. /include/boost/corosio /native /detail /select /select_scheduler.hpp
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1   // 1   //
2   // Copyright (c) 2026 Steve Gerbino 2   // Copyright (c) 2026 Steve Gerbino
3   // Copyright (c) 2026 Michael Vandeberg 3   // Copyright (c) 2026 Michael Vandeberg
4   // 4   //
5   // Distributed under the Boost Software License, Version 1.0. (See accompanying 5   // Distributed under the Boost Software License, Version 1.0. (See accompanying
6   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 6   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7   // 7   //
8   // Official repository: https://github.com/cppalliance/corosio 8   // Official repository: https://github.com/cppalliance/corosio
9   // 9   //
10   10  
11   #ifndef BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP 11   #ifndef BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP
12   #define BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP 12   #define BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP
13   13  
14   #include <boost/corosio/detail/platform.hpp> 14   #include <boost/corosio/detail/platform.hpp>
15   15  
16   #if BOOST_COROSIO_HAS_SELECT 16   #if BOOST_COROSIO_HAS_SELECT
17   17  
18   #include <boost/corosio/detail/config.hpp> 18   #include <boost/corosio/detail/config.hpp>
19   #include <boost/capy/ex/execution_context.hpp> 19   #include <boost/capy/ex/execution_context.hpp>
20   20  
21   #include <boost/corosio/native/detail/reactor/reactor_scheduler.hpp> 21   #include <boost/corosio/native/detail/reactor/reactor_scheduler.hpp>
22   #include <boost/corosio/native/detail/reactor/reactor_signal_pipe.hpp> 22   #include <boost/corosio/native/detail/reactor/reactor_signal_pipe.hpp>
23   23  
24   #include <boost/corosio/native/detail/select/select_traits.hpp> 24   #include <boost/corosio/native/detail/select/select_traits.hpp>
25   #include <boost/corosio/detail/timer_service.hpp> 25   #include <boost/corosio/detail/timer_service.hpp>
26   #include <boost/corosio/native/detail/make_err.hpp> 26   #include <boost/corosio/native/detail/make_err.hpp>
27   #include <boost/corosio/native/detail/posix/posix_resolver_service.hpp> 27   #include <boost/corosio/native/detail/posix/posix_resolver_service.hpp>
28   #include <boost/corosio/native/detail/posix/posix_signal_service.hpp> 28   #include <boost/corosio/native/detail/posix/posix_signal_service.hpp>
29   #include <boost/corosio/native/detail/posix/posix_stream_file_service.hpp> 29   #include <boost/corosio/native/detail/posix/posix_stream_file_service.hpp>
30   #include <boost/corosio/native/detail/posix/posix_random_access_file_service.hpp> 30   #include <boost/corosio/native/detail/posix/posix_random_access_file_service.hpp>
31   31  
32   #include <boost/corosio/detail/except.hpp> 32   #include <boost/corosio/detail/except.hpp>
33   33  
34   #include <sys/select.h> 34   #include <sys/select.h>
35   #include <unistd.h> 35   #include <unistd.h>
36   #include <errno.h> 36   #include <errno.h>
37   #include <fcntl.h> 37   #include <fcntl.h>
38   38  
39   #include <atomic> 39   #include <atomic>
40   #include <chrono> 40   #include <chrono>
41   #include <cstdint> 41   #include <cstdint>
42   #include <limits> 42   #include <limits>
43   #include <mutex> 43   #include <mutex>
44   #include <unordered_map> 44   #include <unordered_map>
45   45  
46   namespace boost::corosio::detail { 46   namespace boost::corosio::detail {
47   47  
48   struct select_op; 48   struct select_op;
49   49  
50   /** POSIX scheduler using select() for I/O multiplexing. 50   /** POSIX scheduler using select() for I/O multiplexing.
51   51  
52   This scheduler implements the scheduler interface using the POSIX select() 52   This scheduler implements the scheduler interface using the POSIX select()
53   call for I/O event notification. It inherits the shared reactor threading 53   call for I/O event notification. It inherits the shared reactor threading
54   model from reactor_scheduler: signal state machine, inline completion 54   model from reactor_scheduler: signal state machine, inline completion
55   budget, work counting, and the do_one event loop. 55   budget, work counting, and the do_one event loop.
