Optimize poison guards to ZSTs when panic=abort

library/std/src/sync/poison.rs

@@ -1,9 +1,13 @@
 use crate::error::Error;
 use crate::fmt;
+
+#[cfg(panic = "unwind")]
 use crate::sync::atomic::{AtomicBool, Ordering};
+#[cfg(panic = "unwind")]
 use crate::thread;
 
 pub struct Flag {
+ #[cfg(panic = "unwind")]
  failed: AtomicBool,
 }
 
@@ -21,7 +25,10 @@ pub struct Flag {
 impl Flag {
  #[inline]
  pub const fn new() -> Flag {
- Flag { failed: AtomicBool::new(false) }
+ Flag {
+ #[cfg(panic = "unwind")]
+ failed: AtomicBool::new(false),
+ }
  }
 
  /// Check the flag for an unguarded borrow, where we only care about existing poison.
@@ -33,29 +40,46 @@ impl Flag {
  /// 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() };
+ let ret = Guard {
+ #[cfg(panic = "unwind")]
+ panicking: thread::panicking(),
+ };
  if self.get() { Err(PoisonError::new(ret)) } else { Ok(ret) }
  }
 
  #[inline]
+ #[cfg(panic = "unwind")]
  pub fn done(&self, guard: &Guard) {
  if !guard.panicking && thread::panicking() {
  self.failed.store(true, Ordering::Relaxed);
  }
  }
 
  #[inline]
+ #[cfg(not(panic = "unwind"))]
+ pub fn done(&self, _guard: &Guard) {}
+
+ #[inline]
+ #[cfg(panic = "unwind")]
  pub fn get(&self) -> bool {
  self.failed.load(Ordering::Relaxed)
  }
 
+ #[inline(always)]
+ #[cfg(not(panic = "unwind"))]
+ pub fn get(&self) -> bool {
+ false
+ }
+
  #[inline]
  pub fn clear(&self) {
+ #[cfg(panic = "unwind")]
  self.failed.store(false, Ordering::Relaxed)
  }
 }
 
 pub struct Guard {
+ #[cfg(panic = "unwind")]
  panicking: bool,
 }
 
@@ -95,6 +119,8 @@ pub struct Guard {
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct PoisonError<T> {
  guard: T,
+ #[cfg(not(panic = "unwind"))]
+ _never: !,
 }
 
 /// An enumeration of possible errors associated with a [`TryLockResult`] which
@@ -165,11 +191,27 @@ impl<T> PoisonError<T> {
  ///
  /// This is generally created by methods like [`Mutex::lock`](crate::sync::Mutex::lock)
  /// or [`RwLock::read`](crate::sync::RwLock::read).
+ ///
+ /// This method may panic if std was built with `panic="abort"`.
+ #[cfg(panic = "unwind")]
  #[stable(feature = "sync_poison", since = "1.2.0")]
  pub fn new(guard: T) -> PoisonError<T> {
  PoisonError { guard }
  }
 
+ /// Creates a `PoisonError`.
+ ///
+ /// This is generally created by methods like [`Mutex::lock`](crate::sync::Mutex::lock)
+ /// or [`RwLock::read`](crate::sync::RwLock::read).
+ ///
+ /// This method may panic if std was built with `panic="abort"`.
+ #[cfg(not(panic = "unwind"))]
+ #[stable(feature = "sync_poison", since = "1.2.0")]
+ #[track_caller]
+ pub fn new(_guard: T) -> PoisonError<T> {
+ panic!("PoisonError created in a libstd built with panic=\"abort\"")
+ }
+
  /// Consumes this error indicating that a lock is poisoned, returning the
  /// underlying guard to allow access regardless.
  ///
@@ -225,6 +267,7 @@ impl<T> From<PoisonError<T>> for TryLockError<T> {
 impl<T> fmt::Debug for TryLockError<T> {
  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  match *self {
+ #[cfg(panic = "unwind")]
  TryLockError::Poisoned(..) => "Poisoned(..)".fmt(f),
  TryLockError::WouldBlock => "WouldBlock".fmt(f),
  }
@@ -235,6 +278,7 @@ impl<T> fmt::Debug for TryLockError<T> {
 impl<T> fmt::Display for TryLockError<T> {
  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  match *self {
+ #[cfg(panic = "unwind")]
  TryLockError::Poisoned(..) => "poisoned lock: another task failed inside",
  TryLockError::WouldBlock => "try_lock failed because the operation would block",
  }
@@ -247,6 +291,7 @@ impl<T> Error for TryLockError<T> {
  #[allow(deprecated, deprecated_in_future)]
  fn description(&self) -> &str {
  match *self {
+ #[cfg(panic = "unwind")]
  TryLockError::Poisoned(ref p) => p.description(),
  TryLockError::WouldBlock => "try_lock failed because the operation would block",
  }
@@ -255,6 +300,7 @@ impl<T> Error for TryLockError<T> {
  #[allow(deprecated)]
  fn cause(&self) -> Option<&dyn Error> {
  match *self {
+ #[cfg(panic = "unwind")]
  TryLockError::Poisoned(ref p) => Some(p),
  _ => None,
  }
@@ -267,6 +313,7 @@ where
 {
  match result {
  Ok(t) => Ok(f(t)),
+ #[cfg(panic = "unwind")]
  Err(PoisonError { guard }) => Err(PoisonError::new(f(guard))),
  }
 }