. /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   /** Deregister a persistently registered descriptor. 116   /** Deregister a persistently registered descriptor.
117   117  
118   @param fd The file descriptor to deregister. 118   @param fd The file descriptor to deregister.
119   */ 119   */
120   void deregister_descriptor(int fd) const; 120   void deregister_descriptor(int fd) const;
121   121  
122   /** Interrupt the reactor so it rebuilds its fd_sets. 122   /** Interrupt the reactor so it rebuilds its fd_sets.
123   123  
124   Called when a write, connect, or write-wait op is registered 124   Called when a write, connect, or write-wait op is registered
125   after the reactor's snapshot was taken. Without this, 125   after the reactor's snapshot was taken. Without this,
126   select() may block not watching for writability on the fd. 126   select() may block not watching for writability on the fd.
127   */ 127   */
128   void notify_reactor() const; 128   void notify_reactor() const;
129   129  
130   /// Watch the read end of the POSIX signal self-pipe (see scheduler.hpp). 130   /// Watch the read end of the POSIX signal self-pipe (see scheduler.hpp).
HITCBC 131   61 [[nodiscard]] std::error_code register_signal_reader(int read_fd) override 131   61 [[nodiscard]] std::error_code register_signal_reader(int read_fd) override
132   { 132   {
HITCBC 133   61 return register_descriptor(read_fd, signal_pipe_reader_.arm()); 133   61 return register_descriptor(read_fd, signal_pipe_reader_.arm());
134   } 134   }
135   135  
136   private: 136   private:
137   void run_task(lock_type& lock, context_type& ctx, long timeout_us) override; 137   void run_task(lock_type& lock, context_type& ctx, long timeout_us) override;
138   void interrupt_reactor() const override; 138   void interrupt_reactor() const override;
139   long calculate_timeout(long requested_timeout_us) const; 139   long calculate_timeout(long requested_timeout_us) const;
140   140  
141   // Watches the global signal self-pipe's read end (armed lazily by 141   // Watches the global signal self-pipe's read end (armed lazily by
142   // register_signal_reader on the first signal registration). 142   // register_signal_reader on the first signal registration).
143   reactor_signal_pipe_reader signal_pipe_reader_; 143   reactor_signal_pipe_reader signal_pipe_reader_;
144   144  
145   // Self-pipe for interrupting select() 145   // Self-pipe for interrupting select()
146   int pipe_fds_[2]; // [0]=read, [1]=write 146   int pipe_fds_[2]; // [0]=read, [1]=write
147   147  
148   // Per-fd tracking for fd_set building 148   // Per-fd tracking for fd_set building
149   mutable std::unordered_map<int, reactor_descriptor_state*> 149   mutable std::unordered_map<int, reactor_descriptor_state*>
150   registered_descs_; 150   registered_descs_;
151   mutable int max_fd_ = -1; 151   mutable int max_fd_ = -1;
152   }; 152   };
153   153  
HITCBC 154   950 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int) 154   983 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
HITCBC 155   950 : pipe_fds_{-1, -1} 155   983 : pipe_fds_{-1, -1}
HITCBC 156   950 , max_fd_(-1) 156   983 , max_fd_(-1)
157   { 157   {
HITCBC 158   950 if (::pipe(pipe_fds_) < 0) 158   983 if (::pipe(pipe_fds_) < 0)
HITCBC 159   1 detail::throw_system_error(make_err(errno), "pipe"); 159   1 detail::throw_system_error(make_err(errno), "pipe");
160   160  
HITCBC 161   2838 for (int i = 0; i < 2; ++i) 161   2937 for (int i = 0; i < 2; ++i)
162   { 162   {
HITCBC 163   1895 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0); 163   1961 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
