631 lines
21 KiB
Rust
631 lines
21 KiB
Rust
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Thread local storage
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//!
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//! This module provides an implementation of thread local storage for Rust
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//! programs. Thread local storage is a method of storing data into a global
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//! variable which each thread in the program will have its own copy of.
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//! Threads do not share this data, so accesses do not need to be synchronized.
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//!
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//! At a high level, this module provides two variants of storage:
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//!
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//! * Owning thread local storage. This is a type of thread local key which
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//! owns the value that it contains, and will destroy the value when the
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//! thread exits. This variant is created with the `thread_local!` macro and
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//! can contain any value which is `'static` (no borrowed pointers.
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//!
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//! * Scoped thread local storage. This type of key is used to store a reference
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//! to a value into local storage temporarily for the scope of a function
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//! call. There are no restrictions on what types of values can be placed
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//! into this key.
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//!
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//! Both forms of thread local storage provide an accessor function, `with`,
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//! which will yield a shared reference to the value to the specified
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//! closure. Thread local keys only allow shared access to values as there is no
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//! way to guarantee uniqueness if a mutable borrow was allowed. Most values
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//! will want to make use of some form of **interior mutability** through the
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//! `Cell` or `RefCell` types.
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#![macro_escape]
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#![experimental]
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use prelude::*;
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use cell::UnsafeCell;
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// Sure wish we had macro hygiene, no?
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#[doc(hidden)] pub use self::imp::Key as KeyInner;
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#[doc(hidden)] pub use self::imp::destroy_value;
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#[doc(hidden)] pub use sys_common::thread_local::INIT_INNER as OS_INIT_INNER;
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#[doc(hidden)] pub use sys_common::thread_local::StaticKey as OsStaticKey;
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pub mod scoped;
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/// A thread local storage key which owns its contents.
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///
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/// This key uses the fastest possible implementation available to it for the
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/// target platform. It is instantiated with the `thread_local!` macro and the
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/// primary method is the `with` method.
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///
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/// The `with` method yields a reference to the contained value which cannot be
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/// sent across tasks or escape the given closure.
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///
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/// # Initialization and Destruction
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///
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/// Initialization is dynamically performed on the first call to `with()`
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/// within a thread, and values support destructors which will be run when a
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/// thread exits.
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///
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/// # Example
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///
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/// ```
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/// use std::cell::RefCell;
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///
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/// thread_local!(static FOO: RefCell<uint> = RefCell::new(1));
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///
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/// FOO.with(|f| {
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/// assert_eq!(*f.borrow(), 1);
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/// *f.borrow_mut() = 2;
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/// });
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///
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/// // each thread starts out with the initial value of 1
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/// spawn(move|| {
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/// FOO.with(|f| {
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/// assert_eq!(*f.borrow(), 1);
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/// *f.borrow_mut() = 3;
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/// });
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/// });
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///
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/// // we retain our original value of 2 despite the child thread
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/// FOO.with(|f| {
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/// assert_eq!(*f.borrow(), 2);
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/// });
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/// ```
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pub struct Key<T> {
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// The key itself may be tagged with #[thread_local], and this `Key` is
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// stored as a `static`, and it's not valid for a static to reference the
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// address of another thread_local static. For this reason we kinda wonkily
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// work around this by generating a shim function which will give us the
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// address of the inner TLS key at runtime.
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//
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// This is trivially devirtualizable by LLVM because we never store anything
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// to this field and rustc can declare the `static` as constant as well.
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#[doc(hidden)]
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pub inner: fn() -> &'static KeyInner<UnsafeCell<Option<T>>>,
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// initialization routine to invoke to create a value
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#[doc(hidden)]
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pub init: fn() -> T,
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}
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/// Declare a new thread local storage key of type `std::thread_local::Key`.
