rust/src/libstd/thread_local/mod.rs
2015-02-17 15:14:17 -08:00

757 lines
26 KiB
Rust

// Copyright 2014-2015 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.
//! Thread local storage
//!
//! This module provides an implementation of thread local storage for Rust
//! programs. Thread local storage is a method of storing data into a global
//! variable which each thread in the program will have its own copy of.
//! Threads do not share this data, so accesses do not need to be synchronized.
//!
//! At a high level, this module provides two variants of storage:
//!
//! * Owning thread local storage. This is a type of thread local key which
//! owns the value that it contains, and will destroy the value when the
//! thread exits. This variant is created with the `thread_local!` macro and
//! can contain any value which is `'static` (no borrowed pointers.
//!
//! * Scoped thread local storage. This type of key is used to store a reference
//! to a value into local storage temporarily for the scope of a function
//! call. There are no restrictions on what types of values can be placed
//! into this key.
//!
//! Both forms of thread local storage provide an accessor function, `with`,
//! which will yield a shared reference to the value to the specified
//! closure. Thread local keys only allow shared access to values as there is no
//! way to guarantee uniqueness if a mutable borrow was allowed. Most values
//! will want to make use of some form of **interior mutability** through the
//! `Cell` or `RefCell` types.
#![stable(feature = "rust1", since = "1.0.0")]
use prelude::v1::*;
use cell::UnsafeCell;
#[macro_use]
pub mod scoped;
// Sure wish we had macro hygiene, no?
#[doc(hidden)]
#[stable(feature = "rust1", since = "1.0.0")]
pub mod __impl {
pub use super::imp::Key as KeyInner;
pub use super::imp::destroy_value;
pub use sys_common::thread_local::INIT_INNER as OS_INIT_INNER;
pub use sys_common::thread_local::StaticKey as OsStaticKey;
}
/// A thread local storage key which owns its contents.
///
/// This key uses the fastest possible implementation available to it for the
/// target platform. It is instantiated with the `thread_local!` macro and the
/// primary method is the `with` method.
///
/// The `with` method yields a reference to the contained value which cannot be
/// sent across tasks or escape the given closure.
///
/// # Initialization and Destruction
///
/// Initialization is dynamically performed on the first call to `with()`
/// within a thread, and values support destructors which will be run when a
/// thread exits.
///
/// # Example
///
/// ```
/// use std::cell::RefCell;
/// use std::thread;
///
/// thread_local!(static FOO: RefCell<uint> = RefCell::new(1));
///
/// FOO.with(|f| {
/// assert_eq!(*f.borrow(), 1);
/// *f.borrow_mut() = 2;
/// });
///
/// // each thread starts out with the initial value of 1
/// thread::spawn(move|| {
/// FOO.with(|f| {
/// assert_eq!(*f.borrow(), 1);
/// *f.borrow_mut() = 3;
/// });
/// });
///
/// // we retain our original value of 2 despite the child thread
/// FOO.with(|f| {
/// assert_eq!(*f.borrow(), 2);
/// });
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Key<T> {
// The key itself may be tagged with #[thread_local], and this `Key` is
// stored as a `static`, and it's not valid for a static to reference the
// address of another thread_local static. For this reason we kinda wonkily
// work around this by generating a shim function which will give us the
// address of the inner TLS key at runtime.
//
// This is trivially devirtualizable by LLVM because we never store anything
// to this field and rustc can declare the `static` as constant as well.
#[doc(hidden)]
pub inner: fn() -> &'static __impl::KeyInner<UnsafeCell<Option<T>>>,
// initialization routine to invoke to create a value
#[doc(hidden)]
pub init: fn() -> T,
}
/// Declare a new thread local storage key of type `std::thread_local::Key`.