HITCBC 164   1895 if (flags == -1) 164   1961 if (flags == -1)
165   { 165   {
HITCBC 166   2 int errn = errno; 166   2 int errn = errno;
HITCBC 167   2 ::close(pipe_fds_[0]); 167   2 ::close(pipe_fds_[0]);
HITCBC 168   2 ::close(pipe_fds_[1]); 168   2 ::close(pipe_fds_[1]);
HITCBC 169   2 detail::throw_system_error(make_err(errn), "fcntl F_GETFL"); 169   2 detail::throw_system_error(make_err(errn), "fcntl F_GETFL");
170   } 170   }
HITCBC 171   1893 if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1) 171   1959 if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1)
172   { 172   {
HITCBC 173   2 int errn = errno; 173   2 int errn = errno;
HITCBC 174   2 ::close(pipe_fds_[0]); 174   2 ::close(pipe_fds_[0]);
HITCBC 175   2 ::close(pipe_fds_[1]); 175   2 ::close(pipe_fds_[1]);
HITCBC 176   2 detail::throw_system_error(make_err(errn), "fcntl F_SETFL"); 176   2 detail::throw_system_error(make_err(errn), "fcntl F_SETFL");
177   } 177   }
HITCBC 178   1891 if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1) 178   1957 if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1)
179   { 179   {
HITCBC 180   2 int errn = errno; 180   2 int errn = errno;
HITCBC 181   2 ::close(pipe_fds_[0]); 181   2 ::close(pipe_fds_[0]);
HITCBC 182   2 ::close(pipe_fds_[1]); 182   2 ::close(pipe_fds_[1]);
HITCBC 183   2 detail::throw_system_error(make_err(errn), "fcntl F_SETFD"); 183   2 detail::throw_system_error(make_err(errn), "fcntl F_SETFD");
184   } 184   }
185   } 185   }
186   186  
HITCBC 187   943 timer_svc_ = &get_timer_service(ctx, *this); 187   976 timer_svc_ = &get_timer_service(ctx, *this);
HITCBC 188   943 timer_svc_->set_on_earliest_changed( 188   976 timer_svc_->set_on_earliest_changed(
HITCBC 189   3684 timer_service::callback(this, [](void* p) { 189   3640 timer_service::callback(this, [](void* p) {
HITCBC 190   2741 static_cast<select_scheduler*>(p)->interrupt_reactor(); 190   2664 static_cast<select_scheduler*>(p)->interrupt_reactor();
HITCBC 191   2741 })); 191   2664 }));
192   192  
HITCBC 193   943 completed_ops_.push(&task_op_); 193   976 completed_ops_.push(&task_op_);
HITCBC 194   964 } 194   997 }
195   195  
HITCBC 196   1886 inline select_scheduler::~select_scheduler() 196   1952 inline select_scheduler::~select_scheduler()
197   { 197   {
HITCBC 198   943 if (pipe_fds_[0] >= 0) 198   976 if (pipe_fds_[0] >= 0)
HITCBC 199   943 ::close(pipe_fds_[0]); 199   976 ::close(pipe_fds_[0]);
HITCBC 200   943 if (pipe_fds_[1] >= 0) 200   976 if (pipe_fds_[1] >= 0)
HITCBC 201   943 ::close(pipe_fds_[1]); 201   976 ::close(pipe_fds_[1]);
HITCBC 202   1886 } 202   1952 }
203   203  
204   inline void 204   inline void
HITCBC 205   943 select_scheduler::shutdown() 205   976 select_scheduler::shutdown()
206   { 206   {
HITCBC 207   943 shutdown_drain(); 207   976 shutdown_drain();
208   208  
HITCBC 209   943 if (pipe_fds_[1] >= 0) 209   976 if (pipe_fds_[1] >= 0)
HITCBC 210   943 interrupt_reactor(); 210   976 interrupt_reactor();
HITCBC 211   943 } 211   976 }
212   212  
213   inline std::error_code 213   inline std::error_code
HITCBC 214   4826 select_scheduler::register_descriptor( 214   4888 select_scheduler::register_descriptor(
215   int fd, reactor_descriptor_state* desc) const 215   int fd, reactor_descriptor_state* desc) const
216   { 216   {
HITCBC 217   4826 if (fd < 0 || fd >= FD_SETSIZE) 217   4888 if (fd < 0 || fd >= FD_SETSIZE)
HITCBC 218   1 return make_err(EMFILE); 218   1 return make_err(EMFILE);
219   219  
HITCBC 220   4825 desc->registered_events = reactor_event_read | reactor_event_write; 220   4887 desc->registered_events = reactor_event_read | reactor_event_write;
HITCBC 221   4825 desc->fd = fd; 221   4887 desc->fd = fd;
