. /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   3472 timer_service::callback(this, [](void* p) { 189   3396 timer_service::callback(this, [](void* p) {
HITCBC 190   2881 static_cast<select_scheduler*>(p)->interrupt_reactor(); 190   2805 static_cast<select_scheduler*>(p)->interrupt_reactor();
HITCBC 191   2881 })); 191   2805 }));
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   4426 select_scheduler::register_descriptor( 219   4338 select_scheduler::register_descriptor(
220   int fd, reactor_descriptor_state* desc) const 220   int fd, reactor_descriptor_state* desc) const
221   { 221   {
HITCBC 222   4426 if (fd < 0 || fd >= FD_SETSIZE) 222   4338 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   4426 desc->registered_events = reactor_event_read | reactor_event_write; 225   4338 desc->registered_events = reactor_event_read | reactor_event_write;
HITCBC 226   4426 desc->fd = fd; 226   4338 desc->fd = fd;
HITCBC 227   4426 desc->scheduler_ = this; 227   4338 desc->scheduler_ = this;
HITCBC 228   4426 desc->mutex.set_enabled(reactor_io_locking_); 228   4338 desc->mutex.set_enabled(reactor_io_locking_);
HITCBC 229   4426 desc->ready_events_.store(0, std::memory_order_relaxed); 229   4338 desc->ready_events_.store(0, std::memory_order_relaxed);
230   230  
231   { 231   {
HITCBC 232   4426 conditionally_enabled_mutex::scoped_lock lock(desc->mutex); 232   4338 conditionally_enabled_mutex::scoped_lock lock(desc->mutex);
HITCBC 233   4426 desc->impl_ref_.reset(); 233   4338 desc->impl_ref_.reset();
HITCBC 234   4426 desc->read_ready = false; 234   4338 desc->read_ready = false;
HITCBC 235   4426 desc->write_ready = false; 235   4338 desc->write_ready = false;
HITCBC 236   4426 } 236   4338 }
237   237  
238   { 238   {
HITCBC 239   4426 mutex_type::scoped_lock lock(mutex_); 239   4338 mutex_type::scoped_lock lock(mutex_);
HITCBC 240   4426 registered_descs_[fd] = desc; 240   4338 registered_descs_[fd] = desc;
HITCBC 241   4426 if (fd > max_fd_) 241   4338 if (fd > max_fd_)
HITCBC 242   4421 max_fd_ = fd; 242   4333 max_fd_ = fd;
HITCBC 243   4426 } 243   4338 }
244   244  
HITCBC 245   4426 interrupt_reactor(); 245   4338 interrupt_reactor();
HITCBC 246   4426 } 246   4338 }
247   247  
248   inline void 248   inline void
HITCBC 249   4385 select_scheduler::deregister_descriptor(int fd) const 249   4297 select_scheduler::deregister_descriptor(int fd) const
250   { 250   {
HITCBC 251   4385 mutex_type::scoped_lock lock(mutex_); 251   4297 mutex_type::scoped_lock lock(mutex_);
252   252  
HITCBC 253   4385 auto it = registered_descs_.find(fd); 253   4297 auto it = registered_descs_.find(fd);
HITCBC 254   4385 if (it == registered_descs_.end()) 254   4297 if (it == registered_descs_.end())
MISUBC 255   ✗ return; 255   ✗ return;
256   256  
HITCBC 257   4385 registered_descs_.erase(it); 257   4297 registered_descs_.erase(it);
258   258  
HITCBC 259   4385 if (fd == max_fd_) 259   4297 if (fd == max_fd_)
260   { 260   {
HITCBC 261   4264 max_fd_ = pipe_fds_[0]; 261   4176 max_fd_ = pipe_fds_[0];
HITCBC 262   8274 for (auto& [registered_fd, state] : registered_descs_) 262   8098 for (auto& [registered_fd, state] : registered_descs_)
263   { 263   {
HITCBC 264   4010 if (registered_fd > max_fd_) 264   3922 if (registered_fd > max_fd_)
HITCBC 265   3963 max_fd_ = registered_fd; 265   3875 max_fd_ = registered_fd;
266   } 266   }
267   } 267   }
HITCBC 268   4385 } 268   4297 }
269   269  
270   inline void 270   inline void
HITCBC 271   2095 select_scheduler::notify_reactor() const 271   2051 select_scheduler::notify_reactor() const
272   { 272   {
HITCBC 273   2095 interrupt_reactor(); 273   2051 interrupt_reactor();
HITCBC 274   2095 } 274   2051 }
275   275  
276   inline void 276   inline void
HITCBC 277   10453 select_scheduler::interrupt_reactor() const 277   10245 select_scheduler::interrupt_reactor() const
278   { 278   {
HITCBC 279   10453 char byte = 1; 279   10245 char byte = 1;
