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use crate::error::Error;
use crate::fmt;
use crate::sync::atomic::{AtomicBool, Ordering};
use crate::thread;
pub struct Flag {
failed: AtomicBool,
}
// Note that the Ordering uses to access the `failed` field of `Flag` below is
// always `Relaxed`, and that's because this isn't actually protecting any data,
// it's just a flag whether we've panicked or not.
//
// The actual location that this matters is when a mutex is **locked** which is
// where we have external synchronization ensuring that we see memory
// reads/writes to this flag.
//
// As a result, if it matters, we should see the correct value for `failed` in
// all cases.
impl Flag {
#[inline]
pub const fn new() -> Flag {
Flag { failed: AtomicBool::new(false) }
}
/// Check the flag for an unguarded borrow, where we only care about existing poison.
#[inline]
pub fn borrow(&self) -> LockResult<()> {
if self.get() { Err(PoisonError::new(())) } else { Ok(()) }
}
/// Check the flag for a guarded borrow, where we may also set poison when `done`.
#[inline]
pub fn guard(&self) -> LockResult<Guard> {
let ret = Guard { panicking: thread::panicking() };
if self.get() { Err(PoisonError::new(ret)) } else { Ok(ret) }
}
#[inline]
pub fn done(&self, guard: &Guard) {
if !guard.panicking && thread::panicking() {
self.failed.store(true, Ordering::Relaxed);
}
}
#[inline]
pub fn get(&self) -> bool {
self.failed.load(Ordering::Relaxed)
}
#[inline]
pub fn clear(&self) {
self.failed.store(false, Ordering::Relaxed)
}
}
pub struct Guard {
panicking: bool,
}
/// A type of error which can be returned whenever a lock is acquired.
///
/// Both [`Mutex`]es and [`RwLock`]s are poisoned whenever a thread fails while the lock
/// is held. The precise semantics for when a lock is poisoned is documented on
/// each lock, but once a lock is poisoned then all future acquisitions will
/// return this error.
///
/// # Examples
///
/// ```
/// use std::sync::{Arc, Mutex};
/// use std::thread;
///
/// let mutex = Arc::new(Mutex::new(1));
///
/// // poison the mutex
/// let c_mutex = Arc::clone(&mutex);
/// let _ = thread::spawn(move || {
/// let mut data = c_mutex.lock().unwrap();
/// *data = 2;
/// panic!();
/// }).join();
///
/// match mutex.lock() {
/// Ok(_) => unreachable!(),
/// Err(p_err) => {
/// let data = p_err.get_ref();
/// println!("recovered: {data}");
/// }
/// };
/// ```
/// [`Mutex`]: crate::sync::Mutex
/// [`RwLock`]: crate::sync::RwLock
#[stable(feature = "rust1", since = "1.0.0")]
pub struct PoisonError<T> {
guard: T,
}
/// An enumeration of possible errors associated with a [`TryLockResult`] which
/// can occur while trying to acquire a lock, from the [`try_lock`] method on a
/// [`Mutex`] or the [`try_read`] and [`try_write`] methods on an [`RwLock`].
///
/// [`try_lock`]: crate::sync::Mutex::try_lock
/// [`try_read`]: crate::sync::RwLock::try_read
/// [`try_write`]: crate::sync::RwLock::try_write
/// [`Mutex`]: crate::sync::Mutex
/// [`RwLock`]: crate::sync::RwLock
#[stable(feature = "rust1", since = "1.0.0")]
pub enum TryLockError<T> {
/// The lock could not be acquired because another thread failed while holding
/// the lock.
#[stable(feature = "rust1", since = "1.0.0")]
Poisoned(#[stable(feature = "rust1", since = "1.0.0")] PoisonError<T>),
/// The lock could not be acquired at this time because the operation would
/// otherwise block.
#[stable(feature = "rust1", since = "1.0.0")]
WouldBlock,
}
/// A type alias for the result of a lock method which can be poisoned.
///
/// The [`Ok`] variant of this result indicates that the primitive was not
/// poisoned, and the `Guard` is contained within. The [`Err`] variant indicates
/// that the primitive was poisoned. Note that the [`Err`] variant *also* carries
/// the associated guard, and it can be acquired through the [`into_inner`]
/// method.
