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// Copyright 2017 Mikhail Zabaluev <mikhail.zabaluev@gmail.com> // See the COPYRIGHT file at the top-level directory of this source tree. // // 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. //! Controlled panics using dynamic type checking. //! //! Sometimes there is a need to test how Rust code behaves on occurrence //! of a panic. A panic can be invoked on purpose in a thread spawned by the //! test and the effects observed after the thread is joined. //! The problem with "benign" panics is that it may be cumbersome to tell them //! apart from panics indicating actual errors, such as assertion failures. //! //! Another issue is the behavior of the default panic hook. //! It is very useful for getting information about the cause of an //! unexpected thread panic, but for tests causing panics on purpose it //! produces annoying output noise. The panic hook can be overridden, //! but custom panic hooks affect the entire program, which in typical //! usage is the test runner; it is easy to misuse them causing important //! error information to go unreported. //! //! The simplest way, as provided by the standard library, to propagate //! a panic that occurred in a child thread to the thread that spawned it //! is to call `unwrap` on the result of `JoinHandle::join`. Unfortunately, //! due to [an issue](https://github.com/rust-lang/rfcs/issues/1389) with //! the implementation of `Any`, the resulting panic message does not relay //! information from the child thread's panic. //! //! This crate provides utilities and an ergonomic interface for testing //! panics in a controlled and output-friendly way using dynamic type checks //! to discern between expected and unexpected panics. //! //! # Expected Panic Type //! //! The recommended way to designate panics as expected is by using values of //! a custom type as the parameter for `panic!`. The type could be as simple //! as a token unit-like struct, or it can be equipped to carry additional //! information from the panic site. //! Any panic value type shall be `Sized`, `'static`, and `Send`. //! For the value to be usable in testing, it should also implement //! at least `Debug` and `PartialEq`. //! //! # Examples //! //! ``` //! use panic_control::{Context, Outcome}; //! use panic_control::{chain_hook_ignoring, spawn_quiet}; //! use panic_control::ThreadResultExt; //! //! use std::thread; //! //! #[derive(Debug, PartialEq, Eq)] //! enum Expected { //! Token, //! Int(i32), //! String(String) //! } //! //! // Rust's stock test runner does not provide a way to do global //! // initialization and the tests are run in parallel in a random //! // order by default. So this is our solution, to be called at //! // the beginning of every test exercising a panic with an //! // Expected value. //! fn silence_expected_panics() { //! use std::sync::{Once, ONCE_INIT}; //! static HOOK_ONCE: Once = ONCE_INIT; //! HOOK_ONCE.call_once(|| { //! chain_hook_ignoring::<Expected>() //! }); //! } //! //! # struct TypeUnderTest; //! # impl TypeUnderTest { //! # fn new() -> TypeUnderTest { TypeUnderTest } //! # fn doing_fine(&self) -> bool { true } //! # } //! // ... //! //! silence_expected_panics(); //! let thread_builder = thread::Builder::new() //! .name("My panicky thread".into()); //! let ctx = Context::<Expected>::from(thread_builder); //! let h = ctx.spawn(|| { //! let unwind_me = TypeUnderTest::new(); //! assert!(unwind_me.doing_fine()); //! // ^-- If this fails, join() will return Err //! panic!(Expected::String("Rainbows and unicorns!".into())); //! }); //! let outcome = h.join().unwrap_or_propagate(); //! match outcome { //! Outcome::Panicked(Expected::String(s)) => { //! println!("thread panicked as expected: {}", s); //! } //! _ => panic!("unexpected value returned from join()") //! } //! //! let ctx = Context::<Expected>::new(); //! let h = ctx.spawn_quiet(|| { //! let h = spawn_quiet(|| { //! panic!("Sup dawg, we heard you like panics \ //! so we put a panic in your panic!"); //! }); //! h.join().unwrap_or_propagate(); //! }); //! let res = h.join(); //! let msg = res.panic_value_as_str().unwrap(); //! assert!