. /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   585 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int) 154   585 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
HITCBC 155   585 : pipe_fds_{-1, -1} 155   585 : pipe_fds_{-1, -1}
HITCBC 156   585 , max_fd_(-1) 156   585 , max_fd_(-1)
157   { 157   {
HITCBC 158   585 if (::pipe(pipe_fds_) < 0) 158   585 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   1755 for (int i = 0; i < 2; ++i) 161   1755 for (int i = 0; i < 2; ++i)
162   { 162   {
HITCBC 163   1170 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0); 163   1170 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
HITCBC 164   1170 if (flags == -1) 164   1170 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   1170 if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1) 171   1170 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   1170 if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1) 178   1170 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   585 timer_svc_ = &get_timer_service(ctx, *this); 187   585 timer_svc_ = &get_timer_service(ctx, *this);
HITCBC 188   585 timer_svc_->set_on_earliest_changed( 188   585 timer_svc_->set_on_earliest_changed(
HITCBC 189   3321 timer_service::callback(this, [](void* p) { 189   2630 timer_service::callback(this, [](void* p) {
HITCBC 190   2736 static_cast<select_scheduler*>(p)->interrupt_reactor(); 190   2045 static_cast<select_scheduler*>(p)->interrupt_reactor();
HITCBC 191   2736 })); 191   2045 }));
192   192  
HITCBC 193   585 get_resolver_service(ctx, *this); 193   585 get_resolver_service(ctx, *this);
HITCBC 194   585 get_signal_service(ctx, *this); 194   585 get_signal_service(ctx, *this);
HITCBC 195   585 get_stream_file_service(ctx, *this); 195   585 get_stream_file_service(ctx, *this);
HITCBC 196   585 get_random_access_file_service(ctx, *this); 196   585 get_random_access_file_service(ctx, *this);
197   197  
HITCBC 198   585 completed_ops_.push(&task_op_); 198   585 completed_ops_.push(&task_op_);
HITCBC 199   585 } 199   585 }
200   200  
HITCBC 201   1170 inline select_scheduler::~select_scheduler() 201   1170 inline select_scheduler::~select_scheduler()
202   { 202   {
HITCBC 203   585 if (pipe_fds_[0] >= 0) 203   585 if (pipe_fds_[0] >= 0)
HITCBC 204   585 ::close(pipe_fds_[0]); 204   585 ::close(pipe_fds_[0]);
HITCBC 205   585 if (pipe_fds_[1] >= 0) 205   585 if (pipe_fds_[1] >= 0)
HITCBC 206   585 ::close(pipe_fds_[1]); 206   585 ::close(pipe_fds_[1]);
HITCBC 207   1170 } 207   1170 }
208   208  
209   inline void 209   inline void
HITCBC 210   585 select_scheduler::shutdown() 210   585 select_scheduler::shutdown()
211   { 211   {
HITCBC 212   585 shutdown_drain(); 212   585 shutdown_drain();
213   213  
HITCBC 214   585 if (pipe_fds_[1] >= 0) 214   585 if (pipe_fds_[1] >= 0)
HITCBC 215   585 interrupt_reactor(); 215   585 interrupt_reactor();
HITCBC 216   585 } 216   585 }
217   217  
218   inline void 218   inline void
HITCBC 219   4374 select_scheduler::register_descriptor( 219   3290 select_scheduler::register_descriptor(
220   int fd, reactor_descriptor_state* desc) const 220   int fd, reactor_descriptor_state* desc) const
221   { 221   {
HITCBC 222   4374 if (fd < 0 || fd >= FD_SETSIZE) 222   3290 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   4374 desc->registered_events = reactor_event_read | reactor_event_write; 225   3290 desc->registered_events = reactor_event_read | reactor_event_write;
HITCBC 226   4374 desc->fd = fd; 226   3290 desc->fd = fd;
HITCBC 227   4374 desc->scheduler_ = this; 227   3290 desc->scheduler_ = this;
