libs/corosio/src/corosio/src/detail/select/op.hpp
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libs/corosio/src/corosio/src/detail/select/op.hpp
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|---|---|---|---|
| 1 | // | ||
| 2 | // Copyright (c) 2026 Steve Gerbino | ||
| 3 | // | ||
| 4 | // Distributed under the Boost Software License, Version 1.0. (See accompanying | ||
| 5 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | ||
| 6 | // | ||
| 7 | // Official repository: https://github.com/cppalliance/corosio | ||
| 8 | // | ||
| 9 | |||
| 10 | #ifndef BOOST_COROSIO_DETAIL_SELECT_OP_HPP | ||
| 11 | #define BOOST_COROSIO_DETAIL_SELECT_OP_HPP | ||
| 12 | |||
| 13 | #include <boost/corosio/detail/platform.hpp> | ||
| 14 | |||
| 15 | #if BOOST_COROSIO_HAS_SELECT | ||
| 16 | |||
| 17 | #include <boost/corosio/detail/config.hpp> | ||
| 18 | #include <boost/corosio/io_object.hpp> | ||
| 19 | #include <boost/corosio/endpoint.hpp> | ||
| 20 | #include <boost/capy/ex/executor_ref.hpp> | ||
| 21 | #include <boost/capy/coro.hpp> | ||
| 22 | #include <boost/capy/error.hpp> | ||
| 23 | #include <system_error> | ||
| 24 | |||
| 25 | #include "src/detail/make_err.hpp" | ||
| 26 | #include "src/detail/scheduler_op.hpp" | ||
| 27 | #include "src/detail/endpoint_convert.hpp" | ||
| 28 | |||
| 29 | #include <unistd.h> | ||
| 30 | #include <errno.h> | ||
| 31 | #include <fcntl.h> | ||
| 32 | |||
| 33 | #include <atomic> | ||
| 34 | #include <cstddef> | ||
| 35 | #include <memory> | ||
| 36 | #include <optional> | ||
| 37 | #include <stop_token> | ||
| 38 | |||
| 39 | #include <netinet/in.h> | ||
| 40 | #include <sys/select.h> | ||
| 41 | #include <sys/socket.h> | ||
| 42 | #include <sys/uio.h> | ||
| 43 | |||
| 44 | /* | ||
| 45 | select Operation State | ||
| 46 | ====================== | ||
| 47 | |||
| 48 | Each async I/O operation has a corresponding select_op-derived struct that | ||
| 49 | holds the operation's state while it's in flight. The socket impl owns | ||
| 50 | fixed slots for each operation type (conn_, rd_, wr_), so only one | ||
| 51 | operation of each type can be pending per socket at a time. | ||
| 52 | |||
| 53 | This mirrors the epoll_op design for consistency across backends. | ||
| 54 | |||
| 55 | Completion vs Cancellation Race | ||
| 56 | ------------------------------- | ||
| 57 | The `registered` atomic uses a tri-state (unregistered, registering, | ||
| 58 | registered) to handle two races: (1) between register_fd() and the | ||
| 59 | reactor seeing an event, and (2) between reactor completion and cancel(). | ||
| 60 | |||
| 61 | The registering state closes the window where an event could arrive | ||
| 62 | after register_fd() but before the boolean was set. The reactor and | ||
| 63 | cancel() both treat registering the same as registered when claiming. | ||
| 64 | |||
| 65 | Whoever atomically exchanges to unregistered "claims" the operation | ||
| 66 | and is responsible for completing it. The loser sees unregistered and | ||
| 67 | does nothing. The initiating thread uses compare_exchange to transition | ||
| 68 | from registering to registered; if this fails, the reactor or cancel | ||
