. /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   27  
28   #include <boost/corosio/detail/except.hpp> 28   #include <boost/corosio/detail/except.hpp>
29   29  
30   #include <sys/select.h> 30   #include <sys/select.h>
31   #include <unistd.h> 31   #include <unistd.h>
32   #include <errno.h> 32   #include <errno.h>
33   #include <fcntl.h> 33   #include <fcntl.h>
34   34  
35   #include <atomic> 35   #include <atomic>
36   #include <chrono> 36   #include <chrono>
37   #include <cstdint> 37   #include <cstdint>
38   #include <limits> 38   #include <limits>
39   #include <mutex> 39   #include <mutex>
40   #include <new> 40   #include <new>
41   #include <unordered_map> 41   #include <unordered_map>
42   42  
43   namespace boost::corosio::detail { 43   namespace boost::corosio::detail {
44   44  
45   struct select_op; 45   struct select_op;
46   46  
47   /** POSIX scheduler using select() for I/O multiplexing. 47   /** POSIX scheduler using select() for I/O multiplexing.
48   48  
49   This scheduler implements the scheduler interface using the POSIX select() 49   This scheduler implements the scheduler interface using the POSIX select()
50   call for I/O event notification. It inherits the shared reactor threading 50   call for I/O event notification. It inherits the shared reactor threading
51   model from reactor_scheduler: signal state machine, inline completion 51   model from reactor_scheduler: signal state machine, inline completion
52   budget, work counting, and the do_one event loop. 52   budget, work counting, and the do_one event loop.
53   53  
54   The design mirrors epoll_scheduler for behavioral consistency: 54   The design mirrors epoll_scheduler for behavioral consistency:
55   - Same single-reactor thread coordination model 55   - Same single-reactor thread coordination model
56   - Same deferred I/O pattern (reactor marks ready; workers do I/O) 56   - Same deferred I/O pattern (reactor marks ready; workers do I/O)
57   - Same timer integration pattern 57   - Same timer integration pattern
58   58  
59   Known Limitations: 59   Known Limitations:
60   - FD_SETSIZE (~1024) limits maximum concurrent connections 60   - FD_SETSIZE (~1024) limits maximum concurrent connections
61   - O(n) scanning: rebuilds fd_sets each iteration 61   - O(n) scanning: rebuilds fd_sets each iteration
62   - Level-triggered only (no edge-triggered mode) 62   - Level-triggered only (no edge-triggered mode)
63   63  
64   @par Thread Safety 64   @par Thread Safety
65   All public member functions are thread-safe. 65   All public member functions are thread-safe.
66   */ 66   */
67   class BOOST_COROSIO_DECL select_scheduler final : public reactor_scheduler 67   class BOOST_COROSIO_DECL select_scheduler final : public reactor_scheduler
68   { 68   {
69   public: 69   public:
70   /** Construct the scheduler. 70   /** Construct the scheduler.
71   71  
72   Creates a self-pipe for reactor interruption. 72   Creates a self-pipe for reactor interruption.
73   73  
74   @param ctx Reference to the owning execution_context. 74   @param ctx Reference to the owning execution_context.
75   @param concurrency_hint Hint for expected thread count (unused). 75   @param concurrency_hint Hint for expected thread count (unused).
76   */ 76   */
77   select_scheduler(capy::execution_context& ctx, int concurrency_hint = -1); 77   select_scheduler(capy::execution_context& ctx, int concurrency_hint = -1);
78   78  
79   /// Destroy the scheduler. 79   /// Destroy the scheduler.
80   ~select_scheduler() override; 80   ~select_scheduler() override;
81   81  
82   select_scheduler(select_scheduler const&) = delete; 82   select_scheduler(select_scheduler const&) = delete;
83   select_scheduler& operator=(select_scheduler const&) = delete; 83   select_scheduler& operator=(select_scheduler const&) = delete;
84   84  
85   /// Shut down the scheduler, draining pending operations. 85   /// Shut down the scheduler, draining pending operations.
86   void shutdown() override; 86   void shutdown() override;
87   87  
88   /** Return the maximum file descriptor value supported. 88   /** Return the maximum file descriptor value supported.
89   89  
90   Returns FD_SETSIZE - 1, the maximum fd value that can be 90   Returns FD_SETSIZE - 1, the maximum fd value that can be
91   monitored by select(). Operations with fd >= FD_SETSIZE 91   monitored by select(). Operations with fd >= FD_SETSIZE
92   will fail with EINVAL. 92   will fail with EINVAL.
