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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 219010 ~work_guard()
251 {
252 219010 self->work_finished();
253 219010 }
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 2376 timer_service::callback(this, [](void* p) {
302 2241 static_cast<select_scheduler*>(p)->interrupt_reactor();
303 2241 }));
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 2592 select_scheduler::post(std::coroutine_handle<> h) const
350 {
351 struct post_handler final : scheduler_op
352 {
353 std::coroutine_handle<> h_;
354
355 2592 explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
356
357 5184 ~post_handler() override = default;
358
359 2592 void operator()() override
360 {
361 2592 auto h = h_;
362 2592 delete this;
363 2592 h.resume();
364 2592 }
365
366 ✗ void destroy() override
367 {
368 ✗ delete this;
369 ✗ }
370 };
371
372 2592 auto ph = std::make_unique<post_handler>(h);
373 2592 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
374
375 2592 std::unique_lock lock(mutex_);
376 2592 completed_ops_.push(ph.release());
377 2592 wake_one_thread_and_unlock(lock);
378 2592 }
379
380 inline void
381 212232 select_scheduler::post(scheduler_op* h) const
382 {
383 212232 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
384
385 212232 std::unique_lock lock(mutex_);
386 212232 completed_ops_.push(h);
387 212232 wake_one_thread_and_unlock(lock);
388 212232 }
389
390 inline bool
391 559 select_scheduler::running_in_this_thread() const noexcept
392 {
393 559 for (auto* c = select::context_stack.get(); c != nullptr; c = c->next)
394 369 if (c->key == this)
395 369 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 219086 while (do_one(-1))
444 218986 if (n != (std::numeric_limits<std::size_t>::max)())
445 218986 ++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 4349 select_scheduler::register_fd(int fd, select_op* op, int events) const
520 {
521 // Validate fd is within select() limits
522 4349 if (fd < 0 || fd >= FD_SETSIZE)
523 ✗ detail::throw_system_error(make_err(EINVAL), "select: fd out of range");
524
525 {
526 4349 std::lock_guard lock(mutex_);
527
528 4349 auto& state = registered_fds_[fd];
529 4349 if (events & event_read)
530 2316 state.read_op = op;
531 4349 if (events & event_write)
532 2033 state.write_op = op;
533
534 4349 if (fd > max_fd_)
535 232 max_fd_ = fd;
536 4349 }
537
538 // Wake the reactor so a thread blocked in select() rebuilds its fd_sets
539 // with the newly registered fd.
540 4349 interrupt_reactor();
541 4349 }
542
543 inline void
544 4283 select_scheduler::deregister_fd(int fd, int events) const
545 {
546 4283 std::lock_guard lock(mutex_);
547
548 4283 auto it = registered_fds_.find(fd);
549 4283 if (it == registered_fds_.end())
550 4120 return;
551
552 163 if (events & event_read)
553 163 it->second.read_op = nullptr;
554 163 if (events & event_write)
555 ✗ it->second.write_op = nullptr;
556
557 // Remove entry if both are null
558 163 if (!it->second.read_op && !it->second.write_op)
559 {
560 163 registered_fds_.erase(it);
561
562 // Recalculate max_fd_ if needed
563 163 if (fd == max_fd_)
564 {
565 162 max_fd_ = pipe_fds_[0]; // At minimum, the pipe read end
566 162 for (auto& [registered_fd, state] : registered_fds_)
567 {
568 ✗ if (registered_fd > max_fd_)
569 ✗ max_fd_ = registered_fd;
570 }
571 }
572 }
573 4283 }
574
575 inline void
576 7171 select_scheduler::work_started() noexcept
577 {
578 7171 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
579 7171 }
580
581 inline void
582 221995 select_scheduler::work_finished() noexcept
583 {
584 443990 if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
585 103 stop();
586 221995 }
587
588 inline void
589 9059 select_scheduler::interrupt_reactor() const
590 {
591 9059 char byte = 1;
592 9059 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
593 9059 }
594
595 inline void
596 214824 select_scheduler::wake_one_thread_and_unlock(
597 std::unique_lock<std::mutex>& lock) const
598 {
599 214824 if (idle_thread_count_ > 0)
600 {
601 // Idle worker exists - wake it via condvar
602 ✗ wakeup_event_.notify_one();
603 ✗ lock.unlock();
604 }
605 214824 else if (reactor_running_ && !reactor_interrupted_)
606 {
607 // No idle workers but reactor is running - interrupt it
608 2231 reactor_interrupted_ = true;
609 2231 lock.unlock();
610 2231 interrupt_reactor();
611 }
612 else
613 {
614 // No one to wake
615 212593 lock.unlock();
616 }
617 214824 }
618
619 inline long
620 6082 select_scheduler::calculate_timeout(long requested_timeout_us) const
621 {
622 6082 if (requested_timeout_us == 0)
623 ✗ return 0;
624
625 6082 auto nearest = timer_svc_->nearest_expiry();
626 6082 if (nearest == timer_service::time_point::max())
627 37 return requested_timeout_us;
628
629 6045 auto now = std::chrono::steady_clock::now();
630 6045 if (nearest <= now)
631 325 return 0;
632
633 auto timer_timeout_us =
634 5720 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
635 5720 .count();
636
637 // Clamp to [0, LONG_MAX] to prevent truncation on 32-bit long platforms
638 5720 constexpr auto long_max =
639 static_cast<long long>((std::numeric_limits<long>::max)());
640 auto capped_timer_us =
641 5720 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