| 69 | already claimed the op. | ||
| 70 | |||
| 71 | Impl Lifetime Management | ||
| 72 | ------------------------ | ||
| 73 | When cancel() posts an op to the scheduler's ready queue, the socket impl | ||
| 74 | might be destroyed before the scheduler processes the op. The `impl_ptr` | ||
| 75 | member holds a shared_ptr to the impl, keeping it alive until the op | ||
| 76 | completes. | ||
| 77 | |||
| 78 | EOF Detection | ||
| 79 | ------------- | ||
| 80 | For reads, 0 bytes with no error means EOF. But an empty user buffer also | ||
| 81 | returns 0 bytes. The `empty_buffer_read` flag distinguishes these cases. | ||
| 82 | |||
| 83 | SIGPIPE Prevention | ||
| 84 | ------------------ | ||
| 85 | Writes use sendmsg() with MSG_NOSIGNAL instead of writev() to prevent | ||
| 86 | SIGPIPE when the peer has closed. | ||
| 87 | */ | ||
| 88 | |||
| 89 | namespace boost::corosio::detail { | ||
| 90 | |||
| 91 | // Forward declarations for cancellation support | ||
| 92 | class select_socket_impl; | ||
| 93 | class select_acceptor_impl; | ||
| 94 | |||
| 95 | /** Registration state for async operations. | ||
| 96 | |||
| 97 | Tri-state enum to handle the race between register_fd() and | ||
| 98 | run_reactor() seeing an event. Setting REGISTERING before | ||
| 99 | calling register_fd() ensures events delivered during the | ||
| 100 | registration window are not dropped. | ||
| 101 | */ | ||
| 102 | enum class select_registration_state : std::uint8_t | ||
| 103 | { | ||
| 104 | unregistered, ///< Not registered with reactor | ||
| 105 | registering, ///< register_fd() called, not yet confirmed | ||
| 106 | registered ///< Fully registered, ready for events | ||
| 107 | }; | ||
| 108 | |||
| 109 | struct select_op : scheduler_op | ||
| 110 | { | ||
| 111 | struct canceller | ||
| 112 | { | ||
| 113 | select_op* op; | ||
| 114 | void operator()() const noexcept; | ||
| 115 | }; | ||
| 116 | |||
| 117 | capy::coro h; | ||
| 118 | capy::executor_ref ex; | ||
| 119 | std::error_code* ec_out = nullptr; | ||
| 120 | std::size_t* bytes_out = nullptr; | ||
| 121 | |||
| 122 | int fd = -1; | ||
| 123 | int errn = 0; | ||
| 124 | std::size_t bytes_transferred = 0; | ||
| 125 | |||
| 126 | std::atomic<bool> cancelled{false}; | ||
| 127 | std::atomic<select_registration_state> registered{select_registration_state::unregistered}; | ||
| 128 | std::optional<std::stop_callback<canceller>> stop_cb; | ||
| 129 | |||
| 130 | // Prevents use-after-free when socket is closed with pending ops. | ||
| 131 | std::shared_ptr<void> impl_ptr; | ||
| 132 | |||
| 133 | // For stop_token cancellation - pointer to owning socket/acceptor impl. | ||
| 134 | select_socket_impl* socket_impl_ = nullptr; | ||
| 135 | select_acceptor_impl* acceptor_impl_ = nullptr; | ||
| 136 | |||
| 137 | 12165 | select_op() = default; | |
| 138 | |||
| 139 | 166381 | void reset() noexcept | |
| 140 | { | ||
| 141 | 166381 | fd = -1; | |
| 142 | 166381 | errn = 0; | |
| 143 | 166381 | bytes_transferred = 0; | |
| 144 | 166381 | cancelled.store(false, std::memory_order_relaxed); | |
| 145 | 166381 | registered.store(select_registration_state::unregistered, std::memory_order_relaxed); | |
