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

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/native/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
160 // Per-fd state for tracking registered operations
161 struct fd_state
162 {
163 select_op* read_op = nullptr;
164 select_op* write_op = nullptr;
165 };
166 mutable std::unordered_map<int, fd_state> registered_fds_;
167 mutable int max_fd_ = -1;
168
169 // Single reactor thread coordination
170 mutable bool reactor_running_ = false;
171 mutable bool reactor_interrupted_ = false;
172 mutable int idle_thread_count_ = 0;
173
174 // Sentinel operation for interleaving reactor runs with handler execution.
175 // Ensures the reactor runs periodically even when handlers are continuously
176 // posted, preventing timer starvation.
177 struct task_op final : scheduler_op
178 {
179 ✗ void operator()() override {}
180 ✗ void destroy() override {}
181 };
182 task_op task_op_;
183 };
184
185 /*
186 select Scheduler - Single Reactor Model
187 =======================================
188
189 This scheduler mirrors the epoll_scheduler design but uses select() instead
190 of epoll for I/O multiplexing. The thread coordination strategy is identical:
191 one thread becomes the "reactor" while others wait on a condition variable.
192
193 Thread Model
194 ------------
195 - ONE thread runs select() at a time (the reactor thread)
196 - OTHER threads wait on wakeup_event_ (condition variable) for handlers
197 - When work is posted, exactly one waiting thread wakes via notify_one()
198
199 Key Differences from epoll
200 --------------------------
201 - Uses self-pipe instead of eventfd for interruption (more portable)
202 - fd_set rebuilding each iteration (O(n) vs O(1) for epoll)
203 - FD_SETSIZE limit (~1024 fds on most systems)
204 - Level-triggered only (no edge-triggered mode)
205
206 Self-Pipe Pattern
207 -----------------
208 To interrupt a blocking select() call (e.g., when work is posted or a timer
209 expires), we write a byte to pipe_fds_[1]. The read end pipe_fds_[0] is
210 always in the read_fds set, so select() returns immediately. We drain the
211 pipe to clear the readable state.
212
213 fd-to-op Mapping
214 ----------------
215 We use an unordered_map<int, fd_state> to track which operations are
216 registered for each fd. This allows O(1) lookup when select() returns
217 ready fds. Each fd can have at most one read op and one write op registered.
218 */
219
220 namespace select {
221
222 struct BOOST_COROSIO_SYMBOL_VISIBLE scheduler_context
223 {
224 select_scheduler const* key;
225 scheduler_context* next;
226 };
227
228 inline thread_local_ptr<scheduler_context> context_stack;
229
230 struct thread_context_guard
231 {
232 scheduler_context frame_;
233
234 148x explicit thread_context_guard(select_scheduler const* ctx) noexcept
235 148x : frame_{ctx, context_stack.get()}
236 {
237 148x context_stack.set(&frame_);
238 148x }
239
240 148x ~thread_context_guard() noexcept
241 {
242 148x context_stack.set(frame_.next);
243 148x }
244 };
245
246 struct work_guard
247 {
248 select_scheduler* self;
249 175800x ~work_guard()
250 {
251 175800x self->work_finished();
252 175800x }
253 };
254
255 } // namespace select
256
257 168x inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
258 168x : pipe_fds_{-1, -1}
259 168x , outstanding_work_(0)
260 168x , stopped_(false)
261 168x , max_fd_(-1)
262 168x , reactor_running_(false)
263 168x , reactor_interrupted_(false)
264 336x , idle_thread_count_(0)
265 {
266 // Create self-pipe for interrupting select()
267 168x if (::pipe(pipe_fds_) < 0)
268 ✗ detail::throw_system_error(make_err(errno), "pipe");
269
270 // Set both ends to non-blocking and close-on-exec
271 504x for (int i = 0; i < 2; ++i)
272 {
273 336x int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
274 336x if (flags == -1)
275 {
276 ✗ int errn = errno;
277 ✗ ::close(pipe_fds_[0]);
278 ✗ ::close(pipe_fds_[1]);
279 ✗ detail::throw_system_error(make_err(errn), "fcntl F_GETFL");
280 }
281 336x if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1)
282 {
