1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! OS-based thread local storage
13 //! This module provides an implementation of OS-based thread local storage,
14 //! using the native OS-provided facilities (think `TlsAlloc` or
15 //! `pthread_setspecific`). The interface of this differs from the other types
16 //! of thread-local-storage provided in this crate in that OS-based TLS can only
19 //! This module also provides two flavors of TLS. One is intended for static
20 //! initialization, and does not contain a `Drop` implementation to deallocate
21 //! the OS-TLS key. The other is a type which does implement `Drop` and hence
22 //! has a safe interface.
26 //! This module should likely not be used directly unless other primitives are
27 //! being built on. types such as `thread_local::scoped::Key` are likely much
28 //! more useful in practice than this OS-based version which likely requires
29 //! unsafe code to interoperate with.
33 //! Using a dynamically allocated TLS key. Note that this key can be shared
34 //! among many threads via an `Arc`.
37 //! let key = Key::new(None);
38 //! assert!(key.get().is_null());
39 //! key.set(1 as *mut u8);
40 //! assert!(!key.get().is_null());
42 //! drop(key); // deallocate this TLS slot.
45 //! Sometimes a statically allocated key is either required or easier to work
49 //! static KEY: StaticKey = INIT;
52 //! assert!(KEY.get().is_null());
53 //! KEY.set(1 as *mut u8);
57 #![allow(non_camel_case_types)]
62 use rustrt::exclusive::Exclusive;
63 use sync::atomic::{mod, AtomicUint};
64 use sync::{Once, ONCE_INIT};
66 use sys::thread_local as imp;
68 /// A type for TLS keys that are statically allocated.
70 /// This type is entirely `unsafe` to use as it does not protect against
71 /// use-after-deallocation or use-during-deallocation.
73 /// The actual OS-TLS key is lazily allocated when this is used for the first
74 /// time. The key is also deallocated when the Rust runtime exits or `destroy`
75 /// is called, whichever comes first.
80 /// use tls::os::{StaticKey, INIT};
82 /// static KEY: StaticKey = INIT;
85 /// assert!(KEY.get().is_null());
86 /// KEY.set(1 as *mut u8);
89 pub struct StaticKey {
90 /// Inner static TLS key (internals), created with by `INIT_INNER` in this
92 pub inner: StaticKeyInner,
93 /// Destructor for the TLS value.
95 /// See `Key::new` for information about when the destructor runs and how
97 pub dtor: Option<unsafe extern fn(*mut u8)>,
100 /// Inner contents of `StaticKey`, created by the `INIT_INNER` constant.
101 pub struct StaticKeyInner {
106 /// A type for a safely managed OS-based TLS slot.
108 /// This type allocates an OS TLS key when it is initialized and will deallocate
109 /// the key when it falls out of scope. When compared with `StaticKey`, this
110 /// type is entirely safe to use.
112 /// Implementations will likely, however, contain unsafe code as this type only
113 /// operates on `*mut u8`, an unsafe pointer.
118 /// use tls::os::Key;
120 /// let key = Key::new(None);
121 /// assert!(key.get().is_null());
122 /// key.set(1 as *mut u8);
123 /// assert!(!key.get().is_null());
125 /// drop(key); // deallocate this TLS slot.
131 /// Constant initialization value for static TLS keys.
133 /// This value specifies no destructor by default.
134 pub const INIT: StaticKey = StaticKey {
139 /// Constant initialization value for the inner part of static TLS keys.
141 /// This value allows specific configuration of the destructor for a TLS key.
142 pub const INIT_INNER: StaticKeyInner = StaticKeyInner {
143 key: atomic::INIT_ATOMIC_UINT,
147 static INIT_KEYS: Once = ONCE_INIT;
148 static mut KEYS: *mut Exclusive<Vec<imp::Key>> = 0 as *mut _;
151 /// Gets the value associated with this TLS key
153 /// This will lazily allocate a TLS key from the OS if one has not already
156 pub unsafe fn get(&self) -> *mut u8 { imp::get(self.key()) }
158 /// Sets this TLS key to a new value.
160 /// This will lazily allocate a TLS key from the OS if one has not already
163 pub unsafe fn set(&self, val: *mut u8) { imp::set(self.key(), val) }
165 /// Deallocates this OS TLS key.
167 /// This function is unsafe as there is no guarantee that the key is not
168 /// currently in use by other threads or will not ever be used again.
170 /// Note that this does *not* run the user-provided destructor if one was
171 /// specified at definition time. Doing so must be done manually.
172 pub unsafe fn destroy(&self) {
173 match self.inner.key.swap(0, atomic::SeqCst) {
175 n => { imp::destroy(n as imp::Key) }
180 unsafe fn key(&self) -> imp::Key {
181 match self.inner.key.load(atomic::Relaxed) {
182 0 => self.lazy_init() as imp::Key,
187 unsafe fn lazy_init(&self) -> uint {
188 let key = imp::create(self.dtor);
190 match self.inner.key.compare_and_swap(0, key as uint, atomic::SeqCst) {
191 // The CAS succeeded, so we've created the actual key
193 // If someone beat us to the punch, use their key instead
194 n => { imp::destroy(key); n }
200 /// Create a new managed OS TLS key.
202 /// This key will be deallocated when the key falls out of scope.
204 /// The argument provided is an optionally-specified destructor for the
205 /// value of this TLS key. When a thread exits and the value for this key
206 /// is non-null the destructor will be invoked. The TLS value will be reset
207 /// to null before the destructor is invoked.
209 /// Note that the destructor will not be run when the `Key` goes out of
212 pub fn new(dtor: Option<unsafe extern fn(*mut u8)>) -> Key {
213 Key { key: unsafe { imp::create(dtor) } }
216 /// See StaticKey::get
218 pub fn get(&self) -> *mut u8 {
219 unsafe { imp::get(self.key) }
222 /// See StaticKey::set
224 pub fn set(&self, val: *mut u8) {
225 unsafe { imp::set(self.key, val) }
231 unsafe { imp::destroy(self.key) }
238 use super::{Key, StaticKey, INIT_INNER};
240 fn assert_sync<T: Sync>() {}
241 fn assert_send<T: Send>() {}
245 assert_sync::<Key>();
246 assert_send::<Key>();
248 let k1 = Key::new(None);
249 let k2 = Key::new(None);
250 assert!(k1.get().is_null());
251 assert!(k2.get().is_null());
254 assert_eq!(k1.get() as uint, 1);
255 assert_eq!(k2.get() as uint, 2);
260 static K1: StaticKey = StaticKey { inner: INIT_INNER, dtor: None };
261 static K2: StaticKey = StaticKey { inner: INIT_INNER, dtor: None };
264 assert!(K1.get().is_null());
265 assert!(K2.get().is_null());
268 assert_eq!(K1.get() as uint, 1);
269 assert_eq!(K2.get() as uint, 2);