| 146 | 166381 | impl_ptr.reset(); | |
| 147 | 166381 | socket_impl_ = nullptr; | |
| 148 | 166381 | acceptor_impl_ = nullptr; | |
| 149 | 166381 | } | |
| 150 | |||
| 151 | 162348 | void operator()() override | |
| 152 | { | ||
| 153 | 162348 | stop_cb.reset(); | |
| 154 | |||
| 155 |
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162348 | if (ec_out) |
| 156 | { | ||
| 157 |
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162348 | if (cancelled.load(std::memory_order_acquire)) |
| 158 | 198 | *ec_out = capy::error::canceled; | |
| 159 |
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162150 | else if (errn != 0) |
| 160 | 1 | *ec_out = make_err(errn); | |
| 161 |
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162149 | else if (is_read_operation() && bytes_transferred == 0) |
| 162 | 5 | *ec_out = capy::error::eof; | |
| 163 | else | ||
| 164 | 162144 | *ec_out = {}; | |
| 165 | } | ||
| 166 | |||
| 167 |
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162348 | if (bytes_out) |
| 168 | 162348 | *bytes_out = bytes_transferred; | |
| 169 | |||
| 170 | // Move to stack before destroying the frame | ||
| 171 | 162348 | capy::executor_ref saved_ex( std::move( ex ) ); | |
| 172 | 162348 | capy::coro saved_h( std::move( h ) ); | |
| 173 | 162348 | impl_ptr.reset(); | |
| 174 |
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162348 | saved_ex.dispatch( saved_h ); |
| 175 | 162348 | } | |
| 176 | |||
| 177 | 81110 | virtual bool is_read_operation() const noexcept { return false; } | |
| 178 | virtual void cancel() noexcept = 0; | ||
| 179 | |||
| 180 | ✗ | void destroy() override | |
| 181 | { | ||
| 182 | ✗ | stop_cb.reset(); | |
| 183 | ✗ | impl_ptr.reset(); | |
| 184 | ✗ | } | |
| 185 | |||
| 186 | 18662 | void request_cancel() noexcept | |
| 187 | { | ||
| 188 | 18662 | cancelled.store(true, std::memory_order_release); | |
| 189 | 18662 | } | |
| 190 | |||
| 191 | void start(std::stop_token token) | ||
| 192 | { | ||
| 193 | cancelled.store(false, std::memory_order_release); | ||
| 194 | stop_cb.reset(); | ||
| 195 | socket_impl_ = nullptr; | ||
| 196 | acceptor_impl_ = nullptr; | ||
| 197 | |||
| 198 | if (token.stop_possible()) | ||
| 199 | stop_cb.emplace(token, canceller{this}); | ||
| 200 | } | ||
| 201 | |||
| 202 | 164364 | void start(std::stop_token token, select_socket_impl* impl) | |
| 203 | { | ||
| 204 | 164364 | cancelled.store(false, std::memory_order_release); | |
| 205 | 164364 | stop_cb.reset(); | |
| 206 | 164364 | socket_impl_ = impl; | |
| 207 | 164364 | acceptor_impl_ = nullptr; | |
| 208 | |||
| 209 |
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164364 | if (token.stop_possible()) |
| 210 | 98 | stop_cb.emplace(token, canceller{this}); | |
| 211 | 164364 | } | |
| 212 | |||
| 213 | 2017 | void start(std::stop_token token, select_acceptor_impl* impl) | |
| 214 | { | ||
| 215 | 2017 | cancelled.store(false, std::memory_order_release); | |
| 216 | 2017 | stop_cb.reset(); | |
| 217 | 2017 | socket_impl_ = nullptr; | |
| 218 | 2017 | acceptor_impl_ = impl; | |
| 219 | |||
| 220 |
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2017 | if (token.stop_possible()) |
