. /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   605 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int) 154   617 inline select_scheduler::select_scheduler(capy::execution_context& ctx, int)
HITCBC 155   605 : pipe_fds_{-1, -1} 155   617 : pipe_fds_{-1, -1}
HITCBC 156   605 , max_fd_(-1) 156   617 , max_fd_(-1)
157   { 157   {
HITCBC 158   605 if (::pipe(pipe_fds_) < 0) 158   617 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   1815 for (int i = 0; i < 2; ++i) 161   1851 for (int i = 0; i < 2; ++i)
162   { 162   {
HITCBC 163   1210 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0); 163   1234 int flags = ::fcntl(pipe_fds_[i], F_GETFL, 0);
HITCBC 164   1210 if (flags == -1) 164   1234 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   1210 if (::fcntl(pipe_fds_[i], F_SETFL, flags | O_NONBLOCK) == -1) 171   1234 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   1210 if (::fcntl(pipe_fds_[i], F_SETFD, FD_CLOEXEC) == -1) 178   1234 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   605 timer_svc_ = &get_timer_service(ctx, *this); 187   617 timer_svc_ = &get_timer_service(ctx, *this);
HITCBC 188   605 timer_svc_->set_on_earliest_changed( 188   617 timer_svc_->set_on_earliest_changed(
HITCBC 189   4599 timer_service::callback(this, [](void* p) { 189   5146 timer_service::callback(this, [](void* p) {
HITCBC 190   3994 static_cast<select_scheduler*>(p)->interrupt_reactor(); 190   4529 static_cast<select_scheduler*>(p)->interrupt_reactor();
HITCBC 191   3994 })); 191   4529 }));
192   192  
HITCBC 193   605 get_resolver_service(ctx, *this); 193   617 get_resolver_service(ctx, *this);
HITCBC 194   605 get_signal_service(ctx, *this); 194   617 get_signal_service(ctx, *this);
HITCBC 195   605 get_stream_file_service(ctx, *this); 195   617 get_stream_file_service(ctx, *this);
HITCBC 196   605 get_random_access_file_service(ctx, *this); 196   617 get_random_access_file_service(ctx, *this);
197   197  
HITCBC 198   605 completed_ops_.push(&task_op_); 198   617 completed_ops_.push(&task_op_);
HITCBC 199   605 } 199   617 }
200   200  
HITCBC 201   1210 inline select_scheduler::~select_scheduler() 201   1234 inline select_scheduler::~select_scheduler()
202   { 202   {
HITCBC 203   605 if (pipe_fds_[0] >= 0) 203   617 if (pipe_fds_[0] >= 0)
HITCBC 204   605 ::close(pipe_fds_[0]); 204   617 ::close(pipe_fds_[0]);
HITCBC 205   605 if (pipe_fds_[1] >= 0) 205   617 if (pipe_fds_[1] >= 0)
HITCBC 206   605 ::close(pipe_fds_[1]); 206   617 ::close(pipe_fds_[1]);
HITCBC 207   1210 } 207   1234 }
208   208  
209   inline void 209   inline void
HITCBC 210   605 select_scheduler::shutdown() 210   617 select_scheduler::shutdown()
211   { 211   {
HITCBC 212   605 shutdown_drain(); 212   617 shutdown_drain();
213   213  
HITCBC 214   605 if (pipe_fds_[1] >= 0) 214   617 if (pipe_fds_[1] >= 0)
HITCBC 215   605 interrupt_reactor(); 215   617 interrupt_reactor();
HITCBC 216   605 } 216   617 }
217   217  
218   inline void 218   inline void
HITCBC 219   6618 select_scheduler::register_descriptor( 219   7707 select_scheduler::register_descriptor(
220   int fd, reactor_descriptor_state* desc) const 220   int fd, reactor_descriptor_state* desc) const
221   { 221   {
HITCBC 222   6618 if (fd < 0 || fd >= FD_SETSIZE) 222   7707 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   6618 desc->registered_events = reactor_event_read | reactor_event_write; 225   7707 desc->registered_events = reactor_event_read | reactor_event_write;
HITCBC 226   6618 desc->fd = fd; 226   7707 desc->fd = fd;
HITCBC 227   6618 desc->scheduler_ = this; 227   7707 desc->scheduler_ = this;
