. /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   591 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
HITCBC 155   591 : pipe_fds_{-1, -1} 155   591 : pipe_fds_{-1, -1}
HITCBC 156   591 , max_fd_(-1) 156   591 , max_fd_(-1)
157   { 157   {
HITCBC 158   591 if (::pipe(pipe_fds_) < 0) 158   591 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   1773 for (int i = 0; i < 2; ++i)
162   { 162   {
HITCBC 163   1182 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0); 163   1182 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
HITCBC 164   1182 if (flags == -1) 164   1182 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   1182 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   1182 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   591 timer_svc_ = &get_timer_service(ctx, *this);
HITCBC 188   591 timer_svc_->set_on_earliest_changed( 188   591 timer_svc_->set_on_earliest_changed(
HITCBC 189   3326 timer_service::callback(this, [](void* p) { 189   3332 timer_service::callback(this, [](void* p) {
HITCBC 190   2735 static_cast<select_scheduler*>(p)->interrupt_reactor(); 190   2741 static_cast<select_scheduler*>(p)->interrupt_reactor();
HITCBC 191   2735 })); 191   2741 }));
192   192  
HITCBC 193   591 get_resolver_service(ctx, *this); 193   591 get_resolver_service(ctx, *this);
HITCBC 194   591 get_signal_service(ctx, *this); 194   591 get_signal_service(ctx, *this);
HITCBC 195   591 get_stream_file_service(ctx, *this); 195   591 get_stream_file_service(ctx, *this);
HITCBC 196   591 get_random_access_file_service(ctx, *this); 196   591 get_random_access_file_service(ctx, *this);
197   197  
HITCBC 198   591 completed_ops_.push(&task_op_); 198   591 completed_ops_.push(&task_op_);
HITCBC 199   591 } 199   591 }
200   200  
HITCBC 201   1182 inline select_scheduler::~select_scheduler() 201   1182 inline select_scheduler::~select_scheduler()
202   { 202   {
HITCBC 203   591 if (pipe_fds_[0] >= 0) 203   591 if (pipe_fds_[0] >= 0)
HITCBC 204   591 ::close(pipe_fds_[0]); 204   591 ::close(pipe_fds_[0]);
HITCBC 205   591 if (pipe_fds_[1] >= 0) 205   591 if (pipe_fds_[1] >= 0)
HITCBC 206   591 ::close(pipe_fds_[1]); 206   591 ::close(pipe_fds_[1]);
HITCBC 207   1182 } 207   1182 }
208   208  
209   inline void 209   inline void
HITCBC 210   591 select_scheduler::shutdown() 210   591 select_scheduler::shutdown()
211   { 211   {
HITCBC 212   591 shutdown_drain(); 212   591 shutdown_drain();
213   213  
HITCBC 214   591 if (pipe_fds_[1] >= 0) 214   591 if (pipe_fds_[1] >= 0)
HITCBC 215   591 interrupt_reactor(); 215   591 interrupt_reactor();
HITCBC 216   591 } 216   591 }
217   217  
218   inline void 218   inline void
HITCBC 219   4387 select_scheduler::register_descriptor( 219   4346 select_scheduler::register_descriptor(
220   int fd, reactor_descriptor_state* desc) const 220   int fd, reactor_descriptor_state* desc) const
221   { 221   {
HITCBC 222   4387 if (fd < 0 || fd >= FD_SETSIZE) 222   4346 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   4387 desc->registered_events = reactor_event_read | reactor_event_write; 225   4346 desc->registered_events = reactor_event_read | reactor_event_write;
HITCBC 226   4387 desc->fd = fd; 226   4346 desc->fd = fd;
HITCBC 227   4387 desc->scheduler_ = this; 227   4346 desc->scheduler_ = this;
HITCBC 228   4387 desc->mutex.set_enabled(reactor_io_locking_); 228   4346 desc->mutex.set_enabled(reactor_io_locking_);
HITCBC 229   4387 desc->ready_events_.store(0, std::memory_order_relaxed); 229   4346 desc->ready_events_.store(0, std::memory_order_relaxed);