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#[macro_export]
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#[doc(hidden)]
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macro_rules! thread_local {
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(static $name:ident: $t:ty = $init:expr) => (
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static $name: ::std::thread_local::Key<$t> = {
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use std::cell::UnsafeCell as __UnsafeCell;
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use std::thread_local::KeyInner as __KeyInner;
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use std::option::Option as __Option;
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use std::option::Option::None as __None;
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__thread_local_inner!(static __KEY: __UnsafeCell<__Option<$t>> = {
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__UnsafeCell { value: __None }
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});
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fn __init() -> $t { $init }
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fn __getit() -> &'static __KeyInner<__UnsafeCell<__Option<$t>>> {
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&__KEY
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}
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::std::thread_local::Key { inner: __getit, init: __init }
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};
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);
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(pub static $name:ident: $t:ty = $init:expr) => (
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pub static $name: ::std::thread_local::Key<$t> = {
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use std::cell::UnsafeCell as __UnsafeCell;
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use std::thread_local::KeyInner as __KeyInner;
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use std::option::Option as __Option;
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use std::option::Option::None as __None;
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__thread_local_inner!(static __KEY: __UnsafeCell<__Option<$t>> = {
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__UnsafeCell { value: __None }
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});
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fn __init() -> $t { $init }
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fn __getit() -> &'static __KeyInner<__UnsafeCell<__Option<$t>>> {
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&__KEY
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}
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::std::thread_local::Key { inner: __getit, init: __init }
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};
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);
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}
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// Macro pain #4586:
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//
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// When cross compiling, rustc will load plugins and macros from the *host*
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// platform before search for macros from the target platform. This is primarily
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// done to detect, for example, plugins. Ideally the macro below would be
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// defined once per module below, but unfortunately this means we have the
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// following situation:
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//
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// 1. We compile libstd for x86_64-unknown-linux-gnu, this thread_local!() macro
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// will inject #[thread_local] statics.
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// 2. We then try to compile a program for arm-linux-androideabi
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// 3. The compiler has a host of linux and a target of android, so it loads
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// macros from the *linux* libstd.
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// 4. The macro generates a #[thread_local] field, but the android libstd does
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// not use #[thread_local]
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// 5. Compile error about structs with wrong fields.
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//
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// To get around this, we're forced to inject the #[cfg] logic into the macro
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// itself. Woohoo.
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#[macro_export]
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macro_rules! __thread_local_inner {
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(static $name:ident: $t:ty = $init:expr) => (
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#[cfg_attr(any(target_os = "macos", target_os = "linux"), thread_local)]
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static $name: ::std::thread_local::KeyInner<$t> =
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__thread_local_inner!($init, $t);
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);
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(pub static $name:ident: $t:ty = $init:expr) => (
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#[cfg_attr(any(target_os = "macos", target_os = "linux"), thread_local)]
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pub static $name: ::std::thread_local::KeyInner<$t> =
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__thread_local_inner!($init, $t);
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);
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($init:expr, $t:ty) => ({
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#[cfg(any(target_os = "macos", target_os = "linux"))]
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const INIT: ::std::thread_local::KeyInner<$t> = {
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::std::thread_local::KeyInner {
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inner: ::std::cell::UnsafeCell { value: $init },
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dtor_registered: ::std::cell::UnsafeCell { value: false },
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dtor_running: ::std::cell::UnsafeCell { value: false },
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}
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};
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#[cfg(not(any(target_os = "macos", target_os = "linux")))]
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const INIT: ::std::thread_local::KeyInner<$t> = {
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unsafe extern fn __destroy(ptr: *mut u8) {
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::std::thread_local::destroy_value::<$t>(ptr);
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}
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::std::thread_local::KeyInner {
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inner: ::std::cell::UnsafeCell { value: $init },
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os: ::std::thread_local::OsStaticKey {
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inner: ::std::thread_local::OS_INIT_INNER,
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dtor: ::std::option::Option::Some(__destroy),
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},
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}
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};
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INIT
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});
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}
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impl<T: 'static> Key<T> {
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/// Acquire a reference to the value in this TLS key.
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///
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/// This will lazily initialize the value if this thread has not referenced
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/// this key yet.
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///
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/// # Panics
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///
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/// This function will `panic!()` if the key currently has its
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/// destructor running, and it **may** panic if the destructor has
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/// previously been run for this thread.
