      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

    // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! Panic support in the standard library

    #![unstable(feature = "std_panic", reason = "awaiting feedback",
                issue = "27719")]

    use any::Any;
    use boxed::Box;
    use cell::UnsafeCell;
    use ops::{Deref, DerefMut};
    use ptr::{Unique, Shared};
    use rc::Rc;
    use sync::{Arc, Mutex, RwLock};
    use sys_common::unwind;
    use thread::Result;

    pub use panicking::{take_hook, set_hook, PanicInfo, Location};

    ///
    #[rustc_deprecated(since = "1.9.0", reason = "renamed to set_hook")]
    #[unstable(feature = "panic_handler", reason = "awaiting feedback", issue = "30449")]
    pub fn set_handler<F>(handler: F) where F: Fn(&PanicInfo) + 'static + Sync + Send {
        set_hook(Box::new(handler))
    }

    ///
    #[rustc_deprecated(since = "1.9.0", reason = "renamed to take_hook")]
    #[unstable(feature = "panic_handler", reason = "awaiting feedback", issue = "30449")]
    pub fn take_handler() -> Box<Fn(&PanicInfo) + 'static + Sync + Send> {
        take_hook()
    }

    /// A marker trait which represents "panic safe" types in Rust.
    ///
    /// This trait is implemented by default for many types and behaves similarly in
    /// terms of inference of implementation to the `Send` and `Sync` traits. The
    /// purpose of this trait is to encode what types are safe to cross a `recover`
    /// boundary with no fear of panic safety.
    ///
    /// ## What is panic safety?
    ///
    /// In Rust a function can "return" early if it either panics or calls a
    /// function which transitively panics. This sort of control flow is not always
    /// anticipated, and has the possibility of causing subtle bugs through a
    /// combination of two cricial components:
    ///
    /// 1. A data structure is in a temporarily invalid state when the thread
    ///    panics.
    /// 2. This broken invariant is then later observed.
    ///
    /// Typically in Rust, it is difficult to perform step (2) because catching a
    /// panic involves either spawning a thread (which in turns makes it difficult
    /// to later witness broken invariants) or using the `recover` function in this
    /// module. Additionally, even if an invariant is witnessed, it typically isn't a
    /// problem in Rust because there's no uninitialized values (like in C or C++).
    ///
    /// It is possible, however, for **logical** invariants to be broken in Rust,
    /// which can end up causing behavioral bugs. Another key aspect of panic safety
    /// in Rust is that, in the absence of `unsafe` code, a panic cannot lead to
    /// memory unsafety.
    ///
    /// That was a bit of a whirlwind tour of panic safety, but for more information
    /// about panic safety and how it applies to Rust, see an [associated RFC][rfc].
    ///
    /// [rfc]: https://github.com/rust-lang/rfcs/blob/master/text/1236-stabilize-catch-panic.md
    ///
    /// ## What is `RecoverSafe`?
    ///
    /// Now that we've got an idea of what panic safety is in Rust, it's also
    /// important to understand what this trait represents. As mentioned above, one
    /// way to witness broken invariants is through the `recover` function in this
    /// module as it allows catching a panic and then re-using the environment of
    /// the closure.
    ///
    /// Simply put, a type `T` implements `RecoverSafe` if it cannot easily allow
    /// witnessing a broken invariant through the use of `recover` (catching a
    /// panic). This trait is a marker trait, so it is automatically implemented for
    /// many types, and it is also structurally composed (e.g. a struct is recover
    /// safe if all of its components are recover safe).
    ///
    /// Note, however, that this is not an unsafe trait, so there is not a succinct
    /// contract that this trait is providing. Instead it is intended as more of a
    /// "speed bump" to alert users of `recover` that broken invariants may be
    /// witnessed and may need to be accounted for.
    ///
    /// ## Who implements `RecoverSafe`?
    ///
    /// Types such as `&mut T` and `&RefCell<T>` are examples which are **not**
    /// recover safe. The general idea is that any mutable state which can be shared
    /// across `recover` is not recover safe by default. This is because it is very
    /// easy to witness a broken invariant outside of `recover` as the data is
    /// simply accessed as usual.
    ///
    /// Types like `&Mutex<T>`, however, are recover safe because they implement
    /// poisoning by default. They still allow witnessing a broken invariant, but
    /// they already provide their own "speed bumps" to do so.
    ///
    /// ## When should `RecoverSafe` be used?
    ///
    /// Is not intended that most types or functions need to worry about this trait.
    /// It is only used as a bound on the `recover` function and as mentioned above,
    /// the lack of `unsafe` means it is mostly an advisory. The `AssertRecoverSafe`
    /// wrapper struct in this module can be used to force this trait to be
    /// implemented for any closed over variables passed to the `recover` function
    /// (more on this below).
    #[unstable(feature = "recover", reason = "awaiting feedback", issue = "27719")]
    #[rustc_on_unimplemented = "the type {Self} may not be safely transferred \
                                across a recover boundary"]
    pub trait RecoverSafe {}

