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
234 127 explicit thread_context_guard(select_scheduler const* ctx) noexcept
235 127 : frame_{ctx, context_stack.get()}
236 {
237 127 context_stack.set(&frame_);
238 127 }
239
240 127 ~thread_context_guard() noexcept
241 {
242 127 context_stack.set(frame_.next);
243 127 }
244 };
245
246 struct work_guard
247 {
248 select_scheduler* self;
249 154054 ~work_guard()
250 {
251 154054 self->work_finished();
252 154054 }
253 };
254
255 } // namespace select
256
257 139 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
258 139 : pipe_fds_{-1, -1}
259 139 , outstanding_work_(0)
260 139 , stopped_(false)
261 139 , max_fd_(-1)
262 139 , reactor_running_(false)
263 139 , reactor_interrupted_(false)
264 278 , idle_thread_count_(0)
265 {
266 // Create self-pipe for interrupting select()
267 139 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
271 417 for (int i = 0; i < 2; ++i)
272 {
273 278 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
274 278 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 }
281 278 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 }
288 278 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
297 139 timer_svc_ = &get_timer_service(ctx, *this);
298 139 timer_svc_->set_on_earliest_changed(
299 3684 timer_service::callback(this, [](void* p) {
300 3545 static_cast<select_scheduler*>(p)->interrupt_reactor();
301 3545 }));
302
303 // Initialize resolver service
304 139 get_resolver_service(ctx, *this);
305
306 // Initialize signal service
307 139 get_signal_service(ctx, *this);
308
309 // Push task sentinel to interleave reactor runs with handler execution
310 139 completed_ops_.push(&task_op_);
311 139 }
312
313 278 inline select_scheduler::~select_scheduler()
314 {
315 139 if (pipe_fds_[0] >= 0)
316 139 ::close(pipe_fds_[0]);
317 139 if (pipe_fds_[1] >= 0)
318 139 ::close(pipe_fds_[1]);
319 278 }
320
321 inline void
322 139 select_scheduler::shutdown()
323 {
324 {
325 139 std::unique_lock lock(mutex_);
326
327 285 while (auto* h = completed_ops_.pop())
328 {
329 146 if (h == &task_op_)
330 139 continue;
331 7 lock.unlock();
332 7 h->destroy();
333 7 lock.lock();
334 146 }
335 139 }
336
337 139 if (pipe_fds_[1] >= 0)
338 139 interrupt_reactor();
339
340 139 wakeup_event_.notify_all();
341 139 }
342
343 inline void
344 3895 select_scheduler::post(std::coroutine_handle<> h) const
345 {
346 struct post_handler final : scheduler_op
347 {
348 std::coroutine_handle<> h_;
349
350 3895 explicit post_handler(std::coroutine_handle<> h) : h_(h) {}
351
352 7790 ~post_handler() override = default;
353
354 3892 void operator()() override
355 {
356 3892 auto h = h_;
357 3892 delete this;
358 3892 h.resume();
359 3892 }
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 3895 auto ph = std::make_unique<post_handler>(h);
370 3895 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
371
372 3895 std::unique_lock lock(mutex_);
373 3895 completed_ops_.push(ph.release());
374 3895 wake_one_thread_and_unlock(lock);
375 3895 }
376
377 inline void
378 143389 select_scheduler::post(scheduler_op* h) const
379 {
380 143389 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
381
382 143389 std::unique_lock lock(mutex_);
383 143389 completed_ops_.push(h);
384 143389 wake_one_thread_and_unlock(lock);
385 143389 }
386
387 inline bool
388 564 select_scheduler::running_in_this_thread() const noexcept
389 {
390 564 for (auto* c = select::context_stack.get(); c != nullptr; c = c->next)
391 367 if (c->key == this)
392 367 return true;
393 197 return false;
394 }
395
396 inline void
397 105 select_scheduler::stop()
398 {
399 105 bool expected = false;
400 105 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 {
406 105 std::lock_guard lock(mutex_);
407 105 wakeup_event_.notify_all();
408 105 }
409 105 interrupt_reactor();
410 }
411 105 }
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 37 select_scheduler::restart()
421 {
422 37 stopped_.store(false, std::memory_order_release);
423 37 }
424
425 inline std::size_t
426 101 select_scheduler::run()
427 {
428 101 if (stopped_.load(std::memory_order_acquire))
429 ✗ return 0;
430
431 202 if (outstanding_work_.load(std::memory_order_acquire) == 0)
432 {
433 ✗ stop();
434 ✗ return 0;
435 }
436
437 101 select::thread_context_guard ctx(this);
438
439 101 std::size_t n = 0;
440 154129 while (do_one(-1))
441 154028 if (n != (std::numeric_limits<std::size_t>::max)())
442 154028 ++n;
443 101 return n;
444 101 }
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 6938 select_scheduler::register_fd(int fd, select_op* op, int events) const
517 {
518 // Validate fd is within select() limits
519 6938 if (fd < 0 || fd >= FD_SETSIZE)
520 ✗ detail::throw_system_error(make_err(EINVAL), "select: fd out of range");
521
522 {
523 6938 std::lock_guard lock(mutex_);
524
525 6938 auto& state = registered_fds_[fd];
526 6938 if (events & event_read)
527 3609 state.read_op = op;
528 6938 if (events & event_write)
529 3329 state.write_op = op;
530
531 6938 if (fd > max_fd_)
532 231 max_fd_ = fd;
533 6938 }
534
535 // Wake the reactor so a thread blocked in select() rebuilds its fd_sets
536 // with the newly registered fd.
