1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479
use crate::sync::mpsc::chan; use crate::sync::mpsc::error::{ClosedError, SendError, TryRecvError, TrySendError}; use crate::sync::semaphore_ll as semaphore; cfg_time! { use crate::sync::mpsc::error::SendTimeoutError; use crate::time::Duration; } use std::fmt; use std::task::{Context, Poll}; /// Send values to the associated `Receiver`. /// /// Instances are created by the [`channel`](channel) function. pub struct Sender<T> { chan: chan::Tx<T, Semaphore>, } impl<T> Clone for Sender<T> { fn clone(&self) -> Self { Sender { chan: self.chan.clone(), } } } impl<T> fmt::Debug for Sender<T> { fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { fmt.debug_struct("Sender") .field("chan", &self.chan) .finish() } } /// Receive values from the associated `Sender`. /// /// Instances are created by the [`channel`](channel) function. pub struct Receiver<T> { /// The channel receiver chan: chan::Rx<T, Semaphore>, } impl<T> fmt::Debug for Receiver<T> { fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { fmt.debug_struct("Receiver") .field("chan", &self.chan) .finish() } } /// Creates a bounded mpsc channel for communicating between asynchronous tasks, /// returning the sender/receiver halves. /// /// All data sent on `Sender` will become available on `Receiver` in the same /// order as it was sent. /// /// The `Sender` can be cloned to `send` to the same channel from multiple code /// locations. Only one `Receiver` is supported. /// /// If the `Receiver` is disconnected while trying to `send`, the `send` method /// will return a `SendError`. Similarly, if `Sender` is disconnected while /// trying to `recv`, the `recv` method will return a `RecvError`. /// /// # Examples /// /// ```rust /// use tokio::sync::mpsc; /// /// #[tokio::main] /// async fn main() { /// let (mut tx, mut rx) = mpsc::channel(100); /// /// tokio::spawn(async move { /// for i in 0..10 { /// if let Err(_) = tx.send(i).await { /// println!("receiver dropped"); /// return; /// } /// } /// }); /// /// while let Some(i) = rx.recv().await { /// println!("got = {}", i); /// } /// } /// ``` pub fn channel<T>(buffer: usize) -> (Sender<T>, Receiver<T>) { assert!(buffer > 0, "mpsc bounded channel requires buffer > 0"); let semaphore = (semaphore::Semaphore::new(buffer), buffer); let (tx, rx) = chan::channel(semaphore); let tx = Sender::new(tx); let rx = Receiver::new(rx); (tx, rx) } /// Channel semaphore is a tuple of the semaphore implementation and a `usize` /// representing the channel bound. type Semaphore = (semaphore::Semaphore, usize); impl<T> Receiver<T> { pub(crate) fn new(chan: chan::Rx<T, Semaphore>) -> Receiver<T> { Receiver { chan } } /// Receives the next value for this receiver. /// /// `None` is returned when all `Sender` halves have dropped, indicating /// that no further values can be sent on the channel. /// /// # Examples /// /// ``` /// use tokio::sync::mpsc; /// /// #[tokio::main] /// async fn main() { /// let (mut tx, mut rx) = mpsc::channel(100); /// /// tokio::spawn(async move { /// tx.send("hello").await.unwrap(); /// }); /// /// assert_eq!(Some("hello"), rx.recv().await); /// assert_eq!(None, rx.recv().await); /// } /// ``` /// /// Values are buffered: /// /// ``` /// use tokio::sync::mpsc; /// /// #[tokio::main] /// async fn main() { /// let (mut tx, mut rx) = mpsc::channel(100); /// /// tx.send("hello").await.unwrap(); /// tx.send("world").await.unwrap(); /// /// assert_eq!(Some("hello"), rx.recv().await); /// assert_eq!(Some("world"), rx.recv().await); /// } /// ``` pub async fn recv(&mut self) -> Option<T> { use crate::future::poll_fn; poll_fn(|cx| self.poll_recv(cx)).await } #[doc(hidden)] // TODO: document pub fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<T>> { self.chan.recv(cx) } /// Attempts to return a pending value on this receiver without blocking. /// /// This method will never block the caller in order to wait for data to /// become available. Instead, this will always return immediately with /// a possible option of pending data on the channel. /// /// This is useful for a flavor of "optimistic check" before deciding to /// block on a receiver. /// /// Compared with recv, this function has two failure cases instead of /// one (one for disconnection, one for an empty buffer). pub fn try_recv(&mut self) -> Result<T, TryRecvError> { self.chan.try_recv() } /// Closes the receiving half of a channel, without dropping it. /// /// This prevents any further messages from being sent on the channel while /// still enabling the receiver to drain messages that are buffered. pub fn close(&mut self) { self.chan.close(); } } impl<T> Unpin