ✗ if (::getsockopt(
792 ✗ fd, SOL_SOCKET, SO_ERROR, &errn, &len) < 0)
793 ✗ errn = errno;
794 ✗ if (errn == 0)
795 ✗ errn = EIO;
796 ✗ op->complete(errn, 0);
797 }
798 else
799 {
800 2683 op->perform_io();
801 }
802
803 2683 completed_ops_.push(op);
804 2683 ++completions_queued;
805 }
806 }
807
808 // Clean up empty entries
809 10572 if (!state.read_op && !state.write_op)
810 5484 registered_fds_.erase(it);
811 }
812 8481 }
813
814 78615 if (completions_queued > 0)
815 {
816 2805 if (completions_queued == 1)
817 126 wakeup_event_.notify_one();
818 else
819 2679 wakeup_event_.notify_all();
820 }
821 78615 }
822
823 inline std::size_t
824 142170 select_scheduler::do_one(long timeout_us)
825 {
826 142170 std::unique_lock lock(mutex_);
827
828 for (;;)
829 {
830 220785 if (stopped_.load(std::memory_order_acquire))
831 111 return 0;
832
833 220674 scheduler_op* op = completed_ops_.pop();
834
835 220674 if (op == &task_op_)
836 {
837 78615 bool more_handlers = !completed_ops_.empty();
838
839 78615 if (!more_handlers)
840 {
841 16238 if (outstanding_work_.load(std::memory_order_acquire) == 0)
842 {
843 ✗ completed_ops_.push(&task_op_);
844 ✗ return 0;
845 }
846 8119 if (timeout_us == 0)
847 {
848 ✗ completed_ops_.push(&task_op_);
849 ✗ return 0;
850 }
851 }
852
853 78615 reactor_interrupted_ = more_handlers || timeout_us == 0;
854 78615 reactor_running_ = true;
855
856 78615 if (more_handlers && idle_thread_count_ > 0)
857 ✗ wakeup_event_.notify_one();
858
859 78615 run_reactor(lock);
860
861 78615 reactor_running_ = false;
862 78615 completed_ops_.push(&task_op_);
863 78615 continue;
864 78615 }
865
866 142059 if (op != nullptr)
867 {
868 142059 lock.unlock();
869 142059 select::work_guard g{this};
870 142059 (*op)();
871 142059 return 1;
872 142059 }
873
874 ✗ if (outstanding_work_.load(std::memory_order_acquire) == 0)
875 ✗ return 0;
876
877 ✗ if (timeout_us == 0)
878 ✗ return 0;
879
880 ✗ ++idle_thread_count_;
881 ✗ if (timeout_us < 0)
882 ✗ wakeup_event_.wait(lock);
883 else
884 ✗ wakeup_event_.wait_for(lock, std::chrono::microseconds(timeout_us));
885 ✗ --idle_thread_count_;
886 78615 }
887 142170 }
888
889 } // namespace boost::corosio::detail
890
891 #endif // BOOST_COROSIO_HAS_SELECT
892
893 #endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP
894