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pub fn with<F, R>(&'static self, f: F) -> R
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where F: FnOnce(&T) -> R {
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let slot = (self.inner)();
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unsafe {
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let slot = slot.get().expect("cannot access a TLS value during or \
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after it is destroyed");
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if (*slot.get()).is_none() {
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*slot.get() = Some((self.init)());
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}
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f((*slot.get()).as_ref().unwrap())
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}
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}
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/// Test this TLS key to determine whether its value has been destroyed for
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/// the current thread or not.
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///
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/// This will not initialize the key if it is not already initialized.
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pub fn destroyed(&'static self) -> bool {
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unsafe { (self.inner)().get().is_none() }
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}
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}
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#[cfg(any(target_os = "macos", target_os = "linux"))]
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mod imp {
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use prelude::*;
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use cell::UnsafeCell;
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use intrinsics;
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use ptr;
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#[doc(hidden)]
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pub struct Key<T> {
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// Place the inner bits in an `UnsafeCell` to currently get around the
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// "only Sync statics" restriction. This allows any type to be placed in
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// the cell.
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//
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// Note that all access requires `T: 'static` so it can't be a type with
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// any borrowed pointers still.
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pub inner: UnsafeCell<T>,
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// Metadata to keep track of the state of the destructor. Remember that
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// these variables are thread-local, not global.
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pub dtor_registered: UnsafeCell<bool>, // should be Cell
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pub dtor_running: UnsafeCell<bool>, // should be Cell
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}
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#[doc(hidden)]
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impl<T> Key<T> {
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pub unsafe fn get(&'static self) -> Option<&'static T> {
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if intrinsics::needs_drop::<T>() && *self.dtor_running.get() {
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return None
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}
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self.register_dtor();
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Some(&*self.inner.get())
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}
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unsafe fn register_dtor(&self) {
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if !intrinsics::needs_drop::<T>() || *self.dtor_registered.get() {
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return
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}
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register_dtor(self as *const _ as *mut u8,
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destroy_value::<T>);
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*self.dtor_registered.get() = true;
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}
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}
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// Since what appears to be glibc 2.18 this symbol has been shipped which
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// GCC and clang both use to invoke destructors in thread_local globals, so
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// let's do the same!
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//
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// Note, however, that we run on lots older linuxes, as well as cross
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// compiling from a newer linux to an older linux, so we also have a
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// fallback implementation to use as well.
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//
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// Due to rust-lang/rust#18804, make sure this is not generic!
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#[cfg(target_os = "linux")]
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unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
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use mem;
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use libc;
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use sys_common::thread_local as os;
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extern {
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static __dso_handle: *mut u8;
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#[linkage = "extern_weak"]
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static __cxa_thread_atexit_impl: *const ();
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}
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if !__cxa_thread_atexit_impl.is_null() {
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type F = unsafe extern fn(dtor: unsafe extern fn(*mut u8),
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arg: *mut u8,
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dso_handle: *mut u8) -> libc::c_int;
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mem::transmute::<*const (), F>(__cxa_thread_atexit_impl)
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(dtor, t, __dso_handle);
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return
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}
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// The fallback implementation uses a vanilla OS-based TLS key to track
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// the list of destructors that need to be run for this thread. The key
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// then has its own destructor which runs all the other destructors.
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//
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// The destructor for DTORS is a little special in that it has a `while`
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// loop to continuously drain the list of registered destructors. It
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// *should* be the case that this loop always terminates because we
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// provide the guarantee that a TLS key cannot be set after it is
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// flagged for destruction.
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static DTORS: os::StaticKey = os::StaticKey {
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inner: os::INIT_INNER,
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dtor: Some(run_dtors),
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};
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type List = Vec<(*mut u8, unsafe extern fn(*mut u8))>;
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if DTORS.get().is_null() {
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let v: Box<List> = box Vec::new();
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DTORS.set(mem::transmute(v));
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}
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let list: &mut List = &mut *(DTORS.get() as *mut List);
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list.push((t, dtor));
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unsafe extern fn run_dtors(mut ptr: *mut u8) {
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while !ptr.is_null() {
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let list: Box<List> = mem::transmute(ptr);
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for &(ptr, dtor) in list.iter() {
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dtor(ptr);
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}
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ptr = DTORS.get();
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DTORS.set(0 as *mut _);
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}
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}
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}
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// OSX's analog of the above linux function is this _tlv_atexit function.
