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
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
234 138 explicit thread_context_guard(select_scheduler const* ctx) noexcept
235 138 : frame_{ctx, context_stack.get()}
236 {
237 138 context_stack.set(&frame_);
238 138 }
239
240 138 ~thread_context_guard() noexcept
241 {
242 138 context_stack.set(frame_.next);
243 138 }
244 };
245
246 struct work_guard
247 {
248 select_scheduler* self;
249 256132 ~work_guard()
250 {
251 256132 self->work_finished();
252 256132 }
253 };
254
255 } // namespace select
256
257 158 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
258 158 : pipe_fds_{-1, -1}
259 158 , outstanding_work_(0)
260 158 , stopped_(false)
261 158 , max_fd_(-1)
262 158 , reactor_running_(false)
263 158 , reactor_interrupted_(false)
264 316 , idle_thread_count_(0)
265 {
266 // Create self-pipe for interrupting select()
267 158 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
271 474 for (int i = 0; i < 2; ++i)
272 {
273 316 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
274 316 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 }
281 316 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 }
288 316 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
297 158 timer_svc_ = &get_timer_service(ctx, *this);
298 158 timer_svc_->set_on_earliest_changed(
299 3535 timer_service::callback(this, [](void* p) {
300 3377 static_cast<select_scheduler*>(p)->interrupt_reactor();
301 3377 }));
302
303 // Initialize resolver service
304 158 get_resolver_service(ctx, *this);
305
306 // Initialize signal service
307 158 get_signal_service(ctx, *this);
308
309 // Push task sentinel to interleave reactor runs with handler execution
310 158 completed_ops_.push(&task_op_);
311 158 }
312
313 316 inline select_scheduler::~select_scheduler()
314 {
315 158 if (pipe_fds_[0] >= 0)
316 158 ::close(pipe_fds_[0]);
317 158 if (pipe_fds_[1] >= 0)
318 158 ::close(pipe_fds_[1]);
319 316 }
320
321 inline void
322 158 select_scheduler::shutdown()
323 {
324 {
325 158 std::unique_lock lock(mutex_);
326
327 323 while (auto* h = completed_ops_.pop())
328 {
329 165 if (h == &task_op_)
330 158 continue;
331 7 lock.unlock();
332 7 h->destroy();
333 7 lock.lock();
334 165 }
335 158 }
336
337 158 if (pipe_fds_[1] >= 0)
338 158 interrupt_reactor();
339
340 158 wakeup_event_.notify_all();
341 158 }
342
343 inline void
344 3754 select_scheduler::post(std::coroutine_handle<> h) const
345 {
346 struct post_handler final : scheduler_op
347 {
348 std::coroutine_handle<> h_;
349
350 3754 explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
351
352 7508 ~post_handler() override = default;
353
354 3751 void operator()() override
355 {
356 3751 auto h = h_;
357 3751 delete this;
358 3751 h.resume();
359 3751 }
360
361 3 void destroy() override
362 {
363 3 auto h = h_;
364 3 delete this;
365 3 h.destroy();
366 3 }
367 };
368
369 3754 auto ph = std::make_unique<post_handler>(h);
370 3754 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
371
372 3754 std::unique_lock lock(mutex_);
373 3754 completed_ops_.push(ph.release());
