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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443
#![cfg_attr(not(feature = "sync"), allow(dead_code, unreachable_pub))]
//! A multi-producer, multi-consumer channel that only retains the *last* sent
//! value.
//!
//! This channel is useful for watching for changes to a value from multiple
//! points in the code base, for example, changes to configuration values.
//!
//! # Usage
//!
//! [`channel`] returns a [`Sender`] / [`Receiver`] pair. These are the producer
//! and consumer halves of the channel. The channel is created with an initial
//! value.
//!
//! Each [`Receiver`] independently tracks the last value *seen* by its caller.
//!
//! To access the **current** value stored in the channel and mark it as *seen*
//! by a given [`Receiver`], use [`Receiver::borrow_and_update()`].
//!
//! To access the current value **without** marking it as *seen*, use
//! [`Receiver::borrow()`]. (If the value has already been marked *seen*,
//! [`Receiver::borrow()`] is equivalent to [`Receiver::borrow_and_update()`].)
//!
//! For more information on when to use these methods, see
//! [here](#borrow_and_update-versus-borrow).
//!
//! ## Change notifications
//!
//! The [`Receiver`] half provides an asynchronous [`changed`] method. This
//! method is ready when a new, *unseen* value is sent via the [`Sender`] half.
//!
//! * [`Receiver::changed()`] returns `Ok(())` on receiving a new value, or
//! `Err(`[`error::RecvError`]`)` if the [`Sender`] has been dropped.
//! * If the current value is *unseen* when calling [`changed`], then
//! [`changed`] will return immediately. If the current value is *seen*, then
//! it will sleep until either a new message is sent via the [`Sender`] half,
//! or the [`Sender`] is dropped.
//! * On completion, the [`changed`] method marks the new value as *seen*.
//! * At creation, the initial value is considered *seen*. In other words,
//! [`Receiver::changed()`] will not return until a subsequent value is sent.
//! * New [`Receiver`] instances can be created with [`Sender::subscribe()`].
//! The current value at the time the [`Receiver`] is created is considered
//! *seen*.
//!
//! ## `borrow_and_update` versus `borrow`
//!
//! If the receiver intends to await notifications from [`changed`] in a loop,
//! [`Receiver::borrow_and_update()`] should be preferred over
//! [`Receiver::borrow()`]. This avoids a potential race where a new value is
//! sent between [`changed`] being ready and the value being read. (If
//! [`Receiver::borrow()`] is used, the loop may run twice with the same value.)
//!
//! If the receiver is only interested in the current value, and does not intend
//! to wait for changes, then [`Receiver::borrow()`] can be used. It may be more
//! convenient to use [`borrow`](Receiver::borrow) since it's an `&self`
//! method---[`borrow_and_update`](Receiver::borrow_and_update) requires `&mut
//! self`.
//!
//! # Examples
//!
//! The following example prints `hello! world! `.
//!
//! ```
//! use tokio::sync::watch;
//! use tokio::time::{Duration, sleep};
//!
//! # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
//! let (tx, mut rx) = watch::channel("hello");
//!
//! tokio::spawn(async move {
//! // Use the equivalent of a "do-while" loop so the initial value is
//! // processed before awaiting the `changed()` future.
//! loop {
//! println!("{}! ", *rx.borrow_and_update());
//! if rx.changed().await.is_err() {
//! break;
//! }
//! }
//! });
//!
//! sleep(Duration::from_millis(100)).await;
//! tx.send("world")?;
//! # Ok(())
//! # }
//! ```
//!
//! # Closing
//!
//! [`Sender::is_closed`] and [`Sender::closed`] allow the producer to detect
//! when all [`Receiver`] handles have been dropped. This indicates that there
//! is no further interest in the values being produced and work can be stopped.
//!
//! The value in the channel will not be dropped until the sender and all
//! receivers have been dropped.
//!
//! # Thread safety
//!
//! Both [`Sender`] and [`Receiver`] are thread safe. They can be moved to other
//! threads and can be used in a concurrent environment. Clones of [`Receiver`]
//! handles may be moved to separate threads and also used concurrently.
//!
//! [`Sender`]: crate::sync::watch::Sender
//! [`Receiver`]: crate::sync::watch::Receiver
//! [`changed`]: crate::sync::watch::Receiver::changed
//! [`Receiver::changed()`]: crate::sync::watch::Receiver::changed
//! [`Receiver::borrow()`]: crate::sync::watch::Receiver::borrow
//! [`Receiver::borrow_and_update()`]:
//! crate::sync::watch::Receiver::borrow_and_update
//! [`channel`]: crate::sync::watch::channel
//! [`Sender::is_closed`]: crate::sync::watch::Sender::is_closed
//! [`Sender::closed`]: crate::sync::watch::Sender::closed
//! [`Sender::subscribe()`]: crate::sync::watch::Sender::subscribe
use crate::sync::notify::Notify;
use crate::loom::sync::atomic::AtomicUsize;
use crate::loom::sync::atomic::Ordering::{AcqRel, Relaxed};
use crate::loom::sync::{Arc, RwLock, RwLockReadGuard};
use std::fmt;
use std::mem;
use std::ops;
use std::panic;
/// Receives values from the associated [`Sender`](struct@Sender).
///
/// Instances are created by the [`channel`](fn@channel) function.
///
/// To turn this receiver into a `Stream`, you can use the [`WatchStream`]
/// wrapper.
