src/corosio/src/detail/select/op.hpp
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src/corosio/src/detail/select/op.hpp
| Line | Branch | Hits | Source Code |
|---|---|---|---|
| 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 <coroutine> | ||
| 22 | #include <boost/capy/error.hpp> | ||
| 23 | #include <system_error> | ||
| 24 | |||
| 25 | #include "src/detail/make_err.hpp" | ||
| 26 | #include "src/detail/dispatch_coro.hpp" | ||
| 27 | #include "src/detail/scheduler_op.hpp" | ||
| 28 | #include "src/detail/endpoint_convert.hpp" | ||
| 29 | |||
| 30 | #include <unistd.h> | ||
| 31 | #include <errno.h> | ||
| 32 | #include <fcntl.h> | ||
| 33 | |||
| 34 | #include <atomic> | ||
| 35 | #include <cstddef> | ||
| 36 | #include <memory> | ||
| 37 | #include <optional> | ||
| 38 | #include <stop_token> | ||
| 39 | |||
| 40 | #include <netinet/in.h> | ||
| 41 | #include <sys/select.h> | ||
| 42 | #include <sys/socket.h> | ||
| 43 | #include <sys/uio.h> | ||
| 44 | |||
| 45 | /* | ||
| 46 | select Operation State | ||
| 47 | ====================== | ||
| 48 | |||
| 49 | Each async I/O operation has a corresponding select_op-derived struct that | ||
| 50 | holds the operation's state while it's in flight. The socket impl owns | ||
| 51 | fixed slots for each operation type (conn_, rd_, wr_), so only one | ||
| 52 | operation of each type can be pending per socket at a time. | ||
| 53 | |||
| 54 | This mirrors the epoll_op design for consistency across backends. | ||
| 55 | |||
| 56 | Completion vs Cancellation Race | ||
| 57 | ------------------------------- | ||
| 58 | The `registered` atomic uses a tri-state (unregistered, registering, | ||
| 59 | registered) to handle two races: (1) between register_fd() and the | ||
| 60 | reactor seeing an event, and (2) between reactor completion and cancel(). | ||
| 61 | |||
| 62 | The registering state closes the window where an event could arrive | ||
| 63 | after register_fd() but before the boolean was set. The reactor and | ||
| 64 | cancel() both treat registering the same as registered when claiming. | ||
| 65 | |||
| 66 | Whoever atomically exchanges to unregistered "claims" the operation | ||
| 67 | and is responsible for completing it. The loser sees unregistered and | ||
| 68 | does nothing. The initiating thread uses compare_exchange to transition | ||
| 69 | from registering to registered; if this fails, the reactor or cancel | ||
| 70 | already claimed the op. | ||
| 71 | |||
| 72 | Impl Lifetime Management | ||
| 73 | ------------------------ | ||
| 74 | When cancel() posts an op to the scheduler's ready queue, the socket impl | ||
| 75 | might be destroyed before the scheduler processes the op. The `impl_ptr` | ||
| 76 | member holds a shared_ptr to the impl, keeping it alive until the op | ||
| 77 | completes. | ||
| 78 | |||
| 79 | EOF Detection | ||
| 80 | ------------- | ||
| 81 | For reads, 0 bytes with no error means EOF. But an empty user buffer also | ||
| 82 | returns 0 bytes. The `empty_buffer_read` flag distinguishes these cases. | ||
| 83 | |||
| 84 | SIGPIPE Prevention | ||
| 85 | ------------------ | ||
| 86 | Writes use sendmsg() with MSG_NOSIGNAL instead of writev() to prevent | ||
| 87 | SIGPIPE when the peer has closed. | ||
| 88 | */ | ||
| 89 | |||
| 90 | namespace boost::corosio::detail { | ||
| 91 | |||
| 92 | // Forward declarations for cancellation support | ||
| 93 | class select_socket_impl; | ||
| 94 | class select_acceptor_impl; | ||
| 95 | |||
| 96 | /** Registration state for async operations. | ||
| 97 | |||
| 98 | Tri-state enum to handle the race between register_fd() and | ||
| 99 | run_reactor() seeing an event. Setting REGISTERING before | ||
| 100 | calling register_fd() ensures events delivered during the | ||
| 101 | registration window are not dropped. | ||