for Receiver<T> {} cfg_stream! { impl<T> crate::stream::Stream for Receiver<T> { type Item = T; fn poll_next(mut self: std::pin::Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> { self.poll_recv(cx) } } } impl<T> Sender<T> { pub(crate) fn new(chan: chan::Tx<T, Semaphore>) -> Sender<T> { Sender { chan } } /// Sends a value, waiting until there is capacity. /// /// A successful send occurs when it is determined that the other end of the /// channel has not hung up already. An unsuccessful send would be one where /// the corresponding receiver has already been closed. Note that a return /// value of `Err` means that the data will never be received, but a return /// value of `Ok` does not mean that the data will be received. It is /// possible for the corresponding receiver to hang up immediately after /// this function returns `Ok`. /// /// # Errors /// /// If the receive half of the channel is closed, either due to [`close`] /// being called or the [`Receiver`] handle dropping, the function returns /// an error. The error includes the value passed to `send`. /// /// [`close`]: Receiver::close /// [`Receiver`]: Receiver /// /// # Examples /// /// In the following example, each call to `send` will block until the /// previously sent value was received. /// /// ```rust /// use tokio::sync::mpsc; /// /// #[tokio::main] /// async fn main() { /// let (mut tx, mut rx) = mpsc::channel(1); /// /// tokio::spawn(async move { /// for i in 0..10 { /// if let Err(_) = tx.send(i).await { /// println!("receiver dropped"); /// return; /// } /// } /// }); /// /// while let Some(i) = rx.recv().await { /// println!("got = {}", i); /// } /// } /// ``` pub async fn send(&mut self, value: T) -> Result<(), SendError<T>> { use crate::future::poll_fn; if poll_fn(|cx| self.poll_ready(cx)).await.is_err() { return Err(SendError(value)); } match self.try_send(value) { Ok(()) => Ok(()), Err(TrySendError::Full(_)) => unreachable!(), Err(TrySendError::Closed(value)) => Err(SendError(value)), } } /// Attempts to immediately send a message on this `Sender` /// /// This method differs from [`send`] by returning immediately if the channel's /// buffer is full or no receiver is waiting to acquire some data. Compared /// with [`send`], this function has two failure cases instead of one (one for /// disconnection, one for a full buffer). /// /// This function may be paired with [`poll_ready`] in order to wait for /// channel capacity before trying to send a value. /// /// # Errors /// /// If the channel capacity has been reached, i.e., the channel has `n` /// buffered values where `n` is the argument passed to [`channel`], then an /// error is returned. /// /// If the receive half of the channel is closed, either due to [`close`] /// being called or the [`Receiver`] handle dropping, the function returns /// an error. The error includes the value passed to `send`. /// /// [`send`]: Sender::send /// [`poll_ready`]: Sender::poll_ready /// [`channel`]: channel /// [`close`]: Receiver::close /// /// # Examples /// /// ``` /// use tokio::sync::mpsc; /// /// #[tokio::main] /// async fn main() { /// // Create a channel with buffer size 1 /// let (mut tx1, mut rx) = mpsc::channel(1); /// let mut tx2 = tx1.clone(); /// /// tokio::spawn(async move { /// tx1.send(1).await.unwrap(); /// tx1.send(2).await.unwrap(); /// // task waits until the receiver receives a value. /// }); /// /// tokio::spawn(async move { /// // This will return an error and send /// // no message if the buffer is full /// let _ = tx2.try_send(3); /// }); /// /// let mut msg; /// msg = rx.recv().await.unwrap(); /// println!("message {} received", msg); /// /// msg = rx.recv().await.unwrap(); /// println!("message {} received", msg); /// /// // Third message may have never been sent /// match rx.recv().await { /// Some(msg) => println!("message {} received", msg), /// None => println!("the third message was never sent"), /// } /// } /// ``` pub fn try_send(&mut self, message: T) -> Result<(), TrySendError<T>> { self.chan.try_send(message)?; Ok(()) } /// Sends a value, waiting until there is capacity, but only for a limited time. /// /// Shares the same success and error conditions as [`send`], adding one more /// condition for an unsuccessful send, which is when the provided timeout has /// elapsed, and there is no capacity available. /// /// [`send`]: Sender::send /// /// # Errors /// /// If the receive half of the channel is closed, either due to [`close`] /// being called or the [`Receiver`] having been dropped, /// the function returns an error. The error includes the value passed to `send`. /// /// [`close`]: Receiver::close /// [`Receiver`]: Receiver /// /// # Examples /// /// In the following example, each call to `send_timeout` will block until the /// previously sent value was received, unless the timeout has elapsed. /// /// ```rust /// use tokio::sync::mpsc; /// use tokio::time::{delay_for, Duration}; /// /// #[tokio::main] /// async fn main() { /// let (mut tx, mut rx) = mpsc::channel(1); /// /// tokio::spawn(async move { /// for i in 0..10 { /// if let Err(e) = tx.send_timeout(i, Duration::from_millis(100)).await { /// println!