    /// A marker trait representing types where a shared reference is considered
    /// recover safe.
    ///
    /// This trait is namely not implemented by `UnsafeCell`, the root of all
    /// interior mutability.
    ///
    /// This is a "helper marker trait" used to provide impl blocks for the
    /// `RecoverSafe` trait, for more information see that documentation.
    #[unstable(feature = "recover", reason = "awaiting feedback", issue = "27719")]
    #[rustc_on_unimplemented = "the type {Self} contains interior mutability \
                                and a reference may not be safely transferrable \
                                across a recover boundary"]
    pub trait RefRecoverSafe {}

    /// A simple wrapper around a type to assert that it is panic safe.
    ///
    /// When using `recover` it may be the case that some of the closed over
    /// variables are not panic safe. For example if `&mut T` is captured the
    /// compiler will generate a warning indicating that it is not panic safe. It
    /// may not be the case, however, that this is actually a problem due to the
    /// specific usage of `recover` if panic safety is specifically taken into
    /// account. This wrapper struct is useful for a quick and lightweight
    /// annotation that a variable is indeed panic safe.
    ///
    /// # Examples
    ///
    /// One way to use `AssertRecoverSafe` is to assert that the entire closure
    /// itself is recover safe, bypassing all checks for all variables:
    ///
    /// ```
    /// #![feature(recover, std_panic)]
    ///
    /// use std::panic::{self, AssertRecoverSafe};
    ///
    /// let mut variable = 4;
    ///
    /// // This code will not compile because the closure captures `&mut variable`
    /// // which is not considered panic safe by default.
    ///
    /// // panic::recover(|| {
    /// //     variable += 3;
    /// // });
    ///
    /// // This, however, will compile due to the `AssertRecoverSafe` wrapper
    /// let result = panic::recover(AssertRecoverSafe(|| {
    ///     variable += 3;
    /// }));
    /// // ...
    /// ```
    ///
    /// Wrapping the entire closure amounts to a blanket assertion that all captured
    /// variables are recover safe. This has the downside that if new captures are
    /// added in the future, they will also be considered recover safe. Therefore,
    /// you may prefer to just wrap individual captures, as shown below. This is
    /// more annotation, but it ensures that if a new capture is added which is not
    /// recover safe, you will get a compilation error at that time, which will
    /// allow you to consider whether that new capture in fact represent a bug or
    /// not.
    ///
    /// ```
    /// #![feature(recover, std_panic)]
    ///
    /// use std::panic::{self, AssertRecoverSafe};
    ///
    /// let mut variable = 4;
    /// let other_capture = 3;
    ///
    /// let result = {
    ///     let mut wrapper = AssertRecoverSafe(&mut variable);
    ///     panic::recover(move || {
    ///         **wrapper += other_capture;
    ///     })
    /// };
    /// // ...
    /// ```
    #[unstable(feature = "recover", reason = "awaiting feedback", issue = "27719")]
    pub struct AssertRecoverSafe<T>(pub T);

    // Implementations of the `RecoverSafe` trait:
    //
    // * By default everything is recover safe
    // * pointers T contains mutability of some form are not recover safe
    // * Unique, an owning pointer, lifts an implementation
    // * Types like Mutex/RwLock which are explicilty poisoned are recover safe
    // * Our custom AssertRecoverSafe wrapper is indeed recover safe
    impl RecoverSafe for .. {}
    impl<'a, T: ?Sized> !RecoverSafe for &'a mut T {}
    impl<'a, T: RefRecoverSafe + ?Sized> RecoverSafe for &'a T {}
    impl<T: RefRecoverSafe + ?Sized> RecoverSafe for *const T {}
    impl<T: RefRecoverSafe + ?Sized> RecoverSafe for *mut T {}
    impl<T: RecoverSafe> RecoverSafe for Unique<T> {}
    impl<T: RefRecoverSafe + ?Sized> RecoverSafe for Shared<T> {}
    impl<T: ?Sized> RecoverSafe for Mutex<T> {}
    impl<T: ?Sized> RecoverSafe for RwLock<T> {}
    impl<T> RecoverSafe for AssertRecoverSafe<T> {}

    // not covered via the Shared impl above b/c the inner contents use
    // Cell/AtomicUsize, but the usage here is recover safe so we can lift the
    // impl up one level to Arc/Rc itself
    impl<T: RefRecoverSafe + ?Sized> RecoverSafe for Rc<T> {}
    impl<T: RefRecoverSafe + ?Sized> RecoverSafe for Arc<T> {}

