Initial thread support

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+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Panic support in the standard library
+
+#![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, Shared};
+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, 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 cricial components:
+///
+/// 1. A data structure is in a temporarily invalid state when the thread
+///    panics.
+/// 2. This broken invariant is then later observed.
+///
+/// Typically in Rust, it is difficult to perform step (2) because catching a
+/// panic involves either spawning a thread (which in turns makes it difficult
+/// to later witness broken invariants) or using the `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<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?
+///
+/// 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 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} contains interior mutability \
+                            and a reference may not be safely transferrable \
+                            across a catch_unwind boundary"]
+pub 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<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 explicilty poisoned are unwind safe
+// * Our custom AssertUnwindSafe wrapper is indeed unwind safe
+#[stable(feature = "catch_unwind", since = "1.9.0")]
+impl UnwindSafe for .. {}
+#[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<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 = "unique", issue = "27730")]
+impl<T: UnwindSafe + ?Sized> UnwindSafe for Unique<T> {}
+#[unstable(feature = "shared", issue = "27730")]
+impl<T: RefUnwindSafe + ?Sized> UnwindSafe for Shared<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 this is a marker trait and `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 .. {}
+#[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 = "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<T> RefUnwindSafe for atomic::AtomicPtr<T> {}
+
+#[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()
+    }
+}
+
+/// 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<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R> {
+    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")]
+// we always abort so I'm pretty sure there's no reason to ever call this
+pub fn resume_unwind(_payload: Box<Any + Send>) -> ! {
+    unimplemented!()
+}