56   56  
57   The design mirrors epoll_scheduler for behavioral consistency: 57   The design mirrors epoll_scheduler for behavioral consistency:
58   - Same single-reactor thread coordination model 58   - Same single-reactor thread coordination model
59   - Same deferred I/O pattern (reactor marks ready; workers do I/O) 59   - Same deferred I/O pattern (reactor marks ready; workers do I/O)
60   - Same timer integration pattern 60   - Same timer integration pattern
61   61  
62   Known Limitations: 62   Known Limitations:
63   - FD_SETSIZE (~1024) limits maximum concurrent connections 63   - FD_SETSIZE (~1024) limits maximum concurrent connections
64   - O(n) scanning: rebuilds fd_sets each iteration 64   - O(n) scanning: rebuilds fd_sets each iteration
65   - Level-triggered only (no edge-triggered mode) 65   - Level-triggered only (no edge-triggered mode)
66   66  
67   @par Thread Safety 67   @par Thread Safety
68   All public member functions are thread-safe. 68   All public member functions are thread-safe.
69   */ 69   */
70   class BOOST_COROSIO_DECL select_scheduler final : public reactor_scheduler 70   class BOOST_COROSIO_DECL select_scheduler final : public reactor_scheduler
71   { 71   {
72   public: 72   public:
73   /** Construct the scheduler. 73   /** Construct the scheduler.
74   74  
75   Creates a self-pipe for reactor interruption. 75   Creates a self-pipe for reactor interruption.
76   76  
77   @param ctx Reference to the owning execution_context. 77   @param ctx Reference to the owning execution_context.
78   @param concurrency_hint Hint for expected thread count (unused). 78   @param concurrency_hint Hint for expected thread count (unused).
79   */ 79   */
80   select_scheduler(capy::execution_context& ctx, int concurrency_hint = -1); 80   select_scheduler(capy::execution_context& ctx, int concurrency_hint = -1);
81   81  
82   /// Destroy the scheduler. 82   /// Destroy the scheduler.
83   ~select_scheduler() override; 83   ~select_scheduler() override;
84   84  
85   select_scheduler(select_scheduler const&) = delete; 85   select_scheduler(select_scheduler const&) = delete;
86   select_scheduler& operator=(select_scheduler const&) = delete; 86   select_scheduler& operator=(select_scheduler const&) = delete;
87   87  
88   /// Shut down the scheduler, draining pending operations. 88   /// Shut down the scheduler, draining pending operations.
89   void shutdown() override; 89   void shutdown() override;
90   90  
91   /** Return the maximum file descriptor value supported. 91   /** Return the maximum file descriptor value supported.
92   92  
93   Returns FD_SETSIZE - 1, the maximum fd value that can be 93   Returns FD_SETSIZE - 1, the maximum fd value that can be
94   monitored by select(). Operations with fd >= FD_SETSIZE 94   monitored by select(). Operations with fd >= FD_SETSIZE
95   will fail with EINVAL. 95   will fail with EINVAL.
96   96  
97   @return The maximum supported file descriptor value. 97   @return The maximum supported file descriptor value.
98   */ 98   */
99   static constexpr int max_fd() noexcept 99   static constexpr int max_fd() noexcept
100   { 100   {
101   return FD_SETSIZE - 1; 101   return FD_SETSIZE - 1;
102   } 102   }
103   103  
104   /** Register a descriptor for persistent monitoring. 104   /** Register a descriptor for persistent monitoring.
105   105  
106   The fd is added to the registered_descs_ map and will be 106   The fd is added to the registered_descs_ map and will be
107   included in subsequent select() calls. The reactor is 107   included in subsequent select() calls. The reactor is
108   interrupted so a blocked select() rebuilds its fd_sets. 108   interrupted so a blocked select() rebuilds its fd_sets.
109   109  
110   @param fd The file descriptor to register. 110   @param fd The file descriptor to register.
111   @param desc Pointer to descriptor state for this fd. 111   @param desc Pointer to descriptor state for this fd.
112   */ 112   */
113   void register_descriptor(int fd, reactor_descriptor_state* desc) const; 113   void register_descriptor(int fd, reactor_descriptor_state* desc) const;
114   114  
115   /** Deregister a persistently registered descriptor. 115   /** Deregister a persistently registered descriptor.
