. /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   580 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int) 154   584 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
HITCBC 155   580 : pipe_fds_{-1, -1} 155   584 : pipe_fds_{-1, -1}
HITCBC 156   580 , max_fd_(-1) 156   584 , max_fd_(-1)
157   { 157   {
HITCBC 158   580 if (::pipe(pipe_fds_) < 0) 158   584 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   1740 for (int i = 0; i < 2; ++i) 161   1752 for (int i = 0; i < 2; ++i)
162   { 162   {
HITCBC 163   1160 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0); 163   1168 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
HITCBC 164   1160 if (flags == -1) 164   1168 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   1160 if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1) 171   1168 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   1160 if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1) 178   1168 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   580 timer_svc_ = &get_timer_service(ctx, *this); 187   584 timer_svc_ = &get_timer_service(ctx, *this);
HITCBC 188   580 timer_svc_->set_on_earliest_changed( 188   584 timer_svc_->set_on_earliest_changed(
HITCBC 189   4500 timer_service::callback(this, [](void* p) { 189   3469 timer_service::callback(this, [](void* p) {
HITCBC 190   3920 static_cast<select_scheduler*>(p)->interrupt_reactor(); 190   2885 static_cast<select_scheduler*>(p)->interrupt_reactor();
HITCBC 191   3920 })); 191   2885 }));
192   192  
HITCBC 193   580 get_resolver_service(ctx, *this); 193   584 get_resolver_service(ctx, *this);
HITCBC 194   580 get_signal_service(ctx, *this); 194   584 get_signal_service(ctx, *this);
HITCBC 195   580 get_stream_file_service(ctx, *this); 195   584 get_stream_file_service(ctx, *this);
HITCBC 196   580 get_random_access_file_service(ctx, *this); 196   584 get_random_access_file_service(ctx, *this);
197   197  
HITCBC 198   580 completed_ops_.push(&task_op_); 198   584 completed_ops_.push(&task_op_);
HITCBC 199   580 } 199   584 }
200   200  
HITCBC 201   1160 inline select_scheduler::~select_scheduler() 201   1168 inline select_scheduler::~select_scheduler()
202   { 202   {
HITCBC 203   580 if (pipe_fds_[0] >= 0) 203   584 if (pipe_fds_[0] >= 0)
HITCBC 204   580 ::close(pipe_fds_[0]); 204   584 ::close(pipe_fds_[0]);
HITCBC 205   580 if (pipe_fds_[1] >= 0) 205   584 if (pipe_fds_[1] >= 0)
HITCBC 206   580 ::close(pipe_fds_[1]); 206   584 ::close(pipe_fds_[1]);
HITCBC 207   1160 } 207   1168 }
208   208  
209   inline void 209   inline void
HITCBC 210   580 select_scheduler::shutdown() 210   584 select_scheduler::shutdown()
211   { 211   {
HITCBC 212   580 shutdown_drain(); 212   584 shutdown_drain();
213   213  
HITCBC 214   580 if (pipe_fds_[1] >= 0) 214   584 if (pipe_fds_[1] >= 0)
HITCBC 215   580 interrupt_reactor(); 215   584 interrupt_reactor();
HITCBC 216   580 } 216   584 }
217   217  
218   inline void 218   inline void
HITCBC 219   6479 select_scheduler::register_descriptor( 219   4596 select_scheduler::register_descriptor(
220   int fd, reactor_descriptor_state* desc) const 220   int fd, reactor_descriptor_state* desc) const
221   { 221   {
HITCBC 222   6479 if (fd < 0 || fd >= FD_SETSIZE) 222   4596 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   6479 desc->registered_events = reactor_event_read | reactor_event_write; 225   4596 desc->registered_events = reactor_event_read | reactor_event_write;
HITCBC 226   6479 desc->fd = fd; 226   4596 desc->fd = fd;
HITCBC 227   6479 desc->scheduler_ = this; 227   4596 desc->scheduler_ = this;