283 ✗ int errn = errno;
284 ✗ ::close(pipe_fds_[0]);
285 ✗ ::close(pipe_fds_[1]);
286 ✗ detail::throw_system_error(make_err(errn), "fcntl F_SETFL");
287 }
288 336x if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1)
289 {
290 ✗ int errn = errno;
291 ✗ ::close(pipe_fds_[0]);
292 ✗ ::close(pipe_fds_[1]);
293 ✗ detail::throw_system_error(make_err(errn), "fcntl F_SETFD");
294 }
295 }
296
297 168x timer_svc_ = &get_timer_service(ctx, *this);
298 168x timer_svc_->set_on_earliest_changed(
299 3569x timer_service::callback(this, [](void* p) {
300 3401x static_cast<select_scheduler*>(p)->interrupt_reactor();
301 3401x }));
302
303 // Initialize resolver service
304 168x get_resolver_service(ctx, *this);
305
306 // Initialize signal service
307 168x get_signal_service(ctx, *this);
308
309 // Push task sentinel to interleave reactor runs with handler execution
310 168x completed_ops_.push(&task_op_);
311 168x }
312
313 336x inline select_scheduler::~select_scheduler()
314 {
315 168x if (pipe_fds_[0] >= 0)
316 168x ::close(pipe_fds_[0]);
317 168x if (pipe_fds_[1] >= 0)
318 168x ::close(pipe_fds_[1]);
319 336x }
320
321 inline void
322 168x select_scheduler::shutdown()
323 {
324 {
325 168x std::unique_lock lock(mutex_);
326
327 343x while (auto* h = completed_ops_.pop())
328 {
329 175x if (h == &task_op_)
330 168x continue;
331 7x lock.unlock();
332 7x h->destroy();
333 7x lock.lock();
334 175x }
335 168x }
336
337 168x if (pipe_fds_[1] >= 0)
338 168x interrupt_reactor();
339
340 168x wakeup_event_.notify_all();
341 168x }
342
343 inline void
344 3787x select_scheduler::post(std::coroutine_handle<> h) const
345 {
346 struct post_handler final : scheduler_op
347 {
348 std::coroutine_handle<> h_;
349
350 3787x explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
351
352 7574x ~post_handler() override = default;
353
354 3784x void operator()() override
355 {
356 3784x auto h = h_;
357 3784x delete this;
358 3784x h.resume();
359 3784x }
360
361 3x void destroy() override
362 {
363 3x auto h = h_;
364 3x delete this;
365 3x h.destroy();
366 3x }
367 };
368
369 3787x auto ph = std::make_unique<post_handler>(h);
370 3787x outstanding_work_.fetch_add(1, std::memory_order_relaxed);
371
372 3787x std::unique_lock lock(mutex_);
373 3787x completed_ops_.push(ph.release());
374 3787x wake_one_thread_and_unlock(lock);
375 3787x }
376
377 inline void
378 165546x select_scheduler::post(scheduler_op* h) const
379 {
380 165546x outstanding_work_.fetch_add(1, std::memory_order_relaxed);
381
382 165546x std::unique_lock lock(mutex_);
383 165546x completed_ops_.push(h);
384 165546x wake_one_thread_and_unlock(lock);
385 165546x }
386
387 inline bool
388 585x select_scheduler::running_in_this_thread() const noexcept
389 {
390 585x for (auto* c = select::context_stack.get(); c != nullptr; c = c->next)
391 355x if (c->key == this)
392 355x return true;
393 230x return false;
394 }
395
396 inline void
397 126x select_scheduler::stop()
398 {
399 126x bool expected = false;
400 126x if (stopped_.compare_exchange_strong(
401 expected, true, std::memory_order_release,
402 std::memory_order_relaxed))
403 {
404 // Wake all threads so they notice stopped_ and exit
405 {
406 126x std::lock_guard lock(mutex_);
407 126x wakeup_event_.notify_all();
408 126x }
409 126x interrupt_reactor();
410 }
411 126x }
412
413 inline bool
414 3x select_scheduler::stopped() const noexcept
415 {
416 3x return stopped_.load(std::memory_order_acquire);
417 }
418
419 inline void
420 38x select_scheduler::restart()
421 {
422 38x stopped_.store(false, std::memory_order_release);
423 38x }
424
425 inline std::size_t
426 122x select_scheduler::run()
427 {
428 122x if (stopped_.load(std::memory_order_acquire))
429 ✗ return 0;
430
431 244x if (outstanding_work_.load(std::memory_order_acquire) == 0)
432 {
433 ✗ stop();
434 ✗ return 0;
435 }
436
437 122x select::thread_context_guard ctx(this);
438
439 122x std::size_t n = 0;
440 175896x while (do_one(-1))
441 175774x if (n != (std::numeric_limits<std::size_t>::max)())
442 175774x ++n;
443 122x return n;
444 122x }
445
446 inline std::size_t