HITCBC 228   6618 desc->mutex.set_enabled(reactor_io_locking_); 228   7707 desc->mutex.set_enabled(reactor_io_locking_);
HITCBC 229   6618 desc->ready_events_.store(0, std::memory_order_relaxed); 229   7707 desc->ready_events_.store(0, std::memory_order_relaxed);
230   230  
231   { 231   {
HITCBC 232   6618 conditionally_enabled_mutex::scoped_lock lock(desc->mutex); 232   7707 conditionally_enabled_mutex::scoped_lock lock(desc->mutex);
HITCBC 233   6618 desc->impl_ref_.reset(); 233   7707 desc->impl_ref_.reset();
HITCBC 234   6618 desc->read_ready = false; 234   7707 desc->read_ready = false;
HITCBC 235   6618 desc->write_ready = false; 235   7707 desc->write_ready = false;
HITCBC 236   6618 } 236   7707 }
237   237  
238   { 238   {
HITCBC 239   6618 mutex_type::scoped_lock lock(mutex_); 239   7707 mutex_type::scoped_lock lock(mutex_);
HITCBC 240   6618 registered_descs_[fd] = desc; 240   7707 registered_descs_[fd] = desc;
HITCBC 241   6618 if (fd > max_fd_) 241   7707 if (fd > max_fd_)
HITCBC 242   6613 max_fd_ = fd; 242   7702 max_fd_ = fd;
HITCBC 243   6618 } 243   7707 }
244   244  
HITCBC 245   6618 interrupt_reactor(); 245   7707 interrupt_reactor();
HITCBC 246   6618 } 246   7707 }
247   247  
248   inline void 248   inline void
HITCBC 249   6577 select_scheduler::deregister_descriptor(int fd) const 249   7666 select_scheduler::deregister_descriptor(int fd) const
250   { 250   {
HITCBC 251   6577 mutex_type::scoped_lock lock(mutex_); 251   7666 mutex_type::scoped_lock lock(mutex_);
252   252  
HITCBC 253   6577 auto it = registered_descs_.find(fd); 253   7666 auto it = registered_descs_.find(fd);
HITCBC 254   6577 if (it == registered_descs_.end()) 254   7666 if (it == registered_descs_.end())
MISUBC 255   ✗ return; 255   ✗ return;
256   256  
HITCBC 257   6577 registered_descs_.erase(it); 257   7666 registered_descs_.erase(it);
258   258  
HITCBC 259   6577 if (fd == max_fd_) 259   7666 if (fd == max_fd_)
260   { 260   {
HITCBC 261   6456 max_fd_ = pipe_fds_[0]; 261   7544 max_fd_ = pipe_fds_[0];
HITCBC 262   12658 for (auto& [registered_fd, state] : registered_descs_) 262   14825 for (auto& [registered_fd, state] : registered_descs_)
263   { 263   {
HITCBC 264   6202 if (registered_fd > max_fd_) 264   7281 if (registered_fd > max_fd_)
HITCBC 265   6155 max_fd_ = registered_fd; 265   7234 max_fd_ = registered_fd;
266   } 266   }
267   } 267   }
HITCBC 268   6577 } 268   7666 }
269   269  
270   inline void 270   inline void
HITCBC 271   3191 select_scheduler::notify_reactor() const 271   3728 select_scheduler::notify_reactor() const
272   { 272   {
HITCBC 273   3191 interrupt_reactor(); 273   3728 interrupt_reactor();
HITCBC 274   3191 } 274   3728 }
275   275  
276   inline void 276   inline void
HITCBC 277   14880 select_scheduler::interrupt_reactor() const 277   17079 select_scheduler::interrupt_reactor() const
278   { 278   {
HITCBC 279   14880 char byte = 1; 279   17079 char byte = 1;
HITCBC 280   14880 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1); 280   17079 [[maybe_unused]] auto r = ::write(pipe_fds_[1], &byte, 1);
HITCBC 281   14880 } 281   17079 }
282   282  
283   inline long 283   inline long
HITCBC 284   292126 select_scheduler::calculate_timeout(long requested_timeout_us) const 284   251504 select_scheduler::calculate_timeout(long requested_timeout_us) const
285   { 285   {
HITCBC 286   292126 if (requested_timeout_us == 0) 286   251504 if (requested_timeout_us == 0)
MISUBC 287   ✗ return 0; 287   ✗ return 0;
288   288  
HITCBC 289   292126 auto nearest = timer_svc_->nearest_expiry(); 289   251504 auto nearest = timer_svc_->nearest_expiry();
