Implement RFC 909: move thread_local into thread

This commit implements [RFC
909](https://github.com/rust-lang/rfcs/pull/909):

The `std::thread_local` module is now deprecated, and its contents are
available directly in `std::thread` as `LocalKey`, `LocalKeyState`, and
`ScopedKey`.

The macros remain exactly as they were, which means little if any code
should break. Nevertheless, this is technically a:

[breaking-change]

Closes #23547

3 files changed, 2078 insertions, 0 deletions

diff --git a/src/libstd/thread/local.rs b/src/libstd/thread/local.rs
new file mode 100644
index 00000000000..43142d2e5bc
--- /dev/null
+++ b/src/libstd/thread/local.rs
@@ -0,0 +1,735 @@
+// Copyright 2014-2015 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.
+
+//! Thread local storage
+
+#![unstable(feature = "thread_local_internals")]
+
+use prelude::v1::*;
+
+use cell::UnsafeCell;
+
+// Sure wish we had macro hygiene, no?
+#[doc(hidden)]
+#[unstable(feature = "thread_local_internals")]
+pub mod __impl {
+    pub use super::imp::Key as KeyInner;
+    pub use super::imp::destroy_value;
+    pub use sys_common::thread_local::INIT_INNER as OS_INIT_INNER;
+    pub use sys_common::thread_local::StaticKey as OsStaticKey;
+}
+
+/// A thread local storage key which owns its contents.
+///
+/// This key uses the fastest possible implementation available to it for the
+/// target platform. It is instantiated with the `thread_local!` macro and the
+/// primary method is the `with` method.
+///
+/// The `with` method yields a reference to the contained value which cannot be
+/// sent across tasks or escape the given closure.
+///
+/// # Initialization and Destruction
+///
+/// Initialization is dynamically performed on the first call to `with()`
+/// within a thread, and values support destructors which will be run when a
+/// thread exits.
+///
+/// # Examples
+///
+/// ```
+/// use std::cell::RefCell;
+/// use std::thread;
+///
+/// thread_local!(static FOO: RefCell<u32> = RefCell::new(1));
+///
+/// FOO.with(|f| {
+///     assert_eq!(*f.borrow(), 1);
+///     *f.borrow_mut() = 2;
+/// });
+///
+/// // each thread starts out with the initial value of 1
+/// thread::spawn(move|| {
+///     FOO.with(|f| {
+///         assert_eq!(*f.borrow(), 1);
+///         *f.borrow_mut() = 3;
+///     });
+/// });
+///
+/// // we retain our original value of 2 despite the child thread
+/// FOO.with(|f| {
+///     assert_eq!(*f.borrow(), 2);
+/// });
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct LocalKey<T> {
+    // The key itself may be tagged with #[thread_local], and this `Key` is
+    // stored as a `static`, and it's not valid for a static to reference the
+    // address of another thread_local static. For this reason we kinda wonkily
+    // work around this by generating a shim function which will give us the
+    // address of the inner TLS key at runtime.
+    //
+    // This is trivially devirtualizable by LLVM because we never store anything
+    // to this field and rustc can declare the `static` as constant as well.
+    #[doc(hidden)]
+    #[unstable(feature = "thread_local_internals")]
+    pub inner: fn() -> &'static __impl::KeyInner<UnsafeCell<Option<T>>>,
+
+    // initialization routine to invoke to create a value
+    #[doc(hidden)]
+    #[unstable(feature = "thread_local_internals")]
+    pub init: fn() -> T,
+}
+
+/// Declare a new thread local storage key of type `std::thread::LocalKey`.
+#[macro_export]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[allow_internal_unstable]
+macro_rules! thread_local {
+    (static $name:ident: $t:ty = $init:expr) => (
+        static $name: ::std::thread::LocalKey<$t> = {
+            use std::cell::UnsafeCell as __UnsafeCell;
+            use std::thread::__local::__impl::KeyInner as __KeyInner;
+            use std::option::Option as __Option;
+            use std::option::Option::None as __None;
+
+            __thread_local_inner!(static __KEY: __UnsafeCell<__Option<$t>> = {
+                __UnsafeCell { value: __None }
+            });
+            fn __init() -> $t { $init }
+            fn __getit() -> &'static __KeyInner<__UnsafeCell<__Option<$t>>> {
+                &__KEY
+            }
+            ::std::thread::LocalKey { inner: __getit, init: __init }
+        };
+    );
+    (pub static $name:ident: $t:ty = $init:expr) => (
+        pub static $name: ::std::thread::LocalKey<$t> = {
+            use std::cell::UnsafeCell as __UnsafeCell;
+            use std::thread::__local::__impl::KeyInner as __KeyInner;
+            use std::option::Option as __Option;
+            use std::option::Option::None as __None;
+
+            __thread_local_inner!(static __KEY: __UnsafeCell<__Option<$t>> = {
+                __UnsafeCell { value: __None }
+            });
+            fn __init() -> $t { $init }
+            fn __getit() -> &'static __KeyInner<__UnsafeCell<__Option<$t>>> {
+                &__KEY
+            }
+            ::std::thread::LocalKey { inner: __getit, init: __init }
+        };
+    );
+}
+
+// Macro pain #4586:
+//
+// When cross compiling, rustc will load plugins and macros from the *host*
+// platform before search for macros from the target platform. This is primarily
+// done to detect, for example, plugins. Ideally the macro below would be
+// defined once per module below, but unfortunately this means we have the
+// following situation:
+//
+// 1. We compile libstd for x86_64-unknown-linux-gnu, this thread_local!() macro
+//    will inject #[thread_local] statics.
+// 2. We then try to compile a program for arm-linux-androideabi
+// 3. The compiler has a host of linux and a target of android, so it loads
+//    macros from the *linux* libstd.
+// 4. The macro generates a #[thread_local] field, but the android libstd does
+//    not use #[thread_local]
+// 5. Compile error about structs with wrong fields.
+//
+// To get around this, we're forced to inject the #[cfg] logic into the macro
+// itself. Woohoo.
+
+#[macro_export]
+#[doc(hidden)]
+#[allow_internal_unstable]
+macro_rules! __thread_local_inner {
+    (static $name:ident: $t:ty = $init:expr) => (
+        #[cfg_attr(all(any(target_os = "macos", target_os = "linux"),
+                       not(target_arch = "aarch64")),
+                   thread_local)]
+        static $name: ::std::thread::__local::__impl::KeyInner<$t> =
+            __thread_local_inner!($init, $t);
+    );
+    (pub static $name:ident: $t:ty = $init:expr) => (
+        #[cfg_attr(all(any(target_os = "macos", target_os = "linux"),
+                       not(target_arch = "aarch64")),
+                   thread_local)]
+        pub static $name: ::std::thread::__local::__impl::KeyInner<$t> =
+            __thread_local_inner!($init, $t);
+    );
+    ($init:expr, $t:ty) => ({
+        #[cfg(all(any(target_os = "macos", target_os = "linux"), not(target_arch = "aarch64")))]
+        const _INIT: ::std::thread::__local::__impl::KeyInner<$t> = {
+            ::std::thread::__local::__impl::KeyInner {
+                inner: ::std::cell::UnsafeCell { value: $init },
+                dtor_registered: ::std::cell::UnsafeCell { value: false },
+                dtor_running: ::std::cell::UnsafeCell { value: false },
+            }
+        };
+
+        #[cfg(any(not(any(target_os = "macos", target_os = "linux")), target_arch = "aarch64"))]
+        const _INIT: ::std::thread::__local::__impl::KeyInner<$t> = {
+            unsafe extern fn __destroy(ptr: *mut u8) {
+                ::std::thread::__local::__impl::destroy_value::<$t>(ptr);
+            }
+
+            ::std::thread::__local::__impl::KeyInner {
+                inner: ::std::cell::UnsafeCell { value: $init },
+                os: ::std::thread::__local::__impl::OsStaticKey {
+                    inner: ::std::thread::__local::__impl::OS_INIT_INNER,
+                    dtor: ::std::option::Option::Some(__destroy as unsafe extern fn(*mut u8)),
+                },
+            }
+        };
+
+        _INIT
+    });
+}
+
+/// Indicator of the state of a thread local storage key.
+#[unstable(feature = "std_misc",
+           reason = "state querying was recently added")]
+#[derive(Eq, PartialEq, Copy)]
+pub enum LocalKeyState {
+    /// All keys are in this state whenever a thread starts. Keys will
+    /// transition to the `Valid` state once the first call to `with` happens
+    /// and the initialization expression succeeds.
+    ///
+    /// Keys in the `Uninitialized` state will yield a reference to the closure
+    /// passed to `with` so long as the initialization routine does not panic.