| 221 | ✗ | stop_cb.emplace(token, canceller{this}); | |
| 222 | 2017 | } | |
| 223 | |||
| 224 | 166264 | void complete(int err, std::size_t bytes) noexcept | |
| 225 | { | ||
| 226 | 166264 | errn = err; | |
| 227 | 166264 | bytes_transferred = bytes; | |
| 228 | 166264 | } | |
| 229 | |||
| 230 | ✗ | virtual void perform_io() noexcept {} | |
| 231 | }; | ||
| 232 | |||
| 233 | |||
| 234 | struct select_connect_op : select_op | ||
| 235 | { | ||
| 236 | endpoint target_endpoint; | ||
| 237 | |||
| 238 | 2016 | void reset() noexcept | |
| 239 | { | ||
| 240 | 2016 | select_op::reset(); | |
| 241 | 2016 | target_endpoint = endpoint{}; | |
| 242 | 2016 | } | |
| 243 | |||
| 244 | 2016 | void perform_io() noexcept override | |
| 245 | { | ||
| 246 | // connect() completion status is retrieved via SO_ERROR, not return value | ||
| 247 | 2016 | int err = 0; | |
| 248 | 2016 | socklen_t len = sizeof(err); | |
| 249 |
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2016 | if (::getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &len) < 0) |
| 250 | ✗ | err = errno; | |
| 251 | 2016 | complete(err, 0); | |
| 252 | 2016 | } | |
| 253 | |||
| 254 | // Defined in sockets.cpp where select_socket_impl is complete | ||
| 255 | void operator()() override; | ||
| 256 | void cancel() noexcept override; | ||
| 257 | }; | ||
| 258 | |||
| 259 | |||
| 260 | struct select_read_op : select_op | ||
| 261 | { | ||
| 262 | static constexpr std::size_t max_buffers = 16; | ||
| 263 | iovec iovecs[max_buffers]; | ||
| 264 | int iovec_count = 0; | ||
| 265 | bool empty_buffer_read = false; | ||
| 266 | |||
| 267 | 81039 | bool is_read_operation() const noexcept override | |
| 268 | { | ||
| 269 | 81039 | return !empty_buffer_read; | |
| 270 | } | ||
| 271 | |||
| 272 | 81233 | void reset() noexcept | |
| 273 | { | ||
| 274 | 81233 | select_op::reset(); | |
| 275 | 81233 | iovec_count = 0; | |
| 276 | 81233 | empty_buffer_read = false; | |
| 277 | 81233 | } | |
| 278 | |||
| 279 | 79 | void perform_io() noexcept override | |
| 280 | { | ||
| 281 | 79 | ssize_t n = ::readv(fd, iovecs, iovec_count); | |
| 282 |
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79 | if (n >= 0) |
| 283 | 79 | complete(0, static_cast<std::size_t>(n)); | |
| 284 | else | ||
| 285 | ✗ | complete(errno, 0); | |
| 286 | 79 | } | |
| 287 | |||
| 288 | void cancel() noexcept override; | ||
| 289 | }; | ||
| 290 | |||
| 291 | |||
| 292 | struct select_write_op : select_op | ||
| 293 | { | ||
| 294 | static constexpr std::size_t max_buffers = 16; | ||
| 295 | iovec iovecs[max_buffers]; | ||
| 296 | int iovec_count = 0; | ||
| 297 | |||
| 298 | 81115 | void reset() noexcept | |
| 299 | { | ||
| 300 | 81115 | select_op::reset(); | |
| 301 | 81115 | iovec_count = 0; | |
| 302 | 81115 | } | |
| 303 | |||
| 304 | ✗ | void perform_io() noexcept override | |
| 305 | { | ||
| 306 | ✗ | msghdr msg{}; | |
| 307 | ✗ | msg.msg_iov = iovecs; | |
| 308 | ✗ | msg.msg_iovlen = static_cast<std::size_t>(iovec_count); | |
| 309 | |||
| 310 | ✗ | ssize_t n = ::sendmsg(fd, &msg, MSG_NOSIGNAL); | |
| 311 | ✗ | if (n >= 0) | |
| 312 | ✗ | complete(0, static_cast<std::size_t>(n)); | |
| 313 | else | ||
