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

 // Copyright 2014 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.

 //! Implementation of various bits and pieces of the `panic!` macro and
 //! associated runtime pieces.
 //!
 //! Specifically, this module contains the implementation of:
 //!
 //! * Panic hooks
 //! * Executing a panic up to doing the actual implementation
 //! * Shims around "try"

 use io::prelude::*;

 use any::Any;
 use cell::RefCell;
 use fmt;
 use intrinsics;
 use mem;
 use ptr;
 use raw;
 use sys::stdio::Stderr;
 use sys_common::rwlock::RWLock;
 use sys_common::thread_info;
 use sys_common::util;
 use thread;

 thread_local! {
     pub static LOCAL_STDERR: RefCell<Option<Box<Write + Send>>> = {
         RefCell::new(None)
     }
 }

 // Binary interface to the panic runtime that the standard library depends on.
 //
 // The standard library is tagged with `#![needs_panic_runtime]` (introduced in
 // RFC 1513) to indicate that it requires some other crate tagged with
 // `#![panic_runtime]` to exist somewhere. Each panic runtime is intended to
 // implement these symbols (with the same signatures) so we can get matched up
 // to them.
 //
 // One day this may look a little less ad-hoc with the compiler helping out to
 // hook up these functions, but it is not this day!
 #[allow(improper_ctypes)]
 extern {
     fn __rust_maybe_catch_panic(f: fn(*mut u8),
                                 data: *mut u8,
                                 data_ptr: *mut usize,
                                 vtable_ptr: *mut usize) -> u32;
     #[unwind]
     fn __rust_start_panic(data: usize, vtable: usize) -> u32;
 }

 #[derive(Copy, Clone)]
 enum Hook {
     Default,
     Custom(*mut (Fn(&PanicInfo) + 'static + Sync + Send)),
 }

 static HOOK_LOCK: RWLock = RWLock::new();
 static mut HOOK: Hook = Hook::Default;

 /// Registers a custom panic hook, replacing any that was previously registered.
 ///
 /// The panic hook is invoked when a thread panics, but before the panic runtime
 /// is invoked. As such, the hook will run with both the aborting and unwinding
 /// runtimes. The default hook prints a message to standard error and generates
 /// a backtrace if requested, but this behavior can be customized with the
 /// `set_hook` and `take_hook` functions.
 ///
 /// The hook is provided with a `PanicInfo` struct which contains information
 /// about the origin of the panic, including the payload passed to `panic!` and
 /// the source code location from which the panic originated.
 ///
 /// The panic hook is a global resource.
 ///
 /// # Panics
 ///
 /// Panics if called from a panicking thread.
 ///
 /// # Examples
 ///
 /// The following will print "Custom panic hook":
 ///
 /// ```should_panic
 /// use std::panic;
 ///
 /// panic::set_hook(Box::new(|_| {
 ///     println!("Custom panic hook");
 /// }));
 ///
 /// panic!("Normal panic");
 /// ```
 #[stable(feature = "panic_hooks", since = "1.10.0")]
 pub fn set_hook(hook: Box<Fn(&PanicInfo) + 'static + Sync + Send>) {
     if thread::panicking() {
         panic!("cannot modify the panic hook from a panicking thread");
     }

     unsafe {
         HOOK_LOCK.write();
         let old_hook = HOOK;
         HOOK = Hook::Custom(Box::into_raw(hook));
         HOOK_LOCK.write_unlock();

         if let Hook::Custom(ptr) = old_hook {
             Box::from_raw(ptr);
         }
     }
 }

 /// Unregisters the current panic hook, returning it.
 ///
 /// If no custom hook is registered, the default hook will be returned.
 ///
 /// # Panics
 ///
 /// Panics if called from a panicking thread.
 ///
 /// # Examples
 ///
 /// The following will print "Normal panic":
 ///
 /// ```should_panic
 /// use std::panic;
 ///
 /// panic::set_hook(Box::new(|_| {
 ///     println!("Custom panic hook");
 /// }));
 ///
 /// let _ = panic::take_hook();
 ///
 /// panic!("Normal panic");
 /// ```
 #[stable(feature = "panic_hooks", since = "1.10.0")]
 pub fn take_hook() -> Box<Fn(&PanicInfo) + 'static + Sync + Send> {
     if thread::panicking() {
         panic!("cannot modify the panic hook from a panicking thread");
     }

     unsafe {
         HOOK_LOCK.write();
         let hook = HOOK;
         HOOK = Hook::Default;
         HOOK_LOCK.write_unlock();

         match hook {
             Hook::Default => Box::new(default_hook),
             Hook::Custom(ptr) => Box::from_raw(ptr),
         }
     }
 }