///
/// [`WatchStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.WatchStream.html
#[derive(Debug)]
pub struct Receiver<T> {
/// Pointer to the shared state
shared: Arc<Shared<T>>,
/// Last observed version
version: Version,
}
/// Sends values to the associated [`Receiver`](struct@Receiver).
///
/// Instances are created by the [`channel`](fn@channel) function.
#[derive(Debug)]
pub struct Sender<T> {
shared: Arc<Shared<T>>,
}
impl<T> Clone for Sender<T> {
fn clone(&self) -> Self {
self.shared.ref_count_tx.fetch_add(1, Relaxed);
Self {
shared: self.shared.clone(),
}
}
}
impl<T: Default> Default for Sender<T> {
fn default() -> Self {
Self::new(T::default())
}
}
/// Returns a reference to the inner value.
///
/// Outstanding borrows hold a read lock on the inner value. This means that
/// long-lived borrows could cause the producer half to block. It is recommended
/// to keep the borrow as short-lived as possible. Additionally, if you are
/// running in an environment that allows `!Send` futures, you must ensure that
/// the returned `Ref` type is never held alive across an `.await` point,
/// otherwise, it can lead to a deadlock.
///
/// The priority policy of the lock is dependent on the underlying lock
/// implementation, and this type does not guarantee that any particular policy
/// will be used. In particular, a producer which is waiting to acquire the lock
/// in `send` might or might not block concurrent calls to `borrow`, e.g.:
///
/// <details><summary>Potential deadlock example</summary>
///
/// ```text
/// // Task 1 (on thread A) | // Task 2 (on thread B)
/// let _ref1 = rx.borrow(); |
/// | // will block
/// | let _ = tx.send(());
/// // may deadlock |
/// let _ref2 = rx.borrow(); |
/// ```
/// </details>
#[derive(Debug)]
pub struct Ref<'a, T> {
inner: RwLockReadGuard<'a, T>,
has_changed: bool,
}
impl<'a, T> Ref<'a, T> {
/// Indicates if the borrowed value is considered as _changed_ since the last
/// time it has been marked as seen.
///
/// Unlike [`Receiver::has_changed()`], this method does not fail if the channel is closed.
///
/// When borrowed from the [`Sender`] this function will always return `false`.
///
/// # Examples
///
/// ```
/// use tokio::sync::watch;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = watch::channel("hello");
///
/// tx.send("goodbye").unwrap();
/// // The sender does never consider the value as changed.
/// assert!(!tx.borrow().has_changed());
///
/// // Drop the sender immediately, just for testing purposes.
/// drop(tx);
///
/// // Even if the sender has already been dropped...
/// assert!(rx.has_changed().is_err());
/// // ...the modified value is still readable and detected as changed.
/// assert_eq!(*rx.borrow(), "goodbye");
/// assert!(rx.borrow().has_changed());
///
/// // Read the changed value and mark it as seen.
/// {
/// let received = rx.borrow_and_update();
/// assert_eq!(*received, "goodbye");
/// assert!(received.has_changed());
/// // Release the read lock when leaving this scope.
/// }
///
/// // Now the value has already been marked as seen and could
/// // never be modified again (after the sender has been dropped).
/// assert!(!rx.borrow().has_changed());
/// }
/// ```
pub fn has_changed(&self) -> bool {
self.has_changed
}
}
struct Shared<T> {
/// The most recent value.
value: RwLock<T>,
/// The current version.
///
/// The lowest bit represents a "closed" state. The rest of the bits
/// represent the current version.
state: AtomicState,
/// Tracks the number of `Receiver` instances.
ref_count_rx: AtomicUsize,
/// Tracks the number of `Sender` instances.
ref_count_tx: AtomicUsize,
/// Notifies waiting receivers that the value changed.
notify_rx: big_notify::BigNotify,
/// Notifies any task listening for `Receiver` dropped events.
notify_tx: Notify,
}
impl<T: fmt::Debug> fmt::Debug for Shared<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let state = self.state.load();
f.debug_struct("Shared")
.field("value", &self.value)
.field("version", &state.version())
.field("is_closed", &state.is_closed())
.field("ref_count_rx", &self.ref_count_rx)
.finish()
}
}
pub mod error {
//! Watch error types.
use std::error::Error;
use std::fmt;
/// Error produced when sending a value fails.
#[derive(PartialEq, Eq, Clone, Copy)]
pub struct SendError<T>(pub T);
// ===== impl SendError =====
impl<T> fmt::Debug for SendError<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("SendError").finish_non_exhaustive()
}
}
impl<T> fmt::Display for SendError<T> {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(fmt, "channel closed")
}
}
impl<T> Error for SendError<T> {}
/// Error produced when receiving a change notification.
#[derive(Debug, Clone)]
pub struct RecvError(pub(super) ());
// ===== impl RecvError =====
impl fmt::Display for RecvError {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(fmt, "channel closed")
}
}
impl Error for RecvError {}
}
mod big_notify {
use super::Notify;
use crate::sync::notify::Notified;
// To avoid contention on the lock inside the `Notify`, we store multiple
// copies of it. Then, we use either circular access or randomness to spread
// out threads over different `Notify` objects.
//
// Some simple benchmarks show that randomness performs slightly better than
// circular access (probably due to contention on `next`), so we prefer to
// use randomness when Tokio is compiled with a random number generator.