| 314 | ✗ | complete(errno, 0); | |
| 315 | ✗ | } | |
| 316 | |||
| 317 | void cancel() noexcept override; | ||
| 318 | }; | ||
| 319 | |||
| 320 | |||
| 321 | struct select_accept_op : select_op | ||
| 322 | { | ||
| 323 | int accepted_fd = -1; | ||
| 324 | io_object::io_object_impl* peer_impl = nullptr; | ||
| 325 | io_object::io_object_impl** impl_out = nullptr; | ||
| 326 | |||
| 327 | 2017 | void reset() noexcept | |
| 328 | { | ||
| 329 | 2017 | select_op::reset(); | |
| 330 | 2017 | accepted_fd = -1; | |
| 331 | 2017 | peer_impl = nullptr; | |
| 332 | 2017 | impl_out = nullptr; | |
| 333 | 2017 | } | |
| 334 | |||
| 335 | 2012 | void perform_io() noexcept override | |
| 336 | { | ||
| 337 | 2012 | sockaddr_in addr{}; | |
| 338 | 2012 | socklen_t addrlen = sizeof(addr); | |
| 339 | |||
| 340 | // Note: select backend uses accept() + fcntl instead of accept4() | ||
| 341 | // for broader POSIX compatibility | ||
| 342 | 2012 | int new_fd = ::accept(fd, reinterpret_cast<sockaddr*>(&addr), &addrlen); | |
| 343 | |||
| 344 |
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2012 | if (new_fd >= 0) |
| 345 | { | ||
| 346 | // Reject fds that exceed select()'s FD_SETSIZE limit. | ||
| 347 | // Better to fail now than during later async operations. | ||
| 348 |
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2012 | if (new_fd >= FD_SETSIZE) |
| 349 | { | ||
| 350 | ✗ | ::close(new_fd); | |
| 351 | ✗ | complete(EINVAL, 0); | |
| 352 | ✗ | return; | |
| 353 | } | ||
| 354 | |||
| 355 | // Set non-blocking and close-on-exec flags. | ||
| 356 | // A non-blocking socket is essential for the async reactor; | ||
| 357 | // if we can't configure it, fail rather than risk blocking. | ||
| 358 | 2012 | int flags = ::fcntl(new_fd, F_GETFL, 0); | |
| 359 |
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2012 | if (flags == -1) |
| 360 | { | ||
| 361 | ✗ | int err = errno; | |
| 362 | ✗ | ::close(new_fd); | |
| 363 | ✗ | complete(err, 0); | |
| 364 | ✗ | return; | |
| 365 | } | ||
| 366 | |||
| 367 |
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2012 | if (::fcntl(new_fd, F_SETFL, flags | O_NONBLOCK) == -1) |
| 368 | { | ||
| 369 | ✗ | int err = errno; | |
| 370 | ✗ | ::close(new_fd); | |
| 371 | ✗ | complete(err, 0); | |
| 372 | ✗ | return; | |
| 373 | } | ||
| 374 | |||
| 375 |
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2012 | if (::fcntl(new_fd, F_SETFD, FD_CLOEXEC) == -1) |
| 376 | { | ||
| 377 | ✗ | int err = errno; | |
| 378 | ✗ | ::close(new_fd); | |
| 379 | ✗ | complete(err, 0); | |
| 380 | ✗ | return; | |
| 381 | } | ||
| 382 | |||
| 383 | 2012 | accepted_fd = new_fd; | |
| 384 | 2012 | complete(0, 0); | |
| 385 | } | ||
| 386 | else | ||
| 387 | { | ||
| 388 | ✗ | complete(errno, 0); | |
| 389 | } | ||
| 390 | } | ||
| 391 | |||
| 392 | // Defined in acceptors.cpp where select_acceptor_impl is complete | ||
| 393 | void operator()() override; | ||
| 394 | void cancel() noexcept override; | ||
| 395 | }; | ||
| 396 | |||
| 397 | } // namespace boost::corosio::detail | ||
| 398 | |||
| 399 | #endif // BOOST_COROSIO_HAS_SELECT | ||
| 400 | |||
| 401 | #endif // BOOST_COROSIO_DETAIL_SELECT_OP_HPP | ||
| 402 |