537 6938 interrupt_reactor();
538 6938 }
539
540 inline void
541 6872 select_scheduler::deregister_fd(int fd, int events) const
542 {
543 6872 std::lock_guard lock(mutex_);
544
545 6872 auto it = registered_fds_.find(fd);
546 6872 if (it == registered_fds_.end())
547 6711 return;
548
549 161 if (events & event_read)
550 161 it->second.read_op = nullptr;
551 161 if (events & event_write)
552 ✗ it->second.write_op = nullptr;
553
554 // Remove entry if both are null
555 161 if (!it->second.read_op && !it->second.write_op)
556 {
557 161 registered_fds_.erase(it);
558
559 // Recalculate max_fd_ if needed
560 161 if (fd == max_fd_)
561 {
562 160 max_fd_ = pipe_fds_[0]; // At minimum, the pipe read end
563 160 for (auto& [registered_fd, state] : registered_fds_)
564 {
565 ✗ if (registered_fd > max_fd_)
566 ✗ max_fd_ = registered_fd;
567 }
568 }
569 }
570 6872 }
571
572 inline void
573 11071 select_scheduler::work_started() noexcept
574 {
575 11071 outstanding_work_.fetch_add(1, std::memory_order_relaxed);
576 11071 }
577
578 inline void
579 158348 select_scheduler::work_finished() noexcept
580 {
581 316696 if (outstanding_work_.fetch_sub(1, std::memory_order_acq_rel) == 1)
582 104 stop();
583 158348 }
584
585 inline void
586 14259 select_scheduler::interrupt_reactor() const
587 {
588 14259 char byte = 1;
589 14259 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
590 14259 }
591
592 inline void
593 147284 select_scheduler::wake_one_thread_and_unlock(
594 std::unique_lock<std::mutex>& lock) const
595 {
596 147284 if (idle_thread_count_ > 0)
597 {
598 // Idle worker exists - wake it via condvar
599 ✗ wakeup_event_.notify_one();
600 ✗ lock.unlock();
601 }
602 147284 else if (reactor_running_ && !reactor_interrupted_)
603 {
604 // No idle workers but reactor is running - interrupt it
605 3532 reactor_interrupted_ = true;
606 3532 lock.unlock();
607 3532 interrupt_reactor();
608 }
609 else
610 {
611 // No one to wake
612 143752 lock.unlock();
613 }
614 147284 }
615
616 inline long
617 10149 select_scheduler::calculate_timeout(long requested_timeout_us) const
618 {
619 10149 if (requested_timeout_us == 0)
620 ✗ return 0;
621
622 10149 auto nearest = timer_svc_->nearest_expiry();
623 10149 if (nearest == timer_service::time_point::max())
624 37 return requested_timeout_us;
625
626 10112 auto now = std::chrono::steady_clock::now();
627 10112 if (nearest <= now)
628 174 return 0;
629
630 auto timer_timeout_us =
631 9938 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
632 9938 .count();
633
634 // Clamp to [0, LONG_MAX] to prevent truncation on 32-bit long platforms
635 9938 constexpr auto long_max =
636 static_cast<long long>((std::numeric_limits<long>::max)());
637 auto capped_timer_us =
638 9938 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
639 9938 static_cast<long long>(0)),
640 9938 long_max);
641
642 9938 if (requested_timeout_us < 0)
643 9938 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 87054 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 87054 reactor_interrupted_ ? 0 : calculate_timeout(-1);
657
658 // Build fd_sets from registered_fds_
659 fd_set read_fds, write_fds, except_fds;
660 1479918 FD_ZERO(&read_fds);
661 1479918 FD_ZERO(&write_fds);
662 1479918 FD_ZERO(&except_fds);
663
664 // Always include the interrupt pipe
665 87054 FD_SET(pipe_fds_[0], &read_fds);
666 87054 int nfds = pipe_fds_[0];
667
668 // Add registered fds
669 103591 for (auto& [fd, state] : registered_fds_)
670 {
671 16537 if (state.read_op)
672 13208 FD_SET(fd, &read_fds);
673 16537 if (state.write_op)
674 {
675 3329 FD_SET(fd, &write_fds);
676 // Also monitor for errors on connect operations
677 3329 FD_SET(fd, &except_fds);
678 }
679 16537 if (fd > nfds)
680 13212 nfds = fd;
681 }
682
683 // Convert timeout to timeval
684 struct timeval tv;
685 87054 struct timeval* tv_ptr = nullptr;
686 87054 if (effective_timeout_us >= 0)
687 {
688 87017 tv.tv_sec = effective_timeout_us / 1000000;
689 87017 tv.tv_usec = effective_timeout_us % 1000000;