///
/// [`into_inner`]: PoisonError::into_inner
#[stable(feature = "rust1", since = "1.0.0")]
pub type LockResult<Guard> = Result<Guard, PoisonError<Guard>>;
/// A type alias for the result of a nonblocking locking method.
///
/// For more information, see [`LockResult`]. A `TryLockResult` doesn't
/// necessarily hold the associated guard in the [`Err`] type as the lock might not
/// have been acquired for other reasons.
#[stable(feature = "rust1", since = "1.0.0")]
pub type TryLockResult<Guard> = Result<Guard, TryLockError<Guard>>;
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> fmt::Debug for PoisonError<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("PoisonError").finish_non_exhaustive()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> fmt::Display for PoisonError<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
"poisoned lock: another task failed inside".fmt(f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> Error for PoisonError<T> {
#[allow(deprecated)]
fn description(&self) -> &str {
"poisoned lock: another task failed inside"
}
}
impl<T> PoisonError<T> {
/// Creates a `PoisonError`.
///
/// This is generally created by methods like [`Mutex::lock`](crate::sync::Mutex::lock)
/// or [`RwLock::read`](crate::sync::RwLock::read).
#[stable(feature = "sync_poison", since = "1.2.0")]
pub fn new(guard: T) -> PoisonError<T> {
PoisonError { guard }
}
/// Consumes this error indicating that a lock is poisoned, returning the
/// underlying guard to allow access regardless.
///
/// # Examples
///
/// ```
/// use std::collections::HashSet;
/// use std::sync::{Arc, Mutex};
/// use std::thread;
///
/// let mutex = Arc::new(Mutex::new(HashSet::new()));
///
/// // poison the mutex
/// let c_mutex = Arc::clone(&mutex);
/// let _ = thread::spawn(move || {
/// let mut data = c_mutex.lock().unwrap();
/// data.insert(10);
/// panic!();
/// }).join();
///
/// let p_err = mutex.lock().unwrap_err();
/// let data = p_err.into_inner();
/// println!("recovered {} items", data.len());
/// ```
#[stable(feature = "sync_poison", since = "1.2.0")]
pub fn into_inner(self) -> T {
self.guard
}
/// Reaches into this error indicating that a lock is poisoned, returning a
/// reference to the underlying guard to allow access regardless.
#[stable(feature = "sync_poison", since = "1.2.0")]
pub fn get_ref(&self) -> &T {
&self.guard
}
/// Reaches into this error indicating that a lock is poisoned, returning a
/// mutable reference to the underlying guard to allow access regardless.
#[stable(feature = "sync_poison", since = "1.2.0")]
pub fn get_mut(&mut self) -> &mut T {
&mut self.guard
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> From<PoisonError<T>> for TryLockError<T> {
fn from(err: PoisonError<T>) -> TryLockError<T> {
TryLockError::Poisoned(err)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> fmt::Debug for TryLockError<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match *self {
TryLockError::Poisoned(..) => "Poisoned(..)".fmt(f),
TryLockError::WouldBlock => "WouldBlock".fmt(f),
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> fmt::Display for TryLockError<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match *self {
TryLockError::Poisoned(..) => "poisoned lock: another task failed inside",
TryLockError::WouldBlock => "try_lock failed because the operation would block",
}
.fmt(f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> Error for TryLockError<T> {
#[allow(deprecated, deprecated_in_future)]
fn description(&self) -> &str {
match *self {
TryLockError::Poisoned(ref p) => p.description(),
TryLockError::WouldBlock => "try_lock failed because the operation would block",
}
}
#[allow(deprecated)]
fn cause(&self) -> Option<&dyn Error> {
match *self {
TryLockError::Poisoned(ref p) => Some(p),
_ => None,
}
}
}
pub fn map_result<T, U, F>(result: LockResult<T>, f: F) -> LockResult<U>
where
F: FnOnce(T) -> U,
{
match result {
Ok(t) => Ok(f(t)),
Err(PoisonError { guard }) => Err(PoisonError::new(f(guard))),
}
}