(msg.contains("panic in your panic")); //! ``` use std::any::Any; use std::cell::Cell; use std::fmt; use std::fmt::Debug; use std::marker; use std::panic; use std::panic::{PanicInfo}; use std::thread; use std::sync::{Once, ONCE_INIT}; /// Enumerates the expected outcomes from joining a panic-checked thread. /// /// `Outcome` values are returned in the `Ok` result variant /// of the `join()` method of a `CheckedJoinHandle`. #[derive(Copy, Clone, Debug, PartialEq, Eq)] pub enum Outcome<T, P> { /// Indicates that the thread closure has /// returned normally, and provides the return value. NoPanic(T), /// Indicates that the thread has panicked with the expected type, /// and provides the panic value. Panicked(P) } impl<T, P> Outcome<T, P> { /// Tests whether the value contains the variant `Panicked`. pub fn has_panicked(&self) -> bool { match *self { Outcome::NoPanic(_) => false, Outcome::Panicked(_) => true, } } } /// Wraps `std::thread::JoinHandle` for panic value discrimination. /// /// A `CheckedJoinHandle` works like a standard `JoinHandle`, /// except that its `join()` method dynamically checks the type of /// the possible panic value for matching the type that is the /// parameter of the `Context` this handle was obtained from, /// and if the type matches, returns the resolved value in the /// "successful panic" result variant. /// /// See the documentation of the `join()` method for details and /// an example of use. pub struct CheckedJoinHandle<T, P> { thread_handle: thread::JoinHandle<T>, phantom: marker::PhantomData<P> } impl<T, P> Debug for CheckedJoinHandle<T, P> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.write_str("CheckedJoinHandle { .. }") } } impl<T, P: Any> CheckedJoinHandle<T, P> { /// Works like `std::thread::JoinHandle::join()`, except that when /// the child thread's panic value is of the expected type, it is /// returned in `Ok(Outcome::Panicked(_))`. If the child thread's /// closure returns normally, its return value is returned in /// `Ok(Outcome::NoPanic(_))` /// /// # Examples /// /// ``` /// use panic_control::{Context, Outcome}; /// use std::thread; /// /// #[derive(Debug, PartialEq, Eq)] /// struct Expected(pub u32); /// /// let ctx = Context::<Expected>::new(); /// let h = ctx.spawn(|| { /// panic!(Expected(42)); /// }); /// /// let outcome = h.join().unwrap(); /// /// match outcome { /// Outcome::Panicked(Expected(n)) => { /// println!("thread panicked as expected with {}", n); /// } /// _ => panic!("unexpected return value from join()") /// } /// ``` pub fn join(self) -> thread::Result<Outcome<T, P>> { match self.thread_handle.join() { Ok(rv) => Ok(Outcome::NoPanic(rv)), Err(box_any) => { match box_any.downcast::<P>() { Ok(p) => Ok(Outcome::Panicked(*p)), Err(e) => Err(e) } } } } } impl<T, P> CheckedJoinHandle<T, P> { /// Returns a reference to the underlying `JoinHandle`. pub fn as_thread_join_handle(&self) -> &thread::JoinHandle<T> { &self.thread_handle } /// Converts into the underlying `JoinHandle`, /// giving up panic discrimination. pub fn into_thread_join_handle(self) -> thread::JoinHandle<T> { self.thread_handle } } impl<T, P> AsRef<thread::JoinHandle<T>> for CheckedJoinHandle<T, P> { fn as_ref(&self) -> &thread::JoinHandle<T> { self.as_thread_join_handle() } } impl<T, P> Into<thread::JoinHandle<T>> for CheckedJoinHandle<T, P> { fn into(self) -> thread::JoinHandle<T> { self.into_thread_join_handle() } } /// The launch pad for a thread checked for the expected panic type. /// /// The generic type `Context` serves as the type system's anchor for the /// expected type of the panic value, which is given as the type parameter. /// It can be constructed from an `std::thread::Builder` providing /// a customized thread configuration. /// /// The method `spawn()` is used to spawn a new thread, similarly to /// how the function `std::thread::spawn()` works. See the documentation /// of the `spawn()` method for detailed description and examples. /// /// # Examples /// /// The example below demonstrates how to construct a `Context` from a /// configured `std::thread::Builder` using the implementation of /// the standard trait `From`. /// /// ``` /// use panic_control::Context; /// use std::thread; /// /// #[derive(Debug, PartialEq, Eq)] /// struct ExpectedToken; /// /// let thread_builder = thread::Builder::new() /// .name("My panicky thread".into()) /// .stack_size(65 * 1024); /// let ctx = Context::<ExpectedToken>::from(thread_builder); /// let h = ctx.spawn(|| { /// // ... /// }); /// h.join().unwrap(); /// ``` pub struct Context<P> { thread_builder: thread::Builder, phantom: marker::PhantomData<P> } impl<P> Debug for