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
#![cfg_attr(not(feature = "sync"), allow(unreachable_pub, dead_code))]
use crate::sync::batch_semaphore as semaphore;
#[cfg(all(tokio_unstable, feature = "tracing"))]
use crate::util::trace;
use std::cell::UnsafeCell;
use std::error::Error;
use std::ops::{Deref, DerefMut};
use std::sync::Arc;
use std::{fmt, marker, mem};
/// An asynchronous `Mutex`-like type.
///
/// This type acts similarly to [`std::sync::Mutex`], with two major
/// differences: [`lock`] is an async method so does not block, and the lock
/// guard is designed to be held across `.await` points.
///
/// # Which kind of mutex should you use?
///
/// Contrary to popular belief, it is ok and often preferred to use the ordinary
/// [`Mutex`][std] from the standard library in asynchronous code.
///
/// The feature that the async mutex offers over the blocking mutex is the
/// ability to keep it locked across an `.await` point. This makes the async
/// mutex more expensive than the blocking mutex, so the blocking mutex should
/// be preferred in the cases where it can be used. The primary use case for the
/// async mutex is to provide shared mutable access to IO resources such as a
/// database connection. If the value behind the mutex is just data, it's
/// usually appropriate to use a blocking mutex such as the one in the standard
/// library or [`parking_lot`].
///
/// Note that, although the compiler will not prevent the std `Mutex` from holding
/// its guard across `.await` points in situations where the task is not movable
/// between threads, this virtually never leads to correct concurrent code in
/// practice as it can easily lead to deadlocks.
///
/// A common pattern is to wrap the `Arc<Mutex<...>>` in a struct that provides
/// non-async methods for performing operations on the data within, and only
/// lock the mutex inside these methods. The [mini-redis] example provides an
/// illustration of this pattern.
///
/// Additionally, when you _do_ want shared access to an IO resource, it is
/// often better to spawn a task to manage the IO resource, and to use message
/// passing to communicate with that task.
///
/// [std]: std::sync::Mutex
/// [`parking_lot`]: https://docs.rs/parking_lot
/// [mini-redis]: https://github.com/tokio-rs/mini-redis/blob/master/src/db.rs
///
/// # Examples:
///
/// ```rust,no_run
/// use tokio::sync::Mutex;
/// use std::sync::Arc;
///
/// #[tokio::main]
/// async fn main() {
/// let data1 = Arc::new(Mutex::new(0));
/// let data2 = Arc::clone(&data1);
///
/// tokio::spawn(async move {
/// let mut lock = data2.lock().await;
/// *lock += 1;
/// });
///
/// let mut lock = data1.lock().await;
/// *lock += 1;
/// }
/// ```
///
///
/// ```rust,no_run
/// use tokio::sync::Mutex;
/// use std::sync::Arc;
///
/// #[tokio::main]
/// async fn main() {
/// let count = Arc::new(Mutex::new(0));
///
/// for i in 0..5 {
/// let my_count = Arc::clone(&count);
/// tokio::spawn(async move {
/// for j in 0..10 {
/// let mut lock = my_count.lock().await;
/// *lock += 1;
/// println!("{} {} {}", i, j, lock);
/// }
/// });
/// }
///
/// loop {
/// if *count.lock().await >= 50 {
/// break;
/// }
/// }
/// println!("Count hit 50.");
/// }
/// ```
/// There are a few things of note here to pay attention to in this example.
/// 1. The mutex is wrapped in an [`Arc`] to allow it to be shared across
/// threads.
/// 2. Each spawned task obtains a lock and releases it on every iteration.
/// 3. Mutation of the data protected by the Mutex is done by de-referencing
/// the obtained lock as seen on lines 12 and 19.
///
/// Tokio's Mutex works in a simple FIFO (first in, first out) style where all
/// calls to [`lock`] complete in the order they were performed. In that way the
/// Mutex is "fair" and predictable in how it distributes the locks to inner
/// data. Locks are released and reacquired after every iteration, so basically,
/// each thread goes to the back of the line after it increments the value once.
/// Note that there's some unpredictability to the timing between when the
/// threads are started, but once they are going they alternate predictably.