| 102 | */ | ||
| 103 | enum class select_registration_state : std::uint8_t | ||
| 104 | { | ||
| 105 | unregistered, ///< Not registered with reactor | ||
| 106 | registering, ///< register_fd() called, not yet confirmed | ||
| 107 | registered ///< Fully registered, ready for events | ||
| 108 | }; | ||
| 109 | |||
| 110 | struct select_op : scheduler_op | ||
| 111 | { | ||
| 112 | struct canceller | ||
| 113 | { | ||
| 114 | select_op* op; | ||
| 115 | void operator()() const noexcept; | ||
| 116 | }; | ||
| 117 | |||
| 118 | std::coroutine_handle<> h; | ||
| 119 | capy::executor_ref ex; | ||
| 120 | std::error_code* ec_out = nullptr; | ||
| 121 | std::size_t* bytes_out = nullptr; | ||
| 122 | |||
| 123 | int fd = -1; | ||
| 124 | int errn = 0; | ||
| 125 | std::size_t bytes_transferred = 0; | ||
| 126 | |||
| 127 | std::atomic<bool> cancelled{false}; | ||
| 128 | std::atomic<select_registration_state> registered{select_registration_state::unregistered}; | ||
| 129 | std::optional<std::stop_callback<canceller>> stop_cb; | ||
| 130 | |||
| 131 | // Prevents use-after-free when socket is closed with pending ops. | ||
| 132 | std::shared_ptr<void> impl_ptr; | ||
| 133 | |||
| 134 | // For stop_token cancellation - pointer to owning socket/acceptor impl. | ||
| 135 | select_socket_impl* socket_impl_ = nullptr; | ||
| 136 | select_acceptor_impl* acceptor_impl_ = nullptr; | ||
| 137 | |||
| 138 | 21399 | select_op() = default; | |
| 139 | |||
| 140 | 250500 | void reset() noexcept | |
| 141 | { | ||
| 142 | 250500 | fd = -1; | |
| 143 | 250500 | errn = 0; | |
| 144 | 250500 | bytes_transferred = 0; | |
| 145 | 250500 | cancelled.store(false, std::memory_order_relaxed); | |
| 146 | 250500 | registered.store(select_registration_state::unregistered, std::memory_order_relaxed); | |
| 147 | 250500 | impl_ptr.reset(); | |
| 148 | 250500 | socket_impl_ = nullptr; | |
| 149 | 250500 | acceptor_impl_ = nullptr; | |
| 150 | 250500 | } | |
| 151 | |||
| 152 | 243389 | void operator()() override | |
| 153 | { | ||
| 154 | 243389 | stop_cb.reset(); | |
| 155 | |||
| 156 |
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243389 | if (ec_out) |
| 157 | { | ||
| 158 |
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243389 | if (cancelled.load(std::memory_order_acquire)) |
| 159 | 201 | *ec_out = capy::error::canceled; | |
| 160 |
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243188 | else if (errn != 0) |
| 161 | 1 | *ec_out = make_err(errn); | |
| 162 |
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243187 | else if (is_read_operation() && bytes_transferred == 0) |
| 163 | 5 | *ec_out = capy::error::eof; | |
| 164 | else | ||
| 165 | 243182 | *ec_out = {}; | |
| 166 | } | ||
| 167 | |||
| 168 |
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243389 | if (bytes_out) |
| 169 | 243389 | *bytes_out = bytes_transferred; | |
| 170 | |||
| 171 | // Move to stack before destroying the frame | ||
| 172 | 243389 | capy::executor_ref saved_ex( std::move( ex ) ); | |
| 173 | 243389 | std::coroutine_handle<> saved_h( std::move( h ) ); | |
| 174 | 243389 | impl_ptr.reset(); | |
| 175 |
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243389 | dispatch_coro(saved_ex, saved_h).resume(); |
| 176 | 243389 | } | |
| 177 | |||
| 178 | 121607 | virtual bool is_read_operation() const noexcept { return false; } | |
| 179 | virtual void cancel() noexcept = 0; | ||
| 180 | |||
| 181 | ✗ | void destroy() override | |
| 182 | { | ||
| 183 | ✗ | stop_cb.reset(); | |
| 184 | ✗ | impl_ptr.reset(); | |
| 185 | ✗ | } | |
| 186 | |||
| 187 | 32776 | void request_cancel() noexcept | |
| 188 | { | ||
| 189 | 32776 | cancelled.store(true, std::memory_order_release); | |
| 190 | 32776 | } | |
| 191 | |||
| 192 | void start(std::stop_token token) | ||