447 ✗ select_scheduler::run_one()
448 {
449 ✗ if (stopped_.load(std::memory_order_acquire))
450 ✗ return 0;
451
452 ✗ if (outstanding_work_.load(std::memory_order_acquire) == 0)
453 {
454 ✗ stop();
455 ✗ return 0;
456 }
457
458 ✗ select::thread_context_guard ctx(this);
459 ✗ return do_one(-1);
460 ✗ }
461
462 inline std::size_t
463 27x select_scheduler::wait_one(long usec)
464 {
465 27x if (stopped_.load(std::memory_order_acquire))
466 3x return 0;
467
468 48x if (outstanding_work_.load(std::memory_order_acquire) == 0)
469 {
470 ✗ stop();
471 ✗ return 0;
472 }
473
474 24x select::thread_context_guard ctx(this);
475 24x return do_one(usec);
476 24x }
477
478 inline std::size_t
479 2x select_scheduler::poll()
480 {
481 2x if (stopped_.load(std::memory_order_acquire))
482 ✗ return 0;
483
484 4x if (outstanding_work_.load(std::memory_order_acquire) == 0)
485 {
486 ✗ stop();
487 ✗ return 0;
488 }
489
490 2x select::thread_context_guard ctx(this);
491
492 2x std::size_t n = 0;
493 4x while (do_one(0))
494 2x if (n != (std::numeric_limits<std::size_t>::max)())
495 2x ++n;
496 2x return n;
497 2x }
498
499 inline std::size_t
500 ✗ select_scheduler::poll_one()
501 {
502 ✗ if (stopped_.load(std::memory_order_acquire))
503 ✗ return 0;
504
505 ✗ if (outstanding_work_.load(std::memory_order_acquire) == 0)
506 {
507 ✗ stop();
508 ✗ return 0;
509 }
510
511 ✗ select::thread_context_guard ctx(this);
512 ✗ return do_one(0);
513 ✗ }
514
515 inline void
516 6631x select_scheduler::register_fd(int fd, select_op* op, int events) const
517 {
518 // Validate fd is within select() limits
519 6631x if (fd < 0 || fd >= FD_SETSIZE)
520 ✗ detail::throw_system_error(make_err(EINVAL), "select: fd out of range");
521
522 {
523 6631x std::lock_guard lock(mutex_);
524
525 6631x auto& state = registered_fds_[fd];
526 6631x if (events & event_read)
527 3451x state.read_op = op;
528 6631x if (events & event_write)
529 3180x state.write_op = op;
530
531 6631x if (fd > max_fd_)
532 246x max_fd_ = fd;
533 6631x }
534
535 // Wake the reactor so a thread blocked in select() rebuilds its fd_sets
536 // with the newly registered fd.
537 6631x interrupt_reactor();
538 6631x }
539
540 inline void
541 6588x select_scheduler::deregister_fd(int fd, int events) const
542 {
543 6588x std::lock_guard lock(mutex_);
544
545 6588x auto it = registered_fds_.find(fd);
546 6588x if (it == registered_fds_.end())
547 6431x return;
548
549 157x if (events & event_read)
550 157x it->second.read_op = nullptr;
551 157x if (events & event_write)
552 ✗ it->second.write_op = nullptr;
553
554 // Remove entry if both are null
555 157x if (!it->second.read_op && !it->second.write_op)
556 {
557 157x registered_fds_.erase(it);
558
559 // Recalculate max_fd_ if needed
560 157x if (fd == max_fd_)
561 {
562 156x max_fd_ = pipe_fds_[0]; // At minimum, the pipe read end
563 156x for (auto& [registered_fd, state] : registered_fds_)
564 {
565 ✗ if (registered_fd > max_fd_)
566 ✗ max_fd_ = registered_fd;
567 }
568 }
569 }
570 6588x }
571
572 inline void
573 10646x select_scheduler::work_started() noexcept
574 {
575 10646x outstanding_work_.fetch_add(1, std::memory_order_relaxed);
576 10646x }
577
578 inline void
579 179972x select_scheduler::work_finished() noexcept
580 {
581 359944x if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
582 125x stop();
583 179972x }
584
585 inline void
586 13706x select_scheduler::interrupt_reactor() const
587 {
588 13706x char byte = 1;
589 13706x [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
590 13706x }
591
592 inline void
593 169333x select_scheduler::wake_one_thread_and_unlock(
594 std::unique_lock<std::mutex>& lock) const
595 {
596 169333x if (idle_thread_count_ > 0)
597 {
598 // Idle worker exists - wake it via condvar
599 ✗ wakeup_event_.notify_one();
600 ✗ lock.unlock();
601 }
602 169333x else if (reactor_running_ && !reactor_interrupted_)
603 {
604 // No idle workers but reactor is running - interrupt it
605 3380x reactor_interrupted_ = true;
606 3380x lock.unlock();
607 3380x interrupt_reactor();
608 }
609 else
610 {
611 // No one to wake