/// Finally, since there is only a single valid lock at any given time, there is
/// no possibility of a race condition when mutating the inner value.
///
/// Note that in contrast to [`std::sync::Mutex`], this implementation does not
/// poison the mutex when a thread holding the [`MutexGuard`] panics. In such a
/// case, the mutex will be unlocked. If the panic is caught, this might leave
/// the data protected by the mutex in an inconsistent state.
///
/// [`Mutex`]: struct@Mutex
/// [`MutexGuard`]: struct@MutexGuard
/// [`Arc`]: struct@std::sync::Arc
/// [`std::sync::Mutex`]: struct@std::sync::Mutex
/// [`Send`]: trait@std::marker::Send
/// [`lock`]: method@Mutex::lock
pub struct Mutex<T: ?Sized> {
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: tracing::Span,
s: semaphore::Semaphore,
c: UnsafeCell<T>,
}
/// A handle to a held `Mutex`. The guard can be held across any `.await` point
/// as it is [`Send`].
///
/// As long as you have this guard, you have exclusive access to the underlying
/// `T`. The guard internally borrows the `Mutex`, so the mutex will not be
/// dropped while a guard exists.
///
/// The lock is automatically released whenever the guard is dropped, at which
/// point `lock` will succeed yet again.
pub struct MutexGuard<'a, T: ?Sized> {
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: tracing::Span,
lock: &'a Mutex<T>,
}
/// An owned handle to a held `Mutex`.
///
/// This guard is only available from a `Mutex` that is wrapped in an [`Arc`]. It
/// is identical to `MutexGuard`, except that rather than borrowing the `Mutex`,
/// it clones the `Arc`, incrementing the reference count. This means that
/// unlike `MutexGuard`, it will have the `'static` lifetime.
///
/// As long as you have this guard, you have exclusive access to the underlying
/// `T`. The guard internally keeps a reference-counted pointer to the original
/// `Mutex`, so even if the lock goes away, the guard remains valid.
///
/// The lock is automatically released whenever the guard is dropped, at which
/// point `lock` will succeed yet again.
///
/// [`Arc`]: std::sync::Arc
pub struct OwnedMutexGuard<T: ?Sized> {
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: tracing::Span,
lock: Arc<Mutex<T>>,
}
/// A handle to a held `Mutex` that has had a function applied to it via [`MutexGuard::map`].
///
/// This can be used to hold a subfield of the protected data.
///
/// [`MutexGuard::map`]: method@MutexGuard::map
#[must_use = "if unused the Mutex will immediately unlock"]
pub struct MappedMutexGuard<'a, T: ?Sized> {
s: &'a semaphore::Semaphore,
data: *mut T,
// Needed to tell the borrow checker that we are holding a `&mut T`
marker: marker::PhantomData<&'a mut T>,
}
// As long as T: Send, it's fine to send and share Mutex<T> between threads.
// If T was not Send, sending and sharing a Mutex<T> would be bad, since you can
// access T through Mutex<T>.
unsafe impl<T> Send for Mutex<T> where T: ?Sized + Send {}
unsafe impl<T> Sync for Mutex<T> where T: ?Sized + Send {}
unsafe impl<T> Sync for MutexGuard<'_, T> where T: ?Sized + Send + Sync {}
unsafe impl<T> Sync for OwnedMutexGuard<T> where T: ?Sized + Send + Sync {}
unsafe impl<'a, T> Sync for MappedMutexGuard<'a, T> where T: ?Sized + Sync + 'a {}
unsafe impl<'a, T> Send for MappedMutexGuard<'a, T> where T: ?Sized + Send + 'a {}
/// Error returned from the [`Mutex::try_lock`], [`RwLock::try_read`] and
/// [`RwLock::try_write`] functions.
///
/// `Mutex::try_lock` operation will only fail if the mutex is already locked.
///
/// `RwLock::try_read` operation will only fail if the lock is currently held
/// by an exclusive writer.
///
/// `RwLock::try_write` operation will if lock is held by any reader or by an
/// exclusive writer.
