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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
235 124 explicit thread_context_guard(select_scheduler const* ctx) noexcept
236 124 : frame_{ctx, context_stack.get()}
237 {
238 124 context_stack.set(&frame_);
239 124 }
240
241 124 ~thread_context_guard() noexcept
242 {
243 124 context_stack.set(frame_.next);
244 124 }
245 };
246
247 struct work_guard
248 {
249 select_scheduler* self;
250 171486 ~work_guard()
251 {
252 171486 self->work_finished();
253 171486 }
254 };
255
256 } // namespace select
257
258 135 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
259 135 : pipe_fds_{-1, -1}
260 135 , outstanding_work_(0)
261 135 , stopped_(false)
262 135 , shutdown_(false)
263 135 , max_fd_(-1)
264 135 , reactor_running_(false)
265 135 , reactor_interrupted_(false)
266 270 , idle_thread_count_(0)
267 {
268 // Create self-pipe for interrupting select()
269 135 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
273 405 for (int i = 0; i < 2; ++i)
274 {
275 270 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
276 270 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 }
283 270 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 }
290 270 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
299 135 timer_svc_ = &get_timer_service(ctx, *this);
300 135 timer_svc_->set_on_earliest_changed(
301 3483 timer_service::callback(this, [](void* p) {
302 3348 static_cast<select_scheduler*>(p)->interrupt_reactor();
303 3348 }));
304
305 // Initialize resolver service
306 135 get_resolver_service(ctx, *this);
307
308 // Initialize signal service
309 135 get_signal_service(ctx, *this);
310
311 // Push task sentinel to interleave reactor runs with handler execution
312 135 completed_ops_.push(&task_op_);
313 135 }
314
315 270 inline select_scheduler::~select_scheduler()
316 {
317 135 if (pipe_fds_[0] >= 0)
318 135 ::close(pipe_fds_[0]);
319 135 if (pipe_fds_[1] >= 0)
320 135 ::close(pipe_fds_[1]);
321 270 }
322
323 inline void
324 135 select_scheduler::shutdown()
325 {
326 {
327 135 std::unique_lock lock(mutex_);
328 135 shutdown_ = true;
329
330 270 while (auto* h = completed_ops_.pop())
331 {
332 135 if (h == &task_op_)
333 135 continue;
334 ✗ lock.unlock();
335 ✗ h->destroy();
336 ✗ lock.lock();
337 135 }
338 135 }
339
340 135 outstanding_work_.store(0, std::memory_order_release);
341
342 135 if (pipe_fds_[1] >= 0)
343 135 interrupt_reactor();
344
345 135 wakeup_event_.notify_all();
346 135 }
347
348 inline void
349 3689 select_scheduler::post(std::coroutine_handle<> h) const
350 {
351 struct post_handler final : scheduler_op
352 {
353 std::coroutine_handle<> h_;
354
355 3689 explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
356
357 7378 ~post_handler() override = default;
358
359 3689 void operator()() override
360 {
361 3689 auto h = h_;
362 3689 delete this;
363 3689 h.resume();
364 3689 }
365
366 ✗ void destroy() override
367 {
368 ✗ delete this;
369 ✗ }
370 };
371
372 3689 auto ph = std::make_unique<post_handler>(h);
373 3689 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
374
375 3689 std::unique_lock lock(mutex_);
376 3689 completed_ops_.push(ph.release());
377 3689 wake_one_thread_and_unlock(lock);
378 3689 }
379
380 inline void
381 161405 select_scheduler::post(scheduler_op* h) const
382 {
383 161405 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
384
385 161405 std::unique_lock lock(mutex_);
386 161405 completed_ops_.push(h);
387 161405 wake_one_thread_and_unlock(lock);
388 161405 }
389
390 inline bool
391 551 select_scheduler::running_in_this_thread() const noexcept
392 {
393 551 for (auto* c = select::context_stack.get(); c != nullptr; c = c->next)
394 361 if (c->key == this)
395 361 return true;
396 190 return false;
397 }
398
399 inline void
400 103 select_scheduler::stop()
401 {
402 103 bool expected = false;
403 103 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 {
409 103 std::lock_guard lock(mutex_);
410 103 wakeup_event_.notify_all();
411 103 }
412 103 interrupt_reactor();
413 }
414 103 }
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 37 select_scheduler::restart()
424 {
425 37 stopped_.store(false, std::memory_order_release);
426 37 }
427
428 inline std::size_t
429 100 select_scheduler::run()
430 {
431 100 if (stopped_.load(std::memory_order_acquire))
432 ✗ return 0;
433
434 200 if (outstanding_work_.load(std::memory_order_acquire) == 0)
435 {
436 ✗ stop();
437 ✗ return 0;
438 }
439
440 100 select::thread_context_guard ctx(this);
441
442 100 std::size_t n = 0;
443 171562 while (do_one(-1))
444 171462 if (n != (std::numeric_limits<std::size_t>::max)())
445 171462 ++n;
446 100 return n;
447 100 }
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 6551 select_scheduler::register_fd(int fd, select_op* op, int events) const
520 {
521 // Validate fd is within select() limits
522 6551 if (fd < 0 || fd >= FD_SETSIZE)
523 ✗ detail::throw_system_error(make_err(EINVAL), "select: fd out of range");
524
525 {
526 6551 std::lock_guard lock(mutex_);
527
528 6551 auto& state = registered_fds_[fd];
529 6551 if (events & event_read)
530 3414 state.read_op = op;
531 6551 if (events & event_write)
532 3137 state.write_op = op;
533
534 6551 if (fd > max_fd_)
535 229 max_fd_ = fd;
536 6551 }
537
538 // Wake the reactor so a thread blocked in select() rebuilds its fd_sets
539 // with the newly registered fd.