HITCBC 228   4374 desc->mutex.set_enabled(reactor_io_locking_); 228   3290 desc->mutex.set_enabled(reactor_io_locking_);
HITCBC 229   4374 desc->ready_events_.store(0, std::memory_order_relaxed); 229   3290 desc->ready_events_.store(0, std::memory_order_relaxed);
230   230  
231   { 231   {
HITCBC 232   4374 conditionally_enabled_mutex::scoped_lock lock(desc->mutex); 232   3290 conditionally_enabled_mutex::scoped_lock lock(desc->mutex);
HITCBC 233   4374 desc->impl_ref_.reset(); 233   3290 desc->impl_ref_.reset();
HITCBC 234   4374 desc->read_ready = false; 234   3290 desc->read_ready = false;
HITCBC 235   4374 desc->write_ready = false; 235   3290 desc->write_ready = false;
HITCBC 236   4374 } 236   3290 }
237   237  
238   { 238   {
HITCBC 239   4374 mutex_type::scoped_lock lock(mutex_); 239   3290 mutex_type::scoped_lock lock(mutex_);
HITCBC 240   4374 registered_descs_[fd] = desc; 240   3290 registered_descs_[fd] = desc;
HITCBC 241   4374 if (fd > max_fd_) 241   3290 if (fd > max_fd_)
HITCBC 242   4369 max_fd_ = fd; 242   3285 max_fd_ = fd;
HITCBC 243   4374 } 243   3290 }
244   244  
HITCBC 245   4374 interrupt_reactor(); 245   3290 interrupt_reactor();
HITCBC 246   4374 } 246   3290 }
247   247  
248   inline void 248   inline void
HITCBC 249   4333 select_scheduler::deregister_descriptor(int fd) const 249   3249 select_scheduler::deregister_descriptor(int fd) const
250   { 250   {
HITCBC 251   4333 mutex_type::scoped_lock lock(mutex_); 251   3249 mutex_type::scoped_lock lock(mutex_);
252   252  
HITCBC 253   4333 auto it = registered_descs_.find(fd); 253   3249 auto it = registered_descs_.find(fd);
HITCBC 254   4333 if (it == registered_descs_.end()) 254   3249 if (it == registered_descs_.end())
MISUBC 255   ✗ return; 255   ✗ return;
256   256  
HITCBC 257   4333 registered_descs_.erase(it); 257   3249 registered_descs_.erase(it);
258   258  
HITCBC 259   4333 if (fd == max_fd_) 259   3249 if (fd == max_fd_)
260   { 260   {
HITCBC 261   4213 max_fd_ = pipe_fds_[0]; 261   3129 max_fd_ = pipe_fds_[0];
HITCBC 262   8173 for (auto& [registered_fd, state] : registered_descs_) 262   6005 for (auto& [registered_fd, state] : registered_descs_)
263   { 263   {
HITCBC 264   3960 if (registered_fd > max_fd_) 264   2876 if (registered_fd > max_fd_)
HITCBC 265   3913 max_fd_ = registered_fd; 265   2829 max_fd_ = registered_fd;
266   } 266   }
267   } 267   }
HITCBC 268   4333 } 268   3249 }
269   269  
270   inline void 270   inline void
HITCBC 271   2070 select_scheduler::notify_reactor() const 271   1528 select_scheduler::notify_reactor() const
272   { 272   {
HITCBC 273   2070 interrupt_reactor(); 273   1528 interrupt_reactor();
HITCBC 274   2070 } 274   1528 }
275   275  
276   inline void 276   inline void
HITCBC 277   10218 select_scheduler::interrupt_reactor() const 277   7901 select_scheduler::interrupt_reactor() const
278   { 278   {
HITCBC 279   10218 char byte = 1; 279   7901 char byte = 1;
HITCBC 280   10218 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1); 280   7901 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
HITCBC 281   10218 } 281   7901 }
282   282  
283   inline long 283   inline long
HITCBC 284   199684 select_scheduler::calculate_timeout(long requested_timeout_us) const 284   79199 select_scheduler::calculate_timeout(long requested_timeout_us) const
285   { 285   {
HITCBC 286   199684 if (requested_timeout_us == 0) 286   79199 if (requested_timeout_us == 0)
MISUBC 287   ✗ return 0; 287   ✗ return 0;
288   288  
HITCBC 289   199684 auto nearest = timer_svc_->nearest_expiry(); 289   79199 auto nearest = timer_svc_->nearest_expiry();