 /// A struct providing information about a panic.
 ///
 /// `PanicInfo` structure is passed to a panic hook set by the [`set_hook`]
 /// function.
 ///
 /// [`set_hook`]: ../../std/panic/fn.set_hook.html
 ///
 /// # Examples
 ///
 /// ```should_panic
 /// use std::panic;
 ///
 /// panic::set_hook(Box::new(|panic_info| {
 ///     println!("panic occurred: {:?}", panic_info.payload().downcast_ref::<&str>().unwrap());
 /// }));
 ///
 /// panic!("Normal panic");
 /// ```
 #[stable(feature = "panic_hooks", since = "1.10.0")]
 #[derive(Debug)]
 pub struct PanicInfo<'a> {
     payload: &'a (Any + Send),
     location: Location<'a>,
 }

 impl<'a> PanicInfo<'a> {
     /// Returns the payload associated with the panic.
     ///
     /// This will commonly, but not always, be a `&'static str` or [`String`].
     ///
     /// [`String`]: ../../std/string/struct.String.html
     ///
     /// # Examples
     ///
     /// ```should_panic
     /// use std::panic;
     ///
     /// panic::set_hook(Box::new(|panic_info| {
     ///     println!("panic occurred: {:?}", panic_info.payload().downcast_ref::<&str>().unwrap());
     /// }));
     ///
     /// panic!("Normal panic");
     /// ```
     #[stable(feature = "panic_hooks", since = "1.10.0")]
     pub fn payload(&self) -> &(Any + Send) {
         self.payload
     }

     /// Returns information about the location from which the panic originated,
     /// if available.
     ///
     /// This method will currently always return [`Some`], but this may change
     /// in future versions.
     ///
     /// [`Some`]: ../../std/option/enum.Option.html#variant.Some
     ///
     /// # Examples
     ///
     /// ```should_panic
     /// use std::panic;
     ///
     /// panic::set_hook(Box::new(|panic_info| {
     ///     if let Some(location) = panic_info.location() {
     ///         println!("panic occurred in file '{}' at line {}", location.file(),
     ///             location.line());
     ///     } else {
     ///         println!("panic occurred but can't get location information...");
     ///     }
     /// }));
     ///
     /// panic!("Normal panic");
     /// ```
     #[stable(feature = "panic_hooks", since = "1.10.0")]
     pub fn location(&self) -> Option<&Location> {
         Some(&self.location)
     }
 }

 /// A struct containing information about the location of a panic.
 ///
 /// This structure is created by the [`location`] method of [`PanicInfo`].
 ///
 /// [`location`]: ../../std/panic/struct.PanicInfo.html#method.location
 /// [`PanicInfo`]: ../../std/panic/struct.PanicInfo.html
 ///
 /// # Examples
 ///
 /// ```should_panic
 /// use std::panic;
 ///
 /// panic::set_hook(Box::new(|panic_info| {
 ///     if let Some(location) = panic_info.location() {
 ///         println!("panic occurred in file '{}' at line {}", location.file(), location.line());
 ///     } else {
 ///         println!("panic occurred but can't get location information...");
 ///     }
 /// }));
 ///
 /// panic!("Normal panic");
 /// ```
 #[derive(Debug)]
 #[stable(feature = "panic_hooks", since = "1.10.0")]
 pub struct Location<'a> {
     file: &'a str,
     line: u32,
     col: u32,
 }

 impl<'a> Location<'a> {
     /// Returns the name of the source file from which the panic originated.
     ///
     /// # Examples
     ///
     /// ```should_panic
     /// use std::panic;
     ///
     /// panic::set_hook(Box::new(|panic_info| {
     ///     if let Some(location) = panic_info.location() {
     ///         println!("panic occurred in file '{}'", location.file());
     ///     } else {
     ///         println!("panic occurred but can't get location information...");
     ///     }
     /// }));
     ///
     /// panic!("Normal panic");
     /// ```
     #[stable(feature = "panic_hooks", since = "1.10.0")]
     pub fn file(&self) -> &str {
         self.file
     }

     /// Returns the line number from which the panic originated.
     ///
     /// # Examples
     ///
     /// ```should_panic
     /// use std::panic;
     ///
     /// panic::set_hook(Box::new(|panic_info| {
     ///     if let Some(location) = panic_info.location() {
     ///         println!("panic occurred at line {}", location.line());
     ///     } else {
     ///         println!("panic occurred but can't get location information...");
     ///     }
     /// }));
     ///
     /// panic!("Normal panic");
     /// ```
     #[stable(feature = "panic_hooks", since = "1.10.0")]
     pub fn line(&self) -> u32 {
         self.line
     }