116   116  
117   @param fd The file descriptor to deregister. 117   @param fd The file descriptor to deregister.
118   */ 118   */
119   void deregister_descriptor(int fd) const; 119   void deregister_descriptor(int fd) const;
120   120  
121   /** Interrupt the reactor so it rebuilds its fd_sets. 121   /** Interrupt the reactor so it rebuilds its fd_sets.
122   122  
123   Called when a write or connect op is registered after 123   Called when a write or connect op is registered after
124   the reactor's snapshot was taken. Without this, select() 124   the reactor's snapshot was taken. Without this, select()
125   may block not watching for writability on the fd. 125   may block not watching for writability on the fd.
126   */ 126   */
127   void notify_reactor() const; 127   void notify_reactor() const;
128   128  
129   /// Watch the read end of the POSIX signal self-pipe (see scheduler.hpp). 129   /// Watch the read end of the POSIX signal self-pipe (see scheduler.hpp).
HITCBC 130   41 void register_signal_reader(int read_fd) override 130   41 void register_signal_reader(int read_fd) override
131   { 131   {
HITCBC 132   41 register_descriptor(read_fd, signal_pipe_reader_.arm()); 132   41 register_descriptor(read_fd, signal_pipe_reader_.arm());
HITCBC 133   41 } 133   41 }
134   134  
135   private: 135   private:
136   void 136   void
137   run_task(lock_type& lock, context_type* ctx, 137   run_task(lock_type& lock, context_type* ctx,
138   long timeout_us) override; 138   long timeout_us) override;
139   void interrupt_reactor() const override; 139   void interrupt_reactor() const override;
140   long calculate_timeout(long requested_timeout_us) const; 140   long calculate_timeout(long requested_timeout_us) const;
141   141  
142   // Watches the global signal self-pipe's read end (armed lazily by 142   // Watches the global signal self-pipe's read end (armed lazily by
143   // register_signal_reader on the first signal registration). 143   // register_signal_reader on the first signal registration).
144   reactor_signal_pipe_reader signal_pipe_reader_; 144   reactor_signal_pipe_reader signal_pipe_reader_;
145   145  
146   // Self-pipe for interrupting select() 146   // Self-pipe for interrupting select()
147   int pipe_fds_[2]; // [0]=read, [1]=write 147   int pipe_fds_[2]; // [0]=read, [1]=write
148   148  
149   // Per-fd tracking for fd_set building 149   // Per-fd tracking for fd_set building
150   mutable std::unordered_map<int, reactor_descriptor_state*> registered_descs_; 150   mutable std::unordered_map<int, reactor_descriptor_state*> registered_descs_;
151   mutable int max_fd_ = -1; 151   mutable int max_fd_ = -1;
152   }; 152   };
153   153  
HITCBC 154   591 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int) 154   605 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
HITCBC 155   591 : pipe_fds_{-1, -1} 155   605 : pipe_fds_{-1, -1}
HITCBC 156   591 , max_fd_(-1) 156   605 , max_fd_(-1)
157   { 157   {
HITCBC 158   591 if (::pipe(pipe_fds_) < 0) 158   605 if (::pipe(pipe_fds_) < 0)
MISUBC 159   ✗ detail::throw_system_error(make_err(errno), "pipe"); 159   ✗ detail::throw_system_error(make_err(errno), "pipe");
160   160  
HITCBC 161   1773 for (int i = 0; i < 2; ++i) 161   1815 for (int i = 0; i < 2; ++i)
162   { 162   {
HITCBC 163   1182 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0); 163   1210 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
HITCBC 164   1182 if (flags == -1) 164   1210 if (flags == -1)
165   { 165   {
MISUBC 166   ✗ int errn = errno; 166   ✗ int errn = errno;
