// 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 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. //! Panic support in the standard library. #![stable(feature = "std_panic", since = "1.9.0")] use any::Any; use cell::UnsafeCell; use fmt; use ops::{Deref, DerefMut}; use panicking; use ptr::{Unique, NonNull}; use rc::Rc; use sync::{Arc, Mutex, RwLock, atomic}; use thread::Result; #[stable(feature = "panic_hooks", since = "1.10.0")] pub use panicking::{take_hook, set_hook}; #[stable(feature = "panic_hooks", since = "1.10.0")] pub use core::panic::{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 `catch_unwind` /// boundary with no fear of unwind safety. /// /// ## What is unwind 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 critical 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 `catch_unwind` function in this /// module. Additionally, even if an invariant is witnessed, it typically isn't a /// problem in Rust because there are 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 unwind 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 unwind safety, but for more information /// about unwind 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 `UnwindSafe`? /// /// Now that we've got an idea of what unwind 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 `catch_unwind` 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 `UnwindSafe` if it cannot easily allow /// witnessing a broken invariant through the use of `catch_unwind` (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 unwind /// safe if all of its components are unwind 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 `catch_unwind` that broken invariants may be /// witnessed and may need to be accounted for. /// /// ## Who implements `UnwindSafe`? /// /// Types such as `&mut T` and `&RefCell` are examples which are **not** /// unwind safe. The general idea is that any mutable state which can be shared /// across `catch_unwind` is not unwind safe by default. This is because it is very /// easy to witness a broken invariant outside of `catch_unwind` as the data is /// simply accessed as usual. /// /// Types like `&Mutex`, however, are unwind 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 `UnwindSafe` 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 `catch_unwind` function and as mentioned above, /// the lack of `unsafe` means it is mostly an advisory. The `AssertUnwindSafe` /// wrapper struct in this module can be used to force this trait to be /// implemented for any closed over variables passed to the `catch_unwind` function /// (more on this below). #[stable(feature = "catch_unwind", since = "1.9.0")] #[rustc_on_unimplemented = "the type {Self} may not be safely transferred \ across an unwind boundary"] pub auto trait UnwindSafe {} /// A marker trait representing types where a shared reference is considered /// unwind 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 /// `UnwindSafe` trait, for more information see that documentation. #[stable(feature = "catch_unwind", since = "1.9.0")] #[rustc_on_unimplemented = "the type {Self} may contain interior mutability \ and a reference may not be safely transferrable \ across a catch_unwind boundary"] pub auto trait RefUnwindSafe {} /// A simple wrapper around a type to assert that it is unwind safe. /// /// When using `catch_unwind` it may be the case that some of the closed over /// variables are not unwind safe. For example if `&mut T` is captured the /// compiler will generate a warning indicating that it is not unwind safe. It /// may not be the case, however, that this is actually a problem due to the /// specific usage of `catch_unwind` if unwind safety is specifically taken into /// account. This wrapper struct is useful for a quick and lightweight /// annotation that a variable is indeed unwind safe. /// /// # Examples /// /// One way to use `AssertUnwindSafe` is to assert that the entire closure /// itself is unwind safe, bypassing all checks for all variables: /// /// ``` /// use std::panic::{self, AssertUnwindSafe}; /// /// let mut variable = 4; /// /// // This code will not compile because the closure captures `&mut variable` /// // which is not considered unwind safe by default. /// /// // panic::catch_unwind(|| { /// // variable += 3; /// // }); /// /// // This, however, will compile due to the `AssertUnwindSafe` wrapper /// let result = panic::catch_unwind(AssertUnwindSafe(|| { /// variable += 3; /// })); /// // ... /// ``` /// /// Wrapping the entire closure amounts to a blanket assertion that all captured /// variables are unwind safe. This has the downside that if new captures are /// added in the future, they will also be considered unwind 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 /// unwind 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. /// /// ``` /// use std::panic::{self, AssertUnwindSafe}; /// /// let mut variable = 4; /// let other_capture = 3; /// /// let result = { /// let mut wrapper = AssertUnwindSafe(&mut variable); /// panic::catch_unwind(move || { /// **wrapper += other_capture; /// }) /// }; /// // ... /// ``` #[stable(feature = "catch_unwind", since = "1.9.0")] pub struct AssertUnwindSafe( #[stable(feature = "catch_unwind", since = "1.9.0")] pub T ); // Implementations of the `UnwindSafe` trait: // // * By default everything is unwind safe // * pointers T contains mutability of some form are not unwind safe // * Unique, an owning pointer, lifts an implementation // * Types like Mutex/RwLock which are explicilty poisoned are unwind safe // * Our custom AssertUnwindSafe wrapper is indeed unwind safe #[stable(feature = "catch_unwind", since = "1.9.0")] impl<'a, T: ?Sized> !UnwindSafe for &'a mut T {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl<'a, T: RefUnwindSafe + ?Sized> UnwindSafe for &'a T {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl UnwindSafe for *const T {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl UnwindSafe for *mut T {} #[unstable(feature = "ptr_internals", issue = "0")] impl UnwindSafe for Unique {} #[stable(feature = "nonnull", since = "1.25.0")] impl UnwindSafe for NonNull {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl UnwindSafe for Mutex {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl UnwindSafe for RwLock {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl UnwindSafe for AssertUnwindSafe {} // not covered via the Shared impl above b/c the inner contents use // Cell/AtomicUsize, but the usage here is unwind safe so we can lift the // impl up one level to Arc/Rc itself #[stable(feature = "catch_unwind", since = "1.9.0")] impl UnwindSafe for Rc {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl UnwindSafe for Arc {} // Pretty simple implementations for the `RefUnwindSafe` marker trait, // basically just saying that `UnsafeCell` is the // only thing which doesn't implement it (which then transitively applies to // everything else). #[stable(feature = "catch_unwind", since = "1.9.0")] impl !RefUnwindSafe for UnsafeCell {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl RefUnwindSafe for AssertUnwindSafe {} #[stable(feature = "unwind_safe_lock_refs", since = "1.12.0")] impl RefUnwindSafe for Mutex {} #[stable(feature = "unwind_safe_lock_refs", since = "1.12.0")] impl RefUnwindSafe for RwLock {} #[cfg(target_has_atomic = "ptr")] #[stable(feature = "unwind_safe_atomic_refs", since = "1.14.0")] impl RefUnwindSafe for atomic::AtomicIsize {} #[cfg(target_has_atomic = "8")] #[unstable(feature = "integer_atomics", issue = "32976")] impl RefUnwindSafe for atomic::AtomicI8 {} #[cfg(target_has_atomic = "16")] #[unstable(feature = "integer_atomics", issue = "32976")] impl RefUnwindSafe for atomic::AtomicI16 {} #[cfg(target_has_atomic = "32")] #[unstable(feature = "integer_atomics", issue = "32976")] impl RefUnwindSafe for atomic::AtomicI32 {} #[cfg(target_has_atomic = "64")] #[unstable(feature = "integer_atomics", issue = "32976")] impl RefUnwindSafe for atomic::AtomicI64 {} #[cfg(target_has_atomic = "ptr")] #[stable(feature = "unwind_safe_atomic_refs", since = "1.14.0")] impl RefUnwindSafe for atomic::AtomicUsize {} #[cfg(target_has_atomic = "8")] #[unstable(feature = "integer_atomics", issue = "32976")] impl RefUnwindSafe for atomic::AtomicU8 {} #[cfg(target_has_atomic = "16")] #[unstable(feature = "integer_atomics", issue = "32976")] impl RefUnwindSafe for atomic::AtomicU16 {} #[cfg(target_has_atomic = "32")] #[unstable(feature = "integer_atomics", issue = "32976")] impl RefUnwindSafe for atomic::AtomicU32 {} #[cfg(target_has_atomic = "64")] #[unstable(feature = "integer_atomics", issue = "32976")] impl RefUnwindSafe for atomic::AtomicU64 {} #[cfg(target_has_atomic = "8")] #[stable(feature = "unwind_safe_atomic_refs", since = "1.14.0")] impl RefUnwindSafe for atomic::AtomicBool {} #[cfg(target_has_atomic = "ptr")] #[stable(feature = "unwind_safe_atomic_refs", since = "1.14.0")] impl RefUnwindSafe for atomic::AtomicPtr {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl Deref for AssertUnwindSafe { type Target = T; fn deref(&self) -> &T { &self.0 } } #[stable(feature = "catch_unwind", since = "1.9.0")] impl DerefMut for AssertUnwindSafe { fn deref_mut(&mut self) -> &mut T { &mut self.0 } } #[stable(feature = "catch_unwind", since = "1.9.0")] impl R> FnOnce<()> for AssertUnwindSafe { type Output = R; extern "rust-call" fn call_once(self, _args: ()) -> R { (self.0)() } } #[stable(feature = "std_debug", since = "1.16.0")] impl fmt::Debug for AssertUnwindSafe { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.debug_tuple("AssertUnwindSafe") .field(&self.0) .finish() } } /// Invokes a closure, capturing the cause of an unwinding 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. Additionally, this function is not guaranteed /// to catch all panics, see the "Notes" section below. /// /// The closure provided is required to adhere to the `UnwindSafe` trait to ensure /// that all captured variables are safe to cross this 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 unwind safe without `unsafe` code. If it /// becomes a problem the associated `AssertUnwindSafe` wrapper type in this /// module can be used to quickly assert that the usage here is indeed unwind /// safe. /// /// [rfc]: https://github.com/rust-lang/rfcs/blob/master/text/1236-stabilize-catch-panic.md /// /// # Notes /// /// Note that this function **may not catch all panics** in Rust. A panic in /// Rust is not always implemented via unwinding, but can be implemented by /// aborting the process as well. This function *only* catches unwinding panics, /// not those that abort the process. /// /// # Examples /// /// ``` /// use std::panic; /// /// let result = panic::catch_unwind(|| { /// println!("hello!"); /// }); /// assert!(result.is_ok()); /// /// let result = panic::catch_unwind(|| { /// panic!("oh no!"); /// }); /// assert!(result.is_err()); /// ``` #[stable(feature = "catch_unwind", since = "1.9.0")] pub fn catch_unwind R + UnwindSafe, R>(f: F) -> Result { unsafe { panicking::try(f) } } /// Triggers a panic without invoking the panic hook. /// /// This is designed to be used in conjunction with `catch_unwind` to, for /// example, carry a panic across a layer of C code. /// /// # Notes /// /// Note that panics in Rust are not always implemented via unwinding, but they /// may be implemented by aborting the process. If this function is called when /// panics are implemented this way then this function will abort the process, /// not trigger an unwind. /// /// # Examples /// /// ```should_panic /// use std::panic; /// /// let result = panic::catch_unwind(|| { /// panic!("oh no!"); /// }); /// /// if let Err(err) = result { /// panic::resume_unwind(err); /// } /// ``` #[stable(feature = "resume_unwind", since = "1.9.0")] pub fn resume_unwind(payload: Box) -> ! { panicking::update_count_then_panic(payload) }