540 6551 interrupt_reactor();
541 6551 }
542
543 inline void
544 6487 select_scheduler::deregister_fd(int fd, int events) const
545 {
546 6487 std::lock_guard lock(mutex_);
547
548 6487 auto it = registered_fds_.find(fd);
549 6487 if (it == registered_fds_.end())
550 6328 return;
551
552 159 if (events & event_read)
553 159 it->second.read_op = nullptr;
554 159 if (events & event_write)
555 ✗ it->second.write_op = nullptr;
556
557 // Remove entry if both are null
558 159 if (!it->second.read_op && !it->second.write_op)
559 {
560 159 registered_fds_.erase(it);
561
562 // Recalculate max_fd_ if needed
563 159 if (fd == max_fd_)
564 {
565 158 max_fd_ = pipe_fds_[0]; // At minimum, the pipe read end
566 158 for (auto& [registered_fd, state] : registered_fds_)
567 {
568 ✗ if (registered_fd > max_fd_)
569 ✗ max_fd_ = registered_fd;
570 }
571 }
572 }
573 6487 }
574
575 inline void
576 10472 select_scheduler::work_started() noexcept
577 {
578 10472 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
579 10472 }
580
581 inline void
582 175566 select_scheduler::work_finished() noexcept
583 {
584 351132 if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
585 103 stop();
586 175566 }
587
588 inline void
589 13476 select_scheduler::interrupt_reactor() const
590 {
591 13476 char byte = 1;
592 13476 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
593 13476 }
594
595 inline void
596 165094 select_scheduler::wake_one_thread_and_unlock(
597 std::unique_lock<std::mutex>& lock) const
598 {
599 165094 if (idle_thread_count_ > 0)
600 {
601 // Idle worker exists - wake it via condvar
602 ✗ wakeup_event_.notify_one();
603 ✗ lock.unlock();
604 }
605 165094 else if (reactor_running_ && !reactor_interrupted_)
606 {
607 // No idle workers but reactor is running - interrupt it
608 3339 reactor_interrupted_ = true;
609 3339 lock.unlock();
610 3339 interrupt_reactor();
611 }
612 else
613 {
614 // No one to wake
615 161755 lock.unlock();
616 }
617 165094 }
618
619 inline long
620 9618 select_scheduler::calculate_timeout(long requested_timeout_us) const
621 {
622 9618 if (requested_timeout_us == 0)
623 ✗ return 0;
624
625 9618 auto nearest = timer_svc_->nearest_expiry();
626 9618 if (nearest == timer_service::time_point::max())
627 37 return requested_timeout_us;
628
629 9581 auto now = std::chrono::steady_clock::now();
630 9581 if (nearest <= now)
631 120 return 0;
632
633 auto timer_timeout_us =
634 9461 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
635 9461 .count();
636
637 // Clamp to [0, LONG_MAX] to prevent truncation on 32-bit long platforms
638 9461 constexpr auto long_max =
639 static_cast<long long>((std::numeric_limits<long>::max)());
640 auto capped_timer_us =
641 9461 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
642 9461 static_cast<long long>(0)),
643 9461 long_max);
644
645 9461 if (requested_timeout_us < 0)
646 9461 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 81962 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 81962 reactor_interrupted_ ? 0 : calculate_timeout(-1);
660
661 // Build fd_sets from registered_fds_
662 fd_set read_fds, write_fds, except_fds;
663 1393354 FD_ZERO(&read_fds);
664 1393354 FD_ZERO(&write_fds);
665 1393354 FD_ZERO(&except_fds);
666
667 // Always include the interrupt pipe
668 81962 FD_SET(pipe_fds_[0], &read_fds);
669 81962 int nfds = pipe_fds_[0];
670
671 // Add registered fds
672 97588 for (auto& [fd, state] : registered_fds_)
673 {
674 15626 if (state.read_op)
675 12489 FD_SET(fd, &read_fds);
676 15626 if (state.write_op)
677 {
678 3137 FD_SET(fd, &write_fds);
679 // Also monitor for errors on connect operations
680 3137 FD_SET(fd, &except_fds);
681 }
682 15626 if (fd > nfds)
683 12492 nfds = fd;
684 }
685
686 // Convert timeout to timeval
687 struct timeval tv;
688 81962 struct timeval* tv_ptr = nullptr;
689 81962 if (effective_timeout_us >= 0)
690 {
691 81925 tv.tv_sec = effective_timeout_us / 1000000;
692 81925 tv.tv_usec = effective_timeout_us % 1000000;