//
// When the random number generator is not available, we fall back to
// circular access.
pub(super) struct BigNotify {
#[cfg(not(all(not(loom), feature = "sync", any(feature = "rt", feature = "macros"))))]
next: std::sync::atomic::AtomicUsize,
inner: [Notify; 8],
}
impl BigNotify {
pub(super) fn new() -> Self {
Self {
#[cfg(not(all(
not(loom),
feature = "sync",
any(feature = "rt", feature = "macros")
)))]
next: std::sync::atomic::AtomicUsize::new(0),
inner: Default::default(),
}
}
pub(super) fn notify_waiters(&self) {
for notify in &self.inner {
notify.notify_waiters();
}
}
/// This function implements the case where randomness is not available.
#[cfg(not(all(not(loom), feature = "sync", any(feature = "rt", feature = "macros"))))]
pub(super) fn notified(&self) -> Notified<'_> {
let i = self.next.fetch_add(1, std::sync::atomic::Ordering::Relaxed) % 8;
self.inner[i].notified()
}
/// This function implements the case where randomness is available.
#[cfg(all(not(loom), feature = "sync", any(feature = "rt", feature = "macros")))]
pub(super) fn notified(&self) -> Notified<'_> {
let i = crate::runtime::context::thread_rng_n(8) as usize;
self.inner[i].notified()
}
}
}
use self::state::{AtomicState, Version};
mod state {
use crate::loom::sync::atomic::AtomicUsize;
use crate::loom::sync::atomic::Ordering;
const CLOSED_BIT: usize = 1;
// Using 2 as the step size preserves the `CLOSED_BIT`.
const STEP_SIZE: usize = 2;
/// The version part of the state. The lowest bit is always zero.
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub(super) struct Version(usize);
/// Snapshot of the state. The first bit is used as the CLOSED bit.
/// The remaining bits are used as the version.
///
/// The CLOSED bit tracks whether the Sender has been dropped. Dropping all
/// receivers does not set it.
#[derive(Copy, Clone, Debug)]
pub(super) struct StateSnapshot(usize);
/// The state stored in an atomic integer.
///
/// The `Sender` uses `Release` ordering for storing a new state
/// and the `Receiver`s use `Acquire` ordering for loading the
/// current state. This ensures that written values are seen by
/// the `Receiver`s for a proper handover.
#[derive(Debug)]
pub(super) struct AtomicState(AtomicUsize);
impl Version {
/// Decrements the version.
pub(super) fn decrement(&mut self) {
// Using a wrapping decrement here is required to ensure that the
// operation is consistent with `std::sync::atomic::AtomicUsize::fetch_add()`
// which wraps on overflow.
self.0 = self.0.wrapping_sub(STEP_SIZE);
}
pub(super) const INITIAL: Self = Version(0);
}
impl StateSnapshot {
/// Extract the version from the state.
pub(super) fn version(self) -> Version {
Version(self.0 & !CLOSED_BIT)
}
/// Is the closed bit set?
pub(super) fn is_closed(self) -> bool {
(self.0 & CLOSED_BIT) == CLOSED_BIT
}
}
impl AtomicState {
/// Create a new `AtomicState` that is not closed and which has the
/// version set to `Version::INITIAL`.
pub(super) fn new() -> Self {
AtomicState(AtomicUsize::new(Version::INITIAL.0))
}
/// Load the current value of the state.
///
/// Only used by the receiver and for debugging purposes.
///
/// The receiver side (read-only) uses `Acquire` ordering for a proper handover
/// of the shared value with the sender side (single writer). The state is always
/// updated after modifying and before releasing the (exclusive) lock on the
/// shared value.
pub(super) fn load(&self) -> StateSnapshot {
StateSnapshot(self.0.load(Ordering::Acquire))
}
/// Increment the version counter.
pub(super) fn increment_version_while_locked(&self) {
// Use `Release` ordering to ensure that the shared value
// has been written before updating the version. The shared
// value is still protected by an exclusive lock during this
// method.
self.0.fetch_add(STEP_SIZE, Ordering::Release);
}
/// Set the closed bit in the state.
pub(super) fn set_closed(&self) {
self.0.fetch_or(CLOSED_BIT, Ordering::Release);
}
}
}
/// Creates a new watch channel, returning the "send" and "receive" handles.
///
/// All values sent by [`Sender`] will become visible to the [`Receiver`] handles.
/// Only the last value sent is made available to the [`Receiver`] half. All
/// intermediate values are dropped.
///
/// # Examples
///
/// The following example prints `hello! world! `.
///
/// ```
/// use tokio::sync::watch;
/// use tokio::time::{Duration, sleep};
///
/// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
/// let (tx, mut rx) = watch::channel("hello");
///
/// tokio::spawn(async move {
/// // Use the equivalent of a "do-while" loop so the initial value is
/// // processed before awaiting the `changed()` future.