     /// Returns the column from which the panic originated.
     ///
     /// # Examples
     ///
     /// ```should_panic
     /// use std::panic;
     ///
     /// panic::set_hook(Box::new(|panic_info| {
     ///     if let Some(location) = panic_info.location() {
     ///         println!("panic occurred at column {}", location.column());
     ///     } else {
     ///         println!("panic occurred but can't get location information...");
     ///     }
     /// }));
     ///
     /// panic!("Normal panic");
     /// ```
     #[stable(feature = "panic_col", since = "1.25")]
     pub fn column(&self) -> u32 {
         self.col
     }
 }

 fn default_hook(info: &PanicInfo) {
     #[cfg(feature = "backtrace")]
     use sys_common::backtrace;

     // If this is a double panic, make sure that we print a backtrace
     // for this panic. Otherwise only print it if logging is enabled.
     #[cfg(feature = "backtrace")]
     let log_backtrace = {
         let panics = update_panic_count(0);

         if panics >= 2 {
             Some(backtrace::PrintFormat::Full)
         } else {
             backtrace::log_enabled()
         }
     };

     let file = info.location.file;
     let line = info.location.line;
     let col = info.location.col;

     let msg = match info.payload.downcast_ref::<&'static str>() {
         Some(s) => *s,
         None => match info.payload.downcast_ref::<String>() {
             Some(s) => &s[..],
             None => "Box<Any>",
         }
     };
     let mut err = Stderr::new().ok();
     let thread = thread_info::current_thread();
     let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");

     let write = |err: &mut ::io::Write| {
         let _ = writeln!(err, "thread '{}' panicked at '{}', {}:{}:{}",
                          name, msg, file, line, col);

         #[cfg(feature = "backtrace")]
         {
             use sync::atomic::{AtomicBool, Ordering};

             static FIRST_PANIC: AtomicBool = AtomicBool::new(true);

             if let Some(format) = log_backtrace {
                 let _ = backtrace::print(err, format);
             } else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
                 let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=1` for a backtrace.");
             }
         }
     };

     let prev = LOCAL_STDERR.with(|s| s.borrow_mut().take());
     match (prev, err.as_mut()) {
         (Some(mut stderr), _) => {
             write(&mut *stderr);
             let mut s = Some(stderr);
             LOCAL_STDERR.with(|slot| {
                 *slot.borrow_mut() = s.take();
             });
         }
         (None, Some(ref mut err)) => { write(err) }
         _ => {}
     }
 }


 #[cfg(not(test))]
 #[doc(hidden)]
 #[unstable(feature = "update_panic_count", issue = "0")]
 pub fn update_panic_count(amt: isize) -> usize {
     use cell::Cell;
     thread_local! { static PANIC_COUNT: Cell<usize> = Cell::new(0) }

     PANIC_COUNT.with(|c| {
         let next = (c.get() as isize + amt) as usize;
         c.set(next);
         return next
     })
 }

 #[cfg(test)]
 pub use realstd::rt::update_panic_count;

 /// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
 pub unsafe fn try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<Any + Send>> {
     #[allow(unions_with_drop_fields)]
     union Data<F, R> {
         f: F,
         r: R,
     }

     // We do some sketchy operations with ownership here for the sake of
     // performance. We can only  pass pointers down to
     // `__rust_maybe_catch_panic` (can't pass objects by value), so we do all
     // the ownership tracking here manually using a union.
     //
     // We go through a transition where:
     //
     // * First, we set the data to be the closure that we're going to call.
     // * When we make the function call, the `do_call` function below, we take
     //   ownership of the function pointer. At this point the `Data` union is
     //   entirely uninitialized.
     // * If the closure successfully returns, we write the return value into the
     //   data's return slot. Note that `ptr::write` is used as it's overwriting
     //   uninitialized data.
     // * Finally, when we come back out of the `__rust_maybe_catch_panic` we're
     //   in one of two states:
     //
     //      1. The closure didn't panic, in which case the return value was
     //         filled in. We move it out of `data` and return it.
     //      2. The closure panicked, in which case the return value wasn't
     //         filled in. In this case the entire `data` union is invalid, so
     //         there is no need to drop anything.
     //
     // Once we stack all that together we should have the "most efficient'
     // method of calling a catch panic whilst juggling ownership.
     let mut any_data = 0;
     let mut any_vtable = 0;
     let mut data = Data {
         f,
     };

     let r = __rust_maybe_catch_panic(do_call::<F, R>,
                                      &mut data as *mut _ as *mut u8,
                                      &mut any_data,
                                      &mut any_vtable);

     return if r == 0 {
         debug_assert!(update_panic_count(0) == 0);
         Ok(data.r)
     } else {
         update_panic_count(-1);
         debug_assert!(update_panic_count(0) == 0);
         Err(mem::transmute(raw::TraitObject {
             data: any_data as *mut _,
             vtable: any_vtable as *mut _,
         }))
     };

     fn do_call<F: FnOnce() -> R, R>(data: *mut u8) {
         unsafe {
             let data = data as *mut Data<F, R>;
             let f = ptr::read(&mut (*data).f);
             ptr::write(&mut (*data).r, f());
         }
     }
 }