693 81925 tv_ptr = &tv;
694 }
695
696 81962 lock.unlock();
697
698 81962 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr);
699 81962 int saved_errno = errno;
700
701 // Process timers outside the lock
702 81962 timer_svc_->process_expired();
703
704 81962 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 81962 lock.lock();
709
710 // Drain the interrupt pipe if readable
711 81962 if (ready > 0 && FD_ISSET(pipe_fds_[0], &read_fds))
712 {
713 char buf[256];
714 19950 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
715 {
716 }
717 }
718
719 // Process I/O completions
720 81962 int completions_queued = 0;
721 81962 if (ready > 0)
722 {
723 // Iterate over registered fds (copy keys to avoid iterator invalidation)
724 9975 std::vector<int> fds_to_check;
725 9975 fds_to_check.reserve(registered_fds_.size());
726 22500 for (auto& [fd, state] : registered_fds_)
727 12525 fds_to_check.push_back(fd);
728
729 22500 for (int fd : fds_to_check)
730 {
731 12525 auto it = registered_fds_.find(fd);
732 12525 if (it == registered_fds_.end())
733 ✗ continue;
734
735 12525 auto& state = it->second;
736
737 // Check for errors (especially for connect operations)
738 12525 bool has_error = FD_ISSET(fd, &except_fds);
739
740 // Process read readiness
741 12525 if (state.read_op && (FD_ISSET(fd, &read_fds) || has_error))
742 {
743 3255 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 3255 auto prev = op->registered.exchange(
747 select_registration_state::unregistered,
748 std::memory_order_acq_rel);
749 3255 if (prev != select_registration_state::unregistered)
750 {
751 3255 state.read_op = nullptr;
752
753 3255 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 3255 op->perform_io();
767 }
768
769 3255 completed_ops_.push(op);
770 3255 ++completions_queued;
771 }
772 }
773
774 // Process write readiness
775 12525 if (state.write_op && (FD_ISSET(fd, &write_fds) || has_error))
776 {
777 3137 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 3137 auto prev = op->registered.exchange(
781 select_registration_state::unregistered,
782 std::memory_order_acq_rel);
783 3137 if (prev != select_registration_state::unregistered)
784 {
785 3137 state.write_op = nullptr;
786
787 3137 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 3137 op->perform_io();
801 }
802
803 3137 completed_ops_.push(op);
804 3137 ++completions_queued;
805 }
806 }
807
808 // Clean up empty entries
809 12525 if (!state.read_op && !state.write_op)
810 6392 registered_fds_.erase(it);
811 }
812 9975 }
813
814 81962 if (completions_queued > 0)
815 {
816 3258 if (completions_queued == 1)
817 124 wakeup_event_.notify_one();
818 else
819 3134 wakeup_event_.notify_all();
820 }
821 81962 }
822
823 inline std::size_t
824 171586 select_scheduler::do_one(long timeout_us)
825 {
826 171586 std::unique_lock lock(mutex_);
827
828 for (;;)
829 {
830 253548 if (stopped_.load(std::memory_order_acquire))
831 100 return 0;
832
833 253448 scheduler_op* op = completed_ops_.pop();
834
835 253448 if (op == &task_op_)
836 {
837 81962 bool more_handlers = !completed_ops_.empty();
838
839 81962 if (!more_handlers)
840 {
841 19236 if (outstanding_work_.load(std::memory_order_acquire) == 0)
842 {
843 ✗ completed_ops_.push(&task_op_);
844 ✗ return 0;
845 }
846 9618 if (timeout_us == 0)
847 {
848 ✗ completed_ops_.push(&task_op_);
849 ✗ return 0;
850 }
851 }
852
853 81962 reactor_interrupted_ = more_handlers || timeout_us == 0;
854 81962 reactor_running_ = true;
855
856 81962 if (more_handlers && idle_thread_count_ > 0)
857 ✗ wakeup_event_.notify_one();
858
859 81962 run_reactor(lock);
860
861 81962 reactor_running_ = false;
862 81962 completed_ops_.push(&task_op_);
863 81962 continue;
864 81962 }
865
866 171486 if (op != nullptr)
867 {
868 171486 lock.unlock();
869 171486 select::work_guard g{this};
870 171486 (*op)();
871 171486 return 1;
872 171486 }
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 81962 }
887 171586 }
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