/// loop {
/// println!("{}! ", *rx.borrow_and_update());
/// if rx.changed().await.is_err() {
/// break;
/// }
/// }
/// });
///
/// sleep(Duration::from_millis(100)).await;
/// tx.send("world")?;
/// # Ok(())
/// # }
/// ```
///
/// [`Sender`]: struct@Sender
/// [`Receiver`]: struct@Receiver
pub fn channel<T>(init: T) -> (Sender<T>, Receiver<T>) {
let shared = Arc::new(Shared {
value: RwLock::new(init),
state: AtomicState::new(),
ref_count_rx: AtomicUsize::new(1),
ref_count_tx: AtomicUsize::new(1),
notify_rx: big_notify::BigNotify::new(),
notify_tx: Notify::new(),
});
let tx = Sender {
shared: shared.clone(),
};
let rx = Receiver {
shared,
version: Version::INITIAL,
};
(tx, rx)
}
impl<T> Receiver<T> {
fn from_shared(version: Version, shared: Arc<Shared<T>>) -> Self {
// No synchronization necessary as this is only used as a counter and
// not memory access.
shared.ref_count_rx.fetch_add(1, Relaxed);
Self { shared, version }
}
/// Returns a reference to the most recently sent value.
///
/// This method does not mark the returned value as seen, so future calls to
/// [`changed`] may return immediately even if you have already seen the
/// value with a call to `borrow`.
///
/// Outstanding borrows hold a read lock on the inner value. This means that
/// long-lived borrows could cause the producer half to block. It is recommended
/// to keep the borrow as short-lived as possible. Additionally, if you are
/// running in an environment that allows `!Send` futures, you must ensure that
/// the returned `Ref` type is never held alive across an `.await` point,
/// otherwise, it can lead to a deadlock.
///
/// The priority policy of the lock is dependent on the underlying lock
/// implementation, and this type does not guarantee that any particular policy
/// will be used. In particular, a producer which is waiting to acquire the lock
/// in `send` might or might not block concurrent calls to `borrow`, e.g.:
///
/// <details><summary>Potential deadlock example</summary>
///
/// ```text
/// // Task 1 (on thread A) | // Task 2 (on thread B)
/// let _ref1 = rx.borrow(); |
/// | // will block
/// | let _ = tx.send(());
/// // may deadlock |
/// let _ref2 = rx.borrow(); |
/// ```
/// </details>
///
/// For more information on when to use this method versus
/// [`borrow_and_update`], see [here](self#borrow_and_update-versus-borrow).
///
/// [`changed`]: Receiver::changed
/// [`borrow_and_update`]: Receiver::borrow_and_update
///
/// # Examples
///
/// ```
/// use tokio::sync::watch;
///
/// let (_, rx) = watch::channel("hello");
/// assert_eq!(*rx.borrow(), "hello");
/// ```
pub fn borrow(&self) -> Ref<'_, T> {
let inner = self.shared.value.read().unwrap();
// After obtaining a read-lock no concurrent writes could occur
// and the loaded version matches that of the borrowed reference.
let new_version = self.shared.state.load().version();
let has_changed = self.version != new_version;
Ref { inner, has_changed }
}
/// Returns a reference to the most recently sent value and marks that value
/// as seen.
///
/// This method marks the current value as seen. Subsequent calls to [`changed`]
/// will not return immediately until the [`Sender`] has modified the shared
/// value again.
///
/// Outstanding borrows hold a read lock on the inner value. This means that
/// long-lived borrows could cause the producer half to block. It is recommended
/// to keep the borrow as short-lived as possible. Additionally, if you are
/// running in an environment that allows `!Send` futures, you must ensure that
/// the returned `Ref` type is never held alive across an `.await` point,
/// otherwise, it can lead to a deadlock.
///
/// The priority policy of the lock is dependent on the underlying lock
/// implementation, and this type does not guarantee that any particular policy
/// will be used. In particular, a producer which is waiting to acquire the lock
/// in `send` might or might not block concurrent calls to `borrow`, e.g.:
///
/// <details><summary>Potential deadlock example</summary>
///
/// ```text
/// // Task 1 (on thread A) | // Task 2 (on thread B)
/// let _ref1 = rx1.borrow_and_update(); |
/// | // will block
/// | let _ = tx.send(());
/// // may deadlock |
/// let _ref2 = rx2.borrow_and_update(); |
/// ```
/// </details>
///
/// For more information on when to use this method versus [`borrow`], see
/// [here](self#borrow_and_update-versus-borrow).
///
/// [`changed`]: Receiver::changed
/// [`borrow`]: Receiver::borrow
pub fn borrow_and_update(&mut self) -> Ref<'_, T> {
let inner = self.shared.value.read().unwrap();
// After obtaining a read-lock no concurrent writes could occur
// and the loaded version matches that of the borrowed reference.
let new_version = self.shared.state.load().version();
let has_changed = self.version != new_version;
// Mark the shared value as seen by updating the version
self.version = new_version;
Ref { inner, has_changed }
}
/// Checks if this channel contains a message that this receiver has not yet
/// seen. The new value is not marked as seen.
///
/// Although this method is called `has_changed`, it does not check new
/// messages for equality, so this call will return true even if the new
/// message is equal to the old message.
///
/// Returns an error if the channel has been closed.
/// # Examples
///
/// ```
/// use tokio::sync::watch;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = watch::channel("hello");
///
/// tx.send("goodbye").unwrap();
///
/// assert!(rx.has_changed().unwrap());
/// assert_eq!(*rx.borrow_and_update(), "goodbye");
///
/// // The value has been marked as seen
/// assert!(!rx.has_changed().unwrap());
///
/// drop(tx);
/// // The `tx` handle has been dropped
/// assert!(rx.has_changed().is_err());
/// }
/// ```
pub fn has_changed(&self) -> Result<bool, error::RecvError> {
// Load the version from the state
let state = self.shared.state.load();
if state.is_closed() {
// The sender has dropped.
return Err(error::RecvError(()));
}
let new_version = state.version();
Ok(self.version != new_version)
}
/// Marks the state as changed.