374 3754 wake_one_thread_and_unlock(lock);
375 3754 }
376
377 inline void
378 245923 select_scheduler::post(scheduler_op* h) const
379 {
380 245923 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
381
382 245923 std::unique_lock lock(mutex_);
383 245923 completed_ops_.push(h);
384 245923 wake_one_thread_and_unlock(lock);
385 245923 }
386
387 inline bool
388 588 select_scheduler::running_in_this_thread() const noexcept
389 {
390 588 for (auto* c = select::context_stack.get(); c != nullptr; c = c->next)
391 369 if (c->key == this)
392 369 return true;
393 219 return false;
394 }
395
396 inline void
397 116 select_scheduler::stop()
398 {
399 116 bool expected = false;
400 116 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 {
406 116 std::lock_guard lock(mutex_);
407 116 wakeup_event_.notify_all();
408 116 }
409 116 interrupt_reactor();
410 }
411 116 }
412
413 inline bool
414 3 select_scheduler::stopped() const noexcept
415 {
416 3 return stopped_.load(std::memory_order_acquire);
417 }
418
419 inline void
420 38 select_scheduler::restart()
421 {
422 38 stopped_.store(false, std::memory_order_release);
423 38 }
424
425 inline std::size_t
426 112 select_scheduler::run()
427 {
428 112 if (stopped_.load(std::memory_order_acquire))
429 ✗ return 0;
430
431 224 if (outstanding_work_.load(std::memory_order_acquire) == 0)
432 {
433 ✗ stop();
434 ✗ return 0;
435 }
436
437 112 select::thread_context_guard ctx(this);
438
439 112 std::size_t n = 0;
440 256218 while (do_one(-1))
441 256106 if (n != (std::numeric_limits<std::size_t>::max)())
442 256106 ++n;
443 112 return n;
444 112 }
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 27 select_scheduler::wait_one(long usec)
464 {
465 27 if (stopped_.load(std::memory_order_acquire))
466 3 return 0;
467
468 48 if (outstanding_work_.load(std::memory_order_acquire) == 0)
469 {
470 ✗ stop();
471 ✗ return 0;
472 }
473
474 24 select::thread_context_guard ctx(this);
475 24 return do_one(usec);
476 24 }
477
478 inline std::size_t
479 2 select_scheduler::poll()
480 {
481 2 if (stopped_.load(std::memory_order_acquire))
482 ✗ return 0;
483
484 4 if (outstanding_work_.load(std::memory_order_acquire) == 0)
485 {
486 ✗ stop();
487 ✗ return 0;
488 }
489
490 2 select::thread_context_guard ctx(this);
491
492 2 std::size_t n = 0;
493 4 while (do_one(0))
494 2 if (n != (std::numeric_limits<std::size_t>::max)())
495 2 ++n;
496 2 return n;
497 2 }
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 6625 select_scheduler::register_fd(int fd, select_op* op, int events) const
517 {
518 // Validate fd is within select() limits
519 6625 if (fd < 0 || fd >= FD_SETSIZE)
520 ✗ detail::throw_system_error(make_err(EINVAL), "select: fd out of range");
521
522 {
523 6625 std::lock_guard lock(mutex_);
524
525 6625 auto& state = registered_fds_[fd];
526 6625 if (events & event_read)
527 3453 state.read_op = op;
528 6625 if (events & event_write)
529 3172 state.write_op = op;
530
531 6625 if (fd > max_fd_)
532 251 max_fd_ = fd;
533 6625 }
534
535 // Wake the reactor so a thread blocked in select() rebuilds its fd_sets
536 // with the newly registered fd.
