src/libstd/sync/poison.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use prelude::v1::*;
  12
  13 use cell::UnsafeCell;
  14 use error::{Error, FromError};
  15 use fmt;
  16 use thread;
  17
  18 pub struct Flag { failed: UnsafeCell<bool> }
  19 pub const FLAG_INIT: Flag = Flag { failed: UnsafeCell { value: false } };
  20
  21 impl Flag {
  22     #[inline]
  23     pub fn borrow(&self) -> LockResult<Guard> {
  24         let ret = Guard { panicking: thread::panicking() };
  25         if unsafe { *self.failed.get() } {
  26             Err(PoisonError::new(ret))
  27         } else {
  28             Ok(ret)
  29         }
  30     }
  31
  32     #[inline]
  33     pub fn done(&self, guard: &Guard) {
  34         if !guard.panicking && thread::panicking() {
  35             unsafe { *self.failed.get() = true; }
  36         }
  37     }
  38
  39     #[inline]
  40     pub fn get(&self) -> bool {
  41         unsafe { *self.failed.get() }
  42     }
  43 }
  44
  45 pub struct Guard {
  46     panicking: bool,
  47 }
  48
  49 /// A type of error which can be returned whenever a lock is acquired.
  50 ///
  51 /// Both Mutexes and RwLocks are poisoned whenever a task fails while the lock
  52 /// is held. The precise semantics for when a lock is poisoned is documented on
  53 /// each lock, but once a lock is poisoned then all future acquisitions will
  54 /// return this error.
  55 #[stable(feature = "rust1", since = "1.0.0")]
  56 pub struct PoisonError<T> {
  57     guard: T,
  58 }
  59
  60 /// An enumeration of possible errors which can occur while calling the
  61 /// `try_lock` method.
  62 #[stable(feature = "rust1", since = "1.0.0")]
  63 pub enum TryLockError<T> {
  64     /// The lock could not be acquired because another task failed while holding
  65     /// the lock.
  66     #[stable(feature = "rust1", since = "1.0.0")]
  67     Poisoned(PoisonError<T>),
  68     /// The lock could not be acquired at this time because the operation would
  69     /// otherwise block.
  70     #[stable(feature = "rust1", since = "1.0.0")]
  71     WouldBlock,
  72 }
  73
  74 /// A type alias for the result of a lock method which can be poisoned.
  75 ///
  76 /// The `Ok` variant of this result indicates that the primitive was not
  77 /// poisoned, and the `Guard` is contained within. The `Err` variant indicates
  78 /// that the primitive was poisoned. Note that the `Err` variant *also* carries
  79 /// the associated guard, and it can be acquired through the `into_inner`
  80 /// method.
  81 #[stable(feature = "rust1", since = "1.0.0")]
  82 pub type LockResult<Guard> = Result<Guard, PoisonError<Guard>>;
  83
  84 /// A type alias for the result of a nonblocking locking method.
  85 ///
  86 /// For more information, see `LockResult`. A `TryLockResult` doesn't
  87 /// necessarily hold the associated guard in the `Err` type as the lock may not
  88 /// have been acquired for other reasons.
  89 #[stable(feature = "rust1", since = "1.0.0")]
  90 pub type TryLockResult<Guard> = Result<Guard, TryLockError<Guard>>;
  91
  92 #[stable(feature = "rust1", since = "1.0.0")]
  93 impl<T> fmt::Debug for PoisonError<T> {
  94     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  95         "PoisonError { inner: .. }".fmt(f)
  96     }
  97 }
  98
  99 #[stable(feature = "rust1", since = "1.0.0")]
 100 impl<T> fmt::Display for PoisonError<T> {
 101     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 102         self.description().fmt(f)
 103     }
 104 }
 105
 106 impl<T> Error for PoisonError<T> {
 107     fn description(&self) -> &str {
 108         "poisoned lock: another task failed inside"
 109     }
 110 }
 111
 112 impl<T> PoisonError<T> {
 113     /// Create a `PoisonError`.
 114     #[unstable(feature = "std_misc")]
 115     pub fn new(guard: T) -> PoisonError<T> {
 116         PoisonError { guard: guard }
 117     }
 118
 119     /// Consumes this error indicating that a lock is poisoned, returning the
 120     /// underlying guard to allow access regardless.
 121     #[unstable(feature = "std_misc")]
 122     #[deprecated(since = "1.0.0", reason = "renamed to into_inner")]
 123     pub fn into_guard(self) -> T { self.guard }
 124
 125     /// Consumes this error indicating that a lock is poisoned, returning the
 126     /// underlying guard to allow access regardless.
 127     #[unstable(feature = "std_misc")]
 128     pub fn into_inner(self) -> T { self.guard }
 129
 130     /// Reaches into this error indicating that a lock is poisoned, returning a
 131     /// reference to the underlying guard to allow access regardless.
 132     #[unstable(feature = "std_misc")]
 133     pub fn get_ref(&self) -> &T { &self.guard }
 134
 135     /// Reaches into this error indicating that a lock is poisoned, returning a
 136     /// mutable reference to the underlying guard to allow access regardless.
 137     #[unstable(feature = "std_misc")]
 138     pub fn get_mut(&mut self) -> &mut T { &mut self.guard }
 139 }
 140
 141 impl<T> FromError<PoisonError<T>> for TryLockError<T> {
 142     fn from_error(err: PoisonError<T>) -> TryLockError<T> {
 143         TryLockError::Poisoned(err)
 144     }
 145 }
 146
 147 #[stable(feature = "rust1", since = "1.0.0")]
 148 impl<T> fmt::Debug for TryLockError<T> {
 149     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 150         match *self {
 151             TryLockError::Poisoned(..) => "Poisoned(..)".fmt(f),
 152             TryLockError::WouldBlock => "WouldBlock".fmt(f)
 153         }
 154     }
 155 }
 156
 157 #[stable(feature = "rust1", since = "1.0.0")]
 158 impl<T> fmt::Display for TryLockError<T> {
 159     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 160         self.description().fmt(f)
 161     }
 162 }
 163
 164 impl<T> Error for TryLockError<T> {
 165     fn description(&self) -> &str {
 166         match *self {
 167             TryLockError::Poisoned(ref p) => p.description(),
 168             TryLockError::WouldBlock => "try_lock failed because the operation would block"
 169         }
 170     }
 171
 172     fn cause(&self) -> Option<&Error> {
 173         match *self {
 174             TryLockError::Poisoned(ref p) => Some(p),
 175             _ => None
 176         }
 177     }
 178 }
 179
 180 pub fn map_result<T, U, F>(result: LockResult<T>, f: F)
 181                            -> LockResult<U>
 182                            where F: FnOnce(T) -> U {
 183     match result {
 184         Ok(t) => Ok(f(t)),
 185         Err(PoisonError { guard }) => Err(PoisonError::new(f(guard)))
 186     }
 187 }