///
/// [`Mutex::try_lock`]: Mutex::try_lock
/// [`RwLock::try_read`]: fn@super::RwLock::try_read
/// [`RwLock::try_write`]: fn@super::RwLock::try_write
#[derive(Debug)]
pub struct TryLockError(pub(super) ());
impl fmt::Display for TryLockError {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(fmt, "operation would block")
}
}
impl Error for TryLockError {}
#[test]
#[cfg(not(loom))]
fn bounds() {
fn check_send<T: Send>() {}
fn check_unpin<T: Unpin>() {}
// This has to take a value, since the async fn's return type is unnameable.
fn check_send_sync_val<T: Send + Sync>(_t: T) {}
fn check_send_sync<T: Send + Sync>() {}
fn check_static<T: 'static>() {}
fn check_static_val<T: 'static>(_t: T) {}
check_send::<MutexGuard<'_, u32>>();
check_send::<OwnedMutexGuard<u32>>();
check_unpin::<Mutex<u32>>();
check_send_sync::<Mutex<u32>>();
check_static::<OwnedMutexGuard<u32>>();
let mutex = Mutex::new(1);
check_send_sync_val(mutex.lock());
let arc_mutex = Arc::new(Mutex::new(1));
check_send_sync_val(arc_mutex.clone().lock_owned());
check_static_val(arc_mutex.lock_owned());
}
impl<T: ?Sized> Mutex<T> {
/// Creates a new lock in an unlocked state ready for use.
///
/// # Examples
///
/// ```
/// use tokio::sync::Mutex;
///
/// let lock = Mutex::new(5);
/// ```
#[track_caller]
pub fn new(t: T) -> Self
where
T: Sized,
{
#[cfg(all(tokio_unstable, feature = "tracing"))]
let resource_span = {
let location = std::panic::Location::caller();
tracing::trace_span!(
"runtime.resource",
concrete_type = "Mutex",
kind = "Sync",
loc.file = location.file(),
loc.line = location.line(),
loc.col = location.column(),
)
};
#[cfg(all(tokio_unstable, feature = "tracing"))]
let s = resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
locked = false,
);
semaphore::Semaphore::new(1)
});
#[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
let s = semaphore::Semaphore::new(1);
Self {
c: UnsafeCell::new(t),
s,
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span,
}
}
/// Creates a new lock in an unlocked state ready for use.
///
/// # Examples
///
/// ```
/// use tokio::sync::Mutex;
///
/// static LOCK: Mutex<i32> = Mutex::const_new(5);
/// ```
#[cfg(all(feature = "parking_lot", not(all(loom, test)),))]
#[cfg_attr(docsrs, doc(cfg(feature = "parking_lot")))]
pub const fn const_new(t: T) -> Self
where
T: Sized,
{
Self {
c: UnsafeCell::new(t),
s: semaphore::Semaphore::const_new(1),
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: tracing::Span::none(),
}
}
/// Locks this mutex, causing the current task to yield until the lock has
/// been acquired. When the lock has been acquired, function returns a
/// [`MutexGuard`].
///
/// # Cancel safety
///
/// This method uses a queue to fairly distribute locks in the order they
/// were requested. Cancelling a call to `lock` makes you lose your place in
/// the queue.
///
/// # Examples
///
/// ```
/// use tokio::sync::Mutex;
///
/// #[tokio::main]
/// async fn main() {
/// let mutex = Mutex::new(1);
///
/// let mut n = mutex.lock().await;
/// *n = 2;
/// }
/// ```
pub async fn lock(&self) -> MutexGuard<'_, T> {
#[cfg(all(tokio_unstable, feature = "tracing"))]
trace::async_op(
|| self.acquire(),
self.resource_span.clone(),
"Mutex::lock",
"poll",
false,
)
.await;
#[cfg(all(tokio_unstable, feature = "tracing"))]
self.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
locked = true,
);
});
#[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
self.acquire().await;
MutexGuard {
lock: self,
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: self.resource_span.clone(),
}
}
/// Blockingly locks this `Mutex`. When the lock has been acquired, function returns a
/// [`MutexGuard`].
///
/// This method is intended for use cases where you
/// need to use this mutex in asynchronous code as well as in synchronous code.
