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]

1 files changed, 12 insertions, 19 deletions

diff --git a/src/libstd/rand/mod.rs b/src/libstd/rand/mod.rs
index 08eb7350bcf..f9f9147b107 100644
--- a/src/libstd/rand/mod.rs
+++ b/src/libstd/rand/mod.rs
@@ -226,7 +226,6 @@ use clone::Clone;
 use io::IoResult;
 use iter::Iterator;
 use mem;
-use option::{Some, None};
 use rc::Rc;
 use result::{Ok, Err};
 use vec::Vec;
@@ -337,24 +336,18 @@ pub struct TaskRng {
 /// explicitly select an RNG, e.g. `IsaacRng` or `Isaac64Rng`.
 pub fn task_rng() -> TaskRng {
     // used to make space in TLS for a random number generator
-    local_data_key!(TASK_RNG_KEY: Rc<RefCell<TaskRngInner>>)
-
-    match TASK_RNG_KEY.get() {
-        None => {
-            let r = match StdRng::new() {
-                Ok(r) => r,
-                Err(e) => panic!("could not initialize task_rng: {}", e)
-            };
-            let rng = reseeding::ReseedingRng::new(r,
-                                                   TASK_RNG_RESEED_THRESHOLD,
-                                                   TaskRngReseeder);
-            let rng = Rc::new(RefCell::new(rng));
-            TASK_RNG_KEY.replace(Some(rng.clone()));
-
-            TaskRng { rng: rng }
-        }
-        Some(rng) => TaskRng { rng: rng.clone() }
-    }
+    thread_local!(static TASK_RNG_KEY: Rc<RefCell<TaskRngInner>> = {
+        let r = match StdRng::new() {
+            Ok(r) => r,
+            Err(e) => panic!("could not initialize task_rng: {}", e)
+        };
+        let rng = reseeding::ReseedingRng::new(r,
+                                               TASK_RNG_RESEED_THRESHOLD,
+                                               TaskRngReseeder);
+        Rc::new(RefCell::new(rng))
+    })
+
+    TaskRng { rng: TASK_RNG_KEY.with(|t| t.clone()) }
 }
 
 impl Rng for TaskRng {