230   230  
231   { 231   {
HITCBC 232   4387 conditionally_enabled_mutex::scoped_lock lock(desc->mutex); 232   4346 conditionally_enabled_mutex::scoped_lock lock(desc->mutex);
HITCBC 233   4387 desc->impl_ref_.reset(); 233   4346 desc->impl_ref_.reset();
HITCBC 234   4387 desc->read_ready = false; 234   4346 desc->read_ready = false;
HITCBC 235   4387 desc->write_ready = false; 235   4346 desc->write_ready = false;
HITCBC 236   4387 } 236   4346 }
237   237  
238   { 238   {
HITCBC 239   4387 mutex_type::scoped_lock lock(mutex_); 239   4346 mutex_type::scoped_lock lock(mutex_);
HITCBC 240   4387 registered_descs_[fd] = desc; 240   4346 registered_descs_[fd] = desc;
HITCBC 241   4387 if (fd > max_fd_) 241   4346 if (fd > max_fd_)
HITCBC 242   4382 max_fd_ = fd; 242   4341 max_fd_ = fd;
HITCBC 243   4387 } 243   4346 }
244   244  
HITCBC 245   4387 interrupt_reactor(); 245   4346 interrupt_reactor();
HITCBC 246   4387 } 246   4346 }
247   247  
248   inline void 248   inline void
HITCBC 249   4346 select_scheduler::deregister_descriptor(int fd) const 249   4305 select_scheduler::deregister_descriptor(int fd) const
250   { 250   {
HITCBC 251   4346 mutex_type::scoped_lock lock(mutex_); 251   4305 mutex_type::scoped_lock lock(mutex_);
252   252  
HITCBC 253   4346 auto it = registered_descs_.find(fd); 253   4305 auto it = registered_descs_.find(fd);
HITCBC 254   4346 if (it == registered_descs_.end()) 254   4305 if (it == registered_descs_.end())
MISUBC 255   ✗ return; 255   ✗ return;
256   256  
HITCBC 257   4346 registered_descs_.erase(it); 257   4305 registered_descs_.erase(it);
258   258  
HITCBC 259   4346 if (fd == max_fd_) 259   4305 if (fd == max_fd_)
260   { 260   {
HITCBC 261   4224 max_fd_ = pipe_fds_[0]; 261   4184 max_fd_ = pipe_fds_[0];
HITCBC 262   8194 for (auto& [registered_fd, state] : registered_descs_) 262   8114 for (auto& [registered_fd, state] : registered_descs_)
263   { 263   {
HITCBC 264   3970 if (registered_fd > max_fd_) 264   3930 if (registered_fd > max_fd_)
HITCBC 265   3923 max_fd_ = registered_fd; 265   3883 max_fd_ = registered_fd;
266   } 266   }
267   } 267   }
HITCBC 268   4346 } 268   4305 }
269   269  
270   inline void 270   inline void
HITCBC 271   2076 select_scheduler::notify_reactor() const 271   2055 select_scheduler::notify_reactor() const
272   { 272   {
HITCBC 273   2076 interrupt_reactor(); 273   2055 interrupt_reactor();
HITCBC 274   2076 } 274   2055 }
275   275  
276   inline void 276   inline void
HITCBC 277   10249 select_scheduler::interrupt_reactor() const 277   10190 select_scheduler::interrupt_reactor() const
278   { 278   {
HITCBC 279   10249 char byte = 1; 279   10190 char byte = 1;
HITCBC 280   10249 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1); 280   10190 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
HITCBC 281   10249 } 281   10190 }
282   282  
283   inline long 283   inline long
HITCBC 284   193751 select_scheduler::calculate_timeout(long requested_timeout_us) const 284   193495 select_scheduler::calculate_timeout(long requested_timeout_us) const
285   { 285   {
HITCBC 286   193751 if (requested_timeout_us == 0) 286   193495 if (requested_timeout_us == 0)
MISUBC 287   ✗ return 0; 287   ✗ return 0;
288   288  
HITCBC 289   193751 auto nearest = timer_svc_->nearest_expiry(); 289   193495 auto nearest = timer_svc_->nearest_expiry();
HITCBC 290   193751 if (nearest == timer_service::time_point::max()) 290   193495 if (nearest == timer_service::time_point::max())
HITCBC 291   570 return requested_timeout_us; 291   565 return requested_timeout_us;