+    Uninitialized,
+
+    /// Once a key has been accessed successfully, it will enter the `Valid`
+    /// state. Keys in the `Valid` state will remain so until the thread exits,
+    /// at which point the destructor will be run and the key will enter the
+    /// `Destroyed` state.
+    ///
+    /// Keys in the `Valid` state will be guaranteed to yield a reference to the
+    /// closure passed to `with`.
+    Valid,
+
+    /// When a thread exits, the destructors for keys will be run (if
+    /// necessary). While a destructor is running, and possibly after a
+    /// destructor has run, a key is in the `Destroyed` state.
+    ///
+    /// Keys in the `Destroyed` states will trigger a panic when accessed via
+    /// `with`.
+    Destroyed,
+}
+
+impl<T: 'static> LocalKey<T> {
+    /// Acquire a reference to the value in this TLS key.
+    ///
+    /// This will lazily initialize the value if this thread has not referenced
+    /// this key yet.
+    ///
+    /// # Panics
+    ///
+    /// This function will `panic!()` if the key currently has its
+    /// destructor running, and it **may** panic if the destructor has
+    /// previously been run for this thread.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn with<F, R>(&'static self, f: F) -> R
+                      where F: FnOnce(&T) -> R {
+        let slot = (self.inner)();
+        unsafe {
+            let slot = slot.get().expect("cannot access a TLS value during or \
+                                          after it is destroyed");
+            f(match *slot.get() {
+                Some(ref inner) => inner,
+                None => self.init(slot),
+            })
+        }
+    }
+
+    unsafe fn init(&self, slot: &UnsafeCell<Option<T>>) -> &T {
+        // Execute the initialization up front, *then* move it into our slot,
+        // just in case initialization fails.
+        let value = (self.init)();
+        let ptr = slot.get();
+        *ptr = Some(value);
+        (*ptr).as_ref().unwrap()
+    }
+
+    /// Query the current state of this key.
+    ///
+    /// A key is initially in the `Uninitialized` state whenever a thread
+    /// starts. It will remain in this state up until the first call to `with`
+    /// within a thread has run the initialization expression successfully.
+    ///
+    /// Once the initialization expression succeeds, the key transitions to the
+    /// `Valid` state which will guarantee that future calls to `with` will
+    /// succeed within the thread.
+    ///
+    /// When a thread exits, each key will be destroyed in turn, and as keys are
+    /// destroyed they will enter the `Destroyed` state just before the
+    /// destructor starts to run. Keys may remain in the `Destroyed` state after
+    /// destruction has completed. Keys without destructors (e.g. with types
+    /// that are `Copy`), may never enter the `Destroyed` state.
+    ///
+    /// Keys in the `Uninitialized` can be accessed so long as the
+    /// initialization does not panic. Keys in the `Valid` state are guaranteed
+    /// to be able to be accessed. Keys in the `Destroyed` state will panic on
+    /// any call to `with`.
+    #[unstable(feature = "std_misc",
+               reason = "state querying was recently added")]
+    pub fn state(&'static self) -> LocalKeyState {
+        unsafe {
+            match (self.inner)().get() {
+                Some(cell) => {
+                    match *cell.get() {
+                        Some(..) => LocalKeyState::Valid,
+                        None => LocalKeyState::Uninitialized,
+                    }
+                }
+                None => LocalKeyState::Destroyed,
+            }
+        }
+    }
+
+    /// Deprecated
+    #[unstable(feature = "std_misc")]
+    #[deprecated(since = "1.0.0",
+                 reason = "function renamed to state() and returns more info")]
+    pub fn destroyed(&'static self) -> bool { self.state() == LocalKeyState::Destroyed }
+}
+
+#[cfg(all(any(target_os = "macos", target_os = "linux"), not(target_arch = "aarch64")))]
+mod imp {
+    use prelude::v1::*;
+
+    use cell::UnsafeCell;
+    use intrinsics;
+    use ptr;
+
+    #[doc(hidden)]
+    #[unstable(feature = "thread_local_internals")]
+    pub struct Key<T> {
+        // Place the inner bits in an `UnsafeCell` to currently get around the
+        // "only Sync statics" restriction. This allows any type to be placed in
+        // the cell.
+        //
+        // Note that all access requires `T: 'static` so it can't be a type with
+        // any borrowed pointers still.
+        #[unstable(feature = "thread_local_internals")]
+        pub inner: UnsafeCell<T>,
+
+        // Metadata to keep track of the state of the destructor. Remember that
+        // these variables are thread-local, not global.
+        #[unstable(feature = "thread_local_internals")]
+        pub dtor_registered: UnsafeCell<bool>, // should be Cell
+        #[unstable(feature = "thread_local_internals")]
+        pub dtor_running: UnsafeCell<bool>, // should be Cell
+    }
+
+    unsafe impl<T> ::marker::Sync for Key<T> { }
+
+    #[doc(hidden)]
+    impl<T> Key<T> {
+        pub unsafe fn get(&'static self) -> Option<&'static T> {
+            if intrinsics::needs_drop::<T>() && *self.dtor_running.get() {
+                return None
+            }
+            self.register_dtor();
+            Some(&*self.inner.get())
+        }
+
+        unsafe fn register_dtor(&self) {
+            if !intrinsics::needs_drop::<T>() || *self.dtor_registered.get() {
+                return
+            }
+
+            register_dtor(self as *const _ as *mut u8,
+                          destroy_value::<T>);
+            *self.dtor_registered.get() = true;
+        }
+    }
+
+    // Since what appears to be glibc 2.18 this symbol has been shipped which
+    // GCC and clang both use to invoke destructors in thread_local globals, so
+    // let's do the same!
+    //
+    // Note, however, that we run on lots older linuxes, as well as cross
+    // compiling from a newer linux to an older linux, so we also have a
+    // fallback implementation to use as well.
+    //
+    // Due to rust-lang/rust#18804, make sure this is not generic!
+    #[cfg(target_os = "linux")]
+    unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
+        use boxed;
+        use mem;
+        use libc;
+        use sys_common::thread_local as os;
+
+        extern {
+            static __dso_handle: *mut u8;
+            #[linkage = "extern_weak"]
+            static __cxa_thread_atexit_impl: *const ();
+        }
+        if !__cxa_thread_atexit_impl.is_null() {
+            type F = unsafe extern fn(dtor: unsafe extern fn(*mut u8),
+                                      arg: *mut u8,
+                                      dso_handle: *mut u8) -> libc::c_int;
+            mem::transmute::<*const (), F>(__cxa_thread_atexit_impl)
+            (dtor, t, __dso_handle);
+            return
+        }
+
+        // The fallback implementation uses a vanilla OS-based TLS key to track
+        // the list of destructors that need to be run for this thread. The key
+        // then has its own destructor which runs all the other destructors.
+        //
+        // The destructor for DTORS is a little special in that it has a `while`
+        // loop to continuously drain the list of registered destructors. It
+        // *should* be the case that this loop always terminates because we
+        // provide the guarantee that a TLS key cannot be set after it is
+        // flagged for destruction.
+        static DTORS: os::StaticKey = os::StaticKey {
+            inner: os::INIT_INNER,
+            dtor: Some(run_dtors as unsafe extern "C" fn(*mut u8)),
+        };
+        type List = Vec<(*mut u8, unsafe extern fn(*mut u8))>;
+        if DTORS.get().is_null() {
+            let v: Box<List> = box Vec::new();
+            DTORS.set(boxed::into_raw(v) as *mut u8);
+        }
+        let list: &mut List = &mut *(DTORS.get() as *mut List);
+        list.push((t, dtor));
+
+        unsafe extern fn run_dtors(mut ptr: *mut u8) {
+            while !ptr.is_null() {
+                let list: Box<List> = Box::from_raw(ptr as *mut List);
+                for &(ptr, dtor) in &*list {
+                    dtor(ptr);
+                }
+                ptr = DTORS.get();
+                DTORS.set(ptr::null_mut());
+            }
+        }
+    }
+
+    // OSX's analog of the above linux function is this _tlv_atexit function.
+    // The disassembly of thread_local globals in C++ (at least produced by
+    // clang) will have this show up in the output.
+    #[cfg(target_os = "macos")]
+    unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
+        extern {
+            fn _tlv_atexit(dtor: unsafe extern fn(*mut u8),
+                           arg: *mut u8);
+        }
+        _tlv_atexit(dtor, t);
+    }
+
+    #[doc(hidden)]
+    #[unstable(feature = "thread_local_internals")]
+    pub unsafe extern fn destroy_value<T>(ptr: *mut u8) {
+        let ptr = ptr as *mut Key<T>;
+        // Right before we run the user destructor be sure to flag the
+        // destructor as running for this thread so calls to `get` will return
+        // `None`.