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// The disassembly of thread_local globals in C++ (at least produced by
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// clang) will have this show up in the output.
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#[cfg(target_os = "macos")]
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unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
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extern {
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fn _tlv_atexit(dtor: unsafe extern fn(*mut u8),
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arg: *mut u8);
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}
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_tlv_atexit(dtor, t);
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}
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#[doc(hidden)]
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pub unsafe extern fn destroy_value<T>(ptr: *mut u8) {
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let ptr = ptr as *mut Key<T>;
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// Right before we run the user destructor be sure to flag the
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// destructor as running for this thread so calls to `get` will return
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// `None`.
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*(*ptr).dtor_running.get() = true;
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ptr::read((*ptr).inner.get() as *const T);
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}
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}
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#[cfg(not(any(target_os = "macos", target_os = "linux")))]
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mod imp {
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use prelude::*;
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use cell::UnsafeCell;
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use mem;
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use sys_common::thread_local::StaticKey as OsStaticKey;
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#[doc(hidden)]
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pub struct Key<T> {
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// Statically allocated initialization expression, using an `UnsafeCell`
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// for the same reasons as above.
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pub inner: UnsafeCell<T>,
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// OS-TLS key that we'll use to key off.
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pub os: OsStaticKey,
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}
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struct Value<T: 'static> {
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key: &'static Key<T>,
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value: T,
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}
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#[doc(hidden)]
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impl<T> Key<T> {
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pub unsafe fn get(&'static self) -> Option<&'static T> {
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self.ptr().map(|p| &*p)
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}
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unsafe fn ptr(&'static self) -> Option<*mut T> {
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let ptr = self.os.get() as *mut Value<T>;
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if !ptr.is_null() {
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if ptr as uint == 1 {
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return None
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}
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return Some(&mut (*ptr).value as *mut T);
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}
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// If the lookup returned null, we haven't initialized our own local
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// copy, so do that now.
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//
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// Also note that this transmute_copy should be ok because the value
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// `inner` is already validated to be a valid `static` value, so we
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// should be able to freely copy the bits.
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let ptr: Box<Value<T>> = box Value {
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key: self,
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value: mem::transmute_copy(&self.inner),
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};
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let ptr: *mut Value<T> = mem::transmute(ptr);
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self.os.set(ptr as *mut u8);
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Some(&mut (*ptr).value as *mut T)
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}
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}
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|
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#[doc(hidden)]
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pub unsafe extern fn destroy_value<T: 'static>(ptr: *mut u8) {
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// The OS TLS ensures that this key contains a NULL value when this
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// destructor starts to run. We set it back to a sentinel value of 1 to
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// ensure that any future calls to `get` for this thread will return
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// `None`.
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//
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// Note that to prevent an infinite loop we reset it back to null right
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// before we return from the destructor ourselves.