292   292  
HITCBC 293   193181 auto now = std::chrono::steady_clock::now(); 293   192930 auto now = std::chrono::steady_clock::now();
HITCBC 294   193181 if (nearest <= now) 294   192930 if (nearest <= now)
HITCBC 295   638 return 0; 295   576 return 0;
296   296  
297   auto timer_timeout_us = 297   auto timer_timeout_us =
HITCBC 298   192543 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now) 298   192354 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
HITCBC 299   192543 .count(); 299   192354 .count();
300   300  
HITCBC 301   192543 constexpr auto long_max = 301   192354 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   192543 (std::min)((std::max)(static_cast<long long>(timer_timeout_us), 304   192354 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
HITCBC 305   192543 static_cast<long long>(0)), 305   192354 static_cast<long long>(0)),
HITCBC 306   192543 long_max); 306   192354 long_max);
307   307  
HITCBC 308   192543 if (requested_timeout_us < 0) 308   192354 if (requested_timeout_us < 0)
HITCBC 309   192543 return static_cast<long>(capped_timer_us); 309   192354 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   216863 select_scheduler::run_task( 317   216020 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   216863 task_interrupted_ ? 0 : calculate_timeout(timeout_us); 321   216020 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   216863 int snapshot_count = 0; 335   216020 int snapshot_count = 0;
336   336  
HITCBC 337   578635 for (auto& [fd, desc] : registered_descs_) 337   585317 for (auto& [fd, desc] : registered_descs_)
338   { 338   {
HITCBC 339   361772 if (snapshot_count < FD_SETSIZE) 339   369297 if (snapshot_count < FD_SETSIZE)
340   { 340   {
HITCBC 341   361772 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex); 341   369297 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex);
HITCBC 342   361772 snapshot[snapshot_count].fd = fd; 342   369297 snapshot[snapshot_count].fd = fd;
HITCBC 343   361772 snapshot[snapshot_count].desc = desc; 343   369297 snapshot[snapshot_count].desc = desc;
HITCBC 344   361772 snapshot[snapshot_count].needs_write = 344   369297 snapshot[snapshot_count].needs_write =
HITCBC 345   361772 (desc->write_op || desc->connect_op); 345   369297 (desc->write_op || desc->connect_op);
HITCBC 346   361772 ++snapshot_count; 346   369297 ++snapshot_count;
HITCBC 347   361772 } 347   369297 }
348   } 348   }
349   349  
HITCBC 350   216863 if (lock.owns_lock()) 350   216020 if (lock.owns_lock())
HITCBC 351   193752 lock.unlock(); 351   193496 lock.unlock();
352   352  
HITCBC 353   216863 task_cleanup on_exit{this, &lock, ctx}; 353   216020 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   3686671 FD_ZERO(&read_fds); 356   3672340 FD_ZERO(&read_fds);
HITCBC 357   3686671 FD_ZERO(&write_fds); 357   3672340 FD_ZERO(&write_fds);
HITCBC 358   3686671 FD_ZERO(&except_fds); 358   3672340 FD_ZERO(&except_fds);
359   359  
HITCBC 360   216863 FD_SET(pipe_fds_[0], &read_fds); 360   216020 FD_SET(pipe_fds_[0], &read_fds);
HITCBC 361   216863 int nfds = pipe_fds_[0]; 361   216020 int nfds = pipe_fds_[0];
362   362  
HITCBC 363   578635 for (int i = 0; i < snapshot_count; ++i) 363   585317 for (int i = 0; i < snapshot_count; ++i)
364   { 364   {
HITCBC 365   361772 int fd = snapshot[i].fd; 365   369297 int fd = snapshot[i].fd;
HITCBC 366   361772 FD_SET(fd, &read_fds); 366   369297 FD_SET(fd, &read_fds);
HITCBC 367   361772 if (snapshot[i].needs_write) 367   369297 if (snapshot[i].needs_write)