    // Pretty simple implementations for the `RefRecoverSafe` marker trait,
    // basically just saying that this is a marker trait and `UnsafeCell` is the
    // only thing which doesn't implement it (which then transitively applies to
    // everything else).
    impl RefRecoverSafe for .. {}
    impl<T: ?Sized> !RefRecoverSafe for UnsafeCell<T> {}
    impl<T> RefRecoverSafe for AssertRecoverSafe<T> {}

    impl<T> AssertRecoverSafe<T> {
        /// Creates a new `AssertRecoverSafe` wrapper around the provided type.
        #[unstable(feature = "recover", reason = "awaiting feedback", issue = "27719")]
        #[rustc_deprecated(reason = "the type's field is now public, construct it directly",
                           since = "1.9.0")]
        pub fn new(t: T) -> AssertRecoverSafe<T> {
            AssertRecoverSafe(t)
        }

        /// Consumes the `AssertRecoverSafe`, returning the wrapped value.
        #[unstable(feature = "recover", reason = "awaiting feedback", issue = "27719")]
        #[rustc_deprecated(reason = "the type's field is now public, access it directly",
                           since = "1.9.0")]
        pub fn into_inner(self) -> T {
            self.0
        }
    }

    impl<T> Deref for AssertRecoverSafe<T> {
        type Target = T;

        fn deref(&self) -> &T {
            &self.0
        }
    }

    impl<T> DerefMut for AssertRecoverSafe<T> {
        fn deref_mut(&mut self) -> &mut T {
            &mut self.0
        }
    }

    impl<R, F: FnOnce() -> R> FnOnce<()> for AssertRecoverSafe<F> {
        type Output = R;

        extern "rust-call" fn call_once(self, _args: ()) -> R {
            (self.0)()
        }
    }

    /// Invokes a closure, capturing the cause of panic if one occurs.
    ///
    /// This function will return `Ok` with the closure's result if the closure
    /// does not panic, and will return `Err(cause)` if the closure panics. The
    /// `cause` returned is the object with which panic was originally invoked.
    ///
    /// It is currently undefined behavior to unwind from Rust code into foreign
    /// code, so this function is particularly useful when Rust is called from
    /// another language (normally C). This can run arbitrary Rust code, capturing a
    /// panic and allowing a graceful handling of the error.
    ///
    /// It is **not** recommended to use this function for a general try/catch
    /// mechanism. The `Result` type is more appropriate to use for functions that
    /// can fail on a regular basis.
    ///
    /// The closure provided is required to adhere to the `RecoverSafe` to ensure
    /// that all captured variables are safe to cross this recover boundary. The
    /// purpose of this bound is to encode the concept of [exception safety][rfc] in
    /// the type system. Most usage of this function should not need to worry about
    /// this bound as programs are naturally panic safe without `unsafe` code. If it
    /// becomes a problem the associated `AssertRecoverSafe` wrapper type in this
    /// module can be used to quickly assert that the usage here is indeed exception
    /// safe.
    ///
    /// [rfc]: https://github.com/rust-lang/rfcs/blob/master/text/1236-stabilize-catch-panic.md
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(recover, std_panic)]
    ///
    /// use std::panic;
    ///
    /// let result = panic::recover(|| {
    ///     println!("hello!");
    /// });
    /// assert!(result.is_ok());
    ///
    /// let result = panic::recover(|| {
    ///     panic!("oh no!");
    /// });
    /// assert!(result.is_err());
    /// ```
    #[unstable(feature = "recover", reason = "awaiting feedback", issue = "27719")]
    pub fn recover<F: FnOnce() -> R + RecoverSafe, R>(f: F) -> Result<R> {
        let mut result = None;
        unsafe {
            let result = &mut result;
            unwind::try(move || *result = Some(f()))?
        }
        Ok(result.unwrap())
    }

    /// Triggers a panic without invoking the panic handler.
    ///
    /// This is designed to be used in conjunction with `recover` to, for example,
    /// carry a panic across a layer of C code.
    ///
    /// # Examples
    ///
    /// ```should_panic
    /// #![feature(std_panic, recover, panic_propagate)]
    ///
    /// use std::panic;
    ///
    /// let result = panic::recover(|| {
    ///     panic!("oh no!");
    /// });
    ///
    /// if let Err(err) = result {
    ///     panic::propagate(err);
    /// }
    /// ```
    #[unstable(feature = "panic_propagate", reason = "awaiting feedback", issue = "30752")]
    pub fn propagate(payload: Box<Any + Send>) -> ! {
        unwind::rust_panic(payload)
    }

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
⇤
  Move up in search results
⇥
  Move down in search results
⏎
  Go to active search result

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)