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let ptr: Box<Value<T>> = mem::transmute(ptr);
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let key = ptr.key;
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key.os.set(1 as *mut u8);
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drop(ptr);
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key.os.set(0 as *mut u8);
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}
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}
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#[cfg(test)]
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mod tests {
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use prelude::*;
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|
|
use cell::UnsafeCell;
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use thread::Thread;
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|
|
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struct Foo(Sender<()>);
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|
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impl Drop for Foo {
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fn drop(&mut self) {
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let Foo(ref s) = *self;
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s.send(());
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}
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}
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#[test]
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fn smoke_no_dtor() {
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thread_local!(static FOO: UnsafeCell<int> = UnsafeCell { value: 1 });
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FOO.with(|f| unsafe {
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assert_eq!(*f.get(), 1);
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*f.get() = 2;
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});
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let (tx, rx) = channel();
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spawn(move|| {
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FOO.with(|f| unsafe {
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assert_eq!(*f.get(), 1);
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});
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tx.send(());
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});
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rx.recv();
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FOO.with(|f| unsafe {
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assert_eq!(*f.get(), 2);
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});
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}
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|
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#[test]
|
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fn smoke_dtor() {
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thread_local!(static FOO: UnsafeCell<Option<Foo>> = UnsafeCell {
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value: None
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});
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|
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let (tx, rx) = channel();
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spawn(move|| unsafe {
|
|
let mut tx = Some(tx);
|
|
FOO.with(|f| {
|
|
*f.get() = Some(Foo(tx.take().unwrap()));
|
|
});
|
|
});
|
|
rx.recv();
|
|
}
|
|
|
|
#[test]
|
|
fn circular() {
|
|
struct S1;
|
|
struct S2;
|
|
thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell {
|
|
value: None
|
|
});
|
|
thread_local!(static K2: UnsafeCell<Option<S2>> = UnsafeCell {
|
|
value: None
|
|
});
|
|
static mut HITS: uint = 0;
|
|
|
|
impl Drop for S1 {
|
|
fn drop(&mut self) {
|
|
unsafe {
|
|
HITS += 1;
|
|
if K2.destroyed() {
|
|
assert_eq!(HITS, 3);
|
|
} else {
|
|
if HITS == 1 {
|
|
K2.with(|s| *s.get() = Some(S2));
|
|
} else {
|
|
assert_eq!(HITS, 3);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
impl Drop for S2 {
|
|
fn drop(&mut self) {
|
|
unsafe {
|
|
HITS += 1;
|
|
assert!(!K1.destroyed());
|
|
assert_eq!(HITS, 2);
|
|
K1.with(|s| *s.get() = Some(S1));
|
|
}
|
|
}
|
|
}
|
|
|
|
Thread::with_join(move|| {
|
|
drop(S1);
|
|
}).join();
|
|
}
|
|
|
|
#[test]
|
|
fn self_referential() {
|
|
struct S1;
|
|
thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell {
|
|
value: None
|
|
});
|
|
|
|
impl Drop for S1 {
|
|
fn drop(&mut self) {
|
|
assert!(K1.destroyed());
|
|
}
|
|
}
|
|
|
|
Thread::with_join(move|| unsafe {
|
|
K1.with(|s| *s.get() = Some(S1));
|
|
}).join();
|
|
}
|
|
|
|
#[test]
|
|
fn dtors_in_dtors_in_dtors() {
|
|
struct S1(Sender<()>);
|
|
thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell {
|
|
value: None
|
|
});
|
|
thread_local!(static K2: UnsafeCell<Option<Foo>> = UnsafeCell {
|
|
value: None
|
|
});
|
|
|
|
impl Drop for S1 {
|
|
fn drop(&mut self) {
|
|
let S1(ref tx) = *self;
|
|
unsafe {
|
|
if !K2.destroyed() {
|
|
K2.with(|s| *s.get() = Some(Foo(tx.clone())));
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
let (tx, rx) = channel();
|
|
spawn(move|| unsafe {
|
|
let mut tx = Some(tx);
|
|
K1.with(|s| *s.get() = Some(S1(tx.take().unwrap())));
|
|
});
|
|
rx.recv();
|
|
}
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod dynamic_tests {
|
|
use prelude::*;
|
|
|
|
use cell::RefCell;
|
|
use collections::HashMap;
|
|
|
|
#[test]
|
|
fn smoke() {
|
|
fn square(i: int) -> int { i * i }
|
|
thread_local!(static FOO: int = square(3));
|
|
|
|
FOO.with(|f| {
|
|
assert_eq!(*f, 9);
|
|
});
|
|
}
|
|
|
|
#[test]
|
|
fn hashmap() {
|
|
fn map() -> RefCell<HashMap<int, int>> {
|
|
let mut m = HashMap::new();
|
|
m.insert(1, 2);
|
|
RefCell::new(m)
|
|
}
|
|
thread_local!(static FOO: RefCell<HashMap<int, int>> = map());
|
|
|
|
FOO.with(|map| {
|
|
assert_eq!(map.borrow()[1], 2);
|
|
});
|
|
}
|
|
|
|
#[test]
|
|
fn refcell_vec() {
|
|
thread_local!(static FOO: RefCell<Vec<uint>> = RefCell::new(vec![1, 2, 3]));
|
|
|
|
FOO.with(|vec| {
|
|
assert_eq!(vec.borrow().len(), 3);
|
|
vec.borrow_mut().push(4);
|
|
assert_eq!(vec.borrow()[3], 4);
|
|
});
|
|
}
|
|
}
|