HITCBC 222   4825 desc->scheduler_ = this; 222   4887 desc->scheduler_ = this;
HITCBC 223   4825 desc->mutex.set_enabled(reactor_io_locking_); 223   4887 desc->mutex.set_enabled(reactor_io_locking_);
HITCBC 224   4825 desc->ready_events_.store(0, std::memory_order_relaxed); 224   4887 desc->ready_events_.store(0, std::memory_order_relaxed);
225   225  
226   { 226   {
HITCBC 227   4825 conditionally_enabled_mutex::scoped_lock lock(desc->mutex); 227   4887 conditionally_enabled_mutex::scoped_lock lock(desc->mutex);
HITCBC 228   4825 desc->impl_ref_.reset(); 228   4887 desc->impl_ref_.reset();
HITCBC 229   4825 desc->read_ready = false; 229   4887 desc->read_ready = false;
HITCBC 230   4825 desc->write_ready = false; 230   4887 desc->write_ready = false;
HITCBC 231   4825 } 231   4887 }
232   232  
233   { 233   {
HITCBC 234   4825 mutex_type::scoped_lock lock(mutex_); 234   4887 mutex_type::scoped_lock lock(mutex_);
235   try 235   try
236   { 236   {
HITCBC 237   4825 registered_descs_[fd] = desc; 237   4887 registered_descs_[fd] = desc;
238   } 238   }
HITCBC 239   1 catch (std::bad_alloc const&) 239   1 catch (std::bad_alloc const&)
240   { 240   {
HITCBC 241   1 return make_err(ENOMEM); 241   1 return make_err(ENOMEM);
HITCBC 242   1 } 242   1 }
HITCBC 243   4824 if (fd > max_fd_) 243   4886 if (fd > max_fd_)
HITCBC 244   4774 max_fd_ = fd; 244   4835 max_fd_ = fd;
HITCBC 245   4825 } 245   4887 }
246   246  
HITCBC 247   4824 interrupt_reactor(); 247   4886 interrupt_reactor();
HITCBC 248   4824 return {}; 248   4886 return {};
249   } 249   }
250   250  
251   inline void 251   inline void
HITCBC 252   4764 select_scheduler::deregister_descriptor(int fd) const 252   4826 select_scheduler::deregister_descriptor(int fd) const
253   { 253   {
HITCBC 254   4764 mutex_type::scoped_lock lock(mutex_); 254   4826 mutex_type::scoped_lock lock(mutex_);
255   255  
HITCBC 256   4764 auto it = registered_descs_.find(fd); 256   4826 auto it = registered_descs_.find(fd);
HITCBC 257   4764 if (it == registered_descs_.end()) 257   4826 if (it == registered_descs_.end())
MISUBC 258   ✗ return; 258   ✗ return;
259   259  
HITCBC 260   4764 registered_descs_.erase(it); 260   4826 registered_descs_.erase(it);
261   261  
HITCBC 262   4764 if (fd == max_fd_) 262   4826 if (fd == max_fd_)
263   { 263   {
HITCBC 264   4429 max_fd_ = pipe_fds_[0]; 264   4491 max_fd_ = pipe_fds_[0];
HITCBC 265   8452 for (auto& [registered_fd, state] : registered_descs_) 265   8554 for (auto& [registered_fd, state] : registered_descs_)
266   { 266   {
HITCBC 267   4023 if (registered_fd > max_fd_) 267   4063 if (registered_fd > max_fd_)
HITCBC 268   3930 max_fd_ = registered_fd; 268   3970 max_fd_ = registered_fd;
269   } 269   }
270   } 270   }
HITCBC 271   4764 } 271   4826 }
272   272  
273   inline void 273   inline void
HITCBC 274   2141 select_scheduler::notify_reactor() const 274   2162 select_scheduler::notify_reactor() const
275   { 275   {
HITCBC 276   2141 interrupt_reactor(); 276   2162 interrupt_reactor();
HITCBC 277   2141 } 277   2162 }
278   278  
279   inline void 279   inline void
HITCBC 280   12367 select_scheduler::interrupt_reactor() const 280   12311 select_scheduler::interrupt_reactor() const
281   { 281   {
HITCBC 282   12367 char byte = 1; 282   12311 char byte = 1;
HITCBC 283   12367 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1); 283   12311 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
HITCBC 284   12367 } 284   12311 }
285   285  
286   inline long 286   inline long
HITCBC 287   254768 select_scheduler::calculate_timeout(long requested_timeout_us) const 287   308536 select_scheduler::calculate_timeout(long requested_timeout_us) const