HITCBC 290   199684 if (nearest == timer_service::time_point::max()) 290   79199 if (nearest == timer_service::time_point::max())
HITCBC 291   567 return requested_timeout_us; 291   567 return requested_timeout_us;
292   292  
HITCBC 293   199117 auto now = std::chrono::steady_clock::now(); 293   78632 auto now = std::chrono::steady_clock::now();
HITCBC 294   199117 if (nearest <= now) 294   78632 if (nearest <= now)
HITCBC 295   597 return 0; 295   625 return 0;
296   296  
297   auto timer_timeout_us = 297   auto timer_timeout_us =
HITCBC 298   198520 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now) 298   78007 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
HITCBC 299   198520 .count(); 299   78007 .count();
300   300  
HITCBC 301   198520 constexpr auto long_max = 301   78007 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   198520 (std::min)((std::max)(static_cast<long long>(timer_timeout_us), 304   78007 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
HITCBC 305   198520 static_cast<long long>(0)), 305   78007 static_cast<long long>(0)),
HITCBC 306   198520 long_max); 306   78007 long_max);
307   307  
HITCBC 308   198520 if (requested_timeout_us < 0) 308   78007 if (requested_timeout_us < 0)
HITCBC 309   198520 return static_cast<long>(capped_timer_us); 309   78007 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   222466 select_scheduler::run_task( 317   89118 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   222466 task_interrupted_ ? 0 : calculate_timeout(timeout_us); 321   89118 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   222466 int snapshot_count = 0; 335   89118 int snapshot_count = 0;
336   336  
HITCBC 337   584532 for (auto& [fd, desc] : registered_descs_) 337   228732 for (auto& [fd, desc] : registered_descs_)
338   { 338   {
HITCBC 339   362066 if (snapshot_count < FD_SETSIZE) 339   139614 if (snapshot_count < FD_SETSIZE)
340   { 340   {
HITCBC 341   362066 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex); 341   139614 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex);
HITCBC 342   362066 snapshot[snapshot_count].fd = fd; 342   139614 snapshot[snapshot_count].fd = fd;
HITCBC 343   362066 snapshot[snapshot_count].desc = desc; 343   139614 snapshot[snapshot_count].desc = desc;
HITCBC 344   362066 snapshot[snapshot_count].needs_write = 344   139614 snapshot[snapshot_count].needs_write =
HITCBC 345   362066 (desc->write_op || desc->connect_op); 345   139614 (desc->write_op || desc->connect_op);
HITCBC 346   362066 ++snapshot_count; 346   139614 ++snapshot_count;
HITCBC 347   362066 } 347   139614 }
348   } 348   }
349   349  
HITCBC 350   222466 if (lock.owns_lock()) 350   89118 if (lock.owns_lock())
HITCBC 351   199685 lock.unlock(); 351   79200 lock.unlock();
352   352  
HITCBC 353   222466 task_cleanup on_exit{this, &lock, ctx}; 353   89118 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   3781922 FD_ZERO(&read_fds); 356   1515006 FD_ZERO(&read_fds);
HITCBC 357   3781922 FD_ZERO(&write_fds); 357   1515006 FD_ZERO(&write_fds);
HITCBC 358   3781922 FD_ZERO(&except_fds); 358   1515006 FD_ZERO(&except_fds);
359   359  
HITCBC 360   222466 FD_SET(pipe_fds_[0], &read_fds); 360   89118 FD_SET(pipe_fds_[0], &read_fds);
HITCBC 361   222466 int nfds = pipe_fds_[0]; 361   89118 int nfds = pipe_fds_[0];
362   362  
HITCBC 363   584532 for (int i = 0; i < snapshot_count; ++i) 363   228732 for (int i = 0; i < snapshot_count; ++i)
364   { 364   {
HITCBC 365   362066 int fd = snapshot[i].fd; 365   139614 int fd = snapshot[i].fd;
HITCBC 366   362066 FD_SET(fd, &read_fds); 366   139614 FD_SET(fd, &read_fds);