537 6625 interrupt_reactor();
538 6625 }
539
540 inline void
541 6578 select_scheduler::deregister_fd(int fd, int events) const
542 {
543 6578 std::lock_guard lock(mutex_);
544
545 6578 auto it = registered_fds_.find(fd);
546 6578 if (it == registered_fds_.end())
547 6415 return;
548
549 163 if (events & event_read)
550 163 it->second.read_op = nullptr;
551 163 if (events & event_write)
552 ✗ it->second.write_op = nullptr;
553
554 // Remove entry if both are null
555 163 if (!it->second.read_op && !it->second.write_op)
556 {
557 163 registered_fds_.erase(it);
558
559 // Recalculate max_fd_ if needed
560 163 if (fd == max_fd_)
561 {
562 162 max_fd_ = pipe_fds_[0]; // At minimum, the pipe read end
563 162 for (auto& [registered_fd, state] : registered_fds_)
564 {
565 ✗ if (registered_fd > max_fd_)
566 ✗ max_fd_ = registered_fd;
567 }
568 }
569 }
570 6578 }
571
572 inline void
573 10614 select_scheduler::work_started() noexcept
574 {
575 10614 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
576 10614 }
577
578 inline void
579 260284 select_scheduler::work_finished() noexcept
580 {
581 520568 if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
582 115 stop();
583 260284 }
584
585 inline void
586 13640 select_scheduler::interrupt_reactor() const
587 {
588 13640 char byte = 1;
589 13640 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
590 13640 }
591
592 inline void
593 249677 select_scheduler::wake_one_thread_and_unlock(
594 std::unique_lock<std::mutex>& lock) const
595 {
596 249677 if (idle_thread_count_ > 0)
597 {
598 // Idle worker exists - wake it via condvar
599 ✗ wakeup_event_.notify_one();
600 ✗ lock.unlock();
601 }
602 249677 else if (reactor_running_ && !reactor_interrupted_)
603 {
604 // No idle workers but reactor is running - interrupt it
605 3364 reactor_interrupted_ = true;
606 3364 lock.unlock();
607 3364 interrupt_reactor();
608 }
609 else
610 {
611 // No one to wake
612 246313 lock.unlock();
613 }
614 249677 }
615
616 inline long
617 9634 select_scheduler::calculate_timeout(long requested_timeout_us) const
618 {
619 9634 if (requested_timeout_us == 0)
620 ✗ return 0;
621
622 9634 auto nearest = timer_svc_->nearest_expiry();
623 9634 if (nearest == timer_service::time_point::max())
624 46 return requested_timeout_us;
625
626 9588 auto now = std::chrono::steady_clock::now();
627 9588 if (nearest <= now)
628 189 return 0;
629
630 auto timer_timeout_us =
631 9399 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
632 9399 .count();
633
634 // Clamp to [0, LONG_MAX] to prevent truncation on 32-bit long platforms
635 9399 constexpr auto long_max =
636 static_cast<long long>((std::numeric_limits<long>::max)());
637 auto capped_timer_us =
638 9399 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
639 9399 static_cast<long long>(0)),
640 9399 long_max);
641
642 9399 if (requested_timeout_us < 0)
643 9399 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 135020 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 135020 reactor_interrupted_ ? 0 : calculate_timeout(-1);
657
658 // Build fd_sets from registered_fds_
659 fd_set read_fds, write_fds, except_fds;
660 2295340 FD_ZERO(&read_fds);
661 2295340 FD_ZERO(&write_fds);
662 2295340 FD_ZERO(&except_fds);
663
664 // Always include the interrupt pipe
665 135020 FD_SET(pipe_fds_[0], &read_fds);
666 135020 int nfds = pipe_fds_[0];
667
668 // Add registered fds
669 150714 for (auto& [fd, state] : registered_fds_)
670 {
671 15694 if (state.read_op)
672 12522 FD_SET(fd, &read_fds);
673 15694 if (state.write_op)
674 {
675 3172 FD_SET(fd, &write_fds);
676 // Also monitor for errors on connect operations
677 3172 FD_SET(fd, &except_fds);
678 }
679 15694 if (fd > nfds)
680 12527 nfds = fd;
681 }
682
683 // Convert timeout to timeval
684 struct timeval tv;
685 135020 struct timeval* tv_ptr = nullptr;
686 135020 if (effective_timeout_us >= 0)
687 {
688 134974 tv.tv_sec = effective_timeout_us / 1000000;
689 134974 tv.tv_usec = effective_timeout_us % 1000000;