///
/// # Panics
///
/// This function panics if called within an asynchronous execution context.
///
/// - If you find yourself in an asynchronous execution context and needing
/// to call some (synchronous) function which performs one of these
/// `blocking_` operations, then consider wrapping that call inside
/// [`spawn_blocking()`][crate::runtime::Handle::spawn_blocking]
/// (or [`block_in_place()`][crate::task::block_in_place]).
///
/// # Examples
///
/// ```
/// use std::sync::Arc;
/// use tokio::sync::Mutex;
///
/// #[tokio::main]
/// async fn main() {
/// let mutex = Arc::new(Mutex::new(1));
/// let lock = mutex.lock().await;
///
/// let mutex1 = Arc::clone(&mutex);
/// let blocking_task = tokio::task::spawn_blocking(move || {
/// // This shall block until the `lock` is released.
/// let mut n = mutex1.blocking_lock();
/// *n = 2;
/// });
///
/// assert_eq!(*lock, 1);
/// // Release the lock.
/// drop(lock);
///
/// // Await the completion of the blocking task.
/// blocking_task.await.unwrap();
///
/// // Assert uncontended.
/// let n = mutex.try_lock().unwrap();
/// assert_eq!(*n, 2);
/// }
///
/// ```
#[cfg(feature = "sync")]
pub fn blocking_lock(&self) -> MutexGuard<'_, T> {
crate::future::block_on(self.lock())
}
/// Locks this mutex, causing the current task to yield until the lock has
/// been acquired. When the lock has been acquired, this returns an
/// [`OwnedMutexGuard`].
///
/// This method is identical to [`Mutex::lock`], except that the returned
/// guard references the `Mutex` with an [`Arc`] rather than by borrowing
/// it. Therefore, the `Mutex` must be wrapped in an `Arc` to call this
/// method, and the guard will live for the `'static` lifetime, as it keeps
/// the `Mutex` alive by holding an `Arc`.
///
/// # Cancel safety
///
/// This method uses a queue to fairly distribute locks in the order they
/// were requested. Cancelling a call to `lock_owned` makes you lose your
/// place in the queue.
///
/// # Examples
///
/// ```
/// use tokio::sync::Mutex;
/// use std::sync::Arc;
///
/// #[tokio::main]
/// async fn main() {
/// let mutex = Arc::new(Mutex::new(1));
///
/// let mut n = mutex.clone().lock_owned().await;
/// *n = 2;
/// }
/// ```
///
/// [`Arc`]: std::sync::Arc
pub async fn lock_owned(self: Arc<Self>) -> OwnedMutexGuard<T> {
#[cfg(all(tokio_unstable, feature = "tracing"))]
trace::async_op(
|| self.acquire(),
self.resource_span.clone(),
"Mutex::lock_owned",
"poll",
false,
)
.await;
#[cfg(all(tokio_unstable, feature = "tracing"))]
self.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
locked = true,
);
});
#[cfg(all(tokio_unstable, feature = "tracing"))]
let resource_span = self.resource_span.clone();
#[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
self.acquire().await;
OwnedMutexGuard {
lock: self,
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span,
}
}
async fn acquire(&self) {
self.s.acquire(1).await.unwrap_or_else(|_| {
// The semaphore was closed. but, we never explicitly close it, and
// we own it exclusively, which means that this can never happen.
unreachable!()
});
}
/// Attempts to acquire the lock, and returns [`TryLockError`] if the
/// lock is currently held somewhere else.
///
/// [`TryLockError`]: TryLockError
/// # Examples
///
/// ```
/// use tokio::sync::Mutex;
/// # async fn dox() -> Result<(), tokio::sync::TryLockError> {
///
/// let mutex = Mutex::new(1);
///
/// let n = mutex.try_lock()?;
/// assert_eq!(*n, 1);
/// # Ok(())
/// # }
/// ```
pub fn try_lock(&self) -> Result<MutexGuard<'_, T>, TryLockError> {
match self.s.try_acquire(1) {
Ok(_) => {
#[cfg(all(tokio_unstable, feature = "tracing"))]
self.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
locked = true,
);
});
Ok(MutexGuard {
lock: self,
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: self.resource_span.clone(),
})
}
Err(_) => Err(TryLockError(())),
}
}
/// Returns a mutable reference to the underlying data.
///
/// Since this call borrows the `Mutex` mutably, no actual locking needs to
/// take place -- the mutable borrow statically guarantees no locks exist.
///
/// # Examples
///
/// ```
/// use tokio::sync::Mutex;
///
/// fn main() {
/// let mut mutex = Mutex::new(1);
///
/// let n = mutex.get_mut();
/// *n = 2;
/// }
/// ```
pub fn get_mut(&mut self) -> &mut T {
unsafe {
// Safety: This is https://github.com/rust-lang/rust/pull/76936
&mut *self.c.get()
}
}
/// Attempts to acquire the lock, and returns [`TryLockError`] if the lock
/// is currently held somewhere else.
///
/// This method is identical to [`Mutex::try_lock`], except that the
/// returned guard references the `Mutex` with an [`Arc`] rather than by
/// borrowing it. Therefore, the `Mutex` must be wrapped in an `Arc` to call
/// this method, and the guard will live for the `'static` lifetime, as it
/// keeps the `Mutex` alive by holding an `Arc`.
///
/// [`TryLockError`]: TryLockError
/// [`Arc`]: std::sync::Arc
/// # Examples
///
/// ```
/// use tokio::sync::Mutex;
/// use std::sync::Arc;
/// # async fn dox() -> Result<(), tokio::sync::TryLockError> {
///
/// let mutex = Arc::new(Mutex::new(1));
///
/// let n = mutex.clone().try_lock_owned()?;
/// assert_eq!(*n, 1);
/// # Ok(())
/// # }
pub fn try_lock_owned(self: Arc<Self>) -> Result<OwnedMutexGuard<T>, TryLockError> {
match self.s.try_acquire(1) {
Ok(_) => {
#[cfg(all(tokio_unstable, feature = "tracing"))]
self.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
locked = true,
);
});
#[cfg(all(tokio_unstable, feature = "tracing"))]
let resource_span = self.resource_span.clone();
Ok(OwnedMutexGuard {
lock: self,
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span,
})
}
Err(_) => Err(TryLockError(())),
}
}
/// Consumes the mutex, returning the underlying data.
/// # Examples
///
/// ```
/// use tokio::sync::Mutex;
///
/// #[tokio::main]
/// async fn main() {
/// let mutex = Mutex::new(1);
///
/// let n = mutex.into_inner();
/// assert_eq!(n, 1);
/// }
/// ```
pub fn into_inner(self) -> T
where
T: Sized,
{
self.c.into_inner()
}
}
impl<T> From<T> for Mutex<T> {
fn from(s: T) -> Self {
Self::new(s)
}
}
impl<T> Default for Mutex<T>
where
T: Default,
{
fn default() -> Self {
Self::new(T::default())
}
}
impl<T: ?Sized> std::fmt::Debug for Mutex<T>
where
T: std::fmt::Debug,
{
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let mut d = f.debug_struct("Mutex");
match self.try_lock() {
Ok(inner) => d.field("data", &&*inner),
Err(_) => d.field("data", &format_args!("<locked>")),
};
d.finish()
}
}
// === impl MutexGuard ===
impl<'a, T: ?Sized> MutexGuard<'a, T> {
/// Makes a new [`MappedMutexGuard`] for a component of the locked data.
///
/// This operation cannot fail as the [`MutexGuard`] passed in already locked the mutex.
///
/// This is an associated function that needs to be used as `MutexGuard::map(...)`. A method
/// would interfere with methods of the same name on the contents of the locked data.
///
/// # Examples
///
/// ```
/// use tokio::sync::{Mutex, MutexGuard};
///
/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
/// struct Foo(u32);
///
/// # #[tokio::main]
/// # async fn main() {
/// let foo = Mutex::new(Foo(1));
///
/// {
/// let mut mapped = MutexGuard::map(foo.lock().await, |f| &mut f.0);
/// *mapped = 2;
/// }
///
/// assert_eq!(Foo(2), *foo.lock().await);
/// # }
/// ```
///
/// [`MutexGuard`]: struct@MutexGuard
/// [`MappedMutexGuard`]: struct@MappedMutexGuard
#[inline]
pub fn map<U, F>(mut this: Self, f: F) -> MappedMutexGuard<'a, U>
where
F: FnOnce(&mut T) -> &mut U,
{
let data = f(&mut *this) as *mut U;
let s = &this.lock.s;
mem::forget(this);
MappedMutexGuard {
s,
data,
marker: marker::PhantomData,
}
}
/// Attempts to make a new [`MappedMutexGuard`] for a component of the locked data. The
/// original guard is returned if the closure returns `None`.
///
/// This operation cannot fail as the [`MutexGuard`] passed in already locked the mutex.
///
/// This is an associated function that needs to be used as `MutexGuard::try_map(...)`. A
/// method would interfere with methods of the same name on the contents of the locked data.
///
/// # Examples
///
/// ```
/// use tokio::sync::{Mutex, MutexGuard};
///
/// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
/// struct Foo(u32);
///
/// # #[tokio::main]
/// # async fn main() {
/// let foo = Mutex::new(Foo(1));
///
/// {
/// let mut mapped = MutexGuard::try_map(foo.lock().await, |f| Some(&mut f.0))
/// .expect("should not fail");
/// *mapped = 2;
/// }
///
/// assert_eq!(Foo(2), *foo.lock().await);
/// # }
/// ```
///
/// [`MutexGuard`]: struct@MutexGuard
/// [`MappedMutexGuard`]: struct@MappedMutexGuard
#[inline]
pub fn try_map<U, F>(mut this: Self, f: F) -> Result<MappedMutexGuard<'a, U>, Self>
where
F: FnOnce(&mut T) -> Option<&mut U>,
{
let data = match f(&mut *this) {
Some(data) => data as *mut U,
None => return Err(this),
};
let s = &this.lock.s;
mem::forget(this);
Ok(MappedMutexGuard {
s,
data,
marker: marker::PhantomData,
})
}
/// Returns a reference to the original `Mutex`.
///
/// ```
/// use tokio::sync::{Mutex, MutexGuard};
///
/// async fn unlock_and_relock<'l>(guard: MutexGuard<'l, u32>) -> MutexGuard<'l, u32> {
/// println!("1. contains: {:?}", *guard);
/// let mutex = MutexGuard::mutex(&guard);
/// drop(guard);
/// let guard = mutex.lock().await;
/// println!("2. contains: {:?}", *guard);
/// guard
/// }
/// #
/// # #[tokio::main]
/// # async fn main() {
/// # let mutex = Mutex::new(0u32);
/// # let guard = mutex.lock().await;
/// # unlock_and_relock(guard).await;
/// # }
/// ```
#[inline]
pub fn mutex(this: &Self) -> &'a Mutex<T> {
this.lock
}
}
impl<T: ?Sized> Drop for MutexGuard<'_, T> {
fn drop(&mut self) {
#[cfg(all(tokio_unstable, feature = "tracing"))]
self.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
locked = false,
);
});
self.lock.s.release(1);
}
}
impl<T: ?Sized> Deref for MutexGuard<'_, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
unsafe { &*self.lock.c.get() }
}
}
impl<T: ?Sized> DerefMut for MutexGuard<'_, T> {
fn deref_mut(&mut self) -> &mut Self::Target {
unsafe { &mut *self.lock.c.get() }
}
}
impl<T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'_, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&**self, f)
}
}
impl<T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'_, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(&**self, f)
}
}
// === impl OwnedMutexGuard ===
impl<T: ?Sized> OwnedMutexGuard<T> {
/// Returns a reference to the original `Arc<Mutex>`.
///
/// ```
/// use std::sync::Arc;
/// use tokio::sync::{Mutex, OwnedMutexGuard};
///
/// async fn unlock_and_relock(guard: OwnedMutexGuard<u32>) -> OwnedMutexGuard<u32> {
/// println!("1. contains: {:?}", *guard);
/// let mutex: Arc<Mutex<u32>> = OwnedMutexGuard::mutex(&guard).clone();
/// drop(guard);
/// let guard = mutex.lock_owned().await;
/// println!("2. contains: {:?}", *guard);
/// guard
/// }
/// #
/// # #[tokio::main]
/// # async fn main() {
/// # let mutex = Arc::new(Mutex::new(0u32));
/// # let guard = mutex.lock_owned().await;
/// # unlock_and_relock(guard).await;
/// # }
/// ```
#[inline]
pub fn mutex(this: &Self) -> &Arc<Mutex<T>> {
&this.lock
}
}
impl<T: ?Sized> Drop for OwnedMutexGuard<T> {
fn drop(&mut self) {
#[cfg(all(tokio_unstable, feature = "tracing"))]
self.resource_span.in_scope(|| {
tracing::trace!(
target: "runtime::resource::state_update",
locked = false,
);
});
self.lock.s.release(1)
}
}
impl<T: ?Sized> Deref for OwnedMutexGuard<T> {
type Target = T;
fn deref(&self) -> &Self::Target {
unsafe { &*self.lock.c.get() }
}
}
impl<T: ?Sized> DerefMut for OwnedMutexGuard<T> {
fn deref_mut(&mut self) -> &mut Self::Target {
unsafe { &mut *self.lock.c.get() }
}
}
impl<T: ?Sized + fmt::Debug> fmt::Debug for OwnedMutexGuard<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&**self, f)
}
}
impl<T: ?Sized + fmt::Display> fmt::Display for OwnedMutexGuard<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(&**self, f)
}
}
// === impl MappedMutexGuard ===
impl<'a, T: ?Sized> MappedMutexGuard<'a, T> {
/// Makes a new [`MappedMutexGuard`] for a component of the locked data.
///
/// This operation cannot fail as the [`MappedMutexGuard`] passed in already locked the mutex.
///
/// This is an associated function that needs to be used as `MappedMutexGuard::map(...)`. A
/// method would interfere with methods of the same name on the contents of the locked data.
///
/// [`MappedMutexGuard`]: struct@MappedMutexGuard
#[inline]
pub fn map<U, F>(mut this: Self, f: F) -> MappedMutexGuard<'a, U>
where
F: FnOnce(&mut T) -> &mut U,
{
let data = f(&mut *this) as *mut U;
let s = this.s;
mem::forget(this);
MappedMutexGuard {
s,
data,
marker: marker::PhantomData,
}
}
/// Attempts to make a new [`MappedMutexGuard`] for a component of the locked data. The
/// original guard is returned if the closure returns `None`.
///
/// This operation cannot fail as the [`MappedMutexGuard`] passed in already locked the mutex.
///
/// This is an associated function that needs to be used as `MappedMutexGuard::try_map(...)`. A
/// method would interfere with methods of the same name on the contents of the locked data.
///
/// [`MappedMutexGuard`]: struct@MappedMutexGuard
#[inline]
pub fn try_map<U, F>(mut this: Self, f: F) -> Result<MappedMutexGuard<'a, U>, Self>
where
F: FnOnce(&mut T) -> Option<&mut U>,
{
let data = match f(&mut *this) {
Some(data) => data as *mut U,
None => return Err(this),
};
let s = this.s;
mem::forget(this);
Ok(MappedMutexGuard {
s,
data,
marker: marker::PhantomData,
})
}
}
impl<'a, T: ?Sized> Drop for MappedMutexGuard<'a, T> {
fn drop(&mut self) {
self.s.release(1)
}
}
impl<'a, T: ?Sized> Deref for MappedMutexGuard<'a, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
unsafe { &*self.data }
}
}
impl<'a, T: ?Sized> DerefMut for MappedMutexGuard<'a, T> {
fn deref_mut(&mut self) -> &mut Self::Target {
unsafe { &mut *self.data }
}
}
impl<'a, T: ?Sized + fmt::Debug> fmt::Debug for MappedMutexGuard<'a, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&**self, f)
}
}
impl<'a, T: ?Sized + fmt::Display> fmt::Display for MappedMutexGuard<'a, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(&**self, f)
}
}