///
/// After invoking this method [`has_changed()`](Self::has_changed)
/// returns `true` and [`changed()`](Self::changed) returns
/// immediately, regardless of whether a new value has been sent.
///
/// This is useful for triggering an initial change notification after
/// subscribing to synchronize new receivers.
pub fn mark_changed(&mut self) {
self.version.decrement();
}
/// Marks the state as unchanged.
///
/// The current value will be considered seen by the receiver.
///
/// This is useful if you are not interested in the current value
/// visible in the receiver.
pub fn mark_unchanged(&mut self) {
let current_version = self.shared.state.load().version();
self.version = current_version;
}
/// Waits for a change notification, then marks the newest value as seen.
///
/// If the newest value in the channel has not yet been marked seen when
/// this method is called, the method marks that value seen and returns
/// immediately. If the newest value has already been marked seen, then the
/// method sleeps until a new message is sent by the [`Sender`] connected to
/// this `Receiver`, or until the [`Sender`] is dropped.
///
/// This method returns an error if and only if the [`Sender`] is dropped.
///
/// For more information, see
/// [*Change notifications*](self#change-notifications) in the module-level documentation.
///
/// # Cancel safety
///
/// This method is cancel safe. If you use it as the event in a
/// [`tokio::select!`](crate::select) statement and some other branch
/// completes first, then it is guaranteed that no values have been marked
/// seen by this call to `changed`.
///
/// [`Sender`]: struct@Sender
///
/// # Examples
///
/// ```
/// use tokio::sync::watch;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = watch::channel("hello");
///
/// tokio::spawn(async move {
/// tx.send("goodbye").unwrap();
/// });
///
/// assert!(rx.changed().await.is_ok());
/// assert_eq!(*rx.borrow_and_update(), "goodbye");
///
/// // The `tx` handle has been dropped
/// assert!(rx.changed().await.is_err());
/// }
/// ```
pub async fn changed(&mut self) -> Result<(), error::RecvError> {
changed_impl(&self.shared, &mut self.version).await
}
/// Waits for a value that satisfies the provided condition.
///
/// This method will call the provided closure whenever something is sent on
/// the channel. Once the closure returns `true`, this method will return a
/// reference to the value that was passed to the closure.
///
/// Before `wait_for` starts waiting for changes, it will call the closure
/// on the current value. If the closure returns `true` when given the
/// current value, then `wait_for` will immediately return a reference to
/// the current value. This is the case even if the current value is already
/// considered seen.
///
/// The watch channel only keeps track of the most recent value, so if
/// several messages are sent faster than `wait_for` is able to call the
/// closure, then it may skip some updates. Whenever the closure is called,
/// it will be called with the most recent value.
///
/// When this function returns, the value that was passed to the closure
/// when it returned `true` will be considered seen.
///
/// If the channel is closed, then `wait_for` will return a `RecvError`.
/// Once this happens, no more messages can ever be sent on the channel.
/// When an error is returned, it is guaranteed that the closure has been
/// called on the last value, and that it returned `false` for that value.
/// (If the closure returned `true`, then the last value would have been
/// returned instead of the error.)
///
/// Like the `borrow` method, the returned borrow holds a read lock on the
/// inner value. This means that long-lived borrows could cause the producer
/// half to block. It is recommended to keep the borrow as short-lived as
/// possible. See the documentation of `borrow` for more information on
/// this.
///
/// [`Receiver::changed()`]: crate::sync::watch::Receiver::changed
///
/// # Examples
///
/// ```
/// use tokio::sync::watch;
///
/// #[tokio::main]
///
/// async fn main() {
/// let (tx, _rx) = watch::channel("hello");
///
/// tx.send("goodbye").unwrap();
///
/// // here we subscribe to a second receiver
/// // now in case of using `changed` we would have
/// // to first check the current value and then wait
/// // for changes or else `changed` would hang.
/// let mut rx2 = tx.subscribe();
///
/// // in place of changed we have use `wait_for`
/// // which would automatically check the current value
/// // and wait for changes until the closure returns true.
/// assert!(rx2.wait_for(|val| *val == "goodbye").await.is_ok());
/// assert_eq!(*rx2.borrow(), "goodbye");
/// }
/// ```
pub async fn wait_for(
&mut self,
mut f: impl FnMut(&T) -> bool,
) -> Result<Ref<'_, T>, error::RecvError> {
let mut closed = false;
loop {
{
let inner = self.shared.value.read().unwrap();
let new_version = self.shared.state.load().version();
let has_changed = self.version != new_version;
self.version = new_version;
if !closed || has_changed {
let result = panic::catch_unwind(panic::AssertUnwindSafe(|| f(&inner)));
match result {
Ok(true) => {
return Ok(Ref { inner, has_changed });
}
Ok(false) => {
// Skip the value.
}
Err(panicked) => {
// Drop the read-lock to avoid poisoning it.
drop(inner);
// Forward the panic to the caller.
panic::resume_unwind(panicked);
// Unreachable
}
};
}
}
if closed {
return Err(error::RecvError(()));
}
// Wait for the value to change.
closed = changed_impl(&self.shared, &mut self.version).await.is_err();
}
}
/// Returns `true` if receivers belong to the same channel.