93   93  
94   @return The maximum supported file descriptor value. 94   @return The maximum supported file descriptor value.
95   */ 95   */
96   static constexpr int max_fd() noexcept 96   static constexpr int max_fd() noexcept
97   { 97   {
98   return FD_SETSIZE - 1; 98   return FD_SETSIZE - 1;
99   } 99   }
100   100  
101   /** Register a descriptor for persistent monitoring. 101   /** Register a descriptor for persistent monitoring.
102   102  
103   The fd is added to the registered_descs_ map and will be 103   The fd is added to the registered_descs_ map and will be
104   included in subsequent select() calls. The reactor is 104   included in subsequent select() calls. The reactor is
105   interrupted so a blocked select() rebuilds its fd_sets. 105   interrupted so a blocked select() rebuilds its fd_sets.
106   106  
107   @param fd The file descriptor to register. 107   @param fd The file descriptor to register.
108   @param desc Pointer to descriptor state for this fd. 108   @param desc Pointer to descriptor state for this fd.
109   109  
110   @return The error if the fd cannot be tracked, otherwise a 110   @return The error if the fd cannot be tracked, otherwise a
111   default constructed error code. 111   default constructed error code.
112   */ 112   */
113   std::error_code 113   std::error_code
114   register_descriptor(int fd, reactor_descriptor_state* desc) const; 114   register_descriptor(int fd, reactor_descriptor_state* desc) const;
115   115  
116   /// No-op: write readiness is watched from registration on. 116   /// No-op: write readiness is watched from registration on.
117   std::error_code 117   std::error_code
HITCBC 118   2701 ensure_write_registered(int, reactor_descriptor_state*) const noexcept 118   2594 ensure_write_registered(int, reactor_descriptor_state*) const noexcept
119   { 119   {
HITCBC 120   2701 return {}; 120   2594 return {};
121   } 121   }
122   122  
123   /** Deregister a persistently registered descriptor. 123   /** Deregister a persistently registered descriptor.
124   124  
125   @param fd The file descriptor to deregister. 125   @param fd The file descriptor to deregister.
126   */ 126   */
127   void deregister_descriptor(int fd) const; 127   void deregister_descriptor(int fd) const;
128   128  
129   /** Interrupt the reactor so it rebuilds its fd_sets. 129   /** Interrupt the reactor so it rebuilds its fd_sets.
130   130  
131   Called when a write, connect, or write-wait op is registered 131   Called when a write, connect, or write-wait op is registered
132   after the reactor's snapshot was taken. Without this, 132   after the reactor's snapshot was taken. Without this,
133   select() may block not watching for writability on the fd. 133   select() may block not watching for writability on the fd.
134   */ 134   */
135   void notify_reactor() const; 135   void notify_reactor() const;
136   136  
137   /// Watch the read end of the POSIX signal self-pipe (see scheduler.hpp). 137   /// Watch the read end of the POSIX signal self-pipe (see scheduler.hpp).
HITCBC 138   274 [[nodiscard]] std::error_code register_signal_reader(int read_fd) override 138   274 [[nodiscard]] std::error_code register_signal_reader(int read_fd) override
139   { 139   {
HITCBC 140   274 return register_descriptor(read_fd, signal_pipe_reader_.arm()); 140   274 return register_descriptor(read_fd, signal_pipe_reader_.arm());
141   } 141   }
142   142  
143   private: 143   private:
144   void run_task(lock_type& lock, context_type& ctx, long timeout_us) override; 144   void run_task(lock_type& lock, context_type& ctx, long timeout_us) override;
145   void interrupt_reactor() const override; 145   void interrupt_reactor() const override;
146   146  
147   /// Rebuild the poll set a blocked select() was given. 147   /// Rebuild the poll set a blocked select() was given.
HITCBC 148   460 void notify_reparked() const override 148   508 void notify_reparked() const override
149   { 149   {
HITCBC 150   460 interrupt_reactor(); 150   508 interrupt_reactor();
HITCBC 151   460 } 151   508 }
152   long calculate_timeout(long requested_timeout_us) const; 152   long calculate_timeout(long requested_timeout_us) const;
153   153  
154   // Watches the global signal self-pipe's read end (armed lazily by 154   // Watches the global signal self-pipe's read end (armed lazily by
155   // register_signal_reader on the first signal registration). 155   // register_signal_reader on the first signal registration).