HITCBC 228   6479 desc->mutex.set_enabled(reactor_io_locking_); 228   4596 desc->mutex.set_enabled(reactor_io_locking_);
HITCBC 229   6479 desc->ready_events_.store(0, std::memory_order_relaxed); 229   4596 desc->ready_events_.store(0, std::memory_order_relaxed);
230   230  
231   { 231   {
HITCBC 232   6479 conditionally_enabled_mutex::scoped_lock lock(desc->mutex); 232   4596 conditionally_enabled_mutex::scoped_lock lock(desc->mutex);
HITCBC 233   6479 desc->impl_ref_.reset(); 233   4596 desc->impl_ref_.reset();
HITCBC 234   6479 desc->read_ready = false; 234   4596 desc->read_ready = false;
HITCBC 235   6479 desc->write_ready = false; 235   4596 desc->write_ready = false;
HITCBC 236   6479 } 236   4596 }
237   237  
238   { 238   {
HITCBC 239   6479 mutex_type::scoped_lock lock(mutex_); 239   4596 mutex_type::scoped_lock lock(mutex_);
HITCBC 240   6479 registered_descs_[fd] = desc; 240   4596 registered_descs_[fd] = desc;
HITCBC 241   6479 if (fd > max_fd_) 241   4596 if (fd > max_fd_)
HITCBC 242   6474 max_fd_ = fd; 242   4591 max_fd_ = fd;
HITCBC 243   6479 } 243   4596 }
244   244  
HITCBC 245   6479 interrupt_reactor(); 245   4596 interrupt_reactor();
HITCBC 246   6479 } 246   4596 }
247   247  
248   inline void 248   inline void
HITCBC 249   6438 select_scheduler::deregister_descriptor(int fd) const 249   4555 select_scheduler::deregister_descriptor(int fd) const
250   { 250   {
HITCBC 251   6438 mutex_type::scoped_lock lock(mutex_); 251   4555 mutex_type::scoped_lock lock(mutex_);
252   252  
HITCBC 253   6438 auto it = registered_descs_.find(fd); 253   4555 auto it = registered_descs_.find(fd);
HITCBC 254   6438 if (it == registered_descs_.end()) 254   4555 if (it == registered_descs_.end())
MISUBC 255   ✗ return; 255   ✗ return;
256   256  
HITCBC 257   6438 registered_descs_.erase(it); 257   4555 registered_descs_.erase(it);
258   258  
HITCBC 259   6438 if (fd == max_fd_) 259   4555 if (fd == max_fd_)
260   { 260   {
HITCBC 261   6323 max_fd_ = pipe_fds_[0]; 261   4435 max_fd_ = pipe_fds_[0];
HITCBC 262   12397 for (auto& [registered_fd, state] : registered_descs_) 262   8617 for (auto& [registered_fd, state] : registered_descs_)
263   { 263   {
HITCBC 264   6074 if (registered_fd > max_fd_) 264   4182 if (registered_fd > max_fd_)
HITCBC 265   6027 max_fd_ = registered_fd; 265   4135 max_fd_ = registered_fd;
266   } 266   }
267   } 267   }
HITCBC 268   6438 } 268   4555 }
269   269  
270   inline void 270   inline void
HITCBC 271   3123 select_scheduler::notify_reactor() const 271   2181 select_scheduler::notify_reactor() const
272   { 272   {
HITCBC 273   3123 interrupt_reactor(); 273   2181 interrupt_reactor();
HITCBC 274   3123 } 274   2181 }
275   275  
276   inline void 276   inline void
HITCBC 277   14546 select_scheduler::interrupt_reactor() const 277   10714 select_scheduler::interrupt_reactor() const
278   { 278   {
HITCBC 279   14546 char byte = 1; 279   10714 char byte = 1;
HITCBC 280   14546 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1); 280   10714 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
HITCBC 281   14546 } 281   10714 }
282   282  
283   inline long 283   inline long
HITCBC 284   262860 select_scheduler::calculate_timeout(long requested_timeout_us) const 284   217261 select_scheduler::calculate_timeout(long requested_timeout_us) const
285   { 285   {
HITCBC 286   262860 if (requested_timeout_us == 0) 286   217261 if (requested_timeout_us == 0)
MISUBC 287   ✗ return 0; 287   ✗ return 0;
288   288  
HITCBC 289   262860 auto nearest = timer_svc_->nearest_expiry(); 289   217261 auto nearest = timer_svc_->nearest_expiry();