| 193 | { | ||
| 194 | cancelled.store(false, std::memory_order_release); | ||
| 195 | stop_cb.reset(); | ||
| 196 | socket_impl_ = nullptr; | ||
| 197 | acceptor_impl_ = nullptr; | ||
| 198 | |||
| 199 | if (token.stop_possible()) | ||
| 200 | stop_cb.emplace(token, canceller{this}); | ||
| 201 | } | ||
| 202 | |||
| 203 | 246944 | void start(std::stop_token token, select_socket_impl* impl) | |
| 204 | { | ||
| 205 | 246944 | cancelled.store(false, std::memory_order_release); | |
| 206 | 246944 | stop_cb.reset(); | |
| 207 | 246944 | socket_impl_ = impl; | |
| 208 | 246944 | acceptor_impl_ = nullptr; | |
| 209 | |||
| 210 |
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246944 | if (token.stop_possible()) |
| 211 | 100 | stop_cb.emplace(token, canceller{this}); | |
| 212 | 246944 | } | |
| 213 | |||
| 214 | 3556 | void start(std::stop_token token, select_acceptor_impl* impl) | |
| 215 | { | ||
| 216 | 3556 | cancelled.store(false, std::memory_order_release); | |
| 217 | 3556 | stop_cb.reset(); | |
| 218 | 3556 | socket_impl_ = nullptr; | |
| 219 | 3556 | acceptor_impl_ = impl; | |
| 220 | |||
| 221 |
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3556 | if (token.stop_possible()) |
| 222 | ✗ | stop_cb.emplace(token, canceller{this}); | |
| 223 | 3556 | } | |
| 224 | |||
| 225 | 250336 | void complete(int err, std::size_t bytes) noexcept | |
| 226 | { | ||
| 227 | 250336 | errn = err; | |
| 228 | 250336 | bytes_transferred = bytes; | |
| 229 | 250336 | } | |
| 230 | |||
| 231 | ✗ | virtual void perform_io() noexcept {} | |
| 232 | }; | ||
| 233 | |||
| 234 | |||
| 235 | struct select_connect_op : select_op | ||
| 236 | { | ||
| 237 | endpoint target_endpoint; | ||
| 238 | |||
| 239 | 3555 | void reset() noexcept | |
| 240 | { | ||
| 241 | 3555 | select_op::reset(); | |
| 242 | 3555 | target_endpoint = endpoint{}; | |
| 243 | 3555 | } | |
| 244 | |||
| 245 | 3555 | void perform_io() noexcept override | |
| 246 | { | ||
| 247 | // connect() completion status is retrieved via SO_ERROR, not return value | ||
| 248 | 3555 | int err = 0; | |
| 249 | 3555 | socklen_t len = sizeof(err); | |
| 250 |
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3555 | if (::getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &len) < 0) |
| 251 | ✗ | err = errno; | |
| 252 | 3555 | complete(err, 0); | |
| 253 | 3555 | } | |
| 254 | |||
| 255 | // Defined in sockets.cpp where select_socket_impl is complete | ||
| 256 | void operator()() override; | ||
| 257 | void cancel() noexcept override; | ||
| 258 | }; | ||
| 259 | |||
| 260 | |||
| 261 | struct select_read_op : select_op | ||
| 262 | { | ||
| 263 | static constexpr std::size_t max_buffers = 16; | ||
| 264 | iovec iovecs[max_buffers]; | ||
| 265 | int iovec_count = 0; | ||
| 266 | bool empty_buffer_read = false; | ||
| 267 | |||
| 268 | 121580 | bool is_read_operation() const noexcept override | |
| 269 | { | ||
| 270 | 121580 | return !empty_buffer_read; | |
| 271 | } | ||
| 272 | |||
| 273 | 121777 | void reset() noexcept | |
| 274 | { | ||
| 275 | 121777 | select_op::reset(); | |
| 276 | 121777 | iovec_count = 0; | |
| 277 | 121777 | empty_buffer_read = false; | |
| 278 | 121777 | } | |
| 279 | |||
| 280 | 124 | void perform_io() noexcept override | |
| 281 | { | ||
| 282 | 124 | ssize_t n = ::readv(fd, iovecs, iovec_count); | |
| 283 |
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124 | if (n >= 0) |
| 284 | 124 | complete(0, static_cast<std::size_t>(n)); | |
| 285 | else | ||
| 286 | ✗ | complete(errno, 0); | |
| 287 | 124 | } | |
| 288 | |||
| 289 | void cancel() noexcept override; | ||
| 290 | }; | ||
| 291 | |||
| 292 | |||
| 293 | struct select_write_op : select_op | ||
| 294 | { | ||
| 295 | static constexpr std::size_t max_buffers = 16; | ||
| 296 | iovec iovecs[max_buffers]; | ||