156   reactor_signal_pipe_reader signal_pipe_reader_; 156   reactor_signal_pipe_reader signal_pipe_reader_;
157   157  
158   // Self-pipe for interrupting select() 158   // Self-pipe for interrupting select()
159   int pipe_fds_[2]; // [0]=read, [1]=write 159   int pipe_fds_[2]; // [0]=read, [1]=write
160   160  
161   // Per-fd tracking for fd_set building 161   // Per-fd tracking for fd_set building
162   mutable std::unordered_map<int, reactor_descriptor_state*> 162   mutable std::unordered_map<int, reactor_descriptor_state*>
163   registered_descs_; 163   registered_descs_;
164   mutable int max_fd_ = -1; 164   mutable int max_fd_ = -1;
165   }; 165   };
166   166  
HITCBC 167   1993 inline select_scheduler::select_scheduler(capy::execution_context&, int) 167   1993 inline select_scheduler::select_scheduler(capy::execution_context&, int)
HITCBC 168   1993 : pipe_fds_{-1, -1} 168   1993 : pipe_fds_{-1, -1}
HITCBC 169   1993 , max_fd_(-1) 169   1993 , max_fd_(-1)
170   { 170   {
HITCBC 171   1993 if (::pipe(pipe_fds_) < 0) 171   1993 if (::pipe(pipe_fds_) < 0)
HITCBC 172   1 detail::throw_system_error(make_err(errno), "pipe"); 172   1 detail::throw_system_error(make_err(errno), "pipe");
173   173  
HITCBC 174   5967 for (int i = 0; i < 2; ++i) 174   5967 for (int i = 0; i < 2; ++i)
175   { 175   {
HITCBC 176   3981 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0); 176   3981 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
HITCBC 177   3981 if (flags == -1) 177   3981 if (flags == -1)
178   { 178   {
HITCBC 179   2 int errn = errno; 179   2 int errn = errno;
HITCBC 180   2 ::close(pipe_fds_[0]); 180   2 ::close(pipe_fds_[0]);
HITCBC 181   2 ::close(pipe_fds_[1]); 181   2 ::close(pipe_fds_[1]);
HITCBC 182   2 detail::throw_system_error(make_err(errn), "fcntl F_GETFL"); 182   2 detail::throw_system_error(make_err(errn), "fcntl F_GETFL");
183   } 183   }
HITCBC 184   3979 if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1) 184   3979 if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1)
185   { 185   {
HITCBC 186   2 int errn = errno; 186   2 int errn = errno;
HITCBC 187   2 ::close(pipe_fds_[0]); 187   2 ::close(pipe_fds_[0]);
HITCBC 188   2 ::close(pipe_fds_[1]); 188   2 ::close(pipe_fds_[1]);
HITCBC 189   2 detail::throw_system_error(make_err(errn), "fcntl F_SETFL"); 189   2 detail::throw_system_error(make_err(errn), "fcntl F_SETFL");
190   } 190   }
HITCBC 191   3977 if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1) 191   3977 if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1)
192   { 192   {
HITCBC 193   2 int errn = errno; 193   2 int errn = errno;
HITCBC 194   2 ::close(pipe_fds_[0]); 194   2 ::close(pipe_fds_[0]);
HITCBC 195   2 ::close(pipe_fds_[1]); 195   2 ::close(pipe_fds_[1]);
HITCBC 196   2 detail::throw_system_error(make_err(errn), "fcntl F_SETFD"); 196   2 detail::throw_system_error(make_err(errn), "fcntl F_SETFD");
197   } 197   }
198   } 198   }
199   199  
HITCBC 200   1986 completed_ops_.push(&task_op_); 200   1986 completed_ops_.push(&task_op_);
HITCBC 201   2007 } 201   2007 }
202   202  
HITCBC 203   3972 inline select_scheduler::~select_scheduler() 203   3972 inline select_scheduler::~select_scheduler()
204   { 204   {
HITCBC 205   1986 if (pipe_fds_[0] >= 0) 205   1986 if (pipe_fds_[0] >= 0)
HITCBC 206   1986 ::close(pipe_fds_[0]); 206   1986 ::close(pipe_fds_[0]);
HITCBC 207   1986 if (pipe_fds_[1] >= 0) 207   1986 if (pipe_fds_[1] >= 0)
HITCBC 208   1986 ::close(pipe_fds_[1]); 208   1986 ::close(pipe_fds_[1]);