642 5720 static_cast<long long>(0)),
643 5720 long_max);
644
645 5720 if (requested_timeout_us < 0)
646 5720 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 115763 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 115763 reactor_interrupted_ ? 0 : calculate_timeout(-1);
660
661 // Build fd_sets from registered_fds_
662 fd_set read_fds, write_fds, except_fds;
663 1967971 FD_ZERO(&read_fds);
664 1967971 FD_ZERO(&write_fds);
665 1967971 FD_ZERO(&except_fds);
666
667 // Always include the interrupt pipe
668 115763 FD_SET(pipe_fds_[0], &read_fds);
669 115763 int nfds = pipe_fds_[0];
670
671 // Add registered fds
672 125642 for (auto& [fd, state] : registered_fds_)
673 {
674 9879 if (state.read_op)
675 7846 FD_SET(fd, &read_fds);
676 9879 if (state.write_op)
677 {
678 2033 FD_SET(fd, &write_fds);
679 // Also monitor for errors on connect operations
680 2033 FD_SET(fd, &except_fds);
681 }
682 9879 if (fd > nfds)
683 7849 nfds = fd;
684 }
685
686 // Convert timeout to timeval
687 struct timeval tv;
688 115763 struct timeval* tv_ptr = nullptr;
689 115763 if (effective_timeout_us >= 0)
690 {
691 115726 tv.tv_sec = effective_timeout_us / 1000000;
692 115726 tv.tv_usec = effective_timeout_us % 1000000;
693 115726 tv_ptr = &tv;
694 }
695
696 115763 lock.unlock();
697
698 115763 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr);
699 115763 int saved_errno = errno;
700
701 // Process timers outside the lock
702 115763 timer_svc_->process_expired();
703
704 115763 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 115763 lock.lock();
709
710 // Drain the interrupt pipe if readable
711 115763 if (ready > 0 && FD_ISSET(pipe_fds_[0], &read_fds))
712 {
713 char buf[256];
714 12904 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
715 {
716 }
717 }
718
719 // Process I/O completions
720 115763 int completions_queued = 0;
721 115763 if (ready > 0)
722 {
723 // Iterate over registered fds (copy keys to avoid iterator invalidation)
724 6452 std::vector<int> fds_to_check;
725 6452 fds_to_check.reserve(registered_fds_.size());
726 14341 for (auto& [fd, state] : registered_fds_)
727 7889 fds_to_check.push_back(fd);
728
729 14341 for (int fd : fds_to_check)
730 {
731 7889 auto it = registered_fds_.find(fd);
732 7889 if (it == registered_fds_.end())
733 ✗ continue;
734
735 7889 auto& state = it->second;
736
737 // Check for errors (especially for connect operations)
738 7889 bool has_error = FD_ISSET(fd, &except_fds);
739
740 // Process read readiness
741 7889 if (state.read_op && (FD_ISSET(fd, &read_fds) || has_error))
742 {
743 2153 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 2153 auto prev = op->registered.exchange(
747 select_registration_state::unregistered,
748 std::memory_order_acq_rel);
749 2153 if (prev != select_registration_state::unregistered)
750 {
751 2153 state.read_op = nullptr;
752
753 2153 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 2153 op->perform_io();
767 }
768
769 2153 completed_ops_.push(op);
770 2153 ++completions_queued;
771 }
772 }
773
774 // Process write readiness
775 7889 if (state.write_op && (FD_ISSET(fd, &write_fds) || has_error))
776 {
777 2033 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 2033 auto prev = op->registered.exchange(
781 select_registration_state::unregistered,
782 std::memory_order_acq_rel);
783 2033 if (prev != select_registration_state::unregistered)
784 {
785 2033 state.write_op = nullptr;
786
787 2033 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 2033 op->perform_io();
801 }
802
803 2033 completed_ops_.push(op);
804 2033 ++completions_queued;
805 }
806 }
807
808 // Clean up empty entries
809 7889 if (!state.read_op && !state.write_op)
810 4186 registered_fds_.erase(it);
811 }
812 6452 }
813
814 115763 if (completions_queued > 0)
815 {
816 2156 if (completions_queued == 1)
817 126 wakeup_event_.notify_one();
818 else
819 2030 wakeup_event_.notify_all();
820 }
821 115763 }
822
823 inline std::size_t
824 219110 select_scheduler::do_one(long timeout_us)
825 {
826 219110 std::unique_lock lock(mutex_);
827
828 for (;;)
829 {
830 334873 if (stopped_.load(std::memory_order_acquire))
831 100 return 0;
832
833 334773 scheduler_op* op = completed_ops_.pop();
834
835 334773 if (op == &task_op_)
836 {
837 115763 bool more_handlers = !completed_ops_.empty();
838
839 115763 if (!more_handlers)
840 {
841 12164 if (outstanding_work_.load(std::memory_order_acquire) == 0)
842 {
843 ✗ completed_ops_.push(&task_op_);
844 ✗ return 0;
845 }
846 6082 if (timeout_us == 0)
847 {
848 ✗ completed_ops_.push(&task_op_);
849 ✗ return 0;
850 }
851 }
852
853 115763 reactor_interrupted_ = more_handlers || timeout_us == 0;
854 115763 reactor_running_ = true;
855
856 115763 if (more_handlers && idle_thread_count_ > 0)
857 ✗ wakeup_event_.notify_one();
858
859 115763 run_reactor(lock);
860
861 115763 reactor_running_ = false;
862 115763 completed_ops_.push(&task_op_);
863 115763 continue;
864 115763 }
865
866 219010 if (op != nullptr)
867 {
868 219010 lock.unlock();
869 219010 select::work_guard g{this};
870 219010 (*op)();
871 219010 return 1;
872 219010 }
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 115763 }
887 219110 }
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