| 297 | int iovec_count = 0; | ||
| 298 | |||
| 299 | 121612 | void reset() noexcept | |
| 300 | { | ||
| 301 | 121612 | select_op::reset(); | |
| 302 | 121612 | iovec_count = 0; | |
| 303 | 121612 | } | |
| 304 | |||
| 305 | ✗ | void perform_io() noexcept override | |
| 306 | { | ||
| 307 | ✗ | msghdr msg{}; | |
| 308 | ✗ | msg.msg_iov = iovecs; | |
| 309 | ✗ | msg.msg_iovlen = static_cast<std::size_t>(iovec_count); | |
| 310 | |||
| 311 | ✗ | ssize_t n = ::sendmsg(fd, &msg, MSG_NOSIGNAL); | |
| 312 | ✗ | if (n >= 0) | |
| 313 | ✗ | complete(0, static_cast<std::size_t>(n)); | |
| 314 | else | ||
| 315 | ✗ | complete(errno, 0); | |
| 316 | ✗ | } | |
| 317 | |||
| 318 | void cancel() noexcept override; | ||
| 319 | }; | ||
| 320 | |||
| 321 | |||
| 322 | struct select_accept_op : select_op | ||
| 323 | { | ||
| 324 | int accepted_fd = -1; | ||
| 325 | io_object::io_object_impl* peer_impl = nullptr; | ||
| 326 | io_object::io_object_impl** impl_out = nullptr; | ||
| 327 | |||
| 328 | 3556 | void reset() noexcept | |
| 329 | { | ||
| 330 | 3556 | select_op::reset(); | |
| 331 | 3556 | accepted_fd = -1; | |
| 332 | 3556 | peer_impl = nullptr; | |
| 333 | 3556 | impl_out = nullptr; | |
| 334 | 3556 | } | |
| 335 | |||
| 336 | 3551 | void perform_io() noexcept override | |
| 337 | { | ||
| 338 | 3551 | sockaddr_in addr{}; | |
| 339 | 3551 | socklen_t addrlen = sizeof(addr); | |
| 340 | |||
| 341 | // Note: select backend uses accept() + fcntl instead of accept4() | ||
| 342 | // for broader POSIX compatibility | ||
| 343 | 3551 | int new_fd = ::accept(fd, reinterpret_cast<sockaddr*>(&addr), &addrlen); | |
| 344 | |||
| 345 |
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3551 | if (new_fd >= 0) |
| 346 | { | ||
| 347 | // Reject fds that exceed select()'s FD_SETSIZE limit. | ||
| 348 | // Better to fail now than during later async operations. | ||
| 349 |
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3551 | if (new_fd >= FD_SETSIZE) |
| 350 | { | ||
| 351 | ✗ | ::close(new_fd); | |
| 352 | ✗ | complete(EINVAL, 0); | |
| 353 | ✗ | return; | |
| 354 | } | ||
| 355 | |||
| 356 | // Set non-blocking and close-on-exec flags. | ||
| 357 | // A non-blocking socket is essential for the async reactor; | ||
| 358 | // if we can't configure it, fail rather than risk blocking. | ||
| 359 | 3551 | int flags = ::fcntl(new_fd, F_GETFL, 0); | |
| 360 |
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3551 | if (flags == -1) |
| 361 | { | ||
| 362 | ✗ | int err = errno; | |
| 363 | ✗ | ::close(new_fd); | |
| 364 | ✗ | complete(err, 0); | |
| 365 | ✗ | return; | |
| 366 | } | ||
| 367 | |||
| 368 |
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3551 | if (::fcntl(new_fd, F_SETFL, flags | O_NONBLOCK) == -1) |
| 369 | { | ||
| 370 | ✗ | int err = errno; | |
| 371 | ✗ | ::close(new_fd); | |
| 372 | ✗ | complete(err, 0); | |
| 373 | ✗ | return; | |
| 374 | } | ||
| 375 | |||
| 376 |
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3551 | if (::fcntl(new_fd, F_SETFD, FD_CLOEXEC) == -1) |
| 377 | { | ||
| 378 | ✗ | int err = errno; | |
| 379 | ✗ | ::close(new_fd); | |
| 380 | ✗ | complete(err, 0); | |
| 381 | ✗ | return; | |
| 382 | } | ||
| 383 | |||
| 384 | 3551 | accepted_fd = new_fd; | |
| 385 | 3551 | complete(0, 0); | |
| 386 | } | ||
| 387 | else | ||
| 388 | { | ||
| 389 | ✗ | complete(errno, 0); | |
| 390 | } | ||
| 391 | } | ||
| 392 | |||
| 393 | // Defined in acceptors.cpp where select_acceptor_impl is complete | ||
| 394 | void operator()() override; | ||
| 395 | void cancel() noexcept override; | ||
| 396 | }; | ||
| 397 | |||
| 398 | } // namespace boost::corosio::detail | ||
| 399 | |||
| 400 | #endif // BOOST_COROSIO_HAS_SELECT | ||
| 401 | |||
| 402 | #endif // BOOST_COROSIO_DETAIL_SELECT_OP_HPP | ||
| 403 |