src/libstd/panic.rs - third_party/rust - Git at Google

 // 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_handler, set_handler, PanicInfo, Location};

 /// 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 accesed 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
 ///
 /// ```
 /// #![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 = {
 ///     let mut wrapper = AssertRecoverSafe::new(&mut variable);
 ///     panic::recover(move || {
 ///         **wrapper += 3;
 ///     })
 /// };
 /// // ...
 /// ```
 #[unstable(feature = "recover", reason = "awaiting feedback", issue = "27719")]
 pub struct AssertRecoverSafe<T>(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")]
     pub fn new(t: T) -> AssertRecoverSafe<T> {
         AssertRecoverSafe(t)
     }
 }

 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
     }
 }

 /// 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;
         try!(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)
 }
	// 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_handler, set_handler, PanicInfo, Location};

	/// 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 accesed 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
	///
	/// ```
	/// #![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 = {
	/// let mut wrapper = AssertRecoverSafe::new(&mut variable);
	/// panic::recover(move \|\| {
	/// **wrapper += 3;
	/// })
	/// };
	/// // ...
	/// ```
	#[unstable(feature = "recover", reason = "awaiting feedback", issue = "27719")]
	pub struct AssertRecoverSafe<T>(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")]
	pub fn new(t: T) -> AssertRecoverSafe<T> {
	AssertRecoverSafe(t)
	}
	}

	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
	}
	}

	/// 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;
	try!(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)
	}