MISUBC 167   ✗ ::close(pipe_fds_[0]); 167   ✗ ::close(pipe_fds_[0]);
MISUBC 168   ✗ ::close(pipe_fds_[1]); 168   ✗ ::close(pipe_fds_[1]);
MISUBC 169   ✗ detail::throw_system_error(make_err(errn), "fcntl F_GETFL"); 169   ✗ detail::throw_system_error(make_err(errn), "fcntl F_GETFL");
170   } 170   }
HITCBC 171   1182 if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1) 171   1210 if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1)
172   { 172   {
MISUBC 173   ✗ int errn = errno; 173   ✗ int errn = errno;
MISUBC 174   ✗ ::close(pipe_fds_[0]); 174   ✗ ::close(pipe_fds_[0]);
MISUBC 175   ✗ ::close(pipe_fds_[1]); 175   ✗ ::close(pipe_fds_[1]);
MISUBC 176   ✗ detail::throw_system_error(make_err(errn), "fcntl F_SETFL"); 176   ✗ detail::throw_system_error(make_err(errn), "fcntl F_SETFL");
177   } 177   }
HITCBC 178   1182 if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1) 178   1210 if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1)
179   { 179   {
MISUBC 180   ✗ int errn = errno; 180   ✗ int errn = errno;
MISUBC 181   ✗ ::close(pipe_fds_[0]); 181   ✗ ::close(pipe_fds_[0]);
MISUBC 182   ✗ ::close(pipe_fds_[1]); 182   ✗ ::close(pipe_fds_[1]);
MISUBC 183   ✗ detail::throw_system_error(make_err(errn), "fcntl F_SETFD"); 183   ✗ detail::throw_system_error(make_err(errn), "fcntl F_SETFD");
184   } 184   }
185   } 185   }
186   186  
HITCBC 187   591 timer_svc_ = &get_timer_service(ctx, *this); 187   605 timer_svc_ = &get_timer_service(ctx, *this);
HITCBC 188   591 timer_svc_->set_on_earliest_changed( 188   605 timer_svc_->set_on_earliest_changed(
HITCBC 189   2848 timer_service::callback(this, [](void* p) { 189   5079 timer_service::callback(this, [](void* p) {
HITCBC 190   2257 static_cast<select_scheduler*>(p)->interrupt_reactor(); 190   4474 static_cast<select_scheduler*>(p)->interrupt_reactor();
HITCBC 191   2257 })); 191   4474 }));
192   192  
HITCBC 193   591 get_resolver_service(ctx, *this); 193   605 get_resolver_service(ctx, *this);
HITCBC 194   591 get_signal_service(ctx, *this); 194   605 get_signal_service(ctx, *this);
HITCBC 195   591 get_stream_file_service(ctx, *this); 195   605 get_stream_file_service(ctx, *this);
HITCBC 196   591 get_random_access_file_service(ctx, *this); 196   605 get_random_access_file_service(ctx, *this);
197   197  
HITCBC 198   591 completed_ops_.push(&task_op_); 198   605 completed_ops_.push(&task_op_);
HITCBC 199   591 } 199   605 }
200   200  
HITCBC 201   1182 inline select_scheduler::~select_scheduler() 201   1210 inline select_scheduler::~select_scheduler()
202   { 202   {
HITCBC 203   591 if (pipe_fds_[0] >= 0) 203   605 if (pipe_fds_[0] >= 0)
HITCBC 204   591 ::close(pipe_fds_[0]); 204   605 ::close(pipe_fds_[0]);
HITCBC 205   591 if (pipe_fds_[1] >= 0) 205   605 if (pipe_fds_[1] >= 0)
HITCBC 206   591 ::close(pipe_fds_[1]); 206   605 ::close(pipe_fds_[1]);
HITCBC 207   1182 } 207   1210 }
208   208  
209   inline void 209   inline void
HITCBC 210   591 select_scheduler::shutdown() 210   605 select_scheduler::shutdown()
211   { 211   {
HITCBC 212   591 shutdown_drain(); 212   605 shutdown_drain();
213   213  
HITCBC 214   591 if (pipe_fds_[1] >= 0) 214   605 if (pipe_fds_[1] >= 0)
HITCBC 215   591 interrupt_reactor(); 215   605 interrupt_reactor();
HITCBC 216   591 } 216   605 }
217   217  
218   inline void 218   inline void
HITCBC 219   3176 select_scheduler::register_descriptor( 219   7592 select_scheduler::register_descriptor(
220   int fd, reactor_descriptor_state* desc) const 220   int fd, reactor_descriptor_state* desc) const
221   { 221   {