288   { 288   {
HITCBC 289   254768 if (requested_timeout_us == 0) 289   308536 if (requested_timeout_us == 0)
290   return 0; // LCOV_EXCL_LINE run_task passes 0 via task_interrupted_, never through this argument 290   return 0; // LCOV_EXCL_LINE run_task passes 0 via task_interrupted_, never through this argument
291   291  
HITCBC 292   254768 auto nearest = timer_svc_->nearest_expiry(); 292   308536 auto nearest = timer_svc_->nearest_expiry();
HITCBC 293   254768 if (nearest == timer_service::time_point::max()) 293   308536 if (nearest == timer_service::time_point::max())
HITCBC 294   1123 return requested_timeout_us; 294   1023 return requested_timeout_us;
295   295  
HITCBC 296   253645 auto now = std::chrono::steady_clock::now(); 296   307513 auto now = std::chrono::steady_clock::now();
HITCBC 297   253645 if (nearest <= now) 297   307513 if (nearest <= now)
HITCBC 298   452 return 0; 298   439 return 0;
299   299  
300   auto timer_timeout_us = 300   auto timer_timeout_us =
HITCBC 301   253193 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now) 301   307074 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
HITCBC 302   253193 .count(); 302   307074 .count();
303   303  
HITCBC 304   253193 constexpr auto long_max = 304   307074 constexpr auto long_max =
305   static_cast<long long>((std::numeric_limits<long>::max)()); 305   static_cast<long long>((std::numeric_limits<long>::max)());
306   auto capped_timer_us = 306   auto capped_timer_us =
HITCBC 307   253193 (std::min)((std::max)(static_cast<long long>(timer_timeout_us), 307   307074 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
HITCBC 308   253193 static_cast<long long>(0)), 308   307074 static_cast<long long>(0)),
HITCBC 309   253193 long_max); 309   307074 long_max);
310   310  
HITCBC 311   253193 if (requested_timeout_us < 0) 311   307074 if (requested_timeout_us < 0)
HITCBC 312   253191 return static_cast<long>(capped_timer_us); 312   307072 return static_cast<long>(capped_timer_us);
313   313  
314   return static_cast<long>( 314   return static_cast<long>(
HITCBC 315   2 (std::min)(static_cast<long long>(requested_timeout_us), 315   2 (std::min)(static_cast<long long>(requested_timeout_us),
HITCBC 316   2 capped_timer_us)); 316   2 capped_timer_us));
317   } 317   }
318   318  
319   inline void 319   inline void
HITCBC 320   278561 select_scheduler::run_task(lock_type& lock, context_type& ctx, long timeout_us) 320   332654 select_scheduler::run_task(lock_type& lock, context_type& ctx, long timeout_us)
321   { 321   {
322   long effective_timeout_us = 322   long effective_timeout_us =
HITCBC 323   278561 task_interrupted_ ? 0 : calculate_timeout(timeout_us); 323   332654 task_interrupted_ ? 0 : calculate_timeout(timeout_us);
324   324  
325   // Snapshot registered descriptors while holding lock. 325   // Snapshot registered descriptors while holding lock.
326   // Record which fds need write monitoring to avoid a hot loop: 326   // Record which fds need write monitoring to avoid a hot loop:
327   // select is level-triggered so writable sockets (nearly always 327   // select is level-triggered so writable sockets (nearly always
328   // writable) would cause select() to return immediately every 328   // writable) would cause select() to return immediately every
329   // iteration if unconditionally added to write_fds. Membership 329   // iteration if unconditionally added to write_fds. Membership
330   // stays opt-in: a parked write wait opts in the same way a 330   // stays opt-in: a parked write wait opts in the same way a
331   // parked write or connect op does. 331   // parked write or connect op does.