Context<P> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.debug_struct("Context") .field("thread_builder", &self.thread_builder) .finish() } } impl<P: Any> Default for Context<P> { fn default() -> Context<P> { Context::new() } } impl<P: Any> Context<P> { /// Constructs a context with the default thread configuration. /// /// The type parameter can be specified explicitly: /// /// ``` /// # use panic_control::Context; /// # #[derive(Debug, PartialEq)] struct Expected(pub i32); /// let ctx = Context::<Expected>::new(); /// ``` pub fn new() -> Context<P> { Context { thread_builder: thread::Builder::new(), phantom: marker::PhantomData } } /// Spawns a new thread taking ownership of the `Context`, and /// returns the `CheckedJoinHandle` for the thread. Other than the /// return value, and panicking on an OS failure to create a thread, /// this method behaves exactly like the `spawn()` /// method of `std::thread::Builder` does, and if the `Context` /// was constructed from a `std::thread::Builder`, its /// thread configuration will be applied. /// /// # Panics /// /// Panics if the underlying call to `std::thread::Builder::spawn()` /// returns an `Err` value. Any panics that function can cause apply /// as well. /// /// # Examples /// /// The example below uses some kludges to work around a compiler /// quirk: /// /// ``` /// # use panic_control::{Context, Outcome}; /// # #[derive(Debug, PartialEq)] struct Expected(pub i32); /// let ctx = Context::<Expected>::new(); /// /// #[allow(unreachable_code)] /// let h = ctx.spawn(|| { /// panic!(Expected(42)); /// () /// }); /// /// let outcome = h.join().unwrap(); /// assert_eq!(outcome, Outcome::Panicked(Expected(42))); /// ``` /// /// Note that unless the unreachable return expression is present, /// the compiler would have no information to infer the unspecified /// first type parameter of `Outcome`, so it would settle on a default type /// that is going to be changed to `!` in Rust 1.26. In previous versions /// of the compiler, code that invokes this behavior is /// [denied by a lint](https://github.com/rust-lang/rust/issues/39216), /// so the following example does not compile: /// /// ```ignore /// # use panic_control::{Context, Outcome}; /// # #[derive(Debug, PartialEq)] struct Expected(pub i32); /// let ctx = Context::<Expected>::new(); /// let h = ctx.spawn(|| { /// panic!(Expected(42)); /// }); /// let outcome = h.join().unwrap(); /// assert_eq!(outcome, Outcome::Panicked(Expected(42))); /// ``` /// /// A way to avoid the future incompatibility without resorting /// to warning overrides is to match the `Outcome` value without /// touching the sensitive parts: /// /// ``` /// # use panic_control::{Context, Outcome}; /// # #[derive(Debug, PartialEq)] struct Expected(pub i32); /// let ctx = Context::<Expected>::new(); /// let h = ctx.spawn(|| { /// panic!(Expected(42)); /// }); /// let outcome = h.join().unwrap(); /// match outcome { /// Outcome::Panicked(Expected(n)) => assert_eq!(n, 42), /// _ => panic!("join() returned an unexpected Outcome value") /// } /// ``` pub fn spawn<T, F>(self, f: F) -> CheckedJoinHandle<T, P> where F: FnOnce() -> T, F: Send + 'static, T: Send + 'static { let thread_handle = self.thread_builder.spawn(f).unwrap(); CheckedJoinHandle { thread_handle: thread_handle, phantom: self.phantom } } /// Like `spawn()`, but disables the panic hook /// if the spawned thread panics. /// /// The process-global panic hook, either installed with /// `std::panic::set_hook()` or the standard library default, /// gets augmented with a filter that disables invocation of the /// hook closure if the spawned thread panics. /// /// This function can be used in any order together with other /// functions and methods of this crate that modify the panic hook. /// /// # Caveats /// /// Note that the suppression can apply to the default panic hook /// that is normally used to report assertion failures and other /// unexpected panics on the standard error stream. /// The only remaining way to observe the panic is by checking /// the result of `join()` for the spawned thread. /// /// Other code within the program that modifies the panic hook, /// concurrently to, or after, a call to this function, may cause /// the suppression not to work as intended. See the documentation /// on the function `disable_hook_in_current_thread()` for possible /// pitfalls. /// /// # Examples /// /// ``` /// # use panic_control::{Context, Outcome}; /// # #[derive(Debug, PartialEq)] struct Expected(pub i32); /// let ctx = Context::<Expected>::new(); /// let h = ctx.spawn_quiet(|| { /// assert!