690 87017 tv_ptr = &tv;
691 }
692
693 87054 lock.unlock();
694
695 87054 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr);
696 87054 int saved_errno = errno;
697
698 // Process timers outside the lock
699 87054 timer_svc_->process_expired();
700
701 87054 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 87054 lock.lock();
706
707 // Drain the interrupt pipe if readable
708 87054 if (ready > 0 && FD_ISSET(pipe_fds_[0], &read_fds))
709 {
710 char buf[256];
711 21020 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
712 {
713 }
714 }
715
716 // Process I/O completions
717 87054 int completions_queued = 0;
718 87054 if (ready > 0)
719 {
720 // Iterate over registered fds (copy keys to avoid iterator invalidation)
721 10510 std::vector<int> fds_to_check;
722 10510 fds_to_check.reserve(registered_fds_.size());
723 23754 for (auto& [fd, state] : registered_fds_)
724 13244 fds_to_check.push_back(fd);
725
726 23754 for (int fd : fds_to_check)
727 {
728 13244 auto it = registered_fds_.find(fd);
729 13244 if (it == registered_fds_.end())
730 ✗ continue;
731
732 13244 auto& state = it->second;
733
734 // Check for errors (especially for connect operations)
735 13244 bool has_error = FD_ISSET(fd, &except_fds);
736
737 // Process read readiness
738 13244 if (state.read_op && (FD_ISSET(fd, &read_fds) || has_error))
739 {
740 3448 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 3448 auto prev = op->registered.exchange(
744 select_registration_state::unregistered,
745 std::memory_order_acq_rel);
746 3448 if (prev != select_registration_state::unregistered)
747 {
748 3448 state.read_op = nullptr;
749
750 3448 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 3448 op->perform_io();
764 }
765
766 3448 completed_ops_.push(op);
767 3448 ++completions_queued;
768 }
769 }
770
771 // Process write readiness
772 13244 if (state.write_op && (FD_ISSET(fd, &write_fds) || has_error))
773 {
774 3329 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 3329 auto prev = op->registered.exchange(
778 select_registration_state::unregistered,
779 std::memory_order_acq_rel);
780 3329 if (prev != select_registration_state::unregistered)
781 {
782 3329 state.write_op = nullptr;
783
784 3329 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 3329 op->perform_io();
798 }
799
800 3329 completed_ops_.push(op);
801 3329 ++completions_queued;
802 }
803 }
804
805 // Clean up empty entries
806 13244 if (!state.read_op && !state.write_op)
807 6777 registered_fds_.erase(it);
808 }
809 10510 }
810
811 87054 if (completions_queued > 0)
812 {
813 3452 if (completions_queued == 1)
814 127 wakeup_event_.notify_one();
815 else
816 3325 wakeup_event_.notify_all();
817 }
818 87054 }
819
820 inline std::size_t
821 154157 select_scheduler::do_one(long timeout_us)
822 {
823 154157 std::unique_lock lock(mutex_);
824
825 for (;;)
826 {
827 241211 if (stopped_.load(std::memory_order_acquire))
828 101 return 0;
829
830 241110 scheduler_op* op = completed_ops_.pop();
831
832 241110 if (op == &task_op_)
833 {
834 87056 bool more_handlers = !completed_ops_.empty();
835
836 87056 if (!more_handlers)
837 {
838 20302 if (outstanding_work_.load(std::memory_order_acquire) == 0)
839 {
840 ✗ completed_ops_.push(&task_op_);
841 ✗ return 0;
842 }
843 10151 if (timeout_us == 0)
844 {
845 2 completed_ops_.push(&task_op_);
846 2 return 0;
847 }
848 }
849
850 87054 reactor_interrupted_ = more_handlers || timeout_us == 0;
851 87054 reactor_running_ = true;
852
853 87054 if (more_handlers && idle_thread_count_ > 0)
854 ✗ wakeup_event_.notify_one();
855
856 87054 run_reactor(lock);
857
858 87054 reactor_running_ = false;
859 87054 completed_ops_.push(&task_op_);
860 87054 continue;
861 87054 }
862
863 154054 if (op != nullptr)
864 {
865 154054 lock.unlock();
866 154054 select::work_guard g{this};
867 154054 (*op)();
868 154054 return 1;
869 154054 }
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 87054 }
884 154157 }
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