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//! Panic support in the standard library. #![stable(feature = "std_panic", since = "1.9.0")] use crate::any::Any; use crate::cell::UnsafeCell; use crate::collections; use crate::fmt; use crate::future::Future; use crate::pin::Pin; use crate::ops::{Deref, DerefMut}; use crate::panicking; use crate::ptr::{Unique, NonNull}; use crate::rc::Rc; use crate::sync::{Arc, Mutex, RwLock, atomic}; use crate::task::{Context, Poll}; use crate::thread::Result; #[stable(feature = "panic_hooks", since = "1.10.0")] pub use crate::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. /// /// [`Send`]: ../marker/trait.Send.html /// [`Sync`]: ../marker/trait.Sync.html /// [`catch_unwind`]: ./fn.catch_unwind.html /// /// ## 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 an auto 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<T>` 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<T>`, 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? /// /// It 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 can be used to force this trait to be /// implemented for any closed over variables passed to `catch_unwind`. /// /// [`AssertUnwindSafe`]: ./struct.AssertUnwindSafe.html #[stable(feature = "catch_unwind", since = "1.9.0")] #[rustc_on_unimplemented( message="the type `{Self}` may not be safely transferred across an unwind boundary", label="`{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. /// /// [`UnsafeCell`]: ../cell/struct.UnsafeCell.html /// [`UnwindSafe`]: ./trait.UnwindSafe.html #[stable(feature = "catch_unwind", since = "1.9.0")] #[rustc_on_unimplemented( message="the type `{Self}` may contain interior mutability and a reference may not be safely \ transferrable across a catch_unwind boundary", label="`{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. /// /// [`catch_unwind`]: ./fn.catch_unwind.html /// # 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<T>( #[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 explicitly poisoned are unwind safe // * Our custom AssertUnwindSafe wrapper is indeed unwind safe #[stable(feature = "catch_unwind", since = "1.9.0")] impl<T: ?Sized> !UnwindSafe for &mut T {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl<T: RefUnwindSafe + ?Sized> UnwindSafe for &T {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl<T: RefUnwindSafe + ?Sized> UnwindSafe for *const T {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl<T: RefUnwindSafe + ?Sized> UnwindSafe for *mut T {} #[unstable(feature = "ptr_internals", issue = "0")] impl<T: UnwindSafe + ?Sized> UnwindSafe for Unique<T> {} #[stable(feature = "nonnull", since = "1.25.0")] impl<T: RefUnwindSafe + ?Sized> UnwindSafe for NonNull<T> {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl<T: ?Sized> UnwindSafe for Mutex<T> {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl<T: ?Sized> UnwindSafe for RwLock<T> {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl<T> UnwindSafe for AssertUnwindSafe<T> {} // 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<T: RefUnwindSafe + ?Sized> UnwindSafe for Rc<T> {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl<T: RefUnwindSafe + ?Sized> UnwindSafe for Arc<T> {} // 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<T: ?Sized> !RefUnwindSafe for UnsafeCell<T> {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl<T> RefUnwindSafe for AssertUnwindSafe<T> {} #[stable(feature = "unwind_safe_lock_refs", since = "1.12.0")] impl<T: ?Sized> RefUnwindSafe for Mutex<T> {} #[stable(feature = "unwind_safe_lock_refs", since = "1.12.0")] impl<T: ?Sized> RefUnwindSafe for RwLock<T> {} #[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 = "128")] #[unstable(feature = "integer_atomics", issue = "32976")] impl RefUnwindSafe for atomic::AtomicI128 {} #[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 = "128")] #[unstable(feature = "integer_atomics", issue = "32976")] impl RefUnwindSafe for atomic::AtomicU128 {} #[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<T> RefUnwindSafe for atomic::AtomicPtr<T> {} // https://github.com/rust-lang/rust/issues/62301 #[stable(feature = "hashbrown", since = "1.36.0")] impl<K, V, S> UnwindSafe for collections::HashMap<K, V, S> where K: UnwindSafe, V: UnwindSafe, S: UnwindSafe {} #[stable(feature = "catch_unwind", since = "1.9.0")] impl<T> Deref for AssertUnwindSafe<T> { type Target = T; fn deref(&self) -> &T { &self.0 } } #[stable(feature = "catch_unwind", since = "1.9.0")] impl<T> DerefMut for AssertUnwindSafe<T> { fn deref_mut(&mut self) -> &mut T { &mut self.0 } } #[stable(feature = "catch_unwind", since = "1.9.0")] impl<R, F: FnOnce() -> R> FnOnce<()> for AssertUnwindSafe<F> { type Output = R; extern "rust-call" fn call_once(self, _args: ()) -> R { (self.0)() } } #[stable(feature = "std_debug", since = "1.16.0")] impl<T: fmt::Debug> fmt::Debug for AssertUnwindSafe<T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { f.debug_tuple("AssertUnwindSafe") .field(&self.0) .finish() } } #[stable(feature = "futures_api", since = "1.36.0")] impl<F: Future> Future for AssertUnwindSafe<F> { type Output = F::Output; fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { let pinned_field = unsafe { Pin::map_unchecked_mut(self, |x| &mut x.0) }; F::poll(pinned_field, cx) } } /// 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. /// /// [`Result`]: ../result/enum.Result.html /// /// 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 [`AssertUnwindSafe`] wrapper struct can be used to quickly /// assert that the usage here is indeed unwind safe. /// /// [`AssertUnwindSafe`]: ./struct.AssertUnwindSafe.html /// [`UnwindSafe`]: ./trait.UnwindSafe.html /// /// [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<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R> { unsafe { panicking::r#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. /// /// [`catch_unwind`]: ./fn.catch_unwind.html /// /// # 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<dyn Any + Send>) -> ! { panicking::update_count_then_panic(payload) }