HITCBC 280   10453 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1); 280   10245 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
HITCBC 281   10453 } 281   10245 }
282   282  
283   inline long 283   inline long
HITCBC 284   201892 select_scheduler::calculate_timeout(long requested_timeout_us) const 284   225114 select_scheduler::calculate_timeout(long requested_timeout_us) const
285   { 285   {
HITCBC 286   201892 if (requested_timeout_us == 0) 286   225114 if (requested_timeout_us == 0)
MISUBC 287   ✗ return 0; 287   ✗ return 0;
288   288  
HITCBC 289   201892 auto nearest = timer_svc_->nearest_expiry(); 289   225114 auto nearest = timer_svc_->nearest_expiry();
HITCBC 290   201892 if (nearest == timer_service::time_point::max()) 290   225114 if (nearest == timer_service::time_point::max())
HITCBC 291   566 return requested_timeout_us; 291   568 return requested_timeout_us;
292   292  
HITCBC 293   201326 auto now = std::chrono::steady_clock::now(); 293   224546 auto now = std::chrono::steady_clock::now();
HITCBC 294   201326 if (nearest <= now) 294   224546 if (nearest <= now)
HITCBC 295   497 return 0; 295   604 return 0;
296   296  
297   auto timer_timeout_us = 297   auto timer_timeout_us =
HITCBC 298   200829 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now) 298   223942 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
HITCBC 299   200829 .count(); 299   223942 .count();
300   300  
HITCBC 301   200829 constexpr auto long_max = 301   223942 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   200829 (std::min)((std::max)(static_cast<long long>(timer_timeout_us), 304   223942 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
HITCBC 305   200829 static_cast<long long>(0)), 305   223942 static_cast<long long>(0)),
HITCBC 306   200829 long_max); 306   223942 long_max);
307   307  
HITCBC 308   200829 if (requested_timeout_us < 0) 308   223942 if (requested_timeout_us < 0)
HITCBC 309   200829 return static_cast<long>(capped_timer_us); 309   223942 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   223568 select_scheduler::run_task( 317   248981 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   223568 task_interrupted_ ? 0 : calculate_timeout(timeout_us); 321   248981 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   223568 int snapshot_count = 0; 335   248981 int snapshot_count = 0;
336   336  
HITCBC 337   596074 for (auto& [fd, desc] : registered_descs_) 337   656439 for (auto& [fd, desc] : registered_descs_)
338   { 338   {
HITCBC 339   372506 if (snapshot_count < FD_SETSIZE) 339   407458 if (snapshot_count < FD_SETSIZE)
340   { 340   {
HITCBC 341   372506 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex); 341   407458 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex);
HITCBC 342   372506 snapshot[snapshot_count].fd = fd; 342   407458 snapshot[snapshot_count].fd = fd;
HITCBC 343   372506 snapshot[snapshot_count].desc = desc; 343   407458 snapshot[snapshot_count].desc = desc;
HITCBC 344   372506 snapshot[snapshot_count].needs_write = 344   407458 snapshot[snapshot_count].needs_write =
HITCBC 345   372506 (desc->write_op || desc->connect_op); 345   407458 (desc->write_op || desc->connect_op);
HITCBC 346   372506 ++snapshot_count; 346   407458 ++snapshot_count;
HITCBC 347   372506 } 347   407458 }
348   } 348   }
349   349  
HITCBC 350   223568 if (lock.owns_lock()) 350   248981 if (lock.owns_lock())
HITCBC 351   201893 lock.unlock(); 351   225115 lock.unlock();
352   352  
HITCBC 353   223568 task_cleanup on_exit{this, &lock, ctx}; 353   248981 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   3800656 FD_ZERO(&read_fds); 356   4232677 FD_ZERO(&read_fds);
HITCBC 357   3800656 FD_ZERO(&write_fds); 357   4232677 FD_ZERO(&write_fds);
HITCBC 358   3800656 FD_ZERO(&except_fds); 358   4232677 FD_ZERO(&except_fds);
359   359  
HITCBC 360   223568 FD_SET(pipe_fds_[0], &read_fds); 360   248981 FD_SET(pipe_fds_[0], &read_fds);
HITCBC 361   223568 int nfds = pipe_fds_[0]; 361   248981 int nfds = pipe_fds_[0];