HITCBC 368   12249 FD_SET(fd, &write_fds); 368   12922 FD_SET(fd, &write_fds);
HITCBC 369   361772 FD_SET(fd, &except_fds); 369   369297 FD_SET(fd, &except_fds);
HITCBC 370   361772 if (fd > nfds) 370   369297 if (fd > nfds)
HITCBC 371   216537 nfds = fd; 371   215700 nfds = fd;
372   } 372   }
373   373  
374   struct timeval tv; 374   struct timeval tv;
HITCBC 375   216863 struct timeval* tv_ptr = nullptr; 375   216020 struct timeval* tv_ptr = nullptr;
HITCBC 376   216863 if (effective_timeout_us >= 0) 376   216020 if (effective_timeout_us >= 0)
377   { 377   {
HITCBC 378   216297 tv.tv_sec = effective_timeout_us / 1000000; 378   215459 tv.tv_sec = effective_timeout_us / 1000000;
HITCBC 379   216297 tv.tv_usec = effective_timeout_us % 1000000; 379   215459 tv.tv_usec = effective_timeout_us % 1000000;
HITCBC 380   216297 tv_ptr = &tv; 380   215459 tv_ptr = &tv;
381   } 381   }
382   382  
HITCBC 383   216863 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr); 383   216020 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   216863 if (ready < 0) 388   216020 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   216863 timer_svc_->process_expired(); 396   216020 timer_svc_->process_expired();
397   397  
HITCBC 398   216863 ready_queue local_ops; 398   216020 ready_queue local_ops;
399   399  
HITCBC 400   216863 if (ready > 0) 400   216020 if (ready > 0)
401   { 401   {
HITCBC 402   200770 if (FD_ISSET(pipe_fds_[0], &read_fds)) 402   200255 if (FD_ISSET(pipe_fds_[0], &read_fds))
403   { 403   {
404   char buf[256]; 404   char buf[256];
HITCBC 405   9254 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0) 405   9162 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
406   { 406   {
407   } 407   }
408   } 408   }
409   409  
HITCBC 410   512518 for (int i = 0; i < snapshot_count; ++i) 410   520635 for (int i = 0; i < snapshot_count; ++i)
411   { 411   {
HITCBC 412   311748 int fd = snapshot[i].fd; 412   320380 int fd = snapshot[i].fd;
HITCBC 413   311748 reactor_descriptor_state* desc = snapshot[i].desc; 413   320380 reactor_descriptor_state* desc = snapshot[i].desc;
414   414  
HITCBC 415   311748 std::uint32_t flags = 0; 415   320380 std::uint32_t flags = 0;
HITCBC 416   311748 if (FD_ISSET(fd, &read_fds)) 416   320380 if (FD_ISSET(fd, &read_fds))
HITCBC 417   198368 flags |= reactor_event_read; 417   197879 flags |= reactor_event_read;
HITCBC 418   311748 if (FD_ISSET(fd, &write_fds)) 418   320380 if (FD_ISSET(fd, &write_fds))
HITCBC 419   2073 flags |= reactor_event_write; 419   2052 flags |= reactor_event_write;
HITCBC 420   311748 if (FD_ISSET(fd, &except_fds)) 420   320380 if (FD_ISSET(fd, &except_fds))
MISUBC 421   ✗ flags |= reactor_event_error; 421   ✗ flags |= reactor_event_error;
422   422  
HITCBC 423   311748 if (flags == 0) 423   320380 if (flags == 0)
HITCBC 424   111318 continue; 424   120459 continue;
425   425  
HITCBC 426   200430 desc->add_ready_events(flags); 426   199921 desc->add_ready_events(flags);
427   427  
HITCBC 428   200430 bool expected = false; 428   199921 bool expected = false;
HITCBC 429   200430 if (desc->is_enqueued_.compare_exchange_strong( 429   199921 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   200430 local_ops.push(desc); 433   199921 local_ops.push(desc);
434   } 434   }
435   } 435   }
436   } 436   }
437   437  
HITCBC 438   216863 lock.lock(); 438   216020 lock.lock();
439   439  
HITCBC 440   216863 completed_ops_.splice(local_ops); 440   216020 completed_ops_.splice(local_ops);
HITCBC 441   216863 } 441   216020 }
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