690 134974 tv_ptr = &tv;
691 }
692
693 135020 lock.unlock();
694
695 135020 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr);
696 135020 int saved_errno = errno;
697
698 // Process timers outside the lock
699 135020 timer_svc_->process_expired();
700
701 135020 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 135020 lock.lock();
706
707 // Drain the interrupt pipe if readable
708 135020 if (ready > 0 && FD_ISSET(pipe_fds_[0], &read_fds))
709 {
710 char buf[256];
711 20004 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
712 {
713 }
714 }
715
716 // Process I/O completions
717 135020 int completions_queued = 0;
718 135020 if (ready > 0)
719 {
720 // Iterate over registered fds (copy keys to avoid iterator invalidation)
721 10002 std::vector<int> fds_to_check;
722 10002 fds_to_check.reserve(registered_fds_.size());
723 22574 for (auto& [fd, state] : registered_fds_)
724 12572 fds_to_check.push_back(fd);
725
726 22574 for (int fd : fds_to_check)
727 {
728 12572 auto it = registered_fds_.find(fd);
729 12572 if (it == registered_fds_.end())
730 ✗ continue;
731
732 12572 auto& state = it->second;
733
734 // Check for errors (especially for connect operations)
735 12572 bool has_error = FD_ISSET(fd, &except_fds);
736
737 // Process read readiness
738 12572 if (state.read_op && (FD_ISSET(fd, &read_fds) || has_error))
739 {
740 3290 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 3290 auto prev = op->registered.exchange(
744 select_registration_state::unregistered,
745 std::memory_order_acq_rel);
746 3290 if (prev != select_registration_state::unregistered)
747 {
748 3290 state.read_op = nullptr;
749
750 3290 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 3290 op->perform_io();
764 }
765
766 3290 completed_ops_.push(op);
767 3290 ++completions_queued;
768 }
769 }
770
771 // Process write readiness
772 12572 if (state.write_op && (FD_ISSET(fd, &write_fds) || has_error))
773 {
774 3172 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 3172 auto prev = op->registered.exchange(
778 select_registration_state::unregistered,
779 std::memory_order_acq_rel);
780 3172 if (prev != select_registration_state::unregistered)
781 {
782 3172 state.write_op = nullptr;
783
784 3172 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 3172 op->perform_io();
798 }
799
800 3172 completed_ops_.push(op);
801 3172 ++completions_queued;
802 }
803 }
804
805 // Clean up empty entries
806 12572 if (!state.read_op && !state.write_op)
807 6462 registered_fds_.erase(it);
808 }
809 10002 }
810
811 135020 if (completions_queued > 0)
812 {
813 3295 if (completions_queued == 1)
814 128 wakeup_event_.notify_one();
815 else
816 3167 wakeup_event_.notify_all();
817 }
818 135020 }
819
820 inline std::size_t
821 256246 select_scheduler::do_one(long timeout_us)
822 {
823 256246 std::unique_lock lock(mutex_);
824
825 for (;;)
826 {
827 391266 if (stopped_.load(std::memory_order_acquire))
828 112 return 0;
829
830 391154 scheduler_op* op = completed_ops_.pop();
831
832 391154 if (op == &task_op_)
833 {
834 135022 bool more_handlers = !completed_ops_.empty();
835
836 135022 if (!more_handlers)
837 {
838 19272 if (outstanding_work_.load(std::memory_order_acquire) == 0)
839 {
840 ✗ completed_ops_.push(&task_op_);
841 ✗ return 0;
842 }
843 9636 if (timeout_us == 0)
844 {
845 2 completed_ops_.push(&task_op_);
846 2 return 0;
847 }
848 }
849
850 135020 reactor_interrupted_ = more_handlers || timeout_us == 0;
851 135020 reactor_running_ = true;
852
853 135020 if (more_handlers && idle_thread_count_ > 0)
854 ✗ wakeup_event_.notify_one();
855
856 135020 run_reactor(lock);
857
858 135020 reactor_running_ = false;
859 135020 completed_ops_.push(&task_op_);
860 135020 continue;
861 135020 }
862
863 256132 if (op != nullptr)
864 {
865 256132 lock.unlock();
866 256132 select::work_guard g{this};
867 256132 (*op)();
868 256132 return 1;
869 256132 }
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 135020 }
884 256246 }
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