+        *(*ptr).dtor_running.get() = true;
+        ptr::read((*ptr).inner.get());
+    }
+}
+
+#[cfg(any(not(any(target_os = "macos", target_os = "linux")), target_arch = "aarch64"))]
+mod imp {
+    use prelude::v1::*;
+
+    use alloc::boxed;
+    use cell::UnsafeCell;
+    use mem;
+    use ptr;
+    use sys_common::thread_local::StaticKey as OsStaticKey;
+
+    #[doc(hidden)]
+    #[unstable(feature = "thread_local_internals")]
+    pub struct Key<T> {
+        // Statically allocated initialization expression, using an `UnsafeCell`
+        // for the same reasons as above.
+        #[unstable(feature = "thread_local_internals")]
+        pub inner: UnsafeCell<T>,
+
+        // OS-TLS key that we'll use to key off.
+        #[unstable(feature = "thread_local_internals")]
+        pub os: OsStaticKey,
+    }
+
+    unsafe impl<T> ::marker::Sync for Key<T> { }
+
+    struct Value<T: 'static> {
+        key: &'static Key<T>,
+        value: T,
+    }
+
+    #[doc(hidden)]
+    impl<T> Key<T> {
+        pub unsafe fn get(&'static self) -> Option<&'static T> {
+            self.ptr().map(|p| &*p)
+        }
+
+        unsafe fn ptr(&'static self) -> Option<*mut T> {
+            let ptr = self.os.get() as *mut Value<T>;
+            if !ptr.is_null() {
+                if ptr as usize == 1 {
+                    return None
+                }
+                return Some(&mut (*ptr).value as *mut T);
+            }
+
+            // If the lookup returned null, we haven't initialized our own local
+            // copy, so do that now.
+            //
+            // Also note that this transmute_copy should be ok because the value
+            // `inner` is already validated to be a valid `static` value, so we
+            // should be able to freely copy the bits.
+            let ptr: Box<Value<T>> = box Value {
+                key: self,
+                value: mem::transmute_copy(&self.inner),
+            };
+            let ptr: *mut Value<T> = boxed::into_raw(ptr);
+            self.os.set(ptr as *mut u8);
+            Some(&mut (*ptr).value as *mut T)
+        }
+    }
+
+    #[doc(hidden)]
+    #[unstable(feature = "thread_local_internals")]
+    pub unsafe extern fn destroy_value<T: 'static>(ptr: *mut u8) {
+        // The OS TLS ensures that this key contains a NULL value when this
+        // destructor starts to run. We set it back to a sentinel value of 1 to
+        // ensure that any future calls to `get` for this thread will return
+        // `None`.
+        //
+        // Note that to prevent an infinite loop we reset it back to null right
+        // before we return from the destructor ourselves.
+        let ptr: Box<Value<T>> = Box::from_raw(ptr as *mut Value<T>);
+        let key = ptr.key;
+        key.os.set(1 as *mut u8);
+        drop(ptr);
+        key.os.set(ptr::null_mut());
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use prelude::v1::*;
+
+    use sync::mpsc::{channel, Sender};
+    use cell::UnsafeCell;
+    use super::LocalKeyState;
+    use thread;
+
+    struct Foo(Sender<()>);
+
+    impl Drop for Foo {
+        fn drop(&mut self) {
+            let Foo(ref s) = *self;
+            s.send(()).unwrap();
+        }
+    }
+
+    #[test]
+    fn smoke_no_dtor() {
+        thread_local!(static FOO: UnsafeCell<i32> = UnsafeCell { value: 1 });
+
+        FOO.with(|f| unsafe {
+            assert_eq!(*f.get(), 1);
+            *f.get() = 2;
+        });
+        let (tx, rx) = channel();
+        let _t = thread::spawn(move|| {
+            FOO.with(|f| unsafe {
+                assert_eq!(*f.get(), 1);
+            });
+            tx.send(()).unwrap();
+        });
+        rx.recv().unwrap();
+
+        FOO.with(|f| unsafe {
+            assert_eq!(*f.get(), 2);
+        });
+    }
+
+    #[test]
+    fn states() {
+        struct Foo;
+        impl Drop for Foo {
+            fn drop(&mut self) {
+                assert!(FOO.state() == LocalKeyState::Destroyed);
+            }
+        }
+        fn foo() -> Foo {
+            assert!(FOO.state() == LocalKeyState::Uninitialized);
+            Foo
+        }
+        thread_local!(static FOO: Foo = foo());
+
+        thread::spawn(|| {
+            assert!(FOO.state() == LocalKeyState::Uninitialized);
+            FOO.with(|_| {
+                assert!(FOO.state() == LocalKeyState::Valid);
+            });
+            assert!(FOO.state() == LocalKeyState::Valid);
+        }).join().ok().unwrap();
+    }
+
+    #[test]
+    fn smoke_dtor() {
+        thread_local!(static FOO: UnsafeCell<Option<Foo>> = UnsafeCell {
+            value: None
+        });
+
+        let (tx, rx) = channel();
+        let _t = thread::spawn(move|| unsafe {
+            let mut tx = Some(tx);
+            FOO.with(|f| {
+                *f.get() = Some(Foo(tx.take().unwrap()));
+            });
+        });
+        rx.recv().unwrap();
+    }
+
+    #[test]
+    fn circular() {
+        struct S1;
+        struct S2;
+        thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell {
+            value: None
+        });
+        thread_local!(static K2: UnsafeCell<Option<S2>> = UnsafeCell {
+            value: None
+        });
+        static mut HITS: u32 = 0;
+
+        impl Drop for S1 {
+            fn drop(&mut self) {
+                unsafe {
+                    HITS += 1;
+                    if K2.state() == LocalKeyState::Destroyed {
+                        assert_eq!(HITS, 3);
+                    } else {
+                        if HITS == 1 {
+                            K2.with(|s| *s.get() = Some(S2));
+                        } else {
+                            assert_eq!(HITS, 3);
+                        }
+                    }
+                }
+            }
+        }
+        impl Drop for S2 {
+            fn drop(&mut self) {
+                unsafe {
+                    HITS += 1;
+                    assert!(K1.state() != LocalKeyState::Destroyed);
+                    assert_eq!(HITS, 2);
+                    K1.with(|s| *s.get() = Some(S1));
+                }
+            }
+        }
+
+        thread::spawn(move|| {
+            drop(S1);
+        }).join().ok().unwrap();
+    }
+
+    #[test]
+    fn self_referential() {
+        struct S1;
+        thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell {
+            value: None
+        });
+
+        impl Drop for S1 {
+            fn drop(&mut self) {
+                assert!(K1.state() == LocalKeyState::Destroyed);
+            }
+        }
+
+        thread::spawn(move|| unsafe {
+            K1.with(|s| *s.get() = Some(S1));
+        }).join().ok().unwrap();
+    }
+
+    #[test]
+    fn dtors_in_dtors_in_dtors() {
+        struct S1(Sender<()>);
+        thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell {
+            value: None
+        });
+        thread_local!(static K2: UnsafeCell<Option<Foo>> = UnsafeCell {
+            value: None
+        });
+
+        impl Drop for S1 {
+            fn drop(&mut self) {
+                let S1(ref tx) = *self;
+                unsafe {
+                    if K2.state() != LocalKeyState::Destroyed {
+                        K2.with(|s| *s.get() = Some(Foo(tx.clone())));
+                    }
+                }
+            }
+        }
+
+        let (tx, rx) = channel();
+        let _t = thread::spawn(move|| unsafe {
+            let mut tx = Some(tx);
+            K1.with(|s| *s.get() = Some(S1(tx.take().unwrap())));
+        });
+        rx.recv().unwrap();
+    }
+}
+
+#[cfg(test)]
+mod dynamic_tests {
+    use prelude::v1::*;
+
+    use cell::RefCell;
+    use collections::HashMap;
+
+    #[test]
+    fn smoke() {
+        fn square(i: i32) -> i32 { i * i }
+        thread_local!(static FOO: i32 = square(3));
+
+        FOO.with(|f| {
+            assert_eq!(*f, 9);
+        });
+    }
+
+    #[test]
+    fn hashmap() {
+        fn map() -> RefCell<HashMap<i32, i32>> {
+            let mut m = HashMap::new();
+            m.insert(1, 2);
+            RefCell::new(m)
+        }
+        thread_local!(static FOO: RefCell<HashMap<i32, i32>> = map());
+
+        FOO.with(|map| {
+            assert_eq!(map.borrow()[1], 2);
+        });
+    }
+
+    #[test]
+    fn refcell_vec() {
+        thread_local!(static FOO: RefCell<Vec<u32>> = RefCell::new(vec![1, 2, 3]));
+
+        FOO.with(|vec| {
+            assert_eq!(vec.borrow().len(), 3);
+            vec.borrow_mut().push(4);
+            assert_eq!(vec.borrow()[3], 4);
+        });
+    }
+}
diff --git a/src/libstd/thread/mod.rs b/src/libstd/thread/mod.rs
new file mode 100644
index 00000000000..57baeb1fb74
--- /dev/null
+++ b/src/libstd/thread/mod.rs
@@ -0,0 +1,1026 @@
+// 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.