 /// Determines whether the current thread is unwinding because of panic.
 pub fn panicking() -> bool {
     update_panic_count(0) != 0
 }

 /// Entry point of panic from the libcore crate.
 #[cfg(not(test))]
 #[lang = "panic_fmt"]
 #[unwind]
 pub extern fn rust_begin_panic(msg: fmt::Arguments,
                                file: &'static str,
                                line: u32,
                                col: u32) -> ! {
     begin_panic_fmt(&msg, &(file, line, col))
 }

 /// The entry point for panicking with a formatted message.
 ///
 /// This is designed to reduce the amount of code required at the call
 /// site as much as possible (so that `panic!()` has as low an impact
 /// on (e.g.) the inlining of other functions as possible), by moving
 /// the actual formatting into this shared place.
 #[unstable(feature = "libstd_sys_internals",
            reason = "used by the panic! macro",
            issue = "0")]
 #[inline(never)] #[cold]
 pub fn begin_panic_fmt(msg: &fmt::Arguments,
                        file_line_col: &(&'static str, u32, u32)) -> ! {
     use fmt::Write;

     // We do two allocations here, unfortunately. But (a) they're
     // required with the current scheme, and (b) we don't handle
     // panic + OOM properly anyway (see comment in begin_panic
     // below).

     let mut s = String::new();
     let _ = s.write_fmt(*msg);
     begin_panic(s, file_line_col)
 }

 /// This is the entry point of panicking for panic!() and assert!().
 #[unstable(feature = "libstd_sys_internals",
            reason = "used by the panic! macro",
            issue = "0")]
 #[inline(never)] #[cold] // avoid code bloat at the call sites as much as possible
 pub fn begin_panic<M: Any + Send>(msg: M, file_line_col: &(&'static str, u32, u32)) -> ! {
     // Note that this should be the only allocation performed in this code path.
     // Currently this means that panic!() on OOM will invoke this code path,
     // but then again we're not really ready for panic on OOM anyway. If
     // we do start doing this, then we should propagate this allocation to
     // be performed in the parent of this thread instead of the thread that's
     // panicking.

     rust_panic_with_hook(Box::new(msg), file_line_col)
 }

 /// Executes the primary logic for a panic, including checking for recursive
 /// panics and panic hooks.
 ///
 /// This is the entry point or panics from libcore, formatted panics, and
 /// `Box<Any>` panics. Here we'll verify that we're not panicking recursively,
 /// run panic hooks, and then delegate to the actual implementation of panics.
 #[inline(never)]
 #[cold]
 fn rust_panic_with_hook(msg: Box<Any + Send>,
                         file_line_col: &(&'static str, u32, u32)) -> ! {
     let (file, line, col) = *file_line_col;

     let panics = update_panic_count(1);

     // If this is the third nested call (e.g. panics == 2, this is 0-indexed),
     // the panic hook probably triggered the last panic, otherwise the
     // double-panic check would have aborted the process. In this case abort the
     // process real quickly as we don't want to try calling it again as it'll
     // probably just panic again.
     if panics > 2 {
         util::dumb_print(format_args!("thread panicked while processing \
                                        panic. aborting.\n"));
         unsafe { intrinsics::abort() }
     }

     unsafe {
         let info = PanicInfo {
             payload: &*msg,
             location: Location {
                 file,
                 line,
                 col,
             },
         };
         HOOK_LOCK.read();
         match HOOK {
             Hook::Default => default_hook(&info),
             Hook::Custom(ptr) => (*ptr)(&info),
         }
         HOOK_LOCK.read_unlock();
     }

     if panics > 1 {
         // If a thread panics while it's already unwinding then we
         // have limited options. Currently our preference is to
         // just abort. In the future we may consider resuming
         // unwinding or otherwise exiting the thread cleanly.
         util::dumb_print(format_args!("thread panicked while panicking. \
                                        aborting.\n"));
         unsafe { intrinsics::abort() }
     }

     rust_panic(msg)
 }

 /// Shim around rust_panic. Called by resume_unwind.
 pub fn update_count_then_panic(msg: Box<Any + Send>) -> ! {
     update_panic_count(1);
     rust_panic(msg)
 }

 /// A private no-mangle function on which to slap yer breakpoints.
 #[no_mangle]
 #[allow(private_no_mangle_fns)] // yes we get it, but we like breakpoints
 pub fn rust_panic(msg: Box<Any + Send>) -> ! {
     let code = unsafe {
         let obj = mem::transmute::<_, raw::TraitObject>(msg);
         __rust_start_panic(obj.data as usize, obj.vtable as usize)
     };
     rtabort!("failed to initiate panic, error {}", code)
 }
	// Copyright 2014 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.