(false, "I'm panicking, \ /// but you can only learn about it through join()"); /// }); /// let res = h.join(); /// assert!(res.is_err()); /// ``` pub fn spawn_quiet<T, F>(self, f: F) -> CheckedJoinHandle<T, P> where F: FnOnce() -> T, F: Send + 'static, T: Send + 'static { self.spawn(|| { disable_hook_in_current_thread(); f() }) } } impl<P: Any> From<thread::Builder> for Context<P> { fn from(builder: thread::Builder) -> Context<P> { Context { thread_builder: builder, phantom: marker::PhantomData } } } /// Helpful extension methods for `std::thread::Result`. /// /// The `Result` type defined in `std::thread` is a /// specialization of the standard `Result` with a `Box<Any>` /// in the `Err` variant, which receives the payload /// value of a panic. /// As such, `Result` does not provide convenient ways /// to examine the content of the panic value. Furthermore, /// the generic implementations of `unwrap()` and related methods /// use the `Debug` implementation of the content of `Err` to format /// the panic message, which is /// [not very useful](https://github.com/rust-lang/rfcs/issues/1389) /// in case of `Any`. /// /// When this trait is used in a lexical scope, it augments /// any `Result` value that matches the specialization of /// `std::thread::Result` with methods that facilitate /// examination and reporting of the possible string value /// which is most often found in the dynamically typed /// `Err` variant. The methods are meant to be used on the /// result of `std::thread::JoinHandle::join()` or /// `CheckedJoinHandle::join()`. /// /// # Examples /// /// ``` /// use panic_control::ThreadResultExt; /// /// use panic_control::Context; /// use std::thread; /// /// let h = thread::spawn(|| { /// 42 /// }); /// let n = h.join().unwrap_or_propagate(); /// assert_eq!(n, 42); /// /// #[derive(Debug, PartialEq, Eq)] /// struct Expected; /// /// let ctx = Context::<Expected>::new(); /// let h = ctx.spawn_quiet(|| { /// panic!("No coffee beans left in the bag!"); /// }); /// let res = h.join(); /// let msg = res.panic_value_as_str().unwrap(); /// println!("{}", msg); /// ``` /// pub trait ThreadResultExt<T> : sealed::ThreadResultExtSealed { /// Unwraps a result, yielding the content of an `Ok`. /// /// # Panics /// /// Panics if the value is an `Err`, with a panic message appended with /// the `Err`'s string value if that is found to be such, or a generic /// message otherwise. The message is meant to relay information from /// a panic in a child thread that is observed through this result value, /// as returned by `std::thread::JoinHandle::join()` or /// `CheckedJoinHandle::join()`. fn unwrap_or_propagate(self) -> T; /// If the value is an `Err` and its content is a string, returns the /// content as a string slice. Otherwise returns `None`. fn panic_value_as_str(&self) -> Option<&str>; } fn str_from_any(something: &Any) -> Option<&str> { if let Some(s) = something.downcast_ref::<&'static str>() { Some(*s) } else if let Some(s) = something.downcast_ref::<String>() { Some(&s[..]) } else { None } } fn propagate_panic(box_any: Box<Any + Send>) -> ! { match str_from_any(box_any.as_ref()) { Some(s) => panic!("observed an unexpected thread panic: {}", s), None => panic!("observed an unexpected thread panic \ with undetermined value") } } mod sealed { use std::thread; // trait ThreadResultExt is sealed by this crate: it should only // make sense for thread::Result. pub trait ThreadResultExtSealed { } impl<T> ThreadResultExtSealed for thread::Result<T> { } } impl<T> ThreadResultExt<T> for thread::Result<T> { fn unwrap_or_propagate(self) -> T { match self { Ok(rv) => rv, Err(e) => propagate_panic(e) } } fn panic_value_as_str(&self) -> Option<&str> { match *self { Ok(_) => None, Err(ref ref_box_any) => str_from_any(&**ref_box_any) } } } /// Augments the panic hook, filtering out panics of a particular type. /// /// The current panic hook, either installed with `std::panic::set_hook()` /// or the standard library default, gets chained, again using /// `std::panic::set_hook()`, behind /// a dynamic type check for the panic payload. If it is found to be /// of the same type as the type parameter of this generic function, /// the chained hook is not called. /// /// # Caveats /// /// Every call to this function allocates state data and increases the /// filtering chain for the process-global panic hook, so it should not be /// called repeatedly unless necessary. /// Other code within the program that modifies the panic hook, concurrently /// to, or after, the call to this function, may cause the hook chain to stop /// working as intended. /// This function interoperates in a predictable way only with the other /// functions and methods of this crate that modify the panic hook, /// and only when used in strictly serialized order with those functions, /// unless noted otherwise in those functions' documentation. /// This function is only intended to be used in tests or initialization /// code of a program; /// libraries other than those designed for test purposes should avoid /// using it. /// /// # Examples /// /// ``` /// use panic_control::chain_hook_ignoring; /// use std::sync::{Once, ONCE_INIT}; /// /// #[derive(Debug, PartialEq, Eq)] /// struct PanicToken; /// /// #[derive(Debug, PartialEq, Eq)] /// struct PanicMessage(pub String); /// /// static HOOK_ONCE: Once = ONCE_INIT; /// HOOK_ONCE.call_once(|| { /// chain_hook_ignoring::<PanicToken>(); /// chain_hook_ignoring::<PanicMessage>(); /// }); /// ``` pub fn chain_hook_ignoring<P: 'static>() { chain_hook_ignoring_if(|_: &P| { true }) } /// Augments the panic hook, filtering out panics with a /// statically typed closure. /// /// The current panic hook, either installed with `std::panic::set_hook()` /// or the standard library default, gets chained, again using /// `std::panic::set_hook()`, behind /// the boolean predicate closure passed as the parameter, testing a value /// of a particular type. /// If the panic payload is found to be of the same type and the predicate /// returns true, the chained hook is not called. /// /// # Caveats /// /// Every call to this function allocates state data and increases the /// filtering chain for the process-global panic hook, so it should not be /// called repeatedly unless necessary. /// Other code within the program that modifies the panic hook, concurrently /// to, or after, the call to this function, may cause the hook chain to stop /// working as intended. /// This function interoperates in a predictable way only with the other /// functions and methods of this crate that modify the panic hook, /// and only when used in strictly serialized order with those functions, /// unless noted otherwise in those functions' documentation. /// This function is only intended to be used in tests or initialization /// code of a program; /// libraries other than those designed for test purposes should avoid /// using it. /// /// # Examples /// /// The value types most commonly used in panics are `&'string str` or /// `String`, depending on whether the `panic!` macro was used in the single /// parameter form or the formatting form, respectively. The example below /// filters out either kind if the string message contains a particular /// substring. /// /// ``` /// use panic_control::chain_hook_ignoring_if; /// use std::sync::{Once, ONCE_INIT}; /// /// const MAGIC: &str = "Move along, nothing to see here"; /// /// static HOOK_ONCE: Once = ONCE_INIT; /// HOOK_ONCE.call_once(|| { /// chain_hook_ignoring_if(|s: &&'static str| { /// s.contains(MAGIC) /// }); /// chain_hook_ignoring_if(|s: &String| { /// s.contains(MAGIC) /// }); /// }); /// ``` pub fn chain_hook_ignoring_if<P, F>(predicate: F) where F: Fn(&P) -> bool, F: Send, F: Sync, F: 'static, P: 'static { chain_hook_ignoring_full(move |info| { match info.payload().downcast_ref::<P>() { Some(p) => predicate(p), None => false } }) } /// Augments the panic hook, filtering out panics with a free-form check. /// /// The current panic hook, either installed with `std::panic::set_hook()` /// or the standard library default, gets chained, again using /// `std::panic::set_hook()`, behind /// the boolean predicate closure passed as the parameter, testing the /// `std::panic::PanicInfo` structure passed to the panic hook. /// If the predicate returns true, the chained hook is not called. /// /// # Caveats /// /// Every call to this function allocates state data and increases the /// filtering chain for the process-global panic hook, so it should not be /// called repeatedly unless necessary. /// Other code within the program that modifies the panic hook, concurrently /// to, or after, the call to this function, may cause the hook chain to stop /// working as intended. /// This