("send error: #{:?}", e); /// return; /// } /// } /// }); /// /// while let Some(i) = rx.recv().await { /// println!("got = {}", i); /// delay_for(Duration::from_millis(200)).await; /// } /// } /// ``` #[cfg(feature = "time")] #[cfg_attr(docsrs, doc(cfg(feature = "time")))] pub async fn send_timeout( &mut self, value: T, timeout: Duration, ) -> Result<(), SendTimeoutError<T>> { use crate::future::poll_fn; match crate::time::timeout(timeout, poll_fn(|cx| self.poll_ready(cx))).await { Err(_) => { return Err(SendTimeoutError::Timeout(value)); } Ok(Err(_)) => { return Err(SendTimeoutError::Closed(value)); } Ok(_) => {} } match self.try_send(value) { Ok(()) => Ok(()), Err(TrySendError::Full(_)) => unreachable!(), Err(TrySendError::Closed(value)) => Err(SendTimeoutError::Closed(value)), } } /// Returns `Poll::Ready(Ok(()))` when the channel is able to accept another item. /// /// If the channel is full, then `Poll::Pending` is returned and the task is notified when a /// slot becomes available. /// /// Once `poll_ready` returns `Poll::Ready(Ok(()))`, a call to `try_send` will succeed unless /// the channel has since been closed. To provide this guarantee, the channel reserves one slot /// in the channel for the coming send. This reserved slot is not available to other `Sender` /// instances, so you need to be careful to not end up with deadlocks by blocking after calling /// `poll_ready` but before sending an element. /// /// If, after `poll_ready` succeeds, you decide you do not wish to send an item after all, you /// can use [`disarm`](Sender::disarm) to release the reserved slot. /// /// Until an item is sent or [`disarm`](Sender::disarm) is called, repeated calls to /// `poll_ready` will return either `Poll::Ready(Ok(()))` or `Poll::Ready(Err(_))` if channel /// is closed. pub fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), ClosedError>> { self.chan.poll_ready(cx).map_err(|_| ClosedError::new()) } /// Undo a successful call to `poll_ready`. /// /// Once a call to `poll_ready` returns `Poll::Ready(Ok(()))`, it holds up one slot in the /// channel to make room for the coming send. `disarm` allows you to give up that slot if you /// decide you do not wish to send an item after all. After calling `disarm`, you must call /// `poll_ready` until it returns `Poll::Ready(Ok(()))` before attempting to send again. /// /// Returns `false` if no slot is reserved for this sender (usually because `poll_ready` was /// not previously called, or did not succeed). /// /// # Motivation /// /// Since `poll_ready` takes up one of the finite number of slots in a bounded channel, callers /// need to send an item shortly after `poll_ready` succeeds. If they do not, idle senders may /// take up all the slots of the channel, and prevent active senders from getting any requests /// through. Consider this code that forwards from one channel to another: /// /// ```rust,ignore /// loop { /// ready!(tx.poll_ready(cx))?; /// if let Some(item) = ready!(rx.poll_recv(cx)) { /// tx.try_send(item)?; /// } else { /// break; /// } /// } /// ``` /// /// If many such forwarders exist, and they all forward into a single (cloned) `Sender`, then /// any number of forwarders may be waiting for `rx.poll_recv` at the same time. While they do, /// they are effectively each reducing the channel's capacity by 1. If enough of these /// forwarders are idle, forwarders whose `rx` _do_ have elements will be unable to find a spot /// for them through `poll_ready`, and the system will deadlock. /// /// `disarm` solves this problem by allowing you to give up the reserved slot if you find that /// you have to block. We can then fix the code above by writing: /// /// ```rust,ignore /// loop { /// ready!(tx.poll_ready(cx))?; /// let item = rx.poll_recv(cx); /// if let Poll::Ready(Ok(_)) = item { /// // we're going to send the item below, so don't disarm /// } else { /// // give up our send slot, we won't need it for a while /// tx.disarm(); /// } /// if let Some(item) = ready!(item) { /// tx.try_send(item)?; /// } else { /// break; /// } /// } /// ``` pub fn disarm(&mut self) -> bool { if self.chan.is_ready() { self.chan.disarm(); true } else { false } } }