std: Add a new top-level thread_local module

This commit removes the `std::local_data` module in favor of a new
`std::thread_local` module providing thread local storage. The module provides
two variants of TLS: one which owns its contents and one which is based on
scoped references. Each implementation has pros and cons listed in the
documentation.

Both flavors have accessors through a function called `with` which yield a
reference to a closure provided. Both flavors also panic if a reference cannot
be yielded and provide a function to test whether an access would panic or not.
This is an implementation of [RFC 461][rfc] and full details can be found in
that RFC.

This is a breaking change due to the removal of the `std::local_data` module.
All users can migrate to the new thread local system like so:

    thread_local!(static FOO: Rc<RefCell<Option<T>>> = Rc::new(RefCell::new(None)))

The old `local_data` module inherently contained the `Rc<RefCell<Option<T>>>` as
an implementation detail which must now be explicitly stated by users.

[rfc]: https://github.com/rust-lang/rfcs/pull/461
[breaking-change]

2 files changed, 307 insertions, 0 deletions

diff --git a/src/libstd/sys/common/mod.rs b/src/libstd/sys/common/mod.rs
index cacb128faa5..77edd7c5c4e 100644
--- a/src/libstd/sys/common/mod.rs
+++ b/src/libstd/sys/common/mod.rs
@@ -21,6 +21,7 @@ use collections;
 
 pub mod net;
 pub mod helper_thread;
+pub mod thread_local;
 
 // common error constructors
 
diff --git a/src/libstd/sys/common/thread_local.rs b/src/libstd/sys/common/thread_local.rs
new file mode 100644
index 00000000000..9ad38cbaf65
--- /dev/null
+++ b/src/libstd/sys/common/thread_local.rs
@@ -0,0 +1,306 @@
+// 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.
+
+//! OS-based thread local storage
+//!
+//! This module provides an implementation of OS-based thread local storage,
+//! using the native OS-provided facilities (think `TlsAlloc` or
+//! `pthread_setspecific`). The interface of this differs from the other types
+//! of thread-local-storage provided in this crate in that OS-based TLS can only
+//! get/set pointers,
+//!
+//! This module also provides two flavors of TLS. One is intended for static
+//! initialization, and does not contain a `Drop` implementation to deallocate
+//! the OS-TLS key. The other is a type which does implement `Drop` and hence
+//! has a safe interface.
+//!
+//! # Usage
+//!
+//! This module should likely not be used directly unless other primitives are
+//! being built on. types such as `thread_local::scoped::Key` are likely much
+//! more useful in practice than this OS-based version which likely requires
+//! unsafe code to interoperate with.
+//!
+//! # Example
+//!
+//! Using a dynamically allocated TLS key. Note that this key can be shared
+//! among many threads via an `Arc`.
+//!
+//! ```rust,ignore
+//! let key = Key::new(None);
+//! assert!(key.get().is_null());
+//! key.set(1 as *mut u8);
+//! assert!(!key.get().is_null());
+//!
+//! drop(key); // deallocate this TLS slot.
+//! ```
+//!
+//! Sometimes a statically allocated key is either required or easier to work
+//! with, however.
+//!
+//! ```rust,ignore
+//! static KEY: StaticKey = INIT;
+//!
+//! unsafe {
+//!     assert!(KEY.get().is_null());
+//!     KEY.set(1 as *mut u8);
+//! }
+//! ```
+
+#![allow(non_camel_case_types)]
+
+use prelude::*;
+
+use kinds::marker;
+use mem;
+use rustrt::exclusive::Exclusive;
+use rustrt;
+use sync::atomic::{mod, AtomicUint};
+use sync::{Once, ONCE_INIT};
+
+use sys::thread_local as imp;
+
+/// A type for TLS keys that are statically allocated.
+///
+/// This type is entirely `unsafe` to use as it does not protect against
+/// use-after-deallocation or use-during-deallocation.
+///
+/// The actual OS-TLS key is lazily allocated when this is used for the first
+/// time. The key is also deallocated when the Rust runtime exits or `destroy`
+/// is called, whichever comes first.
+///
+/// # Example
+///
+/// ```ignore
+/// use tls::os::{StaticKey, INIT};
+///
+/// static KEY: StaticKey = INIT;
+///
+/// unsafe {
+///     assert!(KEY.get().is_null());
+///     KEY.set(1 as *mut u8);
+/// }
+/// ```
+pub struct StaticKey {
+    /// Inner static TLS key (internals), created with by `INIT_INNER` in this
+    /// module.
+    pub inner: StaticKeyInner,
+    /// Destructor for the TLS value.
+    ///
+    /// See `Key::new` for information about when the destructor runs and how
+    /// it runs.
+    pub dtor: Option<unsafe extern fn(*mut u8)>,
+}
+
+/// Inner contents of `StaticKey`, created by the `INIT_INNER` constant.
+pub struct StaticKeyInner {
+    key: AtomicUint,
+    nc: marker::NoCopy,
+}
+
+/// A type for a safely managed OS-based TLS slot.
+///
+/// This type allocates an OS TLS key when it is initialized and will deallocate
+/// the key when it falls out of scope. When compared with `StaticKey`, this
+/// type is entirely safe to use.
+///
+/// Implementations will likely, however, contain unsafe code as this type only
+/// operates on `*mut u8`, an unsafe pointer.
+///
+/// # Example
+///
+/// ```rust,ignore
+/// use tls::os::Key;
+///
+/// let key = Key::new(None);
+/// assert!(key.get().is_null());
+/// key.set(1 as *mut u8);
+/// assert!(!key.get().is_null());
+///
+/// drop(key); // deallocate this TLS slot.
+/// ```
+pub struct Key {
+    key: imp::Key,
+}
+
+/// Constant initialization value for static TLS keys.
+///
+/// This value specifies no destructor by default.
+pub const INIT: StaticKey = StaticKey {
+    inner: INIT_INNER,
+    dtor: None,
+};
+
+/// Constant initialization value for the inner part of static TLS keys.
+///
+/// This value allows specific configuration of the destructor for a TLS key.
+pub const INIT_INNER: StaticKeyInner = StaticKeyInner {
+    key: atomic::INIT_ATOMIC_UINT,
+    nc: marker::NoCopy,
+};
+
+static INIT_KEYS: Once = ONCE_INIT;
+static mut KEYS: *mut Exclusive<Vec<imp::Key>> = 0 as *mut _;
+
+impl StaticKey {
+    /// Gets the value associated with this TLS key
+    ///
+    /// This will lazily allocate a TLS key from the OS if one has not already
+    /// been allocated.
+    #[inline]
+    pub unsafe fn get(&self) -> *mut u8 { imp::get(self.key()) }
+
+    /// Sets this TLS key to a new value.
+    ///
+    /// This will lazily allocate a TLS key from the OS if one has not already
+    /// been allocated.
+    #[inline]
+    pub unsafe fn set(&self, val: *mut u8) { imp::set(self.key(), val) }
+
+    /// Deallocates this OS TLS key.
+    ///
+    /// This function is unsafe as there is no guarantee that the key is not
+    /// currently in use by other threads or will not ever be used again.
+    ///
+    /// Note that this does *not* run the user-provided destructor if one was
+    /// specified at definition time. Doing so must be done manually.
+    pub unsafe fn destroy(&self) {
+        match self.inner.key.swap(0, atomic::SeqCst) {
+            0 => {}
+            n => { unregister_key(n as imp::Key); imp::destroy(n as imp::Key) }
+        }
+    }
+
+    #[inline]
+    unsafe fn key(&self) -> imp::Key {
+        match self.inner.key.load(atomic::Relaxed) {
+            0 => self.lazy_init() as imp::Key,
+            n => n as imp::Key
+        }
+    }
+
+    unsafe fn lazy_init(&self) -> uint {
+        let key = imp::create(self.dtor);
+        assert!(key != 0);
+        match self.inner.key.compare_and_swap(0, key as uint, atomic::SeqCst) {
+            // The CAS succeeded, so we've created the actual key
+            0 => {
+                register_key(key);
+                key as uint
+            }
+            // If someone beat us to the punch, use their key instead
+            n => { imp::destroy(key); n }
+        }
+    }
+}
+
+impl Key {
+    /// Create a new managed OS TLS key.
+    ///
+    /// This key will be deallocated when the key falls out of scope.
+    ///
+    /// The argument provided is an optionally-specified destructor for the
+    /// value of this TLS key. When a thread exits and the value for this key
+    /// is non-null the destructor will be invoked. The TLS value will be reset
+    /// to null before the destructor is invoked.
+    ///
+    /// Note that the destructor will not be run when the `Key` goes out of
+    /// scope.
+    #[inline]
+    pub fn new(dtor: Option<unsafe extern fn(*mut u8)>) -> Key {
+        Key { key: unsafe { imp::create(dtor) } }
+    }
+
+    /// See StaticKey::get
+    #[inline]
+    pub fn get(&self) -> *mut u8 {
+        unsafe { imp::get(self.key) }
+    }
+
+    /// See StaticKey::set
+    #[inline]
+    pub fn set(&self, val: *mut u8) {
+        unsafe { imp::set(self.key, val) }
+    }
+}
+
+impl Drop for Key {
+    fn drop(&mut self) {
+        unsafe { imp::destroy(self.key) }
+    }
+}
+
+fn init_keys() {
+    let keys = box Exclusive::new(Vec::<imp::Key>::new());
+    unsafe {
+        KEYS = mem::transmute(keys);
+    }
+
+    rustrt::at_exit(proc() unsafe {
+        let keys: Box<Exclusive<Vec<imp::Key>>> = mem::transmute(KEYS);
+        KEYS = 0 as *mut _;
+        let keys = keys.lock();
+        for key in keys.iter() {
+            imp::destroy(*key);
+        }
+    });
+}
+
+fn register_key(key: imp::Key) {
+    INIT_KEYS.doit(init_keys);
+    let mut keys = unsafe { (*KEYS).lock() };
+    keys.push(key);
+}
+
+fn unregister_key(key: imp::Key) {
+    INIT_KEYS.doit(init_keys);
+    let mut keys = unsafe { (*KEYS).lock() };
+    keys.retain(|k| *k != key);
+}
+
+#[cfg(test)]
+mod tests {
+    use prelude::*;
+    use super::{Key, StaticKey, INIT_INNER};
+
+    fn assert_sync<T: Sync>() {}
+    fn assert_send<T: Send>() {}
+
+    #[test]
+    fn smoke() {
+        assert_sync::<Key>();
+        assert_send::<Key>();
+
+        let k1 = Key::new(None);
+        let k2 = Key::new(None);
+        assert!(k1.get().is_null());
+        assert!(k2.get().is_null());
+        k1.set(1 as *mut _);
+        k2.set(2 as *mut _);
+        assert_eq!(k1.get() as uint, 1);
+        assert_eq!(k2.get() as uint, 2);
+    }
+
+    #[test]
+    fn statik() {
+        static K1: StaticKey = StaticKey { inner: INIT_INNER, dtor: None };
+        static K2: StaticKey = StaticKey { inner: INIT_INNER, dtor: None };
+
+        unsafe {
+            assert!(K1.get().is_null());
+            assert!(K2.get().is_null());
+            K1.set(1 as *mut _);
+            K2.set(2 as *mut _);
+            assert_eq!(K1.get() as uint, 1);
+            assert_eq!(K2.get() as uint, 2);
+        }
+    }
+}
+