HITCBC 290   292126 if (nearest == timer_service::time_point::max()) 290   251504 if (nearest == timer_service::time_point::max())
HITCBC 291   574 return requested_timeout_us; 291   581 return requested_timeout_us;
292   292  
HITCBC 293   291552 auto now = std::chrono::steady_clock::now(); 293   250923 auto now = std::chrono::steady_clock::now();
HITCBC 294   291552 if (nearest <= now) 294   250923 if (nearest <= now)
HITCBC 295   961 return 0; 295   947 return 0;
296   296  
297   auto timer_timeout_us = 297   auto timer_timeout_us =
HITCBC 298   290591 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now) 298   249976 std::chrono::duration_cast<std::chrono::microseconds>(nearest - now)
HITCBC 299   290591 .count(); 299   249976 .count();
300   300  
HITCBC 301   290591 constexpr auto long_max = 301   249976 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   290591 (std::min)((std::max)(static_cast<long long>(timer_timeout_us), 304   249976 (std::min)((std::max)(static_cast<long long>(timer_timeout_us),
HITCBC 305   290591 static_cast<long long>(0)), 305   249976 static_cast<long long>(0)),
HITCBC 306   290591 long_max); 306   249976 long_max);
307   307  
HITCBC 308   290591 if (requested_timeout_us < 0) 308   249976 if (requested_timeout_us < 0)
HITCBC 309   290591 return static_cast<long>(capped_timer_us); 309   249976 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   327341 select_scheduler::run_task( 317   275267 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   327341 task_interrupted_ ? 0 : calculate_timeout(timeout_us); 321   275267 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   327341 int snapshot_count = 0; 335   275267 int snapshot_count = 0;
336   336  
HITCBC 337   873377 for (auto& [fd, desc] : registered_descs_) 337   691346 for (auto& [fd, desc] : registered_descs_)
338   { 338   {
HITCBC 339   546036 if (snapshot_count < FD_SETSIZE) 339   416079 if (snapshot_count < FD_SETSIZE)
340   { 340   {
HITCBC 341   546036 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex); 341   416079 conditionally_enabled_mutex::scoped_lock desc_lock(desc->mutex);
HITCBC 342   546036 snapshot[snapshot_count].fd = fd; 342   416079 snapshot[snapshot_count].fd = fd;
HITCBC 343   546036 snapshot[snapshot_count].desc = desc; 343   416079 snapshot[snapshot_count].desc = desc;
HITCBC 344   546036 snapshot[snapshot_count].needs_write = 344   416079 snapshot[snapshot_count].needs_write =
HITCBC 345   546036 (desc->write_op || desc->connect_op); 345   416079 (desc->write_op || desc->connect_op);
HITCBC 346   546036 ++snapshot_count; 346   416079 ++snapshot_count;
HITCBC 347   546036 } 347   416079 }
348   } 348   }
349   349  
HITCBC 350   327341 if (lock.owns_lock()) 350   275267 if (lock.owns_lock())
HITCBC 351   292127 lock.unlock(); 351   251505 lock.unlock();
352   352  
HITCBC 353   327341 task_cleanup on_exit{this, &lock, ctx}; 353   275267 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   5564797 FD_ZERO(&read_fds); 356   4679539 FD_ZERO(&read_fds);
HITCBC 357   5564797 FD_ZERO(&write_fds); 357   4679539 FD_ZERO(&write_fds);
HITCBC 358   5564797 FD_ZERO(&except_fds); 358   4679539 FD_ZERO(&except_fds);
359   359  
HITCBC 360   327341 FD_SET(pipe_fds_[0], &read_fds); 360   275267 FD_SET(pipe_fds_[0], &read_fds);
HITCBC 361   327341 int nfds = pipe_fds_[0]; 361   275267 int nfds = pipe_fds_[0];
362   362  
HITCBC 363   873377 for (int i = 0; i < snapshot_count; ++i) 363   691346 for (int i = 0; i < snapshot_count; ++i)
364   { 364   {
HITCBC 365   546036 int fd = snapshot[i].fd; 365   416079 int fd = snapshot[i].fd;
HITCBC 366   546036 FD_SET(fd, &read_fds); 366   416079 FD_SET(fd, &read_fds);