+
+//! Native threads
+//!
+//! ## The threading model
+//!
+//! An executing Rust program consists of a collection of native OS threads,
+//! each with their own stack and local state.
+//!
+//! Communication between threads can be done through
+//! [channels](../../std/sync/mpsc/index.html), Rust's message-passing
+//! types, along with [other forms of thread
+//! synchronization](../../std/sync/index.html) and shared-memory data
+//! structures. In particular, types that are guaranteed to be
+//! threadsafe are easily shared between threads using the
+//! atomically-reference-counted container,
+//! [`Arc`](../../std/sync/struct.Arc.html).
+//!
+//! Fatal logic errors in Rust cause *thread panic*, during which
+//! a thread will unwind the stack, running destructors and freeing
+//! owned resources. Thread panic is unrecoverable from within
+//! the panicking thread (i.e. there is no 'try/catch' in Rust), but
+//! the panic may optionally be detected from a different thread. If
+//! the main thread panics, the application will exit with a non-zero
+//! exit code.
+//!
+//! When the main thread of a Rust program terminates, the entire program shuts
+//! down, even if other threads are still running. However, this module provides
+//! convenient facilities for automatically waiting for the termination of a
+//! child thread (i.e., join).
+//!
+//! ## The `Thread` type
+//!
+//! Threads are represented via the `Thread` type, which you can
+//! get in one of two ways:
+//!
+//! * By spawning a new thread, e.g. using the `thread::spawn` function.
+//! * By requesting the current thread, using the `thread::current` function.
+//!
+//! Threads can be named, and provide some built-in support for low-level
+//! synchronization (described below).
+//!
+//! The `thread::current()` function is available even for threads not spawned
+//! by the APIs of this module.
+//!
+//! ## Spawning a thread
+//!
+//! A new thread can be spawned using the `thread::spawn` function:
+//!
+//! ```rust
+//! use std::thread;
+//!
+//! thread::spawn(move || {
+//!     // some work here
+//! });
+//! ```
+//!
+//! In this example, the spawned thread is "detached" from the current
+//! thread. This means that it can outlive its parent (the thread that spawned
+//! it), unless this parent is the main thread.
+//!
+//! ## Scoped threads
+//!
+//! Often a parent thread uses a child thread to perform some particular task,
+//! and at some point must wait for the child to complete before continuing.
+//! For this scenario, use the `thread::scoped` function:
+//!
+//! ```rust
+//! use std::thread;
+//!
+//! let guard = thread::scoped(move || {
+//!     // some work here
+//! });
+//!
+//! // do some other work in the meantime
+//! let output = guard.join();
+//! ```
+//!
+//! The `scoped` function doesn't return a `Thread` directly; instead,
+//! it returns a *join guard*. The join guard is an RAII-style guard
+//! that will automatically join the child thread (block until it
+//! terminates) when it is dropped. You can join the child thread in
+//! advance by calling the `join` method on the guard, which will also
+//! return the result produced by the thread.  A handle to the thread
+//! itself is available via the `thread` method of the join guard.
+//!
+//! ## Configuring threads
+//!
+//! A new thread can be configured before it is spawned via the `Builder` type,
+//! which currently allows you to set the name, stack size, and writers for
+//! `println!` and `panic!` for the child thread:
+//!
+//! ```rust
+//! use std::thread;
+//!
+//! thread::Builder::new().name("child1".to_string()).spawn(move || {
+//!     println!("Hello, world!");
+//! });
+//! ```
+//!
+//! ## Blocking support: park and unpark
+//!
+//! Every thread is equipped with some basic low-level blocking support, via the
+//! `park` and `unpark` functions.
+//!
+//! Conceptually, each `Thread` handle has an associated token, which is
+//! initially not present:
+//!
+//! * The `thread::park()` function blocks the current thread unless or until
+//!   the token is available for its thread handle, at which point it atomically
+//!   consumes the token. It may also return *spuriously*, without consuming the
+//!   token. `thread::park_timeout()` does the same, but allows specifying a
+//!   maximum time to block the thread for.
+//!
+//! * The `unpark()` method on a `Thread` atomically makes the token available
+//!   if it wasn't already.
+//!
+//! In other words, each `Thread` acts a bit like a semaphore with initial count
+//! 0, except that the semaphore is *saturating* (the count cannot go above 1),
+//! and can return spuriously.
+//!
+//! The API is typically used by acquiring a handle to the current thread,
+//! placing that handle in a shared data structure so that other threads can
+//! find it, and then `park`ing. When some desired condition is met, another
+//! thread calls `unpark` on the handle.
+//!
+//! The motivation for this design is twofold:
+//!
+//! * It avoids the need to allocate mutexes and condvars when building new
+//!   synchronization primitives; the threads already provide basic blocking/signaling.
+//!
+//! * It can be implemented very efficiently on many platforms.
+//!
+//! ## Thread-local storage
+//!
+//! This module also provides an implementation of thread local storage for Rust
+//! programs. Thread local storage is a method of storing data into a global
+//! variable which each thread in the program will have its own copy of.
+//! Threads do not share this data, so accesses do not need to be synchronized.
+//!
+//! At a high level, this module provides two variants of storage:
+//!
+//! * Owned thread-local storage. This is a type of thread local key which
+//!   owns the value that it contains, and will destroy the value when the
+//!   thread exits. This variant is created with the `thread_local!` macro and
+//!   can contain any value which is `'static` (no borrowed pointers).
+//!
+//! * Scoped thread-local storage. This type of key is used to store a reference
+//!   to a value into local storage temporarily for the scope of a function
+//!   call. There are no restrictions on what types of values can be placed
+//!   into this key.
+//!
+//! Both forms of thread local storage provide an accessor function, `with`,
+//! which will yield a shared reference to the value to the specified
+//! closure. Thread-local keys only allow shared access to values as there is no
+//! way to guarantee uniqueness if a mutable borrow was allowed. Most values
+//! will want to make use of some form of **interior mutability** through the
+//! `Cell` or `RefCell` types.
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use self::__local::{LocalKey, LocalKeyState};
+
+#[unstable(feature = "scoped_tls",
+            reason = "scoped TLS has yet to have wide enough use to fully consider \
+                      stabilizing its interface")]
+pub use self::__scoped::ScopedKey;
+
+use prelude::v1::*;
+
+use any::Any;
+use cell::UnsafeCell;
+use fmt;
+use io;
+use marker::PhantomData;
+use rt::{self, unwind};
+use sync::{Mutex, Condvar, Arc};
+use sys::thread as imp;
+use sys_common::{stack, thread_info};
+use thunk::Thunk;
+use time::Duration;
+
+#[allow(deprecated)] use old_io::Writer;
+
+////////////////////////////////////////////////////////////////////////////////
+// Thread-local storage
+////////////////////////////////////////////////////////////////////////////////
+
+#[macro_use]
+#[doc(hidden)]
+#[path = "local.rs"] pub mod __local;
+
+#[macro_use]
+#[doc(hidden)]
+#[path = "scoped.rs"] pub mod __scoped;
+
+////////////////////////////////////////////////////////////////////////////////
+// Builder
+////////////////////////////////////////////////////////////////////////////////
+
+/// Thread configuration. Provides detailed control over the properties
+/// and behavior of new threads.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Builder {
+    // A name for the thread-to-be, for identification in panic messages
+    name: Option<String>,
+    // The size of the stack for the spawned thread
+    stack_size: Option<usize>,
+}
+
+impl Builder {
+    /// Generate the base configuration for spawning a thread, from which
+    /// configuration methods can be chained.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn new() -> Builder {
+        Builder {
+            name: None,
+            stack_size: None,
+        }
+    }
+
+    /// Name the thread-to-be. Currently the name is used for identification
+    /// only in panic messages.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn name(mut self, name: String) -> Builder {
+        self.name = Some(name);
+        self
+    }
+
+    /// Set the size of the stack for the new thread.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn stack_size(mut self, size: usize) -> Builder {
+        self.stack_size = Some(size);
+        self
+    }
+
+    /// Redirect thread-local stdout.