	//! Implementation of various bits and pieces of the `panic!` macro and
	//! associated runtime pieces.
	//!
	//! Specifically, this module contains the implementation of:
	//!
	//! * Panic hooks
	//! * Executing a panic up to doing the actual implementation
	//! * Shims around "try"

	use io::prelude::*;

	use any::Any;
	use cell::RefCell;
	use fmt;
	use intrinsics;
	use mem;
	use ptr;
	use raw;
	use sys::stdio::Stderr;
	use sys_common::rwlock::RWLock;
	use sys_common::thread_info;
	use sys_common::util;
	use thread;

	thread_local! {
	pub static LOCAL_STDERR: RefCell<Option<Box<Write + Send>>> = {
	RefCell::new(None)
	}
	}

	// Binary interface to the panic runtime that the standard library depends on.
	//
	// The standard library is tagged with `#![needs_panic_runtime]` (introduced in
	// RFC 1513) to indicate that it requires some other crate tagged with
	// `#![panic_runtime]` to exist somewhere. Each panic runtime is intended to
	// implement these symbols (with the same signatures) so we can get matched up
	// to them.
	//
	// One day this may look a little less ad-hoc with the compiler helping out to
	// hook up these functions, but it is not this day!
	#[allow(improper_ctypes)]
	extern {
	fn __rust_maybe_catch_panic(f: fn(*mut u8),
	data: *mut u8,
	data_ptr: *mut usize,
	vtable_ptr: *mut usize) -> u32;
	#[unwind]
	fn __rust_start_panic(data: usize, vtable: usize) -> u32;
	}

	#[derive(Copy, Clone)]
	enum Hook {
	Default,
	Custom(*mut (Fn(&PanicInfo) + 'static + Sync + Send)),
	}

	static HOOK_LOCK: RWLock = RWLock::new();
	static mut HOOK: Hook = Hook::Default;

	/// Registers a custom panic hook, replacing any that was previously registered.
	///
	/// The panic hook is invoked when a thread panics, but before the panic runtime
	/// is invoked. As such, the hook will run with both the aborting and unwinding
	/// runtimes. The default hook prints a message to standard error and generates
	/// a backtrace if requested, but this behavior can be customized with the
	/// `set_hook` and `take_hook` functions.
	///
	/// The hook is provided with a `PanicInfo` struct which contains information
	/// about the origin of the panic, including the payload passed to `panic!` and
	/// the source code location from which the panic originated.
	///
	/// The panic hook is a global resource.
	///
	/// # Panics
	///
	/// Panics if called from a panicking thread.
	///
	/// # Examples
	///
	/// The following will print "Custom panic hook":
	///
	/// ```should_panic
	/// use std::panic;
	///
	/// panic::set_hook(Box::new(\|_\| {
	/// println!("Custom panic hook");
	/// }));
	///
	/// panic!("Normal panic");
	/// ```
	#[stable(feature = "panic_hooks", since = "1.10.0")]
	pub fn set_hook(hook: Box<Fn(&PanicInfo) + 'static + Sync + Send>) {
	if thread::panicking() {
	panic!("cannot modify the panic hook from a panicking thread");
	}

	unsafe {
	HOOK_LOCK.write();
	let old_hook = HOOK;
	HOOK = Hook::Custom(Box::into_raw(hook));
	HOOK_LOCK.write_unlock();

	if let Hook::Custom(ptr) = old_hook {
	Box::from_raw(ptr);
	}
	}
	}

	/// Unregisters the current panic hook, returning it.
	///
	/// If no custom hook is registered, the default hook will be returned.
	///
	/// # Panics
	///
	/// Panics if called from a panicking thread.
	///
	/// # Examples
	///
	/// The following will print "Normal panic":
	///
	/// ```should_panic
	/// use std::panic;
	///
	/// panic::set_hook(Box::new(\|_\| {
	/// println!("Custom panic hook");
	/// }));
	///
	/// let _ = panic::take_hook();
	///
	/// panic!("Normal panic");
	/// ```
	#[stable(feature = "panic_hooks", since = "1.10.0")]
	pub fn take_hook() -> Box<Fn(&PanicInfo) + 'static + Sync + Send> {
	if thread::panicking() {
	panic!("cannot modify the panic hook from a panicking thread");
	}

	unsafe {
	HOOK_LOCK.write();
	let hook = HOOK;
	HOOK = Hook::Default;
	HOOK_LOCK.write_unlock();

	match hook {
	Hook::Default => Box::new(default_hook),
	Hook::Custom(ptr) => Box::from_raw(ptr),
	}
	}
	}