HITCBC 209   3972 } 209   3972 }
210   210  
211   inline void 211   inline void
HITCBC 212   1986 select_scheduler::shutdown() 212   1986 select_scheduler::shutdown()
213   { 213   {
HITCBC 214   1986 shutdown_drain(); 214   1986 shutdown_drain();
215   215  
HITCBC 216   1986 if (pipe_fds_[1] >= 0) 216   1986 if (pipe_fds_[1] >= 0)
HITCBC 217   1986 interrupt_reactor(); 217   1986 interrupt_reactor();
HITCBC 218   1986 } 218   1986 }
219   219  
220   inline std::error_code 220   inline std::error_code
HITCBC 221   9936 select_scheduler::register_descriptor( 221   9561 select_scheduler::register_descriptor(
222   int fd, reactor_descriptor_state* desc) const 222   int fd, reactor_descriptor_state* desc) const
223   { 223   {
HITCBC 224   9936 if (fd < 0 || fd >= FD_SETSIZE) 224   9561 if (fd < 0 || fd >= FD_SETSIZE)
HITCBC 225   1 return make_err(EMFILE); 225   1 return make_err(EMFILE);
226   226  
227   // A completion queued by an earlier registration of the same state 227   // A completion queued by an earlier registration of the same state
228   // may still be running, so the fields it reads change under its 228   // may still be running, so the fields it reads change under its
229   // mutex, and the mutex mode is only written when it differs. 229   // mutex, and the mutex mode is only written when it differs.
HITCBC 230   9935 if (desc->mutex.enabled() != reactor_io_locking_) 230   9560 if (desc->mutex.enabled() != reactor_io_locking_)
HITCBC 231   3 desc->mutex.set_enabled(reactor_io_locking_); 231   3 desc->mutex.set_enabled(reactor_io_locking_);
232   { 232   {
HITCBC 233   9935 conditionally_enabled_mutex::scoped_lock lock(desc->mutex); 233   9560 conditionally_enabled_mutex::scoped_lock lock(desc->mutex);
HITCBC 234   9935 desc->registered_events = reactor_event_read | reactor_event_write; 234   9560 desc->registered_events = reactor_event_read | reactor_event_write;
HITCBC 235   9935 desc->unpollable = false; // the state is reused across adoptions 235   9560 desc->unpollable = false; // the state is reused across adoptions
HITCBC 236   9935 desc->fd = fd; 236   9560 desc->fd = fd;
HITCBC 237   9935 desc->scheduler_ = this; 237   9560 desc->scheduler_ = this;
HITCBC 238   9935 desc->ready_events_.store(0, std::memory_order_release); 238   9560 desc->ready_events_.store(0, std::memory_order_release);
239   // object_ref_ is not touched: a queued invocation from an 239   // object_ref_ is not touched: a queued invocation from an
240   // earlier registration still owns the reference in it. 240   // earlier registration still owns the reference in it.
HITCBC 241   9935 desc->read_ready = false; 241   9560 desc->read_ready = false;
HITCBC 242   9935 desc->write_ready = false; 242   9560 desc->write_ready = false;
HITCBC 243   9935 } 243   9560 }
244   244  
245   { 245   {
HITCBC 246   9935 mutex_type::scoped_lock lock(mutex_); 246   9560 mutex_type::scoped_lock lock(mutex_);
247   try 247   try
248   { 248   {
HITCBC 249   9935 registered_descs_[fd] = desc; 249   9560 registered_descs_[fd] = desc;
250   } 250   }
HITCBC 251   1 catch (std::bad_alloc const&) 251   1 catch (std::bad_alloc const&)
252   { 252   {
HITCBC 253   1 return make_err(ENOMEM); 253   1 return make_err(ENOMEM);
HITCBC 254   1 } 254   1 }
HITCBC 255   9934 if (fd > max_fd_) 255   9559 if (fd > max_fd_)
HITCBC 256   9427 max_fd_ = fd; 256   9114 max_fd_ = fd;
HITCBC 257   9935 } 257   9560 }
258   258  
HITCBC 259   9934 interrupt_reactor(); 259   9559 interrupt_reactor();
HITCBC 260   9934 return {}; 260   9559 return {};