+    #[unstable(feature = "std_misc",
+               reason = "Will likely go away after proc removal")]
+    #[deprecated(since = "1.0.0",
+                 reason = "the old I/O module is deprecated and this function \
+                           will be removed with no replacement")]
+    #[allow(deprecated)]
+    pub fn stdout(self, _stdout: Box<Writer + Send + 'static>) -> Builder {
+        self
+    }
+
+    /// Redirect thread-local stderr.
+    #[unstable(feature = "std_misc",
+               reason = "Will likely go away after proc removal")]
+    #[deprecated(since = "1.0.0",
+                 reason = "the old I/O module is deprecated and this function \
+                           will be removed with no replacement")]
+    #[allow(deprecated)]
+    pub fn stderr(self, _stderr: Box<Writer + Send + 'static>) -> Builder {
+        self
+    }
+
+    /// Spawn a new thread, and return a join handle for it.
+    ///
+    /// The child thread may outlive the parent (unless the parent thread
+    /// is the main thread; the whole process is terminated when the main
+    /// thread finishes.) The join handle can be used to block on
+    /// termination of the child thread, including recovering its panics.
+    ///
+    /// # Errors
+    ///
+    /// Unlike the `spawn` free function, this method yields an
+    /// `io::Result` to capture any failure to create the thread at
+    /// the OS level.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn spawn<F>(self, f: F) -> io::Result<JoinHandle> where
+        F: FnOnce(), F: Send + 'static
+    {
+        self.spawn_inner(Thunk::new(f)).map(|i| JoinHandle(i))
+    }
+
+    /// Spawn a new child thread that must be joined within a given
+    /// scope, and return a `JoinGuard`.
+    ///
+    /// The join guard can be used to explicitly join the child thread (via
+    /// `join`), returning `Result<T>`, or it will implicitly join the child
+    /// upon being dropped. Because the child thread may refer to data on the
+    /// current thread's stack (hence the "scoped" name), it cannot be detached;
+    /// it *must* be joined before the relevant stack frame is popped. See the
+    /// module documentation for additional details.
+    ///
+    /// # Errors
+    ///
+    /// Unlike the `scoped` free function, this method yields an
+    /// `io::Result` to capture any failure to create the thread at
+    /// the OS level.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn scoped<'a, T, F>(self, f: F) -> io::Result<JoinGuard<'a, T>> where
+        T: Send + 'a, F: FnOnce() -> T, F: Send + 'a
+    {
+        self.spawn_inner(Thunk::new(f)).map(|inner| {
+            JoinGuard { inner: inner, _marker: PhantomData }
+        })
+    }
+
+    fn spawn_inner<T: Send>(self, f: Thunk<(), T>) -> io::Result<JoinInner<T>> {
+        let Builder { name, stack_size } = self;
+
+        let stack_size = stack_size.unwrap_or(rt::min_stack());
+
+        let my_thread = Thread::new(name);
+        let their_thread = my_thread.clone();
+
+        let my_packet = Packet(Arc::new(UnsafeCell::new(None)));
+        let their_packet = Packet(my_packet.0.clone());
+
+        // Spawning a new OS thread guarantees that __morestack will never get
+        // triggered, but we must manually set up the actual stack bounds once
+        // this function starts executing. This raises the lower limit by a bit
+        // because by the time that this function is executing we've already
+        // consumed at least a little bit of stack (we don't know the exact byte
+        // address at which our stack started).
+        let main = move || {
+            let something_around_the_top_of_the_stack = 1;
+            let addr = &something_around_the_top_of_the_stack as *const i32;
+            let my_stack_top = addr as usize;
+            let my_stack_bottom = my_stack_top - stack_size + 1024;
+            unsafe {
+                if let Some(name) = their_thread.name() {
+                    imp::set_name(name);
+                }
+                stack::record_os_managed_stack_bounds(my_stack_bottom,
+                                                      my_stack_top);
+                thread_info::set(imp::guard::current(), their_thread);
+            }
+
+            let mut output = None;
+            let try_result = {
+                let ptr = &mut output;
+
+                // There are two primary reasons that general try/catch is
+                // unsafe. The first is that we do not support nested
+                // try/catch. The fact that this is happening in a newly-spawned
+                // thread suffices. The second is that unwinding while unwinding
+                // is not defined.  We take care of that by having an
+                // 'unwinding' flag in the thread itself. For these reasons,
+                // this unsafety should be ok.
+                unsafe {
+                    unwind::try(move || *ptr = Some(f.invoke(())))
+                }
+            };
+            unsafe {
+                *their_packet.0.get() = Some(match (output, try_result) {
+                    (Some(data), Ok(_)) => Ok(data),
+                    (None, Err(cause)) => Err(cause),
+                    _ => unreachable!()
+                });
+            }
+        };
+
+        Ok(JoinInner {
+            native: try!(unsafe { imp::create(stack_size, Thunk::new(main)) }),
+            thread: my_thread,
+            packet: my_packet,
+            joined: false,
+        })
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Free functions
+////////////////////////////////////////////////////////////////////////////////
+
+/// Spawn a new thread, returning a `JoinHandle` for it.
+///
+/// The join handle will implicitly *detach* the child thread upon being
+/// dropped. In this case, the child thread may outlive the parent (unless
+/// the parent thread is the main thread; the whole process is terminated when
+/// the main thread finishes.) Additionally, the join handle provides a `join`
+/// method that can be used to join the child thread. If the child thread
+/// panics, `join` will return an `Err` containing the argument given to
+/// `panic`.
+///
+/// # Panics
+///
+/// Panicks if the OS fails to create a thread; use `Builder::spawn`
+/// to recover from such errors.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn spawn<F>(f: F) -> JoinHandle where F: FnOnce(), F: Send + 'static {
+    Builder::new().spawn(f).unwrap()
+}
+
+/// Spawn a new *scoped* thread, returning a `JoinGuard` for it.
+///
+/// The join guard can be used to explicitly join the child thread (via
+/// `join`), returning `Result<T>`, or it will implicitly join the child
+/// upon being dropped. Because the child thread may refer to data on the
+/// current thread's stack (hence the "scoped" name), it cannot be detached;
+/// it *must* be joined before the relevant stack frame is popped. See the
+/// module documentation for additional details.
+///
+/// # Panics
+///
+/// Panicks if the OS fails to create a thread; use `Builder::scoped`
+/// to recover from such errors.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn scoped<'a, T, F>(f: F) -> JoinGuard<'a, T> where
+    T: Send + 'a, F: FnOnce() -> T, F: Send + 'a
+{
+    Builder::new().scoped(f).unwrap()
+}
+
+/// Gets a handle to the thread that invokes it.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn current() -> Thread {
+    thread_info::current_thread()
+}
+
+/// Cooperatively give up a timeslice to the OS scheduler.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn yield_now() {
+    unsafe { imp::yield_now() }
+}
+
+/// Determines whether the current thread is unwinding because of panic.
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn panicking() -> bool {
+    unwind::panicking()
+}
+
+/// Put the current thread to sleep for the specified amount of time.
+///
+/// The thread may sleep longer than the duration specified due to scheduling
+/// specifics or platform-dependent functionality. Note that on unix platforms
+/// this function will not return early due to a signal being received or a
+/// spurious wakeup.
+#[unstable(feature = "thread_sleep",
+           reason = "recently added, needs an RFC, and `Duration` itself is \
+                     unstable")]
+pub fn sleep(dur: Duration) {
+    imp::sleep(dur)
+}
+
+/// Block unless or until the current thread's token is made available (may wake spuriously).
+///
+/// See the module doc for more detail.
+//
+// The implementation currently uses the trivial strategy of a Mutex+Condvar
+// with wakeup flag, which does not actually allow spurious wakeups. In the
+// future, this will be implemented in a more efficient way, perhaps along the lines of
+//   http://cr.openjdk.java.net/~stefank/6989984.1/raw_files/new/src/os/linux/vm/os_linux.cpp
+// or futuxes, and in either case may allow spurious wakeups.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn park() {
+    let thread = current();
+    let mut guard = thread.inner.lock.lock().unwrap();
+    while !*guard {
+        guard = thread.inner.cvar.wait(guard).unwrap();
+    }
+    *guard = false;
+}
+
+/// Block unless or until the current thread's token is made available or
+/// the specified duration has been reached (may wake spuriously).
+///
+/// The semantics of this function are equivalent to `park()` except that the
+/// thread will be blocked for roughly no longer than *duration*. This method
+/// should not be used for precise timing due to anomalies such as
+/// preemption or platform differences that may not cause the maximum
+/// amount of time waited to be precisely *duration* long.
+///
+/// See the module doc for more detail.