///
/// # Examples
///
/// ```
/// let (tx, rx) = tokio::sync::watch::channel(true);
/// let rx2 = rx.clone();
/// assert!(rx.same_channel(&rx2));
///
/// let (tx3, rx3) = tokio::sync::watch::channel(true);
/// assert!(!rx3.same_channel(&rx2));
/// ```
pub fn same_channel(&self, other: &Self) -> bool {
Arc::ptr_eq(&self.shared, &other.shared)
}
cfg_process_driver! {
pub(crate) fn try_has_changed(&mut self) -> Option<Result<(), error::RecvError>> {
maybe_changed(&self.shared, &mut self.version)
}
}
}
fn maybe_changed<T>(
shared: &Shared<T>,
version: &mut Version,
) -> Option<Result<(), error::RecvError>> {
// Load the version from the state
let state = shared.state.load();
let new_version = state.version();
if *version != new_version {
// Observe the new version and return
*version = new_version;
return Some(Ok(()));
}
if state.is_closed() {
// The sender has been dropped.
return Some(Err(error::RecvError(())));
}
None
}
async fn changed_impl<T>(
shared: &Shared<T>,
version: &mut Version,
) -> Result<(), error::RecvError> {
crate::trace::async_trace_leaf().await;
loop {
// In order to avoid a race condition, we first request a notification,
// **then** check the current value's version. If a new version exists,
// the notification request is dropped.
let notified = shared.notify_rx.notified();
if let Some(ret) = maybe_changed(shared, version) {
return ret;
}
notified.await;
// loop around again in case the wake-up was spurious
}
}
impl<T> Clone for Receiver<T> {
fn clone(&self) -> Self {
let version = self.version;
let shared = self.shared.clone();
Self::from_shared(version, shared)
}
}
impl<T> Drop for Receiver<T> {
fn drop(&mut self) {
// No synchronization necessary as this is only used as a counter and
// not memory access.
if 1 == self.shared.ref_count_rx.fetch_sub(1, Relaxed) {
// This is the last `Receiver` handle, tasks waiting on `Sender::closed()`
self.shared.notify_tx.notify_waiters();
}
}
}
impl<T> Sender<T> {
/// Creates the sending-half of the [`watch`] channel.
///
/// See documentation of [`watch::channel`] for errors when calling this function.
/// Beware that attempting to send a value when there are no receivers will
/// return an error.
///
/// [`watch`]: crate::sync::watch
/// [`watch::channel`]: crate::sync::watch
///
/// # Examples
/// ```
/// let sender = tokio::sync::watch::Sender::new(0u8);
/// assert!(sender.send(3).is_err());
/// let _rec = sender.subscribe();
/// assert!(sender.send(4).is_ok());
/// ```
pub fn new(init: T) -> Self {
let (tx, _) = channel(init);
tx
}
/// Sends a new value via the channel, notifying all receivers.
///
/// This method fails if the channel is closed, which is the case when
/// every receiver has been dropped. It is possible to reopen the channel
/// using the [`subscribe`] method. However, when `send` fails, the value
/// isn't made available for future receivers (but returned with the
/// [`SendError`]).
///
/// To always make a new value available for future receivers, even if no
/// receiver currently exists, one of the other send methods
/// ([`send_if_modified`], [`send_modify`], or [`send_replace`]) can be
/// used instead.
///
/// [`subscribe`]: Sender::subscribe
/// [`SendError`]: error::SendError
/// [`send_if_modified`]: Sender::send_if_modified
/// [`send_modify`]: Sender::send_modify
/// [`send_replace`]: Sender::send_replace
pub fn send(&self, value: T) -> Result<(), error::SendError<T>> {
// This is pretty much only useful as a hint anyway, so synchronization isn't critical.
if 0 == self.receiver_count() {
return Err(error::SendError(value));
}
self.send_replace(value);
Ok(())
}
/// Modifies the watched value **unconditionally** in-place,
/// notifying all receivers.
///
/// This can be useful for modifying the watched value, without
/// having to allocate a new instance. Additionally, this
/// method permits sending values even when there are no receivers.
///
/// Prefer to use the more versatile function [`Self::send_if_modified()`]
/// if the value is only modified conditionally during the mutable borrow
/// to prevent unneeded change notifications for unmodified values.
///
/// # Panics
///
/// This function panics when the invocation of the `modify` closure panics.
/// No receivers are notified when panicking. All changes of the watched
/// value applied by the closure before panicking will be visible in
/// subsequent calls to `borrow`.
///
/// # Examples
///
/// ```
/// use tokio::sync::watch;
///
/// struct State {
/// counter: usize,
/// }
/// let (state_tx, state_rx) = watch::channel(State { counter: 0 });
/// state_tx.send_modify(|state| state.counter += 1);
/// assert_eq!(state_rx.borrow().counter, 1);
/// ```
pub fn send_modify<F>(&self, modify: F)
where
F: FnOnce(&mut T),
{
self.send_if_modified(|value| {
modify(value);
true
});
}
/// Modifies the watched value **conditionally** in-place,
/// notifying all receivers only if modified.
///
/// This can be useful for modifying the watched value, without
/// having to allocate a new instance. Additionally, this
/// method permits sending values even when there are no receivers.