HITCBC 222   3176 if (fd < 0 || fd >= FD_SETSIZE) 222   7592 if (fd < 0 || fd >= FD_SETSIZE)
MISUBC 223   ✗ detail::throw_system_error(make_err(EINVAL), "select: fd out of range"); 223   ✗ detail::throw_system_error(make_err(EINVAL), "select: fd out of range");
224   224  
HITCBC 225   3176 desc->registered_events = reactor_event_read | reactor_event_write; 225   7592 desc->registered_events = reactor_event_read | reactor_event_write;
HITCBC 226   3176 desc->fd = fd; 226   7592 desc->fd = fd;
HITCBC 227   3176 desc->scheduler_ = this; 227   7592 desc->scheduler_ = this;
HITCBC 228   3176 desc->mutex.set_enabled(reactor_io_locking_); 228   7592 desc->mutex.set_enabled(reactor_io_locking_);
HITCBC 229   3176 desc->ready_events_.store(0, std::memory_order_relaxed); 229   7592 desc->ready_events_.store(0, std::memory_order_relaxed);
230   230  
231   { 231   {
HITCBC 232   3176 conditionally_enabled_mutex::scoped_lock lock(desc->mutex); 232   7592 conditionally_enabled_mutex::scoped_lock lock(desc->mutex);
HITCBC 233   3176 desc->impl_ref_.reset(); 233   7592 desc->impl_ref_.reset();
HITCBC 234   3176 desc->read_ready = false; 234   7592 desc->read_ready = false;
HITCBC 235   3176 desc->write_ready = false; 235   7592 desc->write_ready = false;
HITCBC 236   3176 } 236   7592 }
237   237  
238   { 238   {
HITCBC 239   3176 mutex_type::scoped_lock lock(mutex_); 239   7592 mutex_type::scoped_lock lock(mutex_);
HITCBC 240   3176 registered_descs_[fd] = desc; 240   7592 registered_descs_[fd] = desc;
HITCBC 241   3176 if (fd > max_fd_) 241   7592 if (fd > max_fd_)
HITCBC 242   3171 max_fd_ = fd; 242   7587 max_fd_ = fd;
HITCBC 243   3176 } 243   7592 }
244   244  
HITCBC 245   3176 interrupt_reactor(); 245   7592 interrupt_reactor();
HITCBC 246   3176 } 246   7592 }
247   247  
248   inline void 248   inline void
HITCBC 249   3135 select_scheduler::deregister_descriptor(int fd) const 249   7551 select_scheduler::deregister_descriptor(int fd) const
250   { 250   {
HITCBC 251   3135 mutex_type::scoped_lock lock(mutex_); 251   7551 mutex_type::scoped_lock lock(mutex_);
252   252  
HITCBC 253   3135 auto it = registered_descs_.find(fd); 253   7551 auto it = registered_descs_.find(fd);
HITCBC 254   3135 if (it == registered_descs_.end()) 254   7551 if (it == registered_descs_.end())
MISUBC 255   ✗ return; 255   ✗ return;
256   256  
HITCBC 257   3135 registered_descs_.erase(it); 257   7551 registered_descs_.erase(it);
258   258  
HITCBC 259   3135 if (fd == max_fd_) 259   7551 if (fd == max_fd_)
260   { 260   {
HITCBC 261   3014 max_fd_ = pipe_fds_[0]; 261   7430 max_fd_ = pipe_fds_[0];
HITCBC 262   5774 for (auto& [registered_fd, state] : registered_descs_) 262   14606 for (auto& [registered_fd, state] : registered_descs_)
263   { 263   {
HITCBC 264   2760 if (registered_fd > max_fd_) 264   7176 if (registered_fd > max_fd_)
HITCBC 265   2713 max_fd_ = registered_fd; 265   7129 max_fd_ = registered_fd;
266   } 266   }
267   } 267   }
HITCBC 268   3135 } 268   7551 }
269   269  
270   inline void 270   inline void
HITCBC 271   1470 select_scheduler::notify_reactor() const 271   3678 select_scheduler::notify_reactor() const
272   { 272   {
HITCBC 273   1470 interrupt_reactor(); 273   3678 interrupt_reactor();
HITCBC 274   1470 } 274   3678 }
275   275  
276   inline void 276   inline void
HITCBC 277   7954 select_scheduler::interrupt_reactor() const 277   16819 select_scheduler::interrupt_reactor() const
278   { 278   {
HITCBC 279   7954 char byte = 1; 279   16819 char byte = 1;
HITCBC 280   7954 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1); 280   16819 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