#[macro_export]
#[stable(feature = "rust1", since = "1.0.0")]
macro_rules! thread_local {
(static $name:ident: $t:ty = $init:expr) => (
static $name: ::std::thread_local::Key<$t> = {
use std::cell::UnsafeCell as __UnsafeCell;
use std::thread_local::__impl::KeyInner as __KeyInner;
use std::option::Option as __Option;
use std::option::Option::None as __None;
__thread_local_inner!(static __KEY: __UnsafeCell<__Option<$t>> = {
__UnsafeCell { value: __None }
});
fn __init() -> $t { $init }
fn __getit() -> &'static __KeyInner<__UnsafeCell<__Option<$t>>> {
&__KEY
}
::std::thread_local::Key { inner: __getit, init: __init }
};
);
(pub static $name:ident: $t:ty = $init:expr) => (
pub static $name: ::std::thread_local::Key<$t> = {
use std::cell::UnsafeCell as __UnsafeCell;
use std::thread_local::__impl::KeyInner as __KeyInner;
use std::option::Option as __Option;
use std::option::Option::None as __None;
__thread_local_inner!(static __KEY: __UnsafeCell<__Option<$t>> = {
__UnsafeCell { value: __None }
});
fn __init() -> $t { $init }
fn __getit() -> &'static __KeyInner<__UnsafeCell<__Option<$t>>> {
&__KEY
}
::std::thread_local::Key { inner: __getit, init: __init }
};
);
}
// Macro pain #4586:
//
// When cross compiling, rustc will load plugins and macros from the *host*
// platform before search for macros from the target platform. This is primarily
// done to detect, for example, plugins. Ideally the macro below would be
// defined once per module below, but unfortunately this means we have the
// following situation:
//
// 1. We compile libstd for x86_64-unknown-linux-gnu, this thread_local!() macro
// will inject #[thread_local] statics.
// 2. We then try to compile a program for arm-linux-androideabi
// 3. The compiler has a host of linux and a target of android, so it loads
// macros from the *linux* libstd.
// 4. The macro generates a #[thread_local] field, but the android libstd does
// not use #[thread_local]
// 5. Compile error about structs with wrong fields.
//
// To get around this, we're forced to inject the #[cfg] logic into the macro
// itself. Woohoo.
#[macro_export]
#[doc(hidden)]
macro_rules! __thread_local_inner {
(static $name:ident: $t:ty = $init:expr) => (
#[cfg_attr(all(any(target_os = "macos", target_os = "linux"),
not(target_arch = "aarch64")),
thread_local)]
static $name: ::std::thread_local::__impl::KeyInner<$t> =
__thread_local_inner!($init, $t);
);
(pub static $name:ident: $t:ty = $init:expr) => (
#[cfg_attr(all(any(target_os = "macos", target_os = "linux"),
not(target_arch = "aarch64")),
thread_local)]
pub static $name: ::std::thread_local::__impl::KeyInner<$t> =
__thread_local_inner!($init, $t);
);
($init:expr, $t:ty) => ({
#[cfg(all(any(target_os = "macos", target_os = "linux"), not(target_arch = "aarch64")))]
const _INIT: ::std::thread_local::__impl::KeyInner<$t> = {
::std::thread_local::__impl::KeyInner {
inner: ::std::cell::UnsafeCell { value: $init },
dtor_registered: ::std::cell::UnsafeCell { value: false },
dtor_running: ::std::cell::UnsafeCell { value: false },
}
};
#[cfg(any(not(any(target_os = "macos", target_os = "linux")), target_arch = "aarch64"))]
const _INIT: ::std::thread_local::__impl::KeyInner<$t> = {
unsafe extern fn __destroy(ptr: *mut u8) {
::std::thread_local::__impl::destroy_value::<$t>(ptr);
}
::std::thread_local::__impl::KeyInner {
inner: ::std::cell::UnsafeCell { value: $init },
os: ::std::thread_local::__impl::OsStaticKey {
inner: ::std::thread_local::__impl::OS_INIT_INNER,
dtor: ::std::option::Option::Some(__destroy as unsafe extern fn(*mut u8)),
},
}
};
_INIT
});
}
/// Indicator of the state of a thread local storage key.