	/// A struct providing information about a panic.
	///
	/// `PanicInfo` structure is passed to a panic hook set by the [`set_hook`]
	/// function.
	///
	/// [`set_hook`]: ../../std/panic/fn.set_hook.html
	///
	/// # Examples
	///
	/// ```should_panic
	/// use std::panic;
	///
	/// panic::set_hook(Box::new(\|panic_info\| {
	/// println!("panic occurred: {:?}", panic_info.payload().downcast_ref::<&str>().unwrap());
	/// }));
	///
	/// panic!("Normal panic");
	/// ```
	#[stable(feature = "panic_hooks", since = "1.10.0")]
	#[derive(Debug)]
	pub struct PanicInfo<'a> {
	payload: &'a (Any + Send),
	location: Location<'a>,
	}

	impl<'a> PanicInfo<'a> {
	/// Returns the payload associated with the panic.
	///
	/// This will commonly, but not always, be a `&'static str` or [`String`].
	///
	/// [`String`]: ../../std/string/struct.String.html
	///
	/// # Examples
	///
	/// ```should_panic
	/// use std::panic;
	///
	/// panic::set_hook(Box::new(\|panic_info\| {
	/// println!("panic occurred: {:?}", panic_info.payload().downcast_ref::<&str>().unwrap());
	/// }));
	///
	/// panic!("Normal panic");
	/// ```
	#[stable(feature = "panic_hooks", since = "1.10.0")]
	pub fn payload(&self) -> &(Any + Send) {
	self.payload
	}

	/// Returns information about the location from which the panic originated,
	/// if available.
	///
	/// This method will currently always return [`Some`], but this may change
	/// in future versions.
	///
	/// [`Some`]: ../../std/option/enum.Option.html#variant.Some
	///
	/// # Examples
	///
	/// ```should_panic
	/// use std::panic;
	///
	/// panic::set_hook(Box::new(\|panic_info\| {
	/// if let Some(location) = panic_info.location() {
	/// println!("panic occurred in file '{}' at line {}", location.file(),
	/// location.line());
	/// } else {
	/// println!("panic occurred but can't get location information...");
	/// }
	/// }));
	///
	/// panic!("Normal panic");
	/// ```
	#[stable(feature = "panic_hooks", since = "1.10.0")]
	pub fn location(&self) -> Option<&Location> {
	Some(&self.location)
	}
	}

	/// A struct containing information about the location of a panic.
	///
	/// This structure is created by the [`location`] method of [`PanicInfo`].
	///
	/// [`location`]: ../../std/panic/struct.PanicInfo.html#method.location
	/// [`PanicInfo`]: ../../std/panic/struct.PanicInfo.html
	///
	/// # Examples
	///
	/// ```should_panic
	/// use std::panic;
	///
	/// panic::set_hook(Box::new(\|panic_info\| {
	/// if let Some(location) = panic_info.location() {
	/// println!("panic occurred in file '{}' at line {}", location.file(), location.line());
	/// } else {
	/// println!("panic occurred but can't get location information...");
	/// }
	/// }));
	///
	/// panic!("Normal panic");
	/// ```
	#[derive(Debug)]
	#[stable(feature = "panic_hooks", since = "1.10.0")]
	pub struct Location<'a> {
	file: &'a str,
	line: u32,
	col: u32,
	}

	impl<'a> Location<'a> {
	/// Returns the name of the source file from which the panic originated.
	///
	/// # Examples
	///
	/// ```should_panic
	/// use std::panic;
	///
	/// panic::set_hook(Box::new(\|panic_info\| {
	/// if let Some(location) = panic_info.location() {
	/// println!("panic occurred in file '{}'", location.file());
	/// } else {
	/// println!("panic occurred but can't get location information...");
	/// }
	/// }));
	///
	/// panic!("Normal panic");
	/// ```
	#[stable(feature = "panic_hooks", since = "1.10.0")]
	pub fn file(&self) -> &str {
	self.file
	}

	/// Returns the line number from which the panic originated.
	///
	/// # Examples
	///
	/// ```should_panic
	/// use std::panic;
	///
	/// panic::set_hook(Box::new(\|panic_info\| {
	/// if let Some(location) = panic_info.location() {
	/// println!("panic occurred at line {}", location.line());
	/// } else {
	/// println!("panic occurred but can't get location information...");
	/// }
	/// }));
	///
	/// panic!("Normal panic");
	/// ```
	#[stable(feature = "panic_hooks", since = "1.10.0")]
	pub fn line(&self) -> u32 {
	self.line
	}