HITCBC 281   7954 } 281   16819 }
282   282  
283   inline long 283   inline long
HITCBC 284   187832 select_scheduler::calculate_timeout(long requested_timeout_us) const 284   284810 select_scheduler::calculate_timeout(long requested_timeout_us) const
285   { 285   {
HITCBC 286   187832 if (requested_timeout_us == 0) 286   284810 if (requested_timeout_us == 0)
MISUBC 287   ✗ return 0; 287   ✗ return 0;
288   288  
HITCBC 289   187832 auto nearest = timer_svc_->nearest_expiry(); 289   284810 auto nearest = timer_svc_->nearest_expiry();
HITCBC 290   187832 if (nearest == timer_service::time_point::max()) 290   284810 if (nearest == timer_service::time_point::max())
HITCBC 291   567 return requested_timeout_us; 291   572 return requested_timeout_us;
292   292  
HITCBC 293   187265 auto now = std::chrono::steady_clock::now(); 293   284238 auto now = std::chrono::steady_clock::now();
HITCBC 294   187265 if (nearest <= now) 294   284238 if (nearest <= now)
HITCBC 295   423 return 0; 295   907 return 0;
296   296  
297   auto timer_timeout_us = 297   auto timer_timeout_us =
HITCBC 298   186842 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now) 298   283331 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
HITCBC 299   186842 .count(); 299   283331 .count();
300   300  
HITCBC 301   186842 constexpr auto long_max = 301   283331 constexpr auto long_max =
302   static_cast<long long>((std::numeric_limits<long>::max)()); 302   static_cast<long long>((std::numeric_limits<long>::max)());
303   auto capped_timer_us = 303   auto capped_timer_us =
HITCBC 304   186842 (std::min)((std::max)(static_cast<long long>(timer_timeout_us), 304   283331 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
HITCBC 305   186842 static_cast<long long>(0)), 305   283331 static_cast<long long>(0)),
HITCBC 306   186842 long_max); 306   283331 long_max);
307   307  
HITCBC 308   186842 if (requested_timeout_us < 0) 308   283331 if (requested_timeout_us < 0)
HITCBC 309   186842 return static_cast<long>(capped_timer_us); 309   283331 return static_cast<long>(capped_timer_us);
310   310  
311   return static_cast<long>( 311   return static_cast<long>(
MISUBC 312   ✗ (std::min)(static_cast<long long>(requested_timeout_us), 312   ✗ (std::min)(static_cast<long long>(requested_timeout_us),
MISUBC 313   ✗ capped_timer_us)); 313   ✗ capped_timer_us));
314   } 314   }
315   315  
316   inline void 316   inline void
HITCBC 317   211492 select_scheduler::run_task( 317   317423 select_scheduler::run_task(
318   lock_type& lock, context_type* ctx, long timeout_us) 318   lock_type& lock, context_type* ctx, long timeout_us)
319   { 319   {
320   long effective_timeout_us = 320   long effective_timeout_us =
HITCBC 321   211492 task_interrupted_ ? 0 : calculate_timeout(timeout_us); 321   317423 task_interrupted_ ? 0 : calculate_timeout(timeout_us);
322   322  
323   // Snapshot registered descriptors while holding lock. 323   // Snapshot registered descriptors while holding lock.
324   // Record which fds need write monitoring to avoid a hot loop: 324   // Record which fds need write monitoring to avoid a hot loop:
325   // select is level-triggered so writable sockets (nearly always 325   // select is level-triggered so writable sockets (nearly always
326   // writable) would cause select() to return immediately every 326   // writable) would cause select() to return immediately every
327   // iteration if unconditionally added to write_fds. 327   // iteration if unconditionally added to write_fds.