#[unstable(feature = "std_misc",
reason = "state querying was recently added")]
#[derive(Eq, PartialEq, Copy)]
pub enum State {
/// All keys are in this state whenever a thread starts. Keys will
/// transition to the `Valid` state once the first call to `with` happens
/// and the initialization expression succeeds.
///
/// Keys in the `Uninitialized` state will yield a reference to the closure
/// passed to `with` so long as the initialization routine does not panic.
Uninitialized,
/// Once a key has been accessed successfully, it will enter the `Valid`
/// state. Keys in the `Valid` state will remain so until the thread exits,
/// at which point the destructor will be run and the key will enter the
/// `Destroyed` state.
///
/// Keys in the `Valid` state will be guaranteed to yield a reference to the
/// closure passed to `with`.
Valid,
/// When a thread exits, the destructors for keys will be run (if
/// necessary). While a destructor is running, and possibly after a
/// destructor has run, a key is in the `Destroyed` state.
///
/// Keys in the `Destroyed` states will trigger a panic when accessed via
/// `with`.
Destroyed,
}
impl<T: 'static> Key<T> {
/// Acquire a reference to the value in this TLS key.
///
/// This will lazily initialize the value if this thread has not referenced
/// this key yet.
///
/// # Panics
///
/// This function will `panic!()` if the key currently has its
/// destructor running, and it **may** panic if the destructor has
/// previously been run for this thread.
#[stable(feature = "rust1", since = "1.0.0")]
pub fn with<F, R>(&'static self, f: F) -> R
where F: FnOnce(&T) -> R {
let slot = (self.inner)();
unsafe {
let slot = slot.get().expect("cannot access a TLS value during or \
after it is destroyed");
f(match *slot.get() {
Some(ref inner) => inner,
None => self.init(slot),
})
}
}
unsafe fn init(&self, slot: &UnsafeCell<Option<T>>) -> &T {
// Execute the initialization up front, *then* move it into our slot,
// just in case initialization fails.
let value = (self.init)();
let ptr = slot.get();
*ptr = Some(value);
(*ptr).as_ref().unwrap()
}
/// Query the current state of this key.
///
/// A key is initially in the `Uninitialized` state whenever a thread
/// starts. It will remain in this state up until the first call to `with`
/// within a thread has run the initialization expression successfully.
///
/// Once the initialization expression succeeds, the key transitions to the
/// `Valid` state which will guarantee that future calls to `with` will
/// succeed within the thread.
///
/// When a thread exits, each key will be destroyed in turn, and as keys are
/// destroyed they will enter the `Destroyed` state just before the
/// destructor starts to run. Keys may remain in the `Destroyed` state after
/// destruction has completed. Keys without destructors (e.g. with types
/// that are `Copy`), may never enter the `Destroyed` state.
///
/// Keys in the `Uninitialized` can be accessed so long as the
/// initialization does not panic. Keys in the `Valid` state are guaranteed
/// to be able to be accessed. Keys in the `Destroyed` state will panic on
/// any call to `with`.
#[unstable(feature = "std_misc",
reason = "state querying was recently added")]
pub fn state(&'static self) -> State {
unsafe {
match (self.inner)().get() {
Some(cell) => {
match *cell.get() {
Some(..) => State::Valid,
None => State::Uninitialized,
}
}
None => State::Destroyed,
}
}
}
/// Deprecated
#[unstable(feature = "std_misc")]
#[deprecated(since = "1.0.0",
reason = "function renamed to state() and returns more info")]
pub fn destroyed(&'static self) -> bool { self.state() == State::Destroyed }
}
#[cfg(all(any(target_os = "macos", target_os = "linux"), not(target_arch = "aarch64")))]
mod imp {
use prelude::v1::*;
use cell::UnsafeCell;
use intrinsics;
use ptr;
#[doc(hidden)]
#[stable(since = "1.0.0", feature = "rust1")]
pub struct Key<T> {
// Place the inner bits in an `UnsafeCell` to currently get around the
// "only Sync statics" restriction. This allows any type to be placed in
// the cell.
//
// Note that all access requires `T: 'static` so it can't be a type with
// any borrowed pointers still.