HITCBC 290   262860 if (nearest == timer_service::time_point::max()) 290   217261 if (nearest == timer_service::time_point::max())
HITCBC 291   567 return requested_timeout_us; 291   580 return requested_timeout_us;
292   292  
HITCBC 293   262293 auto now = std::chrono::steady_clock::now(); 293   216681 auto now = std::chrono::steady_clock::now();
HITCBC 294   262293 if (nearest <= now) 294   216681 if (nearest <= now)
HITCBC 295   855 return 0; 295   767 return 0;
296   296  
297   auto timer_timeout_us = 297   auto timer_timeout_us =
HITCBC 298   261438 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now) 298   215914 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
HITCBC 299   261438 .count(); 299   215914 .count();
300   300  
HITCBC 301   261438 constexpr auto long_max = 301   215914 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   261438 (std::min)((std::max)(static_cast<long long>(timer_timeout_us), 304   215914 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
HITCBC 305   261438 static_cast<long long>(0)), 305   215914 static_cast<long long>(0)),
HITCBC 306   261438 long_max); 306   215914 long_max);
307   307  
HITCBC 308   261438 if (requested_timeout_us < 0) 308   215914 if (requested_timeout_us < 0)
HITCBC 309   261438 return static_cast<long>(capped_timer_us); 309   215914 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   296676 select_scheduler::run_task( 317   237213 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   296676 task_interrupted_ ? 0 : calculate_timeout(timeout_us); 321   237213 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   296676 int snapshot_count = 0; 335   237213 int snapshot_count = 0;
336   336  
HITCBC 337   783183 for (auto& [fd, desc] : registered_descs_) 337   606963 for (auto& [fd, desc] : registered_descs_)
338   { 338   {
HITCBC 339   486507 if (snapshot_count < FD_SETSIZE) 339   369750 if (snapshot_count < FD_SETSIZE)
340   { 340   {
HITCBC 341   486507 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex); 341   369750 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex);
HITCBC 342   486507 snapshot[snapshot_count].fd = fd; 342   369750 snapshot[snapshot_count].fd = fd;
HITCBC 343   486507 snapshot[snapshot_count].desc = desc; 343   369750 snapshot[snapshot_count].desc = desc;
HITCBC 344   486507 snapshot[snapshot_count].needs_write = 344   369750 snapshot[snapshot_count].needs_write =
HITCBC 345   486507 (desc->write_op || desc->connect_op); 345   369750 (desc->write_op || desc->connect_op);
HITCBC 346   486507 ++snapshot_count; 346   369750 ++snapshot_count;
HITCBC 347   486507 } 347   369750 }
348   } 348   }
349   349  
HITCBC 350   296676 if (lock.owns_lock()) 350   237213 if (lock.owns_lock())
HITCBC 351   262861 lock.unlock(); 351   217262 lock.unlock();
352   352  
HITCBC 353   296676 task_cleanup on_exit{this, &lock, ctx}; 353   237213 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   5043492 FD_ZERO(&read_fds); 356   4032621 FD_ZERO(&read_fds);
HITCBC 357   5043492 FD_ZERO(&write_fds); 357   4032621 FD_ZERO(&write_fds);
HITCBC 358   5043492 FD_ZERO(&except_fds); 358   4032621 FD_ZERO(&except_fds);
359   359  
HITCBC 360   296676 FD_SET(pipe_fds_[0], &read_fds); 360   237213 FD_SET(pipe_fds_[0], &read_fds);
HITCBC 361   296676 int nfds = pipe_fds_[0]; 361   237213 int nfds = pipe_fds_[0];
362   362  
HITCBC 363   783183 for (int i = 0; i < snapshot_count; ++i) 363   606963 for (int i = 0; i < snapshot_count; ++i)
364   { 364   {
HITCBC 365   486507 int fd = snapshot[i].fd; 365   369750 int fd = snapshot[i].fd;
HITCBC 366   486507 FD_SET(fd, &read_fds); 366   369750 FD_SET(fd, &read_fds);
HITCBC 367   486507 if (snapshot[i].needs_write) 367   369750 if (snapshot[i].needs_write)
HITCBC 368   11282 FD_SET(fd, &write_fds); 368   7832 FD_SET(fd, &write_fds);
HITCBC 369   486507 FD_SET(fd, &except_fds); 369   369750 FD_SET(fd, &except_fds);
HITCBC 370   486507 if (fd > nfds) 370   369750 if (fd > nfds)
HITCBC 371   296360 nfds = fd; 371   236889 nfds = fd;
372   } 372   }
373   373  
374   struct timeval tv; 374   struct timeval tv;
HITCBC 375   296676 struct timeval* tv_ptr = nullptr; 375   237213 struct timeval* tv_ptr = nullptr;
HITCBC 376   296676 if (effective_timeout_us >= 0) 376   237213 if (effective_timeout_us >= 0)
377   { 377   {
HITCBC 378   296112 tv.tv_sec = effective_timeout_us / 1000000; 378   236637 tv.tv_sec = effective_timeout_us / 1000000;
HITCBC 379   296112 tv.tv_usec = effective_timeout_us % 1000000; 379   236637 tv.tv_usec = effective_timeout_us % 1000000;
HITCBC 380   296112 tv_ptr = &tv; 380   236637 tv_ptr = &tv;
381   } 381   }
382   382  
HITCBC 383   296676 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr); 383   237213 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   296676 if (ready < 0) 388   237213 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   296676 timer_svc_->process_expired(); 396   237213 timer_svc_->process_expired();
397   397  
HITCBC 398   296676 ready_queue local_ops; 398   237213 ready_queue local_ops;
399   399  
HITCBC 400   296676 if (ready > 0) 400   237213 if (ready > 0)
401   { 401   {
HITCBC 402   274019 if (FD_ISSET(pipe_fds_[0], &read_fds)) 402   222882 if (FD_ISSET(pipe_fds_[0], &read_fds))
403   { 403   {
404   char buf[256]; 404   char buf[256];
HITCBC 405   13450 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0) 405   9686 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
406   { 406   {
407   } 407   }
408   } 408   }
409   409  
HITCBC 410   699186 for (int i = 0; i < snapshot_count; ++i) 410   549683 for (int i = 0; i < snapshot_count; ++i)
411   { 411   {
HITCBC 412   425167 int fd = snapshot[i].fd; 412   326801 int fd = snapshot[i].fd;
HITCBC 413   425167 reactor_descriptor_state* desc = snapshot[i].desc; 413   326801 reactor_descriptor_state* desc = snapshot[i].desc;
414   414  
HITCBC 415   425167 std::uint32_t flags = 0; 415   326801 std::uint32_t flags = 0;
HITCBC 416   425167 if (FD_ISSET(fd, &read_fds)) 416   326801 if (FD_ISSET(fd, &read_fds))
HITCBC 417   270568 flags |= reactor_event_read; 417   220369 flags |= reactor_event_read;
HITCBC 418   425167 if (FD_ISSET(fd, &write_fds)) 418   326801 if (FD_ISSET(fd, &write_fds))
HITCBC 419   3120 flags |= reactor_event_write; 419   2178 flags |= reactor_event_write;
HITCBC 420   425167 if (FD_ISSET(fd, &except_fds)) 420   326801 if (FD_ISSET(fd, &except_fds))
MISUBC 421   ✗ flags |= reactor_event_error; 421   ✗ flags |= reactor_event_error;
422   422  
HITCBC 423   425167 if (flags == 0) 423   326801 if (flags == 0)
HITCBC 424   151488 continue; 424   104265 continue;
425   425  
HITCBC 426   273679 desc->add_ready_events(flags); 426   222536 desc->add_ready_events(flags);
427   427  
HITCBC 428   273679 bool expected = false; 428   222536 bool expected = false;
HITCBC 429   273679 if (desc->is_enqueued_.compare_exchange_strong( 429   222536 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   273679 local_ops.push(desc); 433   222536 local_ops.push(desc);
434   } 434   }
435   } 435   }
436   } 436   }
437   437  
HITCBC 438   296676 lock.lock(); 438   237213 lock.lock();
439   439  
HITCBC 440   296676 completed_ops_.splice(local_ops); 440   237213 completed_ops_.splice(local_ops);
HITCBC 441   296676 } 441   237213 }
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