function interoperates in a predictable way only with the other /// functions and methods of this crate that modify the panic hook, /// and only when used in strictly serialized order with those functions, /// unless noted otherwise in those functions' documentation. /// This function is only intended to be used in tests or initialization /// code of a program; /// libraries other than those designed for test purposes should avoid /// using it. /// /// # Examples /// /// This example filters out any non-string panics: /// /// ``` /// use panic_control::chain_hook_ignoring_full; /// use std::sync::{Once, ONCE_INIT}; /// /// static HOOK_ONCE: Once = ONCE_INIT; /// HOOK_ONCE.call_once(|| { /// chain_hook_ignoring_full(|info| { /// let payload = info.payload(); /// !(payload.is::<&'static str>() || /// payload.is::<String>()) /// }); /// }); /// ``` pub fn chain_hook_ignoring_full<F>(predicate: F) where F: Fn(&PanicInfo) -> bool, F: Send, F: Sync, F: 'static { // Make sure the thread filter hook is set up, // in case some other thread is calling // {disable,enable}_hook_in_current_thread() init_thread_filter_hook(); chain_hook_waive_init_thread_filter(predicate) } fn chain_hook_waive_init_thread_filter<F>(predicate: F) where F: Fn(&PanicInfo) -> bool, F: Send, F: Sync, F: 'static { let next_hook = panic::take_hook(); panic::set_hook(Box::new(move |info| { if !predicate(info) { next_hook(info); } })); } thread_local!(static IGNORE_HOOK: Cell<bool> = Cell::new(false)); fn init_thread_filter_hook() { static HOOK_ONCE: Once = ONCE_INIT; HOOK_ONCE.call_once(|| { // Avoid recursion and deadlocking on HOOK_ONCE here chain_hook_waive_init_thread_filter(|_| { IGNORE_HOOK.with(|cell| { cell.get() }) }); }); } /// Disables the panic hook for the current thread. /// /// The process-global panic hook, either installed with /// `std::panic::set_hook()` or the standard library default, /// gets augmented with a filter that disables invocation of the /// hook closure if the thread that is calling this function panics. /// /// This function does not allocate resources when called repeatedly in /// the same thread, and it can be used in any order together with other /// functions and methods of this crate that modify the panic hook. /// /// # Caveats /// /// Note that the suppression can apply to the default panic hook /// that is normally used to report assertion failures and other /// unexpected panics on the standard error stream. /// /// Other code within the program that modifies the panic hook, concurrently /// to, or after, a call to this function, may cause the hook chain to stop /// working as intended. /// This function interoperates in a predictable way only with the other /// functions and methods of this crate that modify the panic hook. /// Libraries other than those designed for test purposes should avoid /// using this function. pub fn disable_hook_in_current_thread() { init_thread_filter_hook(); IGNORE_HOOK.with(|cell| { cell.set(true); }); } /// Enables the panic hook for the current thread. /// /// If the panic hook has been disabled for the current thread with /// `disable_hook_in_current_thread()`, calling this function enables it /// back. /// /// This function does not allocate resources when called repeatedly in /// the same thread, and it can be used in any order together with other /// functions and methods of this crate that modify the panic hook. /// /// # Caveats /// /// Other code within the program that modifies the panic hook, concurrently /// to, or after, a call to this function, may cause the hook chain to stop /// working as intended. /// This function interoperates only with the other /// functions and methods of this crate that modify the panic hook. /// Libraries other than those designed for test purposes should avoid /// using this function. pub fn enable_hook_in_current_thread() { init_thread_filter_hook(); IGNORE_HOOK.with(|cell| { cell.set(false); }); } /// Like `std::thread::spawn()`, but disables the panic hook /// if the spawned thread panics. /// /// The process-global panic hook, either installed with /// `std::panic::set_hook()` or the standard library default, /// gets augmented with a filter that disables invocation of the /// hook closure if the spawned thread panics. /// /// This function can be used in any order together with other /// functions and methods of this crate that modify the panic hook. /// /// # Caveats /// /// Note