612 165953x lock.unlock();
613 }
614 169333x }
615
616 inline long
617 9769x select_scheduler::calculate_timeout(long requested_timeout_us) const
618 {
619 9769x if (requested_timeout_us == 0)
620 ✗ return 0;
621
622 9769x auto nearest = timer_svc_->nearest_expiry();
623 9769x if (nearest == timer_service::time_point::max())
624 46x return requested_timeout_us;
625
626 9723x auto now = std::chrono::steady_clock::now();
627 9723x if (nearest <= now)
628 104x return 0;
629
630 auto timer_timeout_us =
631 9619x std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
632 9619x .count();
633
634 // Clamp to [0, LONG_MAX] to prevent truncation on 32-bit long platforms
635 9619x constexpr auto long_max =
636 static_cast<long long>((std::numeric_limits<long>::max)());
637 auto capped_timer_us =
638 9619x (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
639 9619x static_cast<long long>(0)),
640 9619x long_max);
641
642 9619x if (requested_timeout_us < 0)
643 9619x return static_cast<long>(capped_timer_us);
644
645 // requested_timeout_us is already long, so min() result fits in long
646 return static_cast<long>(
647 ✗ (std::min)(static_cast<long long>(requested_timeout_us),
648 ✗ capped_timer_us));
649 }
650
651 inline void
652 86440x select_scheduler::run_reactor(std::unique_lock<std::mutex>& lock)
653 {
654 // Calculate timeout considering timers, use 0 if interrupted
655 long effective_timeout_us =
656 86440x reactor_interrupted_ ? 0 : calculate_timeout(-1);
657
658 // Build fd_sets from registered_fds_
659 fd_set read_fds, write_fds, except_fds;
660 1469480x FD_ZERO(&read_fds);
661 1469480x FD_ZERO(&write_fds);
662 1469480x FD_ZERO(&except_fds);
663
664 // Always include the interrupt pipe
665 86440x FD_SET(pipe_fds_[0], &read_fds);
666 86440x int nfds = pipe_fds_[0];
667
668 // Add registered fds
669 102272x for (auto& [fd, state] : registered_fds_)
670 {
671 15832x if (state.read_op)
672 12652x FD_SET(fd, &read_fds);
673 15832x if (state.write_op)
674 {
675 3180x FD_SET(fd, &write_fds);
676 // Also monitor for errors on connect operations
677 3180x FD_SET(fd, &except_fds);
678 }
679 15832x if (fd > nfds)
680 12657x nfds = fd;
681 }
682
683 // Convert timeout to timeval
684 struct timeval tv;
685 86440x struct timeval* tv_ptr = nullptr;
686 86440x if (effective_timeout_us >= 0)
687 {
688 86394x tv.tv_sec = effective_timeout_us / 1000000;
689 86394x tv.tv_usec = effective_timeout_us % 1000000;
690 86394x tv_ptr = &tv;
691 }
692
693 86440x lock.unlock();
694
695 86440x int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr);
696 86440x int saved_errno = errno;
697
698 // Process timers outside the lock
699 86440x timer_svc_->process_expired();
700
701 86440x if (ready < 0 && saved_errno != EINTR)
702 ✗ detail::throw_system_error(make_err(saved_errno), "select");
703
704 // Re-acquire lock before modifying completed_ops_
705 86440x lock.lock();
706
707 // Drain the interrupt pipe if readable
708 86440x if (ready > 0 && FD_ISSET(pipe_fds_[0], &read_fds))
709 {
710 char buf[256];
711 20252x while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
712 {
713 }
714 }
715
716 // Process I/O completions
717 86440x int completions_queued = 0;
718 86440x if (ready > 0)
719 {
720 // Iterate over registered fds (copy keys to avoid iterator invalidation)
721 10126x std::vector<int> fds_to_check;
722 10126x fds_to_check.reserve(registered_fds_.size());
723 22824x for (auto& [fd, state] : registered_fds_)
724 12698x fds_to_check.push_back(fd);
725
726 22824x for (int fd : fds_to_check)
727 {
728 12698x auto it = registered_fds_.find(fd);
729 12698x if (it == registered_fds_.end())
730 ✗ continue;
731
732 12698x auto& state = it->second;
733
734 // Check for errors (especially for connect operations)
735 12698x bool has_error = FD_ISSET(fd, &except_fds);
736
737 // Process read readiness
738 12698x if (state.read_op && (FD_ISSET(fd, &read_fds) || has_error))
739 {
740 3294x auto* op = state.read_op;
741 // Claim the op by exchanging to unregistered. Both registering and
742 // registered states mean the op is ours to complete.