	/// Returns the column from which the panic originated.
	///
	/// # Examples
	///
	/// ```should_panic
	/// use std::panic;
	///
	/// panic::set_hook(Box::new(\|panic_info\| {
	/// if let Some(location) = panic_info.location() {
	/// println!("panic occurred at column {}", location.column());
	/// } else {
	/// println!("panic occurred but can't get location information...");
	/// }
	/// }));
	///
	/// panic!("Normal panic");
	/// ```
	#[stable(feature = "panic_col", since = "1.25")]
	pub fn column(&self) -> u32 {
	self.col
	}
	}

	fn default_hook(info: &PanicInfo) {
	#[cfg(feature = "backtrace")]
	use sys_common::backtrace;

	// If this is a double panic, make sure that we print a backtrace
	// for this panic. Otherwise only print it if logging is enabled.
	#[cfg(feature = "backtrace")]
	let log_backtrace = {
	let panics = update_panic_count(0);

	if panics >= 2 {
	Some(backtrace::PrintFormat::Full)
	} else {
	backtrace::log_enabled()
	}
	};

	let file = info.location.file;
	let line = info.location.line;
	let col = info.location.col;

	let msg = match info.payload.downcast_ref::<&'static str>() {
	Some(s) => *s,
	None => match info.payload.downcast_ref::<String>() {
	Some(s) => &s[..],
	None => "Box<Any>",
	}
	};
	let mut err = Stderr::new().ok();
	let thread = thread_info::current_thread();
	let name = thread.as_ref().and_then(\|t\| t.name()).unwrap_or("<unnamed>");

	let write = \|err: &mut ::io::Write\| {
	let _ = writeln!(err, "thread '{}' panicked at '{}', {}:{}:{}",
	name, msg, file, line, col);

	#[cfg(feature = "backtrace")]
	{
	use sync::atomic::{AtomicBool, Ordering};

	static FIRST_PANIC: AtomicBool = AtomicBool::new(true);

	if let Some(format) = log_backtrace {
	let _ = backtrace::print(err, format);
	} else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
	let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=1` for a backtrace.");
	}
	}
	};

	let prev = LOCAL_STDERR.with(\|s\| s.borrow_mut().take());
	match (prev, err.as_mut()) {
	(Some(mut stderr), _) => {
	write(&mut *stderr);
	let mut s = Some(stderr);
	LOCAL_STDERR.with(\|slot\| {
	*slot.borrow_mut() = s.take();
	});
	}
	(None, Some(ref mut err)) => { write(err) }
	_ => {}
	}
	}


	#[cfg(not(test))]
	#[doc(hidden)]
	#[unstable(feature = "update_panic_count", issue = "0")]
	pub fn update_panic_count(amt: isize) -> usize {
	use cell::Cell;
	thread_local! { static PANIC_COUNT: Cell<usize> = Cell::new(0) }

	PANIC_COUNT.with(\|c\| {
	let next = (c.get() as isize + amt) as usize;
	c.set(next);
	return next
	})
	}

	#[cfg(test)]
	pub use realstd::rt::update_panic_count;

	/// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
	pub unsafe fn try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<Any + Send>> {
	#[allow(unions_with_drop_fields)]
	union Data<F, R> {
	f: F,
	r: R,
	}

	// We do some sketchy operations with ownership here for the sake of
	// performance. We can only pass pointers down to
	// `__rust_maybe_catch_panic` (can't pass objects by value), so we do all
	// the ownership tracking here manually using a union.
	//
	// We go through a transition where:
	//
	// * First, we set the data to be the closure that we're going to call.
	// * When we make the function call, the `do_call` function below, we take
	// ownership of the function pointer. At this point the `Data` union is
	// entirely uninitialized.
	// * If the closure successfully returns, we write the return value into the
	// data's return slot. Note that `ptr::write` is used as it's overwriting
	// uninitialized data.
	// * Finally, when we come back out of the `__rust_maybe_catch_panic` we're
	// in one of two states:
	//
	// 1. The closure didn't panic, in which case the return value was
	// filled in. We move it out of `data` and return it.
	// 2. The closure panicked, in which case the return value wasn't
	// filled in. In this case the entire `data` union is invalid, so
	// there is no need to drop anything.
	//
	// Once we stack all that together we should have the "most efficient'
	// method of calling a catch panic whilst juggling ownership.
	let mut any_data = 0;
	let mut any_vtable = 0;
	let mut data = Data {
	f,
	};

	let r = __rust_maybe_catch_panic(do_call::<F, R>,
	&mut data as mut _ as mut u8,
	&mut any_data,
	&mut any_vtable);

	return if r == 0 {
	debug_assert!(update_panic_count(0) == 0);
	Ok(data.r)
	} else {
	update_panic_count(-1);
	debug_assert!(update_panic_count(0) == 0);
	Err(mem::transmute(raw::TraitObject {
	data: any_data as *mut _,
	vtable: any_vtable as *mut _,
	}))
	};

	fn do_call<F: FnOnce() -> R, R>(data: *mut u8) {
	unsafe {
	let data = data as *mut Data<F, R>;
	let f = ptr::read(&mut (*data).f);
	ptr::write(&mut (*data).r, f());
	}
	}
	}