328   struct fd_entry 328   struct fd_entry
329   { 329   {
330   int fd; 330   int fd;
331   reactor_descriptor_state* desc; 331   reactor_descriptor_state* desc;
332   bool needs_write; 332   bool needs_write;
333   }; 333   };
334   fd_entry snapshot[FD_SETSIZE]; 334   fd_entry snapshot[FD_SETSIZE];
HITCBC 335   211492 int snapshot_count = 0; 335   317423 int snapshot_count = 0;
336   336  
HITCBC 337   553869 for (auto& [fd, desc] : registered_descs_) 337   836065 for (auto& [fd, desc] : registered_descs_)
338   { 338   {
HITCBC 339   342377 if (snapshot_count < FD_SETSIZE) 339   518642 if (snapshot_count < FD_SETSIZE)
340   { 340   {
HITCBC 341   342377 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex); 341   518642 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex);
HITCBC 342   342377 snapshot[snapshot_count].fd = fd; 342   518642 snapshot[snapshot_count].fd = fd;
HITCBC 343   342377 snapshot[snapshot_count].desc = desc; 343   518642 snapshot[snapshot_count].desc = desc;
HITCBC 344   342377 snapshot[snapshot_count].needs_write = 344   518642 snapshot[snapshot_count].needs_write =
HITCBC 345   342377 (desc->write_op || desc->connect_op); 345   518642 (desc->write_op || desc->connect_op);
HITCBC 346   342377 ++snapshot_count; 346   518642 ++snapshot_count;
HITCBC 347   342377 } 347   518642 }
348   } 348   }
349   349  
HITCBC 350   211492 if (lock.owns_lock()) 350   317423 if (lock.owns_lock())
HITCBC 351   187833 lock.unlock(); 351   284811 lock.unlock();
352   352  
HITCBC 353   211492 task_cleanup on_exit{this, &lock, ctx}; 353   317423 task_cleanup on_exit{this, &lock, ctx};
354   354  
355   fd_set read_fds, write_fds, except_fds; 355   fd_set read_fds, write_fds, except_fds;
HITCBC 356   3595364 FD_ZERO(&read_fds); 356   5396191 FD_ZERO(&read_fds);
HITCBC 357   3595364 FD_ZERO(&write_fds); 357   5396191 FD_ZERO(&write_fds);
HITCBC 358   3595364 FD_ZERO(&except_fds); 358   5396191 FD_ZERO(&except_fds);
359   359  
HITCBC 360   211492 FD_SET(pipe_fds_[0], &read_fds); 360   317423 FD_SET(pipe_fds_[0], &read_fds);
HITCBC 361   211492 int nfds = pipe_fds_[0]; 361   317423 int nfds = pipe_fds_[0];
362   362  
HITCBC 363   553869 for (int i = 0; i < snapshot_count; ++i) 363   836065 for (int i = 0; i < snapshot_count; ++i)
364   { 364   {
HITCBC 365   342377 int fd = snapshot[i].fd; 365   518642 int fd = snapshot[i].fd;
HITCBC 366   342377 FD_SET(fd, &read_fds); 366   518642 FD_SET(fd, &read_fds);
HITCBC 367   342377 if (snapshot[i].needs_write) 367   518642 if (snapshot[i].needs_write)
HITCBC 368   10155 FD_SET(fd, &write_fds); 368   13530 FD_SET(fd, &write_fds);
HITCBC 369   342377 FD_SET(fd, &except_fds); 369   518642 FD_SET(fd, &except_fds);
HITCBC 370   342377 if (fd > nfds) 370   518642 if (fd > nfds)
HITCBC 371   211174 nfds = fd; 371   317065 nfds = fd;
372   } 372   }
373   373  
374   struct timeval tv; 374   struct timeval tv;
HITCBC 375   211492 struct timeval* tv_ptr = nullptr; 375   317423 struct timeval* tv_ptr = nullptr;
HITCBC 376   211492 if (effective_timeout_us >= 0) 376   317423 if (effective_timeout_us >= 0)
377   { 377   {
HITCBC 378   210929 tv.tv_sec = effective_timeout_us / 1000000; 378   316854 tv.tv_sec = effective_timeout_us / 1000000;
HITCBC 379   210929 tv.tv_usec = effective_timeout_us % 1000000; 379   316854 tv.tv_usec = effective_timeout_us % 1000000;
HITCBC 380   210929 tv_ptr = &tv; 380   316854 tv_ptr = &tv;
381   } 381   }
382   382  
HITCBC 383   211492 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr); 383   317423 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr);
384   384  
385   // EINTR: signal interrupted select(), just retry. 385   // EINTR: signal interrupted select(), just retry.