///
/// The `modify` closure must return `true` if the value has actually
/// been modified during the mutable borrow. It should only return `false`
/// if the value is guaranteed to be unmodified despite the mutable
/// borrow.
///
/// Receivers are only notified if the closure returned `true`. If the
/// closure has modified the value but returned `false` this results
/// in a *silent modification*, i.e. the modified value will be visible
/// in subsequent calls to `borrow`, but receivers will not receive
/// a change notification.
///
/// Returns the result of the closure, i.e. `true` if the value has
/// been modified and `false` otherwise.
///
/// # Panics
///
/// This function panics when the invocation of the `modify` closure panics.
/// No receivers are notified when panicking. All changes of the watched
/// value applied by the closure before panicking will be visible in
/// subsequent calls to `borrow`.
///
/// # Examples
///
/// ```
/// use tokio::sync::watch;
///
/// struct State {
/// counter: usize,
/// }
/// let (state_tx, mut state_rx) = watch::channel(State { counter: 1 });
/// let inc_counter_if_odd = |state: &mut State| {
/// if state.counter % 2 == 1 {
/// state.counter += 1;
/// return true;
/// }
/// false
/// };
///
/// assert_eq!(state_rx.borrow().counter, 1);
///
/// assert!(!state_rx.has_changed().unwrap());
/// assert!(state_tx.send_if_modified(inc_counter_if_odd));
/// assert!(state_rx.has_changed().unwrap());
/// assert_eq!(state_rx.borrow_and_update().counter, 2);
///
/// assert!(!state_rx.has_changed().unwrap());
/// assert!(!state_tx.send_if_modified(inc_counter_if_odd));
/// assert!(!state_rx.has_changed().unwrap());
/// assert_eq!(state_rx.borrow_and_update().counter, 2);
/// ```
pub fn send_if_modified<F>(&self, modify: F) -> bool
where
F: FnOnce(&mut T) -> bool,
{
{
// Acquire the write lock and update the value.
let mut lock = self.shared.value.write().unwrap();
// Update the value and catch possible panic inside func.
let result = panic::catch_unwind(panic::AssertUnwindSafe(|| modify(&mut lock)));
match result {
Ok(modified) => {
if !modified {
// Abort, i.e. don't notify receivers if unmodified
return false;
}
// Continue if modified
}
Err(panicked) => {
// Drop the lock to avoid poisoning it.
drop(lock);
// Forward the panic to the caller.
panic::resume_unwind(panicked);
// Unreachable
}
};
self.shared.state.increment_version_while_locked();
// Release the write lock.
//
// Incrementing the version counter while holding the lock ensures
// that receivers are able to figure out the version number of the
// value they are currently looking at.
drop(lock);
}
self.shared.notify_rx.notify_waiters();
true
}
/// Sends a new value via the channel, notifying all receivers and returning
/// the previous value in the channel.
///
/// This can be useful for reusing the buffers inside a watched value.
/// Additionally, this method permits sending values even when there are no
/// receivers.
///
/// # Examples
///
/// ```
/// use tokio::sync::watch;
///
/// let (tx, _rx) = watch::channel(1);
/// assert_eq!(tx.send_replace(2), 1);
/// assert_eq!(tx.send_replace(3), 2);
/// ```
pub fn send_replace(&self, mut value: T) -> T {
// swap old watched value with the new one
self.send_modify(|old| mem::swap(old, &mut value));
value
}
/// Returns a reference to the most recently sent value
///
/// Outstanding borrows hold a read lock on the inner value. This means that
/// long-lived borrows could cause the producer half to block. It is recommended
/// to keep the borrow as short-lived as possible. Additionally, if you are
/// running in an environment that allows `!Send` futures, you must ensure that
/// the returned `Ref` type is never held alive across an `.await` point,
/// otherwise, it can lead to a deadlock.
///
/// # Examples
///
/// ```
/// use tokio::sync::watch;
///
/// let (tx, _) = watch::channel("hello");
/// assert_eq!(*tx.borrow(), "hello");
/// ```
pub fn borrow(&self) -> Ref<'_, T> {
let inner = self.shared.value.read().unwrap();
// The sender/producer always sees the current version
let has_changed = false;
Ref { inner, has_changed }
}
/// Checks if the channel has been closed. This happens when all receivers
/// have dropped.
///
/// # Examples
///
/// ```
/// let (tx, rx) = tokio::sync::watch::channel(());
/// assert!(!tx.is_closed());
///
/// drop(rx);
/// assert!(tx.is_closed());
/// ```
pub fn is_closed(&self) -> bool {
self.receiver_count() == 0
}
/// Completes when all receivers have dropped.
///
/// This allows the producer to get notified when interest in the produced
/// values is canceled and immediately stop doing work. Once a channel is
/// closed, the only way to reopen it is to call [`Sender::subscribe`] to
/// get a new receiver.
///
/// If the channel becomes closed for a brief amount of time (e.g., the last
/// receiver is dropped and then `subscribe` is called), then this call to
/// `closed` might return, but it is also possible that it does not "notice"
/// that the channel was closed for a brief amount of time.
///
/// # Cancel safety
///
/// This method is cancel safe.