261   } 261   }
262   262  
263   inline void 263   inline void
HITCBC 264   9661 select_scheduler::deregister_descriptor(int fd) const 264   9286 select_scheduler::deregister_descriptor(int fd) const
265   { 265   {
HITCBC 266   9661 mutex_type::scoped_lock lock(mutex_); 266   9286 mutex_type::scoped_lock lock(mutex_);
267   267  
HITCBC 268   9661 auto it = registered_descs_.find(fd); 268   9286 auto it = registered_descs_.find(fd);
HITCBC 269   9661 if (it == registered_descs_.end()) 269   9286 if (it == registered_descs_.end())
MISUBC 270   ✗ return; 270   ✗ return;
271   271  
HITCBC 272   9661 registered_descs_.erase(it); 272   9286 registered_descs_.erase(it);
273   273  
HITCBC 274   9661 if (fd == max_fd_) 274   9286 if (fd == max_fd_)
275   { 275   {
HITCBC 276   7761 max_fd_ = pipe_fds_[0]; 276   7502 max_fd_ = pipe_fds_[0];
HITCBC 277   12962 for (auto& [registered_fd, state] : registered_descs_) 277   12383 for (auto& [registered_fd, state] : registered_descs_)
278   { 278   {
HITCBC 279   5201 if (registered_fd > max_fd_) 279   4881 if (registered_fd > max_fd_)
HITCBC 280   4929 max_fd_ = registered_fd; 280   4654 max_fd_ = registered_fd;
281   } 281   }
282   } 282   }
HITCBC 283   9661 } 283   9286 }
284   284  
285   inline void 285   inline void
HITCBC 286   6706 select_scheduler::notify_reactor() const 286   6498 select_scheduler::notify_reactor() const
287   { 287   {
HITCBC 288   6706 interrupt_reactor(); 288   6498 interrupt_reactor();
HITCBC 289   6706 } 289   6498 }
290   290  
291   inline void 291   inline void
HITCBC 292   25418 select_scheduler::interrupt_reactor() const 292   24746 select_scheduler::interrupt_reactor() const
293   { 293   {
HITCBC 294   25418 char byte = 1; 294   24746 char byte = 1;
HITCBC 295   25418 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1); 295   24746 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
HITCBC 296   25418 } 296   24746 }
297   297  
298   inline long 298   inline long
HITCBC 299   13333 select_scheduler::calculate_timeout(long requested_timeout_us) const 299   12842 select_scheduler::calculate_timeout(long requested_timeout_us) const
300   { 300   {
HITCBC 301   13333 if (requested_timeout_us == 0) 301   12842 if (requested_timeout_us == 0)
302   return 0; // LCOV_EXCL_LINE run_task passes 0 via task_interrupted_, never through this argument 302   return 0; // LCOV_EXCL_LINE run_task passes 0 via task_interrupted_, never through this argument
303   303  
HITCBC 304   13333 auto* tsvc = timers(); 304   12842 auto* tsvc = timers();
HITCBC 305   13333 if (!tsvc) 305   12842 if (!tsvc)
HITCBC 306   6868 return requested_timeout_us; 306   6769 return requested_timeout_us;
HITCBC 307   6465 auto nearest = tsvc->nearest_expiry(); 307   6073 auto nearest = tsvc->nearest_expiry();
HITCBC 308   6465 if (nearest == timer_service::time_point::max()) 308   6073 if (nearest == timer_service::time_point::max())
HITCBC 309   141 return requested_timeout_us; 309   137 return requested_timeout_us;
310   310  
HITCBC 311   6324 auto now = std::chrono::steady_clock::now(); 311   5936 auto now = std::chrono::steady_clock::now();
HITCBC 312   6324 if (nearest <= now) 312   5936 if (nearest <= now)
HITCBC 313   105 return 0; 313   167 return 0;
314   314  
315   auto timer_timeout_us = 315   auto timer_timeout_us =
HITCBC 316   6219 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now) 316   5769 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
HITCBC 317   6219 .count(); 317   5769 .count();
318   318  