362   362  
HITCBC 363   596074 for (int i = 0; i < snapshot_count; ++i) 363   656439 for (int i = 0; i < snapshot_count; ++i)
364   { 364   {
HITCBC 365   372506 int fd = snapshot[i].fd; 365   407458 int fd = snapshot[i].fd;
HITCBC 366   372506 FD_SET(fd, &read_fds); 366   407458 FD_SET(fd, &read_fds);
HITCBC 367   372506 if (snapshot[i].needs_write) 367   407458 if (snapshot[i].needs_write)
HITCBC 368   12732 FD_SET(fd, &write_fds); 368   12892 FD_SET(fd, &write_fds);
HITCBC 369   372506 FD_SET(fd, &except_fds); 369   407458 FD_SET(fd, &except_fds);
HITCBC 370   372506 if (fd > nfds) 370   407458 if (fd > nfds)
HITCBC 371   223243 nfds = fd; 371   248653 nfds = fd;
372   } 372   }
373   373  
374   struct timeval tv; 374   struct timeval tv;
HITCBC 375   223568 struct timeval* tv_ptr = nullptr; 375   248981 struct timeval* tv_ptr = nullptr;
HITCBC 376   223568 if (effective_timeout_us >= 0) 376   248981 if (effective_timeout_us >= 0)
377   { 377   {
HITCBC 378   223006 tv.tv_sec = effective_timeout_us / 1000000; 378   248417 tv.tv_sec = effective_timeout_us / 1000000;
HITCBC 379   223006 tv.tv_usec = effective_timeout_us % 1000000; 379   248417 tv.tv_usec = effective_timeout_us % 1000000;
HITCBC 380   223006 tv_ptr = &tv; 380   248417 tv_ptr = &tv;
381   } 381   }
382   382  
HITCBC 383   223568 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr); 383   248981 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   223568 if (ready < 0) 388   248981 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   223568 timer_svc_->process_expired(); 396   248981 timer_svc_->process_expired();
397   397  
HITCBC 398   223568 ready_queue local_ops; 398   248981 ready_queue local_ops;
399   399  
HITCBC 400   223568 if (ready > 0) 400   248981 if (ready > 0)
401   { 401   {
HITCBC 402   208278 if (FD_ISSET(pipe_fds_[0], &read_fds)) 402   232588 if (FD_ISSET(pipe_fds_[0], &read_fds))
403   { 403   {
404   char buf[256]; 404   char buf[256];
HITCBC 405   9324 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0) 405   9160 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
406   { 406   {
407   } 407   }
408   } 408   }
409   409  
HITCBC 410   534771 for (int i = 0; i < snapshot_count; ++i) 410   590472 for (int i = 0; i < snapshot_count; ++i)
411   { 411   {
HITCBC 412   326493 int fd = snapshot[i].fd; 412   357884 int fd = snapshot[i].fd;
HITCBC 413   326493 reactor_descriptor_state* desc = snapshot[i].desc; 413   357884 reactor_descriptor_state* desc = snapshot[i].desc;
414   414  
HITCBC 415   326493 std::uint32_t flags = 0; 415   357884 std::uint32_t flags = 0;
HITCBC 416   326493 if (FD_ISSET(fd, &read_fds)) 416   357884 if (FD_ISSET(fd, &read_fds))
HITCBC 417   205860 flags |= reactor_event_read; 417   230210 flags |= reactor_event_read;
HITCBC 418   326493 if (FD_ISSET(fd, &write_fds)) 418   357884 if (FD_ISSET(fd, &write_fds))
HITCBC 419   2092 flags |= reactor_event_write; 419   2048 flags |= reactor_event_write;
HITCBC 420   326493 if (FD_ISSET(fd, &except_fds)) 420   357884 if (FD_ISSET(fd, &except_fds))
MISUBC 421   ✗ flags |= reactor_event_error; 421   ✗ flags |= reactor_event_error;
422   422  
HITCBC 423   326493 if (flags == 0) 423   357884 if (flags == 0)
HITCBC 424   118551 continue; 424   125636 continue;
425   425  
HITCBC 426   207942 desc->add_ready_events(flags); 426   232248 desc->add_ready_events(flags);
427   427  
HITCBC 428   207942 bool expected = false; 428   232248 bool expected = false;
HITCBC 429   207942 if (desc->is_enqueued_.compare_exchange_strong( 429   232248 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   207942 local_ops.push(desc); 433   232248 local_ops.push(desc);
434   } 434   }
435   } 435   }
436   } 436   }
437   437  
HITCBC 438   223568 lock.lock(); 438   248981 lock.lock();
439   439  
HITCBC 440   223568 completed_ops_.splice(local_ops); 440   248981 completed_ops_.splice(local_ops);
HITCBC 441   223568 } 441   248981 }
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