| //! 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::spawn::Key` are likely much |
| //! more useful in practice than this OS-based version which likely requires |
| //! unsafe code to interoperate with. |
| //! |
| //! # Examples |
| //! |
| //! Using a dynamically allocated TLS key. Note that this key can be shared |
| //! among many threads via an `Arc`. |
| //! |
| //! ```ignore (cannot-doctest-private-modules) |
| //! 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. |
| //! |
| //! ```ignore (cannot-doctest-private-modules) |
| //! static KEY: StaticKey = INIT; |
| //! |
| //! unsafe { |
| //! assert!(KEY.get().is_null()); |
| //! KEY.set(1 as *mut u8); |
| //! } |
| //! ``` |
| |
| #![allow(non_camel_case_types)] |
| #![unstable(feature = "thread_local_internals", issue = "0")] |
| #![allow(dead_code)] // sys isn't exported yet |
| |
| use crate::ptr; |
| use crate::sync::atomic::{self, AtomicUsize, Ordering}; |
| use crate::sys::thread_local as imp; |
| use crate::sys_common::mutex::Mutex; |
| |
| /// 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. |
| /// |
| /// # Examples |
| /// |
| /// ```ignore (cannot-doctest-private-modules) |
| /// 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). |
| key: AtomicUsize, |
| /// Destructor for the TLS value. |
| /// |
| /// See `Key::new` for information about when the destructor runs and how |
| /// it runs. |
| dtor: Option<unsafe extern fn(*mut u8)>, |
| } |
| |
| /// 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`, a raw pointer. |
| /// |
| /// # Examples |
| /// |
| /// ```ignore (cannot-doctest-private-modules) |
| /// 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::new(None); |
| |
| impl StaticKey { |
| pub const fn new(dtor: Option<unsafe extern fn(*mut u8)>) -> StaticKey { |
| StaticKey { |
| key: atomic::AtomicUsize::new(0), |
| dtor, |
| } |
| } |
| |
| /// 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) } |
| |
| #[inline] |
| unsafe fn key(&self) -> imp::Key { |
| match self.key.load(Ordering::Relaxed) { |
| 0 => self.lazy_init() as imp::Key, |
| n => n as imp::Key |
| } |
| } |
| |
| unsafe fn lazy_init(&self) -> usize { |
| // Currently the Windows implementation of TLS is pretty hairy, and |
| // it greatly simplifies creation if we just synchronize everything. |
| // |
| // Additionally a 0-index of a tls key hasn't been seen on windows, so |
| // we just simplify the whole branch. |
| if imp::requires_synchronized_create() { |
| // We never call `INIT_LOCK.init()`, so it is UB to attempt to |
| // acquire this mutex reentrantly! |
| static INIT_LOCK: Mutex = Mutex::new(); |
| let _guard = INIT_LOCK.lock(); |
| let mut key = self.key.load(Ordering::SeqCst); |
| if key == 0 { |
| key = imp::create(self.dtor) as usize; |
| self.key.store(key, Ordering::SeqCst); |
| } |
| rtassert!(key != 0); |
| return key |
| } |
| |
| // POSIX allows the key created here to be 0, but the compare_and_swap |
| // below relies on using 0 as a sentinel value to check who won the |
| // race to set the shared TLS key. As far as I know, there is no |
| // guaranteed value that cannot be returned as a posix_key_create key, |
| // so there is no value we can initialize the inner key with to |
| // prove that it has not yet been set. As such, we'll continue using a |
| // value of 0, but with some gyrations to make sure we have a non-0 |
| // value returned from the creation routine. |
| // FIXME: this is clearly a hack, and should be cleaned up. |
| let key1 = imp::create(self.dtor); |
| let key = if key1 != 0 { |
| key1 |
| } else { |
| let key2 = imp::create(self.dtor); |
| imp::destroy(key1); |
| key2 |
| }; |
| rtassert!(key != 0); |
| match self.key.compare_and_swap(0, key as usize, Ordering::SeqCst) { |
| // The CAS succeeded, so we've created the actual key |
| 0 => key as usize, |
| // If someone beat us to the punch, use their key instead |
| n => { imp::destroy(key); n } |
| } |
| } |
| } |
| |
| impl Key { |
| /// Creates 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) { |
| // Right now Windows doesn't support TLS key destruction, but this also |
| // isn't used anywhere other than tests, so just leak the TLS key. |
| // unsafe { imp::destroy(self.key) } |
| } |
| } |
| |
| pub unsafe fn register_dtor_fallback(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. |
| |
| static DTORS: StaticKey = 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.into_iter() { |
| dtor(ptr); |
| } |
| ptr = DTORS.get(); |
| DTORS.set(ptr::null_mut()); |
| } |
| } |
| } |
| |
| #[cfg(test)] |
| mod tests { |
| use super::{Key, StaticKey}; |
| |
| 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 usize, 1); |
| assert_eq!(k2.get() as usize, 2); |
| } |
| |
| #[test] |
| fn statik() { |
| static K1: StaticKey = StaticKey::new(None); |
| static K2: StaticKey = StaticKey::new(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 usize, 1); |
| assert_eq!(K2.get() as usize, 2); |
| } |
| } |
| } |