386   // EBADF: an fd was closed between snapshot and select(); retry 386   // EBADF: an fd was closed between snapshot and select(); retry
387   // with a fresh snapshot from registered_descs_. 387   // with a fresh snapshot from registered_descs_.
HITCBC 388   211492 if (ready < 0) 388   317423 if (ready < 0)
389   { 389   {
MISUBC 390   ✗ if (errno == EINTR || errno == EBADF) 390   ✗ if (errno == EINTR || errno == EBADF)
MISUBC 391   ✗ return; 391   ✗ return;
MISUBC 392   ✗ detail::throw_system_error(make_err(errno), "select"); 392   ✗ detail::throw_system_error(make_err(errno), "select");
393   } 393   }
394   394  
395   // Process timers outside the lock 395   // Process timers outside the lock
HITCBC 396   211492 timer_svc_->process_expired(); 396   317423 timer_svc_->process_expired();
397   397  
HITCBC 398   211492 ready_queue local_ops; 398   317423 ready_queue local_ops;
399   399  
HITCBC 400   211492 if (ready > 0) 400   317423 if (ready > 0)
401   { 401   {
HITCBC 402   196037 if (FD_ISSET(pipe_fds_[0], &read_fds)) 402   294383 if (FD_ISSET(pipe_fds_[0], &read_fds))
403   { 403   {
404   char buf[256]; 404   char buf[256];
HITCBC 405   6818 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0) 405   15709 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
406   { 406   {
407   } 407   }
408   } 408   }
409   409  
HITCBC 410   490310 for (int i = 0; i < snapshot_count; ++i) 410   749346 for (int i = 0; i < snapshot_count; ++i)
411   { 411   {
HITCBC 412   294273 int fd = snapshot[i].fd; 412   454963 int fd = snapshot[i].fd;
HITCBC 413   294273 reactor_descriptor_state* desc = snapshot[i].desc; 413   454963 reactor_descriptor_state* desc = snapshot[i].desc;
414   414  
HITCBC 415   294273 std::uint32_t flags = 0; 415   454963 std::uint32_t flags = 0;
HITCBC 416   294273 if (FD_ISSET(fd, &read_fds)) 416   454963 if (FD_ISSET(fd, &read_fds))
HITCBC 417   194246 flags |= reactor_event_read; 417   290364 flags |= reactor_event_read;
HITCBC 418   294273 if (FD_ISSET(fd, &write_fds)) 418   454963 if (FD_ISSET(fd, &write_fds))
HITCBC 419   1467 flags |= reactor_event_write; 419   3675 flags |= reactor_event_write;
HITCBC 420   294273 if (FD_ISSET(fd, &except_fds)) 420   454963 if (FD_ISSET(fd, &except_fds))
MISUBC 421   ✗ flags |= reactor_event_error; 421   ✗ flags |= reactor_event_error;
422   422  
HITCBC 423   294273 if (flags == 0) 423   454963 if (flags == 0)
HITCBC 424   98570 continue; 424   160934 continue;
425   425  
HITCBC 426   195703 desc->add_ready_events(flags); 426   294029 desc->add_ready_events(flags);
427   427  
HITCBC 428   195703 bool expected = false; 428   294029 bool expected = false;
HITCBC 429   195703 if (desc->is_enqueued_.compare_exchange_strong( 429   294029 if (desc->is_enqueued_.compare_exchange_strong(
430   expected, true, std::memory_order_release, 430   expected, true, std::memory_order_release,
431   std::memory_order_relaxed)) 431   std::memory_order_relaxed))
432   { 432   {
HITCBC 433   195703 local_ops.push(desc); 433   294029 local_ops.push(desc);
434   } 434   }
435   } 435   }
436   } 436   }
437   437  
HITCBC 438   211492 lock.lock(); 438   317423 lock.lock();
439   439  
HITCBC 440   211492 completed_ops_.splice(local_ops); 440   317423 completed_ops_.splice(local_ops);
HITCBC 441   211492 } 441   317423 }
442   442  
443   } // namespace boost::corosio::detail 443   } // namespace boost::corosio::detail
444   444  
445   #endif // BOOST_COROSIO_HAS_SELECT 445   #endif // BOOST_COROSIO_HAS_SELECT
446   446  
447   #endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP 447   #endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP