mirror of https://github.com/rust-lang/rust.git
std::sync::RwLock docs improvement
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@ -24,19 +24,24 @@ use sys_common::rwlock as sys;
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/// of the underlying data (exclusive access) and the read portion of this lock
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/// typically allows for read-only access (shared access).
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///
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/// In comparison, a [`Mutex`] does not distinguish between readers or writers
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/// that aquire the lock, therefore blocking any threads waiting for the lock to
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/// become available. An `RwLock` will allow any number of readers to aquire the
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/// lock as long as a writer is not holding the lock.
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///
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/// The priority policy of the lock is dependent on the underlying operating
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/// system's implementation, and this type does not guarantee that any
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/// particular policy will be used.
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///
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/// The type parameter `T` represents the data that this lock protects. It is
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/// required that `T` satisfies `Send` to be shared across threads and `Sync` to
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/// allow concurrent access through readers. The RAII guards returned from the
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/// locking methods implement `Deref` (and `DerefMut` for the `write` methods)
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/// to allow access to the contained of the lock.
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/// required that `T` satisfies [`Send`] to be shared across threads and
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/// [`Sync`] to allow concurrent access through readers. The RAII guards
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/// returned from the locking methods implement [`Deref`][] (and [`DerefMut`]
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/// for the `write` methods) to allow access to the contained of the lock.
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///
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/// # Poisoning
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///
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/// An `RwLock`, like `Mutex`, will become poisoned on a panic. Note, however,
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/// An `RwLock`, like [`Mutex`], will become poisoned on a panic. Note, however,
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/// that an `RwLock` may only be poisoned if a panic occurs while it is locked
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/// exclusively (write mode). If a panic occurs in any reader, then the lock
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/// will not be poisoned.
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@ -63,6 +68,12 @@ use sys_common::rwlock as sys;
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/// assert_eq!(*w, 6);
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/// } // write lock is dropped here
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/// ```
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///
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/// [`Deref`]: ../../std/ops/trait.Deref.html
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/// [`DerefMut`]: ../../std/ops/trait.DerefMut.html
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/// [`Send`]: ../../std/marker/trait.Send.html
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/// [`Sync`]: ../../std/marker/trait.Sync.html
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/// [`Mutex`]: struct.Mutex.html
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#[stable(feature = "rust1", since = "1.0.0")]
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pub struct RwLock<T: ?Sized> {
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inner: Box<sys::RWLock>,
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@ -154,6 +165,24 @@ impl<T: ?Sized> RwLock<T> {
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/// # Panics
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///
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/// This function might panic when called if the lock is already held by the current thread.
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///
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/// # Examples
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///
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/// ```
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/// use std::sync::{Arc, RwLock};
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/// use std::thread;
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///
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/// let lock = Arc::new(RwLock::new(1));
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/// let c_lock = lock.clone();
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///
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/// let n = lock.read().unwrap();
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/// assert_eq!(*n, 1);
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///
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/// thread::spawn(move || {
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/// let r = c_lock.read();
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/// assert!(r.is_ok());
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/// }).join().unwrap();
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/// ```
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn read(&self) -> LockResult<RwLockReadGuard<T>> {
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@ -180,6 +209,19 @@ impl<T: ?Sized> RwLock<T> {
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/// is poisoned whenever a writer panics while holding an exclusive lock. An
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/// error will only be returned if the lock would have otherwise been
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/// acquired.
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///
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/// # Examples
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///
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/// ```
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/// use std::sync::RwLock;
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///
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/// let lock = RwLock::new(1);
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///
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/// match lock.try_read() {
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/// Ok(n) => assert_eq!(*n, 1),
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/// Err(_) => unreachable!(),
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/// };
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/// ```
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn try_read(&self) -> TryLockResult<RwLockReadGuard<T>> {
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@ -210,6 +252,19 @@ impl<T: ?Sized> RwLock<T> {
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/// # Panics
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///
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/// This function might panic when called if the lock is already held by the current thread.
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///
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/// # Examples
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///
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/// ```
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/// use std::sync::RwLock;
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///
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/// let lock = RwLock::new(1);
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///
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/// let mut n = lock.write().unwrap();
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/// *n = 2;
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///
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/// assert!(lock.try_read().is_err());
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/// ```
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn write(&self) -> LockResult<RwLockWriteGuard<T>> {
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@ -236,6 +291,19 @@ impl<T: ?Sized> RwLock<T> {
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/// is poisoned whenever a writer panics while holding an exclusive lock. An
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/// error will only be returned if the lock would have otherwise been
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/// acquired.
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///
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/// # Examples
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///
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/// ```
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/// use std::sync::RwLock;
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///
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/// let lock = RwLock::new(1);
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///
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/// let n = lock.read().unwrap();
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/// assert_eq!(*n, 1);
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///
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/// assert!(lock.try_write().is_err());
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/// ```
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn try_write(&self) -> TryLockResult<RwLockWriteGuard<T>> {
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@ -253,6 +321,22 @@ impl<T: ?Sized> RwLock<T> {
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/// If another thread is active, the lock can still become poisoned at any
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/// time. You should not trust a `false` value for program correctness
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/// without additional synchronization.
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///
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/// # Examples
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///
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/// ```
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/// use std::sync::{Arc, RwLock};
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/// use std::thread;
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///
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/// let lock = Arc::new(RwLock::new(0));
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/// let c_lock = lock.clone();
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///
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/// let _ = thread::spawn(move || {
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/// let _lock = c_lock.write().unwrap();
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/// panic!(); // the lock gets poisoned
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/// }).join();
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/// assert_eq!(lock.is_poisoned(), true);
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/// ```
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#[inline]
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#[stable(feature = "sync_poison", since = "1.2.0")]
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pub fn is_poisoned(&self) -> bool {
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@ -267,6 +351,19 @@ impl<T: ?Sized> RwLock<T> {
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/// is poisoned whenever a writer panics while holding an exclusive lock. An
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/// error will only be returned if the lock would have otherwise been
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/// acquired.
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///
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/// # Examples
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///
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/// ```
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/// use std::sync::RwLock;
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///
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/// let lock = RwLock::new(String::new());
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/// {
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/// let mut s = lock.write().unwrap();
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/// *s = "modified".to_owned();
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/// }
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/// assert_eq!(lock.into_inner().unwrap(), "modified");
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/// ```
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#[stable(feature = "rwlock_into_inner", since = "1.6.0")]
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pub fn into_inner(self) -> LockResult<T> where T: Sized {
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// We know statically that there are no outstanding references to
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@ -282,7 +379,7 @@ impl<T: ?Sized> RwLock<T> {
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(ptr::read(inner), ptr::read(poison), ptr::read(data))
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};
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mem::forget(self);
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inner.destroy(); // Keep in sync with the `Drop` impl.
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inner.destroy(); // Keep in sync with the `Drop` impl.
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drop(inner);
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poison::map_result(poison.borrow(), |_| data.into_inner())
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/// is poisoned whenever a writer panics while holding an exclusive lock. An
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/// error will only be returned if the lock would have otherwise been
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/// acquired.
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///
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/// # Examples
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///
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/// ```
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/// use std::sync::RwLock;
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///
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/// let mut lock = RwLock::new(0);
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/// *lock.get_mut().unwrap() = 10;
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/// assert_eq!(*lock.read().unwrap(), 10);
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/// ```
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#[stable(feature = "rwlock_get_mut", since = "1.6.0")]
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pub fn get_mut(&mut self) -> LockResult<&mut T> {
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// We know statically that there are no other references to `self`, so
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@ -486,7 +593,7 @@ mod tests {
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fn test_rw_arc_poison_wr() {
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let arc = Arc::new(RwLock::new(1));
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let arc2 = arc.clone();
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let _: Result<(), _> = thread::spawn(move|| {
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let _: Result<(), _> = thread::spawn(move || {
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let _lock = arc2.write().unwrap();
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panic!();
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}).join();
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let arc = Arc::new(RwLock::new(1));
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assert!(!arc.is_poisoned());
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let arc2 = arc.clone();
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let _: Result<(), _> = thread::spawn(move|| {
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let _: Result<(), _> = thread::spawn(move || {
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let _lock = arc2.write().unwrap();
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panic!();
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}).join();
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@ -510,7 +617,7 @@ mod tests {
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fn test_rw_arc_no_poison_rr() {
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let arc = Arc::new(RwLock::new(1));
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let arc2 = arc.clone();
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let _: Result<(), _> = thread::spawn(move|| {
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let _: Result<(), _> = thread::spawn(move || {
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let _lock = arc2.read().unwrap();
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panic!();
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}).join();
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fn test_rw_arc_no_poison_rw() {
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let arc = Arc::new(RwLock::new(1));
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let arc2 = arc.clone();
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let _: Result<(), _> = thread::spawn(move|| {
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let _: Result<(), _> = thread::spawn(move || {
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let _lock = arc2.read().unwrap();
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panic!()
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}).join();
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@ -535,7 +642,7 @@ mod tests {
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let arc2 = arc.clone();
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let (tx, rx) = channel();
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thread::spawn(move|| {
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thread::spawn(move || {
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let mut lock = arc2.write().unwrap();
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for _ in 0..10 {
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let tmp = *lock;
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let mut children = Vec::new();
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for _ in 0..5 {
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let arc3 = arc.clone();
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children.push(thread::spawn(move|| {
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children.push(thread::spawn(move || {
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let lock = arc3.read().unwrap();
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assert!(*lock >= 0);
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}));
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fn test_rw_arc_access_in_unwind() {
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let arc = Arc::new(RwLock::new(1));
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let arc2 = arc.clone();
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let _ = thread::spawn(move|| -> () {
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let _ = thread::spawn(move || -> () {
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struct Unwinder {
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i: Arc<RwLock<isize>>,
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}
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