+#[unstable(feature = "std_misc", reason = "recently introduced, depends on Duration")]
+pub fn park_timeout(duration: Duration) {
+    let thread = current();
+    let mut guard = thread.inner.lock.lock().unwrap();
+    if !*guard {
+        let (g, _) = thread.inner.cvar.wait_timeout(guard, duration).unwrap();
+        guard = g;
+    }
+    *guard = false;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Thread
+////////////////////////////////////////////////////////////////////////////////
+
+/// The internal representation of a `Thread` handle
+struct Inner {
+    name: Option<String>,
+    lock: Mutex<bool>,          // true when there is a buffered unpark
+    cvar: Condvar,
+}
+
+unsafe impl Sync for Inner {}
+
+#[derive(Clone)]
+#[stable(feature = "rust1", since = "1.0.0")]
+/// A handle to a thread.
+pub struct Thread {
+    inner: Arc<Inner>,
+}
+
+impl Thread {
+    // Used only internally to construct a thread object without spawning
+    fn new(name: Option<String>) -> Thread {
+        Thread {
+            inner: Arc::new(Inner {
+                name: name,
+                lock: Mutex::new(false),
+                cvar: Condvar::new(),
+            })
+        }
+    }
+
+    /// Deprecated: use module-level free function.
+    #[deprecated(since = "1.0.0", reason = "use module-level free function")]
+    #[unstable(feature = "std_misc",
+               reason = "may change with specifics of new Send semantics")]
+    pub fn spawn<F>(f: F) -> Thread where F: FnOnce(), F: Send + 'static {
+        Builder::new().spawn(f).unwrap().thread().clone()
+    }
+
+    /// Deprecated: use module-level free function.
+    #[deprecated(since = "1.0.0", reason = "use module-level free function")]
+    #[unstable(feature = "std_misc",
+               reason = "may change with specifics of new Send semantics")]
+    pub fn scoped<'a, T, F>(f: F) -> JoinGuard<'a, T> where
+        T: Send + 'a, F: FnOnce() -> T, F: Send + 'a
+    {
+        Builder::new().scoped(f).unwrap()
+    }
+
+    /// Deprecated: use module-level free function.
+    #[deprecated(since = "1.0.0", reason = "use module-level free function")]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn current() -> Thread {
+        thread_info::current_thread()
+    }
+
+    /// Deprecated: use module-level free function.
+    #[deprecated(since = "1.0.0", reason = "use module-level free function")]
+    #[unstable(feature = "std_misc", reason = "name may change")]
+    pub fn yield_now() {
+        unsafe { imp::yield_now() }
+    }
+
+    /// Deprecated: use module-level free function.
+    #[deprecated(since = "1.0.0", reason = "use module-level free function")]
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn panicking() -> bool {
+        unwind::panicking()
+    }
+
+    /// Deprecated: use module-level free function.
+    #[deprecated(since = "1.0.0", reason = "use module-level free function")]
+    #[unstable(feature = "std_misc", reason = "recently introduced")]
+    pub fn park() {
+        let thread = current();
+        let mut guard = thread.inner.lock.lock().unwrap();
+        while !*guard {
+            guard = thread.inner.cvar.wait(guard).unwrap();
+        }
+        *guard = false;
+    }
+
+    /// Deprecated: use module-level free function.
+    #[deprecated(since = "1.0.0", reason = "use module-level free function")]
+    #[unstable(feature = "std_misc", reason = "recently introduced")]
+    pub fn park_timeout(duration: Duration) {
+        let thread = current();
+        let mut guard = thread.inner.lock.lock().unwrap();
+        if !*guard {
+            let (g, _) = thread.inner.cvar.wait_timeout(guard, duration).unwrap();
+            guard = g;
+        }
+        *guard = false;
+    }
+
+    /// Atomically makes the handle's token available if it is not already.
+    ///
+    /// See the module doc for more detail.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn unpark(&self) {
+        let mut guard = self.inner.lock.lock().unwrap();
+        if !*guard {
+            *guard = true;
+            self.inner.cvar.notify_one();
+        }
+    }
+
+    /// Get the thread's name.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn name(&self) -> Option<&str> {
+        self.inner.name.as_ref().map(|s| &**s)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Debug for Thread {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.name(), f)
+    }
+}
+
+// a hack to get around privacy restrictions
+impl thread_info::NewThread for Thread {
+    fn new(name: Option<String>) -> Thread { Thread::new(name) }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// JoinHandle and JoinGuard
+////////////////////////////////////////////////////////////////////////////////
+
+/// Indicates the manner in which a thread exited.
+///
+/// A thread that completes without panicking is considered to exit successfully.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub type Result<T> = ::result::Result<T, Box<Any + Send + 'static>>;
+
+struct Packet<T>(Arc<UnsafeCell<Option<Result<T>>>>);
+
+unsafe impl<T:Send> Send for Packet<T> {}
+unsafe impl<T> Sync for Packet<T> {}
+
+/// Inner representation for JoinHandle and JoinGuard
+struct JoinInner<T> {
+    native: imp::rust_thread,
+    thread: Thread,
+    packet: Packet<T>,
+    joined: bool,
+}
+
+impl<T> JoinInner<T> {
+    fn join(&mut self) -> Result<T> {
+        assert!(!self.joined);
+        unsafe { imp::join(self.native) };
+        self.joined = true;
+        unsafe {
+            (*self.packet.0.get()).take().unwrap()
+        }
+    }
+}
+
+/// An owned permission to join on a thread (block on its termination).
+///
+/// Unlike a `JoinGuard`, a `JoinHandle` *detaches* the child thread
+/// when it is dropped, rather than automatically joining on drop.
+///
+/// Due to platform restrictions, it is not possible to `Clone` this
+/// handle: the ability to join a child thread is a uniquely-owned
+/// permission.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct JoinHandle(JoinInner<()>);
+
+impl JoinHandle {
+    /// Extract a handle to the underlying thread
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn thread(&self) -> &Thread {
+        &self.0.thread
+    }
+
+    /// Wait for the associated thread to finish.
+    ///
+    /// If the child thread panics, `Err` is returned with the parameter given
+    /// to `panic`.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn join(mut self) -> Result<()> {
+        self.0.join()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Drop for JoinHandle {
+    fn drop(&mut self) {
+        if !self.0.joined {
+            unsafe { imp::detach(self.0.native) }
+        }
+    }
+}
+
+/// An RAII-style guard that will block until thread termination when dropped.
+///
+/// The type `T` is the return type for the thread's main function.
+///
+/// Joining on drop is necessary to ensure memory safety when stack
+/// data is shared between a parent and child thread.
+///
+/// Due to platform restrictions, it is not possible to `Clone` this
+/// handle: the ability to join a child thread is a uniquely-owned
+/// permission.
+#[must_use = "thread will be immediately joined if `JoinGuard` is not used"]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct JoinGuard<'a, T: 'a> {
+    inner: JoinInner<T>,
+    _marker: PhantomData<&'a T>,
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<'a, T: Send + 'a> Sync for JoinGuard<'a, T> {}
+
+impl<'a, T: Send + 'a> JoinGuard<'a, T> {
+    /// Extract a handle to the thread this guard will join on.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn thread(&self) -> &Thread {
+        &self.inner.thread
+    }
+
+    /// Wait for the associated thread to finish, returning the result of the thread's
+    /// calculation.
+    ///
+    /// # Panics
+    ///
+    /// Panics on the child thread are propagated by panicking the parent.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn join(mut self) -> T {
+        match self.inner.join() {
+            Ok(res) => res,
+            Err(_) => panic!("child thread {:?} panicked", self.thread()),
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Send> JoinGuard<'static, T> {
+    /// Detaches the child thread, allowing it to outlive its parent.
+    #[deprecated(since = "1.0.0", reason = "use spawn instead")]
+    #[unstable(feature = "std_misc")]
+    pub fn detach(mut self) {
+        unsafe { imp::detach(self.inner.native) };
+        self.inner.joined = true; // avoid joining in the destructor
+    }
+}
+
+#[unsafe_destructor]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T: Send + 'a> Drop for JoinGuard<'a, T> {
+    fn drop(&mut self) {
+        if !self.inner.joined {
+            if self.inner.join().is_err() {
+                panic!("child thread {:?} panicked", self.thread());
+            }
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Tests
+////////////////////////////////////////////////////////////////////////////////
+
+#[cfg(test)]
+mod test {
+    use prelude::v1::*;
+
+    use any::Any;
+    use sync::mpsc::{channel, Sender};
+    use boxed::BoxAny;
+    use result;
+    use std::old_io::{ChanReader, ChanWriter};
+    use super::{Builder};
+    use thread;
+    use thunk::Thunk;
+    use time::Duration;
+
+    // !!! These tests are dangerous. If something is buggy, they will hang, !!!