HITCBC 367   362066 if (snapshot[i].needs_write) 367   139614 if (snapshot[i].needs_write)
HITCBC 368   12376 FD_SET(fd, &write_fds); 368   4921 FD_SET(fd, &write_fds);
HITCBC 369   362066 FD_SET(fd, &except_fds); 369   139614 FD_SET(fd, &except_fds);
HITCBC 370   362066 if (fd > nfds) 370   139614 if (fd > nfds)
HITCBC 371   222153 nfds = fd; 371   88785 nfds = fd;
372   } 372   }
373   373  
374   struct timeval tv; 374   struct timeval tv;
HITCBC 375   222466 struct timeval* tv_ptr = nullptr; 375   89118 struct timeval* tv_ptr = nullptr;
HITCBC 376   222466 if (effective_timeout_us >= 0) 376   89118 if (effective_timeout_us >= 0)
377   { 377   {
HITCBC 378   221903 tv.tv_sec = effective_timeout_us / 1000000; 378   88554 tv.tv_sec = effective_timeout_us / 1000000;
HITCBC 379   221903 tv.tv_usec = effective_timeout_us % 1000000; 379   88554 tv.tv_usec = effective_timeout_us % 1000000;
HITCBC 380   221903 tv_ptr = &tv; 380   88554 tv_ptr = &tv;
381   } 381   }
382   382  
HITCBC 383   222466 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr); 383   89118 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   222466 if (ready < 0) 388   89118 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   222466 timer_svc_->process_expired(); 396   89118 timer_svc_->process_expired();
397   397  
HITCBC 398   222466 ready_queue local_ops; 398   89118 ready_queue local_ops;
399   399  
HITCBC 400   222466 if (ready > 0) 400   89118 if (ready > 0)
401   { 401   {
HITCBC 402   206801 if (FD_ISSET(pipe_fds_[0], &read_fds)) 402   82188 if (FD_ISSET(pipe_fds_[0], &read_fds))
403   { 403   {
404   char buf[256]; 404   char buf[256];
HITCBC 405   9216 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0) 405   6898 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
406   { 406   {
407   } 407   }
408   } 408   }
409   409  
HITCBC 410   523147 for (int i = 0; i < snapshot_count; ++i) 410   205441 for (int i = 0; i < snapshot_count; ++i)
411   { 411   {
HITCBC 412   316346 int fd = snapshot[i].fd; 412   123253 int fd = snapshot[i].fd;
HITCBC 413   316346 reactor_descriptor_state* desc = snapshot[i].desc; 413   123253 reactor_descriptor_state* desc = snapshot[i].desc;
414   414  
HITCBC 415   316346 std::uint32_t flags = 0; 415   123253 std::uint32_t flags = 0;
HITCBC 416   316346 if (FD_ISSET(fd, &read_fds)) 416   123253 if (FD_ISSET(fd, &read_fds))
HITCBC 417   204410 flags |= reactor_event_read; 417   80366 flags |= reactor_event_read;
HITCBC 418   316346 if (FD_ISSET(fd, &write_fds)) 418   123253 if (FD_ISSET(fd, &write_fds))
HITCBC 419   2067 flags |= reactor_event_write; 419   1525 flags |= reactor_event_write;
HITCBC 420   316346 if (FD_ISSET(fd, &except_fds)) 420   123253 if (FD_ISSET(fd, &except_fds))
MISUBC 421   ✗ flags |= reactor_event_error; 421   ✗ flags |= reactor_event_error;
422   422  
HITCBC 423   316346 if (flags == 0) 423   123253 if (flags == 0)
HITCBC 424   109880 continue; 424   41373 continue;
425   425  
HITCBC 426   206466 desc->add_ready_events(flags); 426   81880 desc->add_ready_events(flags);
427   427  
HITCBC 428   206466 bool expected = false; 428   81880 bool expected = false;
HITCBC 429   206466 if (desc->is_enqueued_.compare_exchange_strong( 429   81880 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   206466 local_ops.push(desc); 433   81880 local_ops.push(desc);
434   } 434   }
435   } 435   }
436   } 436   }
437   437  
HITCBC 438   222466 lock.lock(); 438   89118 lock.lock();
439   439  
HITCBC 440   222466 completed_ops_.splice(local_ops); 440   89118 completed_ops_.splice(local_ops);
HITCBC 441   222466 } 441   89118 }
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