HITCBC 319   6219 constexpr auto long_max = 319   5769 constexpr auto long_max =
320   static_cast<long long>((std::numeric_limits<long>::max)()); 320   static_cast<long long>((std::numeric_limits<long>::max)());
321   auto capped_timer_us = 321   auto capped_timer_us =
HITCBC 322   6219 (std::min)((std::max)(static_cast<long long>(timer_timeout_us), 322   5769 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
HITCBC 323   6219 static_cast<long long>(0)), 323   5769 static_cast<long long>(0)),
HITCBC 324   6219 long_max); 324   5769 long_max);
325   325  
HITCBC 326   6219 if (requested_timeout_us < 0) 326   5769 if (requested_timeout_us < 0)
HITCBC 327   6213 return static_cast<long>(capped_timer_us); 327   5763 return static_cast<long>(capped_timer_us);
328   328  
329   return static_cast<long>( 329   return static_cast<long>(
HITCBC 330   6 (std::min)(static_cast<long long>(requested_timeout_us), 330   6 (std::min)(static_cast<long long>(requested_timeout_us),
HITCBC 331   6 capped_timer_us)); 331   6 capped_timer_us));
332   } 332   }
333   333  
334   inline void 334   inline void
HITCBC 335   141308 select_scheduler::run_task(lock_type& lock, context_type& ctx, long timeout_us) 335   137104 select_scheduler::run_task(lock_type& lock, context_type& ctx, long timeout_us)
336   { 336   {
337   long effective_timeout_us = 337   long effective_timeout_us =
HITCBC 338   141308 task_interrupted_ ? 0 : calculate_timeout(timeout_us); 338   137104 task_interrupted_ ? 0 : calculate_timeout(timeout_us);
339   339  
340   // Snapshot registered descriptors while holding lock. 340   // Snapshot registered descriptors while holding lock.
341   // Record which directions each fd needs monitored to avoid a hot 341   // Record which directions each fd needs monitored to avoid a hot
342   // loop: select is level-triggered, so a writable socket (nearly 342   // loop: select is level-triggered, so a writable socket (nearly
343   // always writable) or an always-readable fd (/dev/zero, a pipe at 343   // always writable) or an always-readable fd (/dev/zero, a pipe at
344   // EOF) would return select() immediately every iteration if 344   // EOF) would return select() immediately every iteration if
345   // unconditionally added. Membership in both sets is opt-in: a 345   // unconditionally added. Membership in both sets is opt-in: a
346   // parked op or wait in a direction opts that direction in. The 346   // parked op or wait in a direction opts that direction in. The
347   // exceptional set is opt-in too, for any parked op or wait: 347   // exceptional set is opt-in too, for any parked op or wait:
348   // Darwin reports a character device (/dev/zero, /dev/null) as 348   // Darwin reports a character device (/dev/zero, /dev/null) as
349   // exceptional on every call. 349   // exceptional on every call.
350   struct fd_entry 350   struct fd_entry
351   { 351   {
352   int fd; 352   int fd;
353   reactor_descriptor_state* desc; 353   reactor_descriptor_state* desc;
354   std::uint32_t want; 354   std::uint32_t want;
355   }; 355   };
356   fd_entry snapshot[FD_SETSIZE]; 356   fd_entry snapshot[FD_SETSIZE];
HITCBC 357   141308 int snapshot_count = 0; 357   137104 int snapshot_count = 0;
358   358  
359   // The caller may have released the lock to hand queued work to a 359   // The caller may have released the lock to hand queued work to a
360   // peer, and deregister_descriptor() erases from this map under it. 360   // peer, and deregister_descriptor() erases from this map under it.