+    // !!! instead of exiting cleanly. This might wedge the buildbots.       !!!
+
+    #[test]
+    fn test_unnamed_thread() {
+        thread::spawn(move|| {
+            assert!(thread::current().name().is_none());
+        }).join().ok().unwrap();
+    }
+
+    #[test]
+    fn test_named_thread() {
+        Builder::new().name("ada lovelace".to_string()).scoped(move|| {
+            assert!(thread::current().name().unwrap() == "ada lovelace".to_string());
+        }).unwrap().join();
+    }
+
+    #[test]
+    fn test_run_basic() {
+        let (tx, rx) = channel();
+        thread::spawn(move|| {
+            tx.send(()).unwrap();
+        });
+        rx.recv().unwrap();
+    }
+
+    #[test]
+    fn test_join_success() {
+        assert!(thread::scoped(move|| -> String {
+            "Success!".to_string()
+        }).join() == "Success!");
+    }
+
+    #[test]
+    fn test_join_panic() {
+        match thread::spawn(move|| {
+            panic!()
+        }).join() {
+            result::Result::Err(_) => (),
+            result::Result::Ok(()) => panic!()
+        }
+    }
+
+    #[test]
+    fn test_scoped_success() {
+        let res = thread::scoped(move|| -> String {
+            "Success!".to_string()
+        }).join();
+        assert!(res == "Success!");
+    }
+
+    #[test]
+    #[should_fail]
+    fn test_scoped_panic() {
+        thread::scoped(|| panic!()).join();
+    }
+
+    #[test]
+    #[should_fail]
+    fn test_scoped_implicit_panic() {
+        let _ = thread::scoped(|| panic!());
+    }
+
+    #[test]
+    fn test_spawn_sched() {
+        use clone::Clone;
+
+        let (tx, rx) = channel();
+
+        fn f(i: i32, tx: Sender<()>) {
+            let tx = tx.clone();
+            thread::spawn(move|| {
+                if i == 0 {
+                    tx.send(()).unwrap();
+                } else {
+                    f(i - 1, tx);
+                }
+            });
+
+        }
+        f(10, tx);
+        rx.recv().unwrap();
+    }
+
+    #[test]
+    fn test_spawn_sched_childs_on_default_sched() {
+        let (tx, rx) = channel();
+
+        thread::spawn(move|| {
+            thread::spawn(move|| {
+                tx.send(()).unwrap();
+            });
+        });
+
+        rx.recv().unwrap();
+    }
+
+    fn avoid_copying_the_body<F>(spawnfn: F) where F: FnOnce(Thunk<'static>) {
+        let (tx, rx) = channel();
+
+        let x: Box<_> = box 1;
+        let x_in_parent = (&*x) as *const i32 as usize;
+
+        spawnfn(Thunk::new(move|| {
+            let x_in_child = (&*x) as *const i32 as usize;
+            tx.send(x_in_child).unwrap();
+        }));
+
+        let x_in_child = rx.recv().unwrap();
+        assert_eq!(x_in_parent, x_in_child);
+    }
+
+    #[test]
+    fn test_avoid_copying_the_body_spawn() {
+        avoid_copying_the_body(|v| {
+            thread::spawn(move || v.invoke(()));
+        });
+    }
+
+    #[test]
+    fn test_avoid_copying_the_body_thread_spawn() {
+        avoid_copying_the_body(|f| {
+            thread::spawn(move|| {
+                f.invoke(());
+            });
+        })
+    }
+
+    #[test]
+    fn test_avoid_copying_the_body_join() {
+        avoid_copying_the_body(|f| {
+            let _ = thread::spawn(move|| {
+                f.invoke(())
+            }).join();
+        })
+    }
+
+    #[test]
+    fn test_child_doesnt_ref_parent() {
+        // If the child refcounts the parent task, this will stack overflow when
+        // climbing the task tree to dereference each ancestor. (See #1789)
+        // (well, it would if the constant were 8000+ - I lowered it to be more
+        // valgrind-friendly. try this at home, instead..!)
+        const GENERATIONS: u32 = 16;
+        fn child_no(x: u32) -> Thunk<'static> {
+            return Thunk::new(move|| {
+                if x < GENERATIONS {
+                    thread::spawn(move|| child_no(x+1).invoke(()));
+                }
+            });
+        }
+        thread::spawn(|| child_no(0).invoke(()));
+    }
+
+    #[test]
+    fn test_simple_newsched_spawn() {
+        thread::spawn(move || {});
+    }
+
+    #[test]
+    fn test_try_panic_message_static_str() {
+        match thread::spawn(move|| {
+            panic!("static string");
+        }).join() {
+            Err(e) => {
+                type T = &'static str;
+                assert!(e.is::<T>());
+                assert_eq!(*e.downcast::<T>().unwrap(), "static string");
+            }
+            Ok(()) => panic!()
+        }
+    }
+
+    #[test]
+    fn test_try_panic_message_owned_str() {
+        match thread::spawn(move|| {
+            panic!("owned string".to_string());
+        }).join() {
+            Err(e) => {
+                type T = String;
+                assert!(e.is::<T>());
+                assert_eq!(*e.downcast::<T>().unwrap(), "owned string".to_string());
+            }
+            Ok(()) => panic!()
+        }
+    }
+
+    #[test]
+    fn test_try_panic_message_any() {
+        match thread::spawn(move|| {
+            panic!(box 413u16 as Box<Any + Send>);
+        }).join() {
+            Err(e) => {
+                type T = Box<Any + Send>;
+                assert!(e.is::<T>());
+                let any = e.downcast::<T>().unwrap();
+                assert!(any.is::<u16>());
+                assert_eq!(*any.downcast::<u16>().unwrap(), 413);
+            }
+            Ok(()) => panic!()
+        }
+    }
+
+    #[test]
+    fn test_try_panic_message_unit_struct() {
+        struct Juju;
+
+        match thread::spawn(move|| {
+            panic!(Juju)
+        }).join() {
+            Err(ref e) if e.is::<Juju>() => {}
+            Err(_) | Ok(()) => panic!()
+        }
+    }
+
+    #[test]
+    fn test_park_timeout_unpark_before() {
+        for _ in 0..10 {
+            thread::current().unpark();
+            thread::park_timeout(Duration::seconds(10_000_000));
+        }
+    }
+
+    #[test]
+    fn test_park_timeout_unpark_not_called() {
+        for _ in 0..10 {
+            thread::park_timeout(Duration::milliseconds(10));
+        }
+    }
+
+    #[test]
+    fn test_park_timeout_unpark_called_other_thread() {
+        use std::old_io;
+
+        for _ in 0..10 {
+            let th = thread::current();
+
+            let _guard = thread::spawn(move || {
+                old_io::timer::sleep(Duration::milliseconds(50));
+                th.unpark();
+            });
+
+            thread::park_timeout(Duration::seconds(10_000_000));
+        }
+    }
+
+    #[test]
+    fn sleep_smoke() {
+        thread::sleep(Duration::milliseconds(2));
+        thread::sleep(Duration::milliseconds(-2));
+    }
+
+    // NOTE: the corresponding test for stderr is in run-pass/task-stderr, due
+    // to the test harness apparently interfering with stderr configuration.
+}
diff --git a/src/libstd/thread/scoped.rs b/src/libstd/thread/scoped.rs
new file mode 100644
index 00000000000..2a8be2ad82c
--- /dev/null
+++ b/src/libstd/thread/scoped.rs
@@ -0,0 +1,317 @@
+// Copyright 2014-2015 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.
+
+//! Scoped thread-local storage
+//!
+//! This module provides the ability to generate *scoped* thread-local
+//! variables. In this sense, scoped indicates that thread local storage
+//! actually stores a reference to a value, and this reference is only placed
+//! in storage for a scoped amount of time.
+//!
+//! There are no restrictions on what types can be placed into a scoped
+//! variable, but all scoped variables are initialized to the equivalent of
+//! null. Scoped thread local storage is useful when a value is present for a known
+//! period of time and it is not required to relinquish ownership of the
+//! contents.
+//!
+//! # Examples
+//!
+//! ```
+//! scoped_thread_local!(static FOO: u32);
+//!
+//! // Initially each scoped slot is empty.
+//! assert!(!FOO.is_set());
+//!
+//! // When inserting a value, the value is only in place for the duration
+//! // of the closure specified.
+//! FOO.set(&1, || {
+//!     FOO.with(|slot| {
+//!         assert_eq!(*slot, 1);
+//!     });
+//! });
+//! ```
+
+#![unstable(feature = "thread_local_internals")]
+
+use prelude::v1::*;
+
+// macro hygiene sure would be nice, wouldn't it?
+#[doc(hidden)]
+pub mod __impl {
+    pub use super::imp::KeyInner;
+    pub use sys_common::thread_local::INIT as OS_INIT;
+}
+
+/// Type representing a thread local storage key corresponding to a reference
+/// to the type parameter `T`.
+///
+/// Keys are statically allocated and can contain a reference to an instance of
+/// type `T` scoped to a particular lifetime. Keys provides two methods, `set`
+/// and `with`, both of which currently use closures to control the scope of
+/// their contents.
+#[unstable(feature = "scoped_tls",
+           reason = "scoped TLS has yet to have wide enough use to fully consider \
+                     stabilizing its interface")]
+pub struct ScopedKey<T> { #[doc(hidden)] pub inner: __impl::KeyInner<T> }
+
+/// Declare a new scoped thread local storage key.
+///
+/// This macro declares a `static` item on which methods are used to get and
+/// set the value stored within.
+#[macro_export]
+#[allow_internal_unstable]
+macro_rules! scoped_thread_local {
+    (static $name:ident: $t:ty) => (
+        __scoped_thread_local_inner!(static $name: $t);
+    );
+    (pub static $name:ident: $t:ty) => (
+        __scoped_thread_local_inner!(pub static $name: $t);
+    );
+}
+
+#[macro_export]
+#[doc(hidden)]
+#[allow_internal_unstable]
+macro_rules! __scoped_thread_local_inner {
+    (static $name:ident: $t:ty) => (
+        #[cfg_attr(not(any(windows,
+                           target_os = "android",
+                           target_os = "ios",
+                           target_os = "openbsd",
+                           target_arch = "aarch64")),
+                   thread_local)]
+        static $name: ::std::thread::ScopedKey<$t> =
+            __scoped_thread_local_inner!($t);
+    );
+    (pub static $name:ident: $t:ty) => (
+        #[cfg_attr(not(any(windows,
+                           target_os = "android",
+                           target_os = "ios",
+                           target_os = "openbsd",
+                           target_arch = "aarch64")),
+                   thread_local)]
+        pub static $name: ::std::thread::ScopedKey<$t> =
+            __scoped_thread_local_inner!($t);
+    );
+    ($t:ty) => ({
+        use std::thread::ScopedKey as __Key;
+
+        #[cfg(not(any(windows,
+                      target_os = "android",
+                      target_os = "ios",
+                      target_os = "openbsd",
+                      target_arch = "aarch64")))]
+        const _INIT: __Key<$t> = __Key {
+            inner: ::std::thread::__scoped::__impl::KeyInner {
+                inner: ::std::cell::UnsafeCell { value: 0 as *mut _ },
+            }
+        };
+
+        #[cfg(any(windows,
+                  target_os = "android",
+                  target_os = "ios",
+                  target_os = "openbsd",
+                  target_arch = "aarch64"))]
+        const _INIT: __Key<$t> = __Key {
+            inner: ::std::thread::__scoped::__impl::KeyInner {
+                inner: ::std::thread::__scoped::__impl::OS_INIT,
+                marker: ::std::marker::PhantomData::<::std::cell::Cell<$t>>,
+            }
+        };
+
+        _INIT
+    })
+}
+
+#[unstable(feature = "scoped_tls",
+           reason = "scoped TLS has yet to have wide enough use to fully consider \
+                     stabilizing its interface")]
+impl<T> ScopedKey<T> {
+    /// Insert a value into this scoped thread local storage slot for a
+    /// duration of a closure.
+    ///
+    /// While `cb` is running, the value `t` will be returned by `get` unless
+    /// this function is called recursively inside of `cb`.
+    ///
+    /// Upon return, this function will restore the previous value, if any
+    /// was available.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// scoped_thread_local!(static FOO: u32);
+    ///
+    /// FOO.set(&100, || {
+    ///     let val = FOO.with(|v| *v);
+    ///     assert_eq!(val, 100);
+    ///
+    ///     // set can be called recursively
+    ///     FOO.set(&101, || {
+    ///         // ...
+    ///     });
+    ///
+    ///     // Recursive calls restore the previous value.
+    ///     let val = FOO.with(|v| *v);
+    ///     assert_eq!(val, 100);
+    /// });
+    /// ```
+    pub fn set<R, F>(&'static self, t: &T, cb: F) -> R where
+        F: FnOnce() -> R,
+    {
+        struct Reset<'a, T: 'a> {
+            key: &'a __impl::KeyInner<T>,
+            val: *mut T,
+        }
+        #[unsafe_destructor]
+        impl<'a, T> Drop for Reset<'a, T> {
+            fn drop(&mut self) {
+                unsafe { self.key.set(self.val) }
+            }
+        }
+
+        let prev = unsafe {
+            let prev = self.inner.get();
+            self.inner.set(t as *const T as *mut T);
+            prev
+        };
+
+        let _reset = Reset { key: &self.inner, val: prev };
+        cb()
+    }
+
+    /// Get a value out of this scoped variable.
+    ///
+    /// This function takes a closure which receives the value of this
+    /// variable.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if `set` has not previously been called.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// scoped_thread_local!(static FOO: u32);
+    ///
+    /// FOO.with(|slot| {
+    ///     // work with `slot`
+    /// });
+    /// ```
+    pub fn with<R, F>(&'static self, cb: F) -> R where
+        F: FnOnce(&T) -> R
+    {
+        unsafe {
+            let ptr = self.inner.get();
+            assert!(!ptr.is_null(), "cannot access a scoped thread local \
+                                     variable without calling `set` first");
+            cb(&*ptr)
+        }
+    }
+
+    /// Test whether this TLS key has been `set` for the current thread.
+    pub fn is_set(&'static self) -> bool {
+        unsafe { !self.inner.get().is_null() }
+    }
+}
+
+#[cfg(not(any(windows,
+              target_os = "android",
+              target_os = "ios",
+              target_os = "openbsd",
+              target_arch = "aarch64")))]
+mod imp {
+    use std::cell::UnsafeCell;
+
+    #[doc(hidden)]
+    pub struct KeyInner<T> { pub inner: UnsafeCell<*mut T> }
+
+    unsafe impl<T> ::marker::Sync for KeyInner<T> { }
+
+    #[doc(hidden)]
+    impl<T> KeyInner<T> {
+        #[doc(hidden)]
+        pub unsafe fn set(&self, ptr: *mut T) { *self.inner.get() = ptr; }
+        #[doc(hidden)]
+        pub unsafe fn get(&self) -> *mut T { *self.inner.get() }
+    }
+}
+
+#[cfg(any(windows,
+          target_os = "android",
+          target_os = "ios",
+          target_os = "openbsd",
+          target_arch = "aarch64"))]
+mod imp {
+    use marker;
+    use std::cell::Cell;
+    use sys_common::thread_local::StaticKey as OsStaticKey;
+
+    #[doc(hidden)]
+    pub struct KeyInner<T> {
+        pub inner: OsStaticKey,
+        pub marker: marker::PhantomData<Cell<T>>,
+    }
+
+    unsafe impl<T> ::marker::Sync for KeyInner<T> { }
+
+    #[doc(hidden)]
+    impl<T> KeyInner<T> {
+        #[doc(hidden)]
+        pub unsafe fn set(&self, ptr: *mut T) { self.inner.set(ptr as *mut _) }
+        #[doc(hidden)]
+        pub unsafe fn get(&self) -> *mut T { self.inner.get() as *mut _ }
+    }
+}
+
+
+#[cfg(test)]
+mod tests {
+    use cell::Cell;
+    use prelude::v1::*;
+
+    scoped_thread_local!(static FOO: u32);
+
+    #[test]
+    fn smoke() {
+        scoped_thread_local!(static BAR: u32);
+
+        assert!(!BAR.is_set());
+        BAR.set(&1, || {
+            assert!(BAR.is_set());
+            BAR.with(|slot| {
+                assert_eq!(*slot, 1);
+            });
+        });
+        assert!(!BAR.is_set());
+    }
+
+    #[test]
+    fn cell_allowed() {
+        scoped_thread_local!(static BAR: Cell<u32>);
+
+        BAR.set(&Cell::new(1), || {
+            BAR.with(|slot| {
+                assert_eq!(slot.get(), 1);
+            });
+        });
+    }
+
+    #[test]
+    fn scope_item_allowed() {
+        assert!(!FOO.is_set());
+        FOO.set(&1, || {
+            assert!(FOO.is_set());
+            FOO.with(|slot| {
+                assert_eq!(*slot, 1);
+            });
+        });
+        assert!(!FOO.is_set());
+    }
+}