that the suppression can apply to the default panic hook /// that is normally used to report assertion failures and other /// unexpected panics on the standard error stream. /// The only remaining way to observe the panic is by checking /// the result of `join()` for the spawned thread. /// /// Other code within the program that modifies the panic hook, /// concurrently to, or after, a call to this function, may cause /// the suppression not to work as intended. See the documentation /// on the function `disable_hook_in_current_thread()` for possible /// pitfalls. /// /// # Examples /// /// ``` /// use panic_control::spawn_quiet; /// /// let h = spawn_quiet(|| { /// assert!(false, "I'm panicking, \ /// but you can only learn about it through join()"); /// }); /// let res = h.join(); /// assert!(res.is_err()); /// ``` pub fn spawn_quiet<T, F>(f: F) -> thread::JoinHandle<T> where F: FnOnce() -> T, F: Send + 'static, T: Send + 'static { thread::spawn(|| { disable_hook_in_current_thread(); f() }) } #[cfg(test)] mod tests { use super::{Context, Outcome}; use super::{ThreadResultExt}; use super::chain_hook_ignoring; use std::sync::{Once, ONCE_INIT}; use std::thread; #[derive(Debug, PartialEq, Eq)] struct Expected(pub u32); fn silence_expected_panics() { static GUARD: Once = ONCE_INIT; GUARD.call_once(|| { chain_hook_ignoring::<Expected>() }); } #[test] fn no_panic() { let ctx = Context::<Expected>::new(); let h = ctx.spawn(|| { 42 }); let outcome = h.join().unwrap(); assert_eq!(outcome, Outcome::NoPanic(42)); } #[test] fn context_default() { let ctx = Context::<Expected>::default(); // Also use spawn_quiet and exercise the normal return path there let h = ctx.spawn_quiet(|| { 42 }); let outcome = h.join().unwrap(); assert_eq!(outcome, Outcome::NoPanic(42)); } #[test] fn expected_panic() { silence_expected_panics(); let ctx = Context::<Expected>::new(); let h = ctx.spawn(|| { panic!(Expected(42)); }); let outcome = h.join().unwrap(); match outcome { Outcome::Panicked(Expected(n)) => assert_eq!(n, 42), _ => panic!("unexpected Outcome value returned from join()") } } #[test] fn int_literal_gotcha() { let h = Context::<u32>::new().spawn_quiet(|| { panic!(42); }); // This wouldn't work: // let outcome = h.join().unwrap(); // assert_eq!(outcome, Outcome::Panicked(42)); let res = h.join(); assert!(res.is_err()); } #[test] fn from_thread_builder() { silence_expected_panics(); const THREAD_NAME: &str = "a panicky thread"; let thread_builder = thread::Builder::new() .name(THREAD_NAME.into()); let ctx = Context::<Expected>::from(thread_builder); let h = ctx.spawn(|| { let thread = thread::current(); let name = thread.name(); assert!(name.is_some()); assert_eq!(name.unwrap(), THREAD_NAME); 42 }); h.join().unwrap_or_propagate(); } #[test] fn checked_join_handle_inherent_as_ref() { const THREAD_NAME: &str = "a non-panicky thread"; let thread_builder = thread::Builder::new() .name(THREAD_NAME.into()); let ctx = Context::<Expected>::from(thread_builder); let h = ctx.spawn(|| {}); { let h = h.as_thread_join_handle(); let name = h.thread().name().unwrap(); assert_eq!(name, THREAD_NAME); } h.join().unwrap_or_propagate(); } #[test] fn checked_join_handle_trait_as_ref() { const THREAD_NAME: &str = "a non-panicky thread"; let thread_builder = thread::Builder::new() .name(THREAD_NAME.into()); let ctx = Context::<Expected>::from(thread_builder); let h = ctx.spawn(|| {}); { let h: &thread::JoinHandle<()> = h.as_ref(); let name = h.thread().name().unwrap(); assert_eq!(name, THREAD_NAME); } h.join().unwrap_or_propagate(); } #[test] fn checked_join_handle_inherent_into() { silence_expected_panics(); let ctx = Context::<Expected>::new(); let h = ctx.spawn(|| { panic!(Expected(42)); }); let h = h.into_thread_join_handle(); let res = h.join(); assert!(res.is_err()); } #[test] fn checked_join_handle_trait_into() { silence_expected_panics(); let ctx = Context::<Expected>::new(); #[allow(unreachable_code)] let h = ctx.spawn(|| { panic!(Expected(42)); () }); let h: thread::JoinHandle<()> = h.into(); let res = h.join(); assert!(res.is_err()); } #[test] fn debug_impls_omit_phantom() { let ctx = Context::<Expected>::new(); let repr = format!("{:?}", ctx); assert!(repr.starts_with("Context")); assert!(!repr.contains("phantom")); assert!(!repr.contains("PhantomData")); let h = ctx.spawn(|| { }); let repr = format!("{:?}", h); assert_eq!(repr, "CheckedJoinHandle { .. }"); h.join().unwrap(); } }