Merge pull request #19 from FenrirWolf/thread_local

Implement thread local storage

3 files changed, 184 insertions, 0 deletions

diff --git a/ctr-std/src/sys/unix/fast_thread_local.rs b/ctr-std/src/sys/unix/fast_thread_local.rs
new file mode 100644
index 0000000..6eeae2d
--- /dev/null
+++ b/ctr-std/src/sys/unix/fast_thread_local.rs
@@ -0,0 +1,116 @@
+// Copyright 2016 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.
+
+#![cfg(target_thread_local)]
+#![unstable(feature = "thread_local_internals", issue = "0")]
+
+use cell::{Cell, UnsafeCell};
+use intrinsics;
+use ptr;
+
+pub struct Key<T> {
+    inner: UnsafeCell<Option<T>>,
+
+    // Metadata to keep track of the state of the destructor. Remember that
+    // these variables are thread-local, not global.
+    dtor_registered: Cell<bool>,
+    dtor_running: Cell<bool>,
+}
+
+unsafe impl<T> ::marker::Sync for Key<T> { }
+
+impl<T> Key<T> {
+    pub const fn new() -> Key<T> {
+        Key {
+            inner: UnsafeCell::new(None),
+            dtor_registered: Cell::new(false),
+            dtor_running: Cell::new(false)
+        }
+    }
+
+    pub fn get(&'static self) -> Option<&'static UnsafeCell<Option<T>>> {
+        unsafe {
+            if intrinsics::needs_drop::<T>() && self.dtor_running.get() {
+                return None
+            }
+            self.register_dtor();
+        }
+        Some(&self.inner)
+    }
+
+    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.set(true);
+    }
+}
+
+unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
+    // 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.
+    use sys_common::thread_local as os;
+
+    static DTORS: os::StaticKey = os::StaticKey::new(Some(run_dtors));
+    type List = Vec<(*mut u8, unsafe extern fn(*mut u8))>;
+    if DTORS.get().is_null() {
+        let v: Box<List> = box Vec::new();
+        DTORS.set(Box::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.iter() {
+                dtor(ptr);
+            }
+            ptr = DTORS.get();
+            DTORS.set(ptr::null_mut());
+        }
+    }
+}
+
+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.set(true);
+
+    // The OSX implementation of TLS apparently had an odd aspect to it
+    // where the pointer we have may be overwritten while this destructor
+    // is running. Specifically if a TLS destructor re-accesses TLS it may
+    // trigger a re-initialization of all TLS variables, paving over at
+    // least some destroyed ones with initial values.
+    //
+    // This means that if we drop a TLS value in place on OSX that we could
+    // revert the value to its original state halfway through the
+    // destructor, which would be bad!
+    //
+    // Hence, we use `ptr::read` on OSX (to move to a "safe" location)
+    // instead of drop_in_place.
+    if cfg!(target_os = "macos") {
+        ptr::read((*ptr).inner.get());
+    } else {
+        ptr::drop_in_place((*ptr).inner.get());
+    }
+}
diff --git a/ctr-std/src/sys/unix/mod.rs b/ctr-std/src/sys/unix/mod.rs
index 698e31a..13639eb 100644
--- a/ctr-std/src/sys/unix/mod.rs
+++ b/ctr-std/src/sys/unix/mod.rs
@@ -11,10 +11,12 @@
 #![allow(missing_docs, bad_style)]
 
 pub mod ext;
+pub mod fast_thread_local;
 pub mod memchr;
 pub mod os;
 pub mod os_str;
 pub mod path;
+pub mod thread_local;
 
 use io::ErrorKind;
 use libc;
diff --git a/ctr-std/src/sys/unix/thread_local.rs b/ctr-std/src/sys/unix/thread_local.rs
new file mode 100644
index 0000000..abdd9ac
--- /dev/null
+++ b/ctr-std/src/sys/unix/thread_local.rs
@@ -0,0 +1,66 @@
+// Copyright 2016 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.
+
+#![allow(dead_code)] // not used on all platforms
+
+use collections::BTreeMap;
+use ptr;
+use sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT, Ordering};
+
+pub type Key = usize;
+
+type Dtor = unsafe extern fn(*mut u8);
+
+static NEXT_KEY: AtomicUsize = ATOMIC_USIZE_INIT;
+
+static mut KEYS: *mut BTreeMap<Key, Option<Dtor>> = ptr::null_mut();
+
+#[thread_local]
+static mut LOCALS: *mut BTreeMap<Key, *mut u8> = ptr::null_mut();
+
+unsafe fn keys() -> &'static mut BTreeMap<Key, Option<Dtor>> {
+    if KEYS == ptr::null_mut() {
+        KEYS = Box::into_raw(Box::new(BTreeMap::new()));
+    }
+    &mut *KEYS
+}
+
+unsafe fn locals() -> &'static mut BTreeMap<Key, *mut u8> {
+    if LOCALS == ptr::null_mut() {
+        LOCALS = Box::into_raw(Box::new(BTreeMap::new()));
+    }
+    &mut *LOCALS
+}
+
+#[inline]
+pub unsafe fn create(dtor: Option<Dtor>) -> Key {
+    let key = NEXT_KEY.fetch_add(1, Ordering::SeqCst);
+    keys().insert(key, dtor);
+    key
+}
+
+#[inline]
+pub unsafe fn get(key: Key) -> *mut u8 {
+    if let Some(&entry) = locals().get(&key) {
+        entry
+    } else {
+        ptr::null_mut()
+    }
+}
+
+#[inline]
+pub unsafe fn set(key: Key, value: *mut u8) {
+    locals().insert(key, value);
+}
+
+#[inline]
+pub unsafe fn destroy(key: Key) {
+    keys().remove(&key);
+}