///
/// # Examples
///
/// ```
/// use tokio::sync::watch;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, rx) = watch::channel("hello");
///
/// tokio::spawn(async move {
/// // use `rx`
/// drop(rx);
/// });
///
/// // Waits for `rx` to drop
/// tx.closed().await;
/// println!("the `rx` handles dropped")
/// }
/// ```
pub async fn closed(&self) {
crate::trace::async_trace_leaf().await;
while self.receiver_count() > 0 {
let notified = self.shared.notify_tx.notified();
if self.receiver_count() == 0 {
return;
}
notified.await;
// The channel could have been reopened in the meantime by calling
// `subscribe`, so we loop again.
}
}
/// Creates a new [`Receiver`] connected to this `Sender`.
///
/// All messages sent before this call to `subscribe` are initially marked
/// as seen by the new `Receiver`.
///
/// This method can be called even if there are no other receivers. In this
/// case, the channel is reopened.
///
/// # Examples
///
/// The new channel will receive messages sent on this `Sender`.
///
/// ```
/// use tokio::sync::watch;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, _rx) = watch::channel(0u64);
///
/// tx.send(5).unwrap();
///
/// let rx = tx.subscribe();
/// assert_eq!(5, *rx.borrow());
///
/// tx.send(10).unwrap();
/// assert_eq!(10, *rx.borrow());
/// }
/// ```
///
/// The most recent message is considered seen by the channel, so this test
/// is guaranteed to pass.
///
/// ```
/// use tokio::sync::watch;
/// use tokio::time::Duration;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, _rx) = watch::channel(0u64);
/// tx.send(5).unwrap();
/// let mut rx = tx.subscribe();
///
/// tokio::spawn(async move {
/// // by spawning and sleeping, the message is sent after `main`
/// // hits the call to `changed`.
/// # if false {
/// tokio::time::sleep(Duration::from_millis(10)).await;
/// # }
/// tx.send(100).unwrap();
/// });
///
/// rx.changed().await.unwrap();
/// assert_eq!(100, *rx.borrow());
/// }
/// ```
pub fn subscribe(&self) -> Receiver<T> {
let shared = self.shared.clone();
let version = shared.state.load().version();
// The CLOSED bit in the state tracks only whether the sender is
// dropped, so we do not need to unset it if this reopens the channel.
Receiver::from_shared(version, shared)
}
/// Returns the number of receivers that currently exist.
///
/// # Examples
///
/// ```
/// use tokio::sync::watch;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, rx1) = watch::channel("hello");
///
/// assert_eq!(1, tx.receiver_count());
///
/// let mut _rx2 = rx1.clone();
///
/// assert_eq!(2, tx.receiver_count());
/// }
/// ```
pub fn receiver_count(&self) -> usize {
self.shared.ref_count_rx.load(Relaxed)
}
/// Returns `true` if senders belong to the same channel.
///
/// # Examples
///
/// ```
/// let (tx, rx) = tokio::sync::watch::channel(true);
/// let tx2 = tx.clone();
/// assert!(tx.same_channel(&tx2));
///
/// let (tx3, rx3) = tokio::sync::watch::channel(true);
/// assert!(!tx3.same_channel(&tx2));
/// ```
pub fn same_channel(&self, other: &Self) -> bool {
Arc::ptr_eq(&self.shared, &other.shared)
}
}
impl<T> Drop for Sender<T> {
fn drop(&mut self) {
if self.shared.ref_count_tx.fetch_sub(1, AcqRel) == 1 {
self.shared.state.set_closed();
self.shared.notify_rx.notify_waiters();
}
}
}
// ===== impl Ref =====
impl<T> ops::Deref for Ref<'_, T> {
type Target = T;
fn deref(&self) -> &T {
self.inner.deref()
}
}
#[cfg(all(test, loom))]
mod tests {
use futures::future::FutureExt;
use loom::thread;
// test for https://github.com/tokio-rs/tokio/issues/3168
#[test]
fn watch_spurious_wakeup() {
loom::model(|| {
let (send, mut recv) = crate::sync::watch::channel(0i32);
send.send(1).unwrap();
let send_thread = thread::spawn(move || {
send.send(2).unwrap();
send
});
recv.changed().now_or_never();
let send = send_thread.join().unwrap();
let recv_thread = thread::spawn(move || {
recv.changed().now_or_never();
recv.changed().now_or_never();
recv
});
send.send(3).unwrap();
let mut recv = recv_thread.join().unwrap();
let send_thread = thread::spawn(move || {
send.send(2).unwrap();
});
recv.changed().now_or_never();
send_thread.join().unwrap();
});
}
#[test]
fn watch_borrow() {
loom::model(|| {
let (send, mut recv) = crate::sync::watch::channel(0i32);
assert!(send.borrow().eq(&0));
assert!(recv.borrow().eq(&0));
send.send(1).unwrap();
assert!(send.borrow().eq(&1));
let send_thread = thread::spawn(move || {
send.send(2).unwrap();
send
});
recv.changed().now_or_never();
let send = send_thread.join().unwrap();
let recv_thread = thread::spawn(move || {
recv.changed().now_or_never();
recv.changed().now_or_never();
recv
});
send.send(3).unwrap();
let recv = recv_thread.join().unwrap();
assert!(recv.borrow().eq(&3));
assert!(send.borrow().eq(&3));
send.send(2).unwrap();
thread::spawn(move || {
assert!(recv.borrow().eq(&2));
});
assert!(send.borrow().eq(&2));
});
}
}