743 3294x auto prev = op->registered.exchange(
744 select_registration_state::unregistered,
745 std::memory_order_acq_rel);
746 3294x if (prev != select_registration_state::unregistered)
747 {
748 3294x state.read_op = nullptr;
749
750 3294x if (has_error)
751 {
752 ✗ int errn = 0;
753 ✗ socklen_t len = sizeof(errn);
754 ✗ if (::getsockopt(
755 ✗ fd, SOL_SOCKET, SO_ERROR, &errn, &len) < 0)
756 ✗ errn = errno;
757 ✗ if (errn == 0)
758 ✗ errn = EIO;
759 ✗ op->complete(errn, 0);
760 }
761 else
762 {
763 3294x op->perform_io();
764 }
765
766 3294x completed_ops_.push(op);
767 3294x ++completions_queued;
768 }
769 }
770
771 // Process write readiness
772 12698x if (state.write_op && (FD_ISSET(fd, &write_fds) || has_error))
773 {
774 3180x auto* op = state.write_op;
775 // Claim the op by exchanging to unregistered. Both registering and
776 // registered states mean the op is ours to complete.
777 3180x auto prev = op->registered.exchange(
778 select_registration_state::unregistered,
779 std::memory_order_acq_rel);
780 3180x if (prev != select_registration_state::unregistered)
781 {
782 3180x state.write_op = nullptr;
783
784 3180x if (has_error)
785 {
786 ✗ int errn = 0;
787 ✗ socklen_t len = sizeof(errn);
788 ✗ if (::getsockopt(
789 ✗ fd, SOL_SOCKET, SO_ERROR, &errn, &len) < 0)
790 ✗ errn = errno;
791 ✗ if (errn == 0)
792 ✗ errn = EIO;
793 ✗ op->complete(errn, 0);
794 }
795 else
796 {
797 3180x op->perform_io();
798 }
799
800 3180x completed_ops_.push(op);
801 3180x ++completions_queued;
802 }
803 }
804
805 // Clean up empty entries
806 12698x if (!state.read_op && !state.write_op)
807 6474x registered_fds_.erase(it);
808 }
809 10126x }
810
811 86440x if (completions_queued > 0)
812 {
813 3299x if (completions_queued == 1)
814 124x wakeup_event_.notify_one();
815 else
816 3175x wakeup_event_.notify_all();
817 }
818 86440x }
819
820 inline std::size_t
821 175924x select_scheduler::do_one(long timeout_us)
822 {
823 175924x std::unique_lock lock(mutex_);
824
825 for (;;)
826 {
827 262364x if (stopped_.load(std::memory_order_acquire))
828 122x return 0;
829
830 262242x scheduler_op* op = completed_ops_.pop();
831
832 262242x if (op == &task_op_)
833 {
834 86442x bool more_handlers = !completed_ops_.empty();
835
836 86442x if (!more_handlers)
837 {
838 19542x if (outstanding_work_.load(std::memory_order_acquire) == 0)
839 {
840 ✗ completed_ops_.push(&task_op_);
841 ✗ return 0;
842 }
843 9771x if (timeout_us == 0)
844 {
845 2x completed_ops_.push(&task_op_);
846 2x return 0;
847 }
848 }
849
850 86440x reactor_interrupted_ = more_handlers || timeout_us == 0;
851 86440x reactor_running_ = true;
852
853 86440x if (more_handlers && idle_thread_count_ > 0)
854 ✗ wakeup_event_.notify_one();
855
856 86440x run_reactor(lock);
857
858 86440x reactor_running_ = false;
859 86440x completed_ops_.push(&task_op_);
860 86440x continue;
861 86440x }
862
863 175800x if (op != nullptr)
864 {
865 175800x lock.unlock();
866 175800x select::work_guard g{this};
867 175800x (*op)();
868 175800x return 1;
869 175800x }
870
871 ✗ if (outstanding_work_.load(std::memory_order_acquire) == 0)
872 ✗ return 0;
873
874 ✗ if (timeout_us == 0)
875 ✗ return 0;
876
877 ✗ ++idle_thread_count_;
878 ✗ if (timeout_us < 0)
879 ✗ wakeup_event_.wait(lock);
880 else
881 ✗ wakeup_event_.wait_for(lock, std::chrono::microseconds(timeout_us));
882 ✗ --idle_thread_count_;
883 86440x }
884 175924x }
885
886 } // namespace boost::corosio::detail
887
888 #endif // BOOST_COROSIO_HAS_SELECT
889
890 #endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP
891