332   struct fd_entry 332   struct fd_entry
333   { 333   {
334   int fd; 334   int fd;
335   reactor_descriptor_state* desc; 335   reactor_descriptor_state* desc;
336   bool needs_write; 336   bool needs_write;
337   }; 337   };
338   fd_entry snapshot[FD_SETSIZE]; 338   fd_entry snapshot[FD_SETSIZE];
HITCBC 339   278561 int snapshot_count = 0; 339   332654 int snapshot_count = 0;
340   340  
HITCBC 341   754960 for (auto& [fd, desc] : registered_descs_) 341   866974 for (auto& [fd, desc] : registered_descs_)
342   { 342   {
HITCBC 343   476399 if (snapshot_count < FD_SETSIZE) 343   534320 if (snapshot_count < FD_SETSIZE)
344   { 344   {
HITCBC 345   476399 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex); 345   534320 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex);
HITCBC 346   476399 snapshot[snapshot_count].fd = fd; 346   534320 snapshot[snapshot_count].fd = fd;
HITCBC 347   476399 snapshot[snapshot_count].desc = desc; 347   534320 snapshot[snapshot_count].desc = desc;
HITCBC 348   476399 snapshot[snapshot_count].needs_write = 348   534320 snapshot[snapshot_count].needs_write =
HITCBC 349   476399 (desc->write_op || desc->connect_op || desc->wait_write_op); 349   534320 (desc->write_op || desc->connect_op || desc->wait_write_op);
HITCBC 350   476399 ++snapshot_count; 350   534320 ++snapshot_count;
HITCBC 351   476399 } 351   534320 }
352   } 352   }
353   353  
HITCBC 354   278561 if (lock.owns_lock()) 354   332654 if (lock.owns_lock())
HITCBC 355   254769 lock.unlock(); 355   308537 lock.unlock();
356   356  
HITCBC 357   278561 task_cleanup on_exit{this, &lock, ctx}; 357   332654 task_cleanup on_exit{this, &lock, ctx};
358   358  
359   fd_set read_fds, write_fds, except_fds; 359   fd_set read_fds, write_fds, except_fds;
HITCBC 360   4735537 FD_ZERO(&read_fds); 360   5655118 FD_ZERO(&read_fds);
HITCBC 361   4735537 FD_ZERO(&write_fds); 361   5655118 FD_ZERO(&write_fds);
HITCBC 362   4735537 FD_ZERO(&except_fds); 362   5655118 FD_ZERO(&except_fds);
363   363  
HITCBC 364   278561 FD_SET(pipe_fds_[0], &read_fds); 364   332654 FD_SET(pipe_fds_[0], &read_fds);
HITCBC 365   278561 int nfds = pipe_fds_[0]; 365   332654 int nfds = pipe_fds_[0];
366   366  
HITCBC 367   754960 for (int i = 0; i < snapshot_count; ++i) 367   866974 for (int i = 0; i < snapshot_count; ++i)
368   { 368   {
HITCBC 369   476399 int fd = snapshot[i].fd; 369   534320 int fd = snapshot[i].fd;
HITCBC 370   476399 FD_SET(fd, &read_fds); 370   534320 FD_SET(fd, &read_fds);
HITCBC 371   476399 if (snapshot[i].needs_write) 371   534320 if (snapshot[i].needs_write)
HITCBC 372   13245 FD_SET(fd, &write_fds); 372   7948 FD_SET(fd, &write_fds);
HITCBC 373   476399 FD_SET(fd, &except_fds); 373   534320 FD_SET(fd, &except_fds);
HITCBC 374   476399 if (fd > nfds) 374   534320 if (fd > nfds)
HITCBC 375   277921 nfds = fd; 375   332043 nfds = fd;
376   } 376   }
377   377  
378   struct timeval tv; 378   struct timeval tv;
HITCBC 379   278561 struct timeval* tv_ptr = nullptr; 379   332654 struct timeval* tv_ptr = nullptr;
HITCBC 380   278561 if (effective_timeout_us >= 0) 380   332654 if (effective_timeout_us >= 0)
381   { 381   {
HITCBC 382   277749 tv.tv_sec = effective_timeout_us / 1000000; 382   331877 tv.tv_sec = effective_timeout_us / 1000000;
HITCBC 383   277749 tv.tv_usec = effective_timeout_us % 1000000; 383   331877 tv.tv_usec = effective_timeout_us % 1000000;
HITCBC 384   277749 tv_ptr = &tv; 384   331877 tv_ptr = &tv;
385   } 385   }
386   386  
HITCBC 387   278561 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr); 387   332654 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr);
388   388  
389   // EINTR: signal interrupted select(), just retry. 389   // EINTR: signal interrupted select(), just retry.
390   // EBADF: an fd was closed between snapshot and select(); retry 390   // EBADF: an fd was closed between snapshot and select(); retry
391   // with a fresh snapshot from registered_descs_. 391   // with a fresh snapshot from registered_descs_.