#[stable(since = "1.0.0", feature = "rust1")]
pub inner: UnsafeCell<T>,
// Metadata to keep track of the state of the destructor. Remember that
// these variables are thread-local, not global.
#[stable(since = "1.0.0", feature = "rust1")]
pub dtor_registered: UnsafeCell<bool>, // should be Cell
#[stable(since = "1.0.0", feature = "rust1")]
pub dtor_running: UnsafeCell<bool>, // should be Cell
}
unsafe impl<T> ::marker::Sync for Key<T> { }
#[doc(hidden)]
impl<T> Key<T> {
pub unsafe fn get(&'static self) -> Option<&'static T> {
if intrinsics::needs_drop::<T>() && *self.dtor_running.get() {
return None
}
self.register_dtor();
Some(&*self.inner.get())
}
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.get() = true;
}
}
// Since what appears to be glibc 2.18 this symbol has been shipped which
// GCC and clang both use to invoke destructors in thread_local globals, so
// let's do the same!
//
// Note, however, that we run on lots older linuxes, as well as cross
// compiling from a newer linux to an older linux, so we also have a
// fallback implementation to use as well.
//
// Due to rust-lang/rust#18804, make sure this is not generic!
#[cfg(target_os = "linux")]
unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
use mem;
use libc;
use sys_common::thread_local as os;
extern {
static __dso_handle: *mut u8;
#[linkage = "extern_weak"]
static __cxa_thread_atexit_impl: *const ();
}
if !__cxa_thread_atexit_impl.is_null() {
type F = unsafe extern fn(dtor: unsafe extern fn(*mut u8),
arg: *mut u8,
dso_handle: *mut u8) -> libc::c_int;
mem::transmute::<*const (), F>(__cxa_thread_atexit_impl)
(dtor, t, __dso_handle);
return
}
// 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: os::StaticKey = os::StaticKey {
inner: os::INIT_INNER,
dtor: Some(run_dtors as unsafe extern "C" fn(*mut u8)),
};
type List = Vec<(*mut u8, unsafe extern fn(*mut u8))>;
if DTORS.get().is_null() {
let v: Box<List> = box Vec::new();
DTORS.set(mem::transmute(v));
}
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> = mem::transmute(ptr);
for &(ptr, dtor) in &*list {
dtor(ptr);
}
ptr = DTORS.get();
DTORS.set(ptr::null_mut());
}
}
}
// OSX's analog of the above linux function is this _tlv_atexit function.
// The disassembly of thread_local globals in C++ (at least produced by
// clang) will have this show up in the output.
#[cfg(target_os = "macos")]
unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
extern {
fn _tlv_atexit(dtor: unsafe extern fn(*mut u8),
arg: *mut u8);
}
_tlv_atexit(dtor, t);
}
#[doc(hidden)]
#[stable(feature = "rust1", since = "1.0.0")]
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.get() = true;
ptr::read((*ptr).inner.get());
}
}
#[cfg(any(not(any(target_os = "macos", target_os = "linux")), target_arch = "aarch64"))]
mod imp {
use prelude::v1::*;
use cell::UnsafeCell;
use mem;
use ptr;
use sys_common::thread_local::StaticKey as OsStaticKey;
#[doc(hidden)]
#[stable(since = "1.0.0", feature = "rust1")]
pub struct Key<T> {
// Statically allocated initialization expression, using an `UnsafeCell`
// for the same reasons as above.
#[stable(since = "1.0.0", feature = "rust1")]
pub inner: UnsafeCell<T>,
// OS-TLS key that we'll use to key off.
#[stable(since = "1.0.0", feature = "rust1")]
pub os: OsStaticKey,
}
unsafe impl<T> ::marker::Sync for Key<T> { }
struct Value<T: 'static> {
key: &'static Key<T>,
value: T,
}
#[doc(hidden)]
impl<T> Key<T> {
pub unsafe fn get(&'static self) -> Option<&'static T> {
self.ptr().map(|p| &*p)
}
unsafe fn ptr(&'static self) -> Option<*mut T> {
let ptr = self.os.get() as *mut Value<T>;
if !ptr.is_null() {
if ptr as uint == 1 {
return None
}
return Some(&mut (*ptr).value as *mut T);
}
// If the lookup returned null, we haven't initialized our own local
// copy, so do that now.