HITCBC 361   141308 if (!lock.owns_lock()) 361   137104 if (!lock.owns_lock())
HITCBC 362   127972 lock.lock(); 362   124259 lock.lock();
363   363  
HITCBC 364   394687 for (auto& [fd, desc] : registered_descs_) 364   376074 for (auto& [fd, desc] : registered_descs_)
365   { 365   {
HITCBC 366   253379 if (snapshot_count < FD_SETSIZE) 366   238970 if (snapshot_count < FD_SETSIZE)
367   { 367   {
HITCBC 368   253379 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex); 368   238970 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex);
HITCBC 369   253379 snapshot[snapshot_count].fd = fd; 369   238970 snapshot[snapshot_count].fd = fd;
HITCBC 370   253379 snapshot[snapshot_count].desc = desc; 370   238970 snapshot[snapshot_count].desc = desc;
HITCBC 371   253379 snapshot[snapshot_count].want = 371   238970 snapshot[snapshot_count].want =
HITCBC 372   253379 ((desc->read_op || desc->wait_read_op) ? reactor_event_read 372   238970 ((desc->read_op || desc->wait_read_op) ? reactor_event_read
HITCBC 373   253379 : 0) | 373   238970 : 0) |
HITCBC 374   253005 ((desc->write_op || desc->connect_op || desc->wait_write_op) 374   238596 ((desc->write_op || desc->connect_op || desc->wait_write_op)
HITCBC 375   506384 ? reactor_event_write 375   477566 ? reactor_event_write
HITCBC 376   253379 : 0) | 376   238970 : 0) |
HITCBC 377   253379 (desc->wait_error_op ? reactor_event_error : 0); 377   238970 (desc->wait_error_op ? reactor_event_error : 0);
HITCBC 378   253379 ++snapshot_count; 378   238970 ++snapshot_count;
HITCBC 379   253379 } 379   238970 }
380   } 380   }
381   381  
HITCBC 382   141308 if (lock.owns_lock()) 382   137104 if (lock.owns_lock())
HITCBC 383   141307 lock.unlock(); 383   137103 lock.unlock();
384   384  
HITCBC 385   141308 task_cleanup on_exit{this, &lock, ctx}; 385   137104 task_cleanup on_exit{this, &lock, ctx};
386   386  
387   fd_set read_fds, write_fds, except_fds; 387   fd_set read_fds, write_fds, except_fds;
HITCBC 388   2402236 FD_ZERO(&read_fds); 388   2330768 FD_ZERO(&read_fds);
HITCBC 389   2402236 FD_ZERO(&write_fds); 389   2330768 FD_ZERO(&write_fds);
HITCBC 390   2402236 FD_ZERO(&except_fds); 390   2330768 FD_ZERO(&except_fds);
391   391  
HITCBC 392   141308 FD_SET(pipe_fds_[0], &read_fds); 392   137104 FD_SET(pipe_fds_[0], &read_fds);
HITCBC 393   141308 int nfds = pipe_fds_[0]; 393   137104 int nfds = pipe_fds_[0];
394   394  
HITCBC 395   394687 for (int i = 0; i < snapshot_count; ++i) 395   376074 for (int i = 0; i < snapshot_count; ++i)
396   { 396   {
HITCBC 397   253379 int fd = snapshot[i].fd; 397   238970 int fd = snapshot[i].fd;
HITCBC 398   253379 if (snapshot[i].want & reactor_event_read) 398   238970 if (snapshot[i].want & reactor_event_read)
HITCBC 399   112387 FD_SET(fd, &read_fds); 399   112563 FD_SET(fd, &read_fds);
HITCBC 400   253379 if (snapshot[i].want & reactor_event_write) 400   238970 if (snapshot[i].want & reactor_event_write)
HITCBC 401   2965 FD_SET(fd, &write_fds); 401   2858 FD_SET(fd, &write_fds);
HITCBC 402   253379 if (snapshot[i].want != 0) 402   238970 if (snapshot[i].want != 0)
HITCBC 403   115547 FD_SET(fd, &except_fds); 403   115616 FD_SET(fd, &except_fds);
HITCBC 404   253379 if (fd > nfds) 404   238970 if (fd > nfds)
HITCBC 405   139283 nfds = fd; 405   135079 nfds = fd;
406   } 406   }
407   407  
408   struct timeval tv; 408   struct timeval tv;
HITCBC 409   141308 struct timeval* tv_ptr = nullptr; 409   137104 struct timeval* tv_ptr = nullptr;
HITCBC 410   141308 if (effective_timeout_us >= 0) 410   137104 if (effective_timeout_us >= 0)
411   { 411   {
HITCBC 412   134993 tv.tv_sec = effective_timeout_us / 1000000; 412   130745 tv.tv_sec = effective_timeout_us / 1000000;
HITCBC 413   134993 tv.tv_usec = effective_timeout_us % 1000000; 413   130745 tv.tv_usec = effective_timeout_us % 1000000;
HITCBC 414   134993 tv_ptr = &tv; 414   130745 tv_ptr = &tv;
415   } 415   }
416   416  
HITCBC 417   141308 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr); 417   137104 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr);
418   418  
419   // EINTR: signal interrupted select(), just retry. 419   // EINTR: signal interrupted select(), just retry.
420   // EBADF: an fd was closed between snapshot and select(); retry 420   // EBADF: an fd was closed between snapshot and select(); retry
421   // with a fresh snapshot from registered_descs_. 421   // with a fresh snapshot from registered_descs_.