	/// Determines whether the current thread is unwinding because of panic.
	pub fn panicking() -> bool {
	update_panic_count(0) != 0
	}

	/// Entry point of panic from the libcore crate.
	#[cfg(not(test))]
	#[lang = "panic_fmt"]
	#[unwind]
	pub extern fn rust_begin_panic(msg: fmt::Arguments,
	file: &'static str,
	line: u32,
	col: u32) -> ! {
	begin_panic_fmt(&msg, &(file, line, col))
	}

	/// The entry point for panicking with a formatted message.
	///
	/// This is designed to reduce the amount of code required at the call
	/// site as much as possible (so that `panic!()` has as low an impact
	/// on (e.g.) the inlining of other functions as possible), by moving
	/// the actual formatting into this shared place.
	#[unstable(feature = "libstd_sys_internals",
	reason = "used by the panic! macro",
	issue = "0")]
	#[inline(never)] #[cold]
	pub fn begin_panic_fmt(msg: &fmt::Arguments,
	file_line_col: &(&'static str, u32, u32)) -> ! {
	use fmt::Write;

	// We do two allocations here, unfortunately. But (a) they're
	// required with the current scheme, and (b) we don't handle
	// panic + OOM properly anyway (see comment in begin_panic
	// below).

	let mut s = String::new();
	let _ = s.write_fmt(*msg);
	begin_panic(s, file_line_col)
	}

	/// This is the entry point of panicking for panic!() and assert!().
	#[unstable(feature = "libstd_sys_internals",
	reason = "used by the panic! macro",
	issue = "0")]
	#[inline(never)] #[cold] // avoid code bloat at the call sites as much as possible
	pub fn begin_panic<M: Any + Send>(msg: M, file_line_col: &(&'static str, u32, u32)) -> ! {
	// Note that this should be the only allocation performed in this code path.
	// Currently this means that panic!() on OOM will invoke this code path,
	// but then again we're not really ready for panic on OOM anyway. If
	// we do start doing this, then we should propagate this allocation to
	// be performed in the parent of this thread instead of the thread that's
	// panicking.

	rust_panic_with_hook(Box::new(msg), file_line_col)
	}

	/// Executes the primary logic for a panic, including checking for recursive
	/// panics and panic hooks.
	///
	/// This is the entry point or panics from libcore, formatted panics, and
	/// `Box<Any>` panics. Here we'll verify that we're not panicking recursively,
	/// run panic hooks, and then delegate to the actual implementation of panics.
	#[inline(never)]
	#[cold]
	fn rust_panic_with_hook(msg: Box<Any + Send>,
	file_line_col: &(&'static str, u32, u32)) -> ! {
	let (file, line, col) = *file_line_col;

	let panics = update_panic_count(1);

	// If this is the third nested call (e.g. panics == 2, this is 0-indexed),
	// the panic hook probably triggered the last panic, otherwise the
	// double-panic check would have aborted the process. In this case abort the
	// process real quickly as we don't want to try calling it again as it'll
	// probably just panic again.
	if panics > 2 {
	util::dumb_print(format_args!("thread panicked while processing \
	panic. aborting.\n"));
	unsafe { intrinsics::abort() }
	}

	unsafe {
	let info = PanicInfo {
	payload: &*msg,
	location: Location {
	file,
	line,
	col,
	},
	};
	HOOK_LOCK.read();
	match HOOK {
	Hook::Default => default_hook(&info),
	Hook::Custom(ptr) => (*ptr)(&info),
	}
	HOOK_LOCK.read_unlock();
	}

	if panics > 1 {
	// If a thread panics while it's already unwinding then we
	// have limited options. Currently our preference is to
	// just abort. In the future we may consider resuming
	// unwinding or otherwise exiting the thread cleanly.
	util::dumb_print(format_args!("thread panicked while panicking. \
	aborting.\n"));
	unsafe { intrinsics::abort() }
	}

	rust_panic(msg)
	}

	/// Shim around rust_panic. Called by resume_unwind.
	pub fn update_count_then_panic(msg: Box<Any + Send>) -> ! {
	update_panic_count(1);
	rust_panic(msg)
	}

	/// A private no-mangle function on which to slap yer breakpoints.
	#[no_mangle]
	#[allow(private_no_mangle_fns)] // yes we get it, but we like breakpoints
	pub fn rust_panic(msg: Box<Any + Send>) -> ! {
	let code = unsafe {
	let obj = mem::transmute::<_, raw::TraitObject>(msg);
	__rust_start_panic(obj.data as usize, obj.vtable as usize)
	};
	rtabort!("failed to initiate panic, error {}", code)
	}