392   // Both fall through with no ready descriptors rather than 392   // Both fall through with no ready descriptors rather than
393   // returning: the caller handed this function an owned lock that 393   // returning: the caller handed this function an owned lock that
394   // only the epilogue below re-acquires. 394   // only the epilogue below re-acquires.
HITCBC 395   278561 if (ready < 0) 395   332654 if (ready < 0)
396   { 396   {
HITCBC 397   3 if (errno != EINTR && errno != EBADF) 397   3 if (errno != EINTR && errno != EBADF)
HITCBC 398   1 detail::throw_system_error(make_err(errno), "select"); 398   1 detail::throw_system_error(make_err(errno), "select");
HITCBC 399   2 ready = 0; 399   2 ready = 0;
400   } 400   }
401   401  
402   // Process timers outside the lock 402   // Process timers outside the lock
HITCBC 403   278560 timer_svc_->process_expired(); 403   332653 timer_svc_->process_expired();
404   404  
HITCBC 405   278560 ready_queue local_ops; 405   332653 ready_queue local_ops;
406   406  
HITCBC 407   278560 if (ready > 0) 407   332653 if (ready > 0)
408   { 408   {
HITCBC 409   262425 if (FD_ISSET(pipe_fds_[0], &read_fds)) 409   316405 if (FD_ISSET(pipe_fds_[0], &read_fds))
410   { 410   {
411   char buf[256]; 411   char buf[256];
HITCBC 412   11714 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0) 412   11654 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
413   { 413   {
414   } 414   }
415   } 415   }
416   416  
HITCBC 417   690900 for (int i = 0; i < snapshot_count; ++i) 417   804357 for (int i = 0; i < snapshot_count; ++i)
418   { 418   {
HITCBC 419   428475 int fd = snapshot[i].fd; 419   487952 int fd = snapshot[i].fd;
HITCBC 420   428475 reactor_descriptor_state* desc = snapshot[i].desc; 420   487952 reactor_descriptor_state* desc = snapshot[i].desc;
421   421  
HITCBC 422   428475 std::uint32_t flags = 0; 422   487952 std::uint32_t flags = 0;
HITCBC 423   428475 if (FD_ISSET(fd, &read_fds)) 423   487952 if (FD_ISSET(fd, &read_fds))
HITCBC 424   261095 flags |= reactor_event_read; 424   315227 flags |= reactor_event_read;
HITCBC 425   428475 if (FD_ISSET(fd, &write_fds)) 425   487952 if (FD_ISSET(fd, &write_fds))
HITCBC 426   2133 flags |= reactor_event_write; 426   2154 flags |= reactor_event_write;
HITCBC 427   428475 if (FD_ISSET(fd, &except_fds)) 427   487952 if (FD_ISSET(fd, &except_fds))
HITCBC 428   16 flags |= reactor_event_error; 428   16 flags |= reactor_event_error;
429   429  
HITCBC 430   428475 if (flags == 0) 430   487952 if (flags == 0)
HITCBC 431   165256 continue; 431   170580 continue;
432   432  
HITCBC 433   263219 desc->add_ready_events(flags); 433   317372 desc->add_ready_events(flags);
434   434  
HITCBC 435   263219 bool expected = false; 435   317372 bool expected = false;
HITCBC 436   263219 if (desc->is_enqueued_.compare_exchange_strong( 436   317372 if (desc->is_enqueued_.compare_exchange_strong(
437   expected, true, std::memory_order_release, 437   expected, true, std::memory_order_release,
438   std::memory_order_relaxed)) 438   std::memory_order_relaxed))
439   { 439   {
HITCBC 440   263219 local_ops.push(desc); 440   317372 local_ops.push(desc);
441   } 441   }
442   } 442   }
443   } 443   }
444   444  
HITCBC 445   278560 lock.lock(); 445   332653 lock.lock();
446   446  
HITCBC 447   278560 completed_ops_.splice(local_ops); 447   332653 completed_ops_.splice(local_ops);
HITCBC 448   278561 } 448   332654 }
449   449  
450   } // namespace boost::corosio::detail 450   } // namespace boost::corosio::detail
451   451  
452   #endif // BOOST_COROSIO_HAS_SELECT 452   #endif // BOOST_COROSIO_HAS_SELECT
453   453  
454   #endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP 454   #endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_SCHEDULER_HPP