//
// Also note that this transmute_copy should be ok because the value
// `inner` is already validated to be a valid `static` value, so we
// should be able to freely copy the bits.
let ptr: Box<Value<T>> = box Value {
key: self,
value: mem::transmute_copy(&self.inner),
};
let ptr: *mut Value<T> = mem::transmute(ptr);
self.os.set(ptr as *mut u8);
Some(&mut (*ptr).value as *mut T)
}
}
#[doc(hidden)]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe extern fn destroy_value<T: 'static>(ptr: *mut u8) {
// The OS TLS ensures that this key contains a NULL value when this
// destructor starts to run. We set it back to a sentinel value of 1 to
// ensure that any future calls to `get` for this thread will return
// `None`.
//
// Note that to prevent an infinite loop we reset it back to null right
// before we return from the destructor ourselves.
let ptr: Box<Value<T>> = mem::transmute(ptr);
let key = ptr.key;
key.os.set(1 as *mut u8);
drop(ptr);
key.os.set(ptr::null_mut());
}
}
#[cfg(test)]
mod tests {
use prelude::v1::*;
use sync::mpsc::{channel, Sender};
use cell::UnsafeCell;
use super::State;
use thread;
struct Foo(Sender<()>);
impl Drop for Foo {
fn drop(&mut self) {
let Foo(ref s) = *self;
s.send(()).unwrap();
}
}
#[test]
fn smoke_no_dtor() {
thread_local!(static FOO: UnsafeCell<int> = UnsafeCell { value: 1 });
FOO.with(|f| unsafe {
assert_eq!(*f.get(), 1);
*f.get() = 2;
});
let (tx, rx) = channel();
let _t = thread::spawn(move|| {
FOO.with(|f| unsafe {
assert_eq!(*f.get(), 1);
});
tx.send(()).unwrap();
});
rx.recv().unwrap();
FOO.with(|f| unsafe {
assert_eq!(*f.get(), 2);
});
}
#[test]
fn states() {
struct Foo;
impl Drop for Foo {
fn drop(&mut self) {
assert!(FOO.state() == State::Destroyed);
}
}
fn foo() -> Foo {
assert!(FOO.state() == State::Uninitialized);
Foo
}
thread_local!(static FOO: Foo = foo());
thread::spawn(|| {
assert!(FOO.state() == State::Uninitialized);
FOO.with(|_| {
assert!(FOO.state() == State::Valid);
});
assert!(FOO.state() == State::Valid);
}).join().ok().unwrap();
}
#[test]
fn smoke_dtor() {
thread_local!(static FOO: UnsafeCell<Option<Foo>> = UnsafeCell {
value: None
});
let (tx, rx) = channel();
let _t = thread::spawn(move|| unsafe {
let mut tx = Some(tx);
FOO.with(|f| {
*f.get() = Some(Foo(tx.take().unwrap()));
});
});
rx.recv().unwrap();
}
#[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.state() == State::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.state() != State::Destroyed);
assert_eq!(HITS, 2);
K1.with(|s| *s.get() = Some(S1));
}
}
}
thread::spawn(move|| {
drop(S1);
}).join().ok().unwrap();
}
#[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.state() == State::Destroyed);
}
}
thread::spawn(move|| unsafe {
K1.with(|s| *s.get() = Some(S1));
}).join().ok().unwrap();
}
#[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.state() != State::Destroyed {
K2.with(|s| *s.get() = Some(Foo(tx.clone())));
}
}
}
}
let (tx, rx) = channel();
let _t = thread::spawn(move|| unsafe {
let mut tx = Some(tx);
K1.with(|s| *s.get() = Some(S1(tx.take().unwrap())));
});
rx.recv().unwrap();
}
}
#[cfg(test)]
mod dynamic_tests {
use prelude::v1::*;
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);
});
}
}