HITCBC 367   546036 if (snapshot[i].needs_write) 367   416079 if (snapshot[i].needs_write)
HITCBC 368   12405 FD_SET(fd, &write_fds); 368   14408 FD_SET(fd, &write_fds);
HITCBC 369   546036 FD_SET(fd, &except_fds); 369   416079 FD_SET(fd, &except_fds);
HITCBC 370   546036 if (fd > nfds) 370   416079 if (fd > nfds)
HITCBC 371   326983 nfds = fd; 371   274893 nfds = fd;
372   } 372   }
373   373  
374   struct timeval tv; 374   struct timeval tv;
HITCBC 375   327341 struct timeval* tv_ptr = nullptr; 375   275267 struct timeval* tv_ptr = nullptr;
HITCBC 376   327341 if (effective_timeout_us >= 0) 376   275267 if (effective_timeout_us >= 0)
377   { 377   {
HITCBC 378   326770 tv.tv_sec = effective_timeout_us / 1000000; 378   274690 tv.tv_sec = effective_timeout_us / 1000000;
HITCBC 379   326770 tv.tv_usec = effective_timeout_us % 1000000; 379   274690 tv.tv_usec = effective_timeout_us % 1000000;
HITCBC 380   326770 tv_ptr = &tv; 380   274690 tv_ptr = &tv;
381   } 381   }
382   382  
HITCBC 383   327341 int ready = ::select(nfds + 1, &read_fds, &write_fds, &except_fds, tv_ptr); 383   275267 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   327341 if (ready < 0) 388   275267 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   327341 timer_svc_->process_expired(); 396   275267 timer_svc_->process_expired();
397   397  
HITCBC 398   327341 ready_queue local_ops; 398   275267 ready_queue local_ops;
399   399  
HITCBC 400   327341 if (ready > 0) 400   275267 if (ready > 0)
401   { 401   {
HITCBC 402   303539 if (FD_ISSET(pipe_fds_[0], &read_fds)) 402   256854 if (FD_ISSET(pipe_fds_[0], &read_fds))
403   { 403   {
404   char buf[256]; 404   char buf[256];
HITCBC 405   13770 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0) 405   15934 while (::read(pipe_fds_[0], buf, sizeof(buf)) > 0)
406   { 406   {
407   } 407   }
408   } 408   }
409   409  
HITCBC 410   780497 for (int i = 0; i < snapshot_count; ++i) 410   624972 for (int i = 0; i < snapshot_count; ++i)
411   { 411   {
HITCBC 412   476958 int fd = snapshot[i].fd; 412   368118 int fd = snapshot[i].fd;
HITCBC 413   476958 reactor_descriptor_state* desc = snapshot[i].desc; 413   368118 reactor_descriptor_state* desc = snapshot[i].desc;
414   414  
HITCBC 415   476958 std::uint32_t flags = 0; 415   368118 std::uint32_t flags = 0;
HITCBC 416   476958 if (FD_ISSET(fd, &read_fds)) 416   368118 if (FD_ISSET(fd, &read_fds))
HITCBC 417   300004 flags |= reactor_event_read; 417   252764 flags |= reactor_event_read;
HITCBC 418   476958 if (FD_ISSET(fd, &write_fds)) 418   368118 if (FD_ISSET(fd, &write_fds))
HITCBC 419   3188 flags |= reactor_event_write; 419   3725 flags |= reactor_event_write;
HITCBC 420   476958 if (FD_ISSET(fd, &except_fds)) 420   368118 if (FD_ISSET(fd, &except_fds))
MISUBC 421   ✗ flags |= reactor_event_error; 421   ✗ flags |= reactor_event_error;
422   422  
HITCBC 423   476958 if (flags == 0) 423   368118 if (flags == 0)
HITCBC 424   173776 continue; 424   111639 continue;
425   425  
HITCBC 426   303182 desc->add_ready_events(flags); 426   256479 desc->add_ready_events(flags);
427   427  
HITCBC 428   303182 bool expected = false; 428   256479 bool expected = false;
HITCBC 429   303182 if (desc->is_enqueued_.compare_exchange_strong( 429   256479 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   303182 local_ops.push(desc); 433   256479 local_ops.push(desc);
434   } 434   }
435   } 435   }
436   } 436   }
437   437  
HITCBC 438   327341 lock.lock(); 438   275267 lock.lock();
439   439  
HITCBC 440   327341 completed_ops_.splice(local_ops); 440   275267 completed_ops_.splice(local_ops);
HITCBC 441   327341 } 441   275267 }
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