422   // Both fall through with no ready descriptors rather than 422   // Both fall through with no ready descriptors rather than
423   // returning: the caller handed this function an owned lock that 423   // returning: the caller handed this function an owned lock that
424   // only the epilogue below re-acquires. 424   // only the epilogue below re-acquires.
HITCBC 425   141308 if (ready < 0) 425   137104 if (ready < 0)
426   { 426   {
HITCBC 427   3 if (errno != EINTR && errno != EBADF) 427   4 if (errno != EINTR && errno != EBADF)
HITCBC 428   1 detail::throw_system_error(make_err(errno), "select"); 428   1 detail::throw_system_error(make_err(errno), "select");
HITCBC 429   2 ready = 0; 429   3 ready = 0;
430   } 430   }
431   431  
432   // Process timers outside the lock 432   // Process timers outside the lock
HITCBC 433   141307 if (auto* tsvc = timers()) 433   137103 if (auto* tsvc = timers())
HITCBC 434   29561 tsvc->process_expired(); 434   24844 tsvc->process_expired();
435   435  
HITCBC 436   141307 ready_queue local_ops; 436   137103 ready_queue local_ops;
437   437  
HITCBC 438   141307 if (ready > 0) 438   137103 if (ready > 0)
439   { 439   {
HITCBC 440   13769 if (FD_ISSET(pipe_fds_[0], &read_fds)) 440   13444 if (FD_ISSET(pipe_fds_[0], &read_fds))
441   { 441   {
442   char buf[256]; 442   char buf[256];
HITCBC 443   22449 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0) 443   21697 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
444   { 444   {
445   } 445   }
446   } 446   }
447   447  
HITCBC 448   95400 for (int i = 0; i < snapshot_count; ++i) 448   94961 for (int i = 0; i < snapshot_count; ++i)
449   { 449   {
HITCBC 450   81631 int fd = snapshot[i].fd; 450   81517 int fd = snapshot[i].fd;
HITCBC 451   81631 reactor_descriptor_state* desc = snapshot[i].desc; 451   81517 reactor_descriptor_state* desc = snapshot[i].desc;
452   452  
HITCBC 453   81631 std::uint32_t flags = 0; 453   81517 std::uint32_t flags = 0;
HITCBC 454   81631 if (FD_ISSET(fd, &read_fds)) 454   81517 if (FD_ISSET(fd, &read_fds))
HITCBC 455   5233 flags |= reactor_event_read; 455   5250 flags |= reactor_event_read;
HITCBC 456   81631 if (FD_ISSET(fd, &write_fds)) 456   81517 if (FD_ISSET(fd, &write_fds))
HITCBC 457   2681 flags |= reactor_event_write; 457   2574 flags |= reactor_event_write;
HITCBC 458   81631 if (FD_ISSET(fd, &except_fds)) 458   81517 if (FD_ISSET(fd, &except_fds))
HITCBC 459   11 flags |= reactor_event_error; 459   11 flags |= reactor_event_error;
460   460  
HITCBC 461   81631 if (flags == 0) 461   81517 if (flags == 0)
HITCBC 462   73715 continue; 462   73691 continue;
463   463  
HITCBC 464   7916 desc->add_ready_events(flags); 464   7826 desc->add_ready_events(flags);
465   465  
HITCBC 466   7916 bool expected = false; 466   7826 bool expected = false;
HITCBC 467   7916 if (desc->is_enqueued_.compare_exchange_strong( 467   7826 if (desc->is_enqueued_.compare_exchange_strong(
468   expected, true, std::memory_order_release, 468   expected, true, std::memory_order_release,
469   std::memory_order_relaxed)) 469   std::memory_order_relaxed))
470   { 470   {
HITCBC 471   6190 local_ops.push(desc); 471   6044 local_ops.push(desc);
472   } 472   }
473   } 473   }
474   } 474   }
475   475  
HITCBC 476   141307 lock.lock(); 476   137103 lock.lock();
477   477  
HITCBC 478   141307 completed_ops_.splice(local_ops); 478   137103 completed_ops_.splice(local_ops);
HITCBC 479   141308 } 479   137104 }
480   480  
481   } // namespace boost::corosio::detail 481   } // namespace boost::corosio::detail
482   482  
483   #endif // BOOST_COROSIO_HAS_SELECT 483   #endif // BOOST_COROSIO_HAS_SELECT
484   484  
485   #endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP 485   #endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP