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Change TLS to almost be able to contain owned types

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This commit is contained in:
Alex Crichton
2013-07-09 14:52:01 -07:00
parent 692a22e69d
commit 5c3a2e7eeb
4 changed files with 144 additions and 86 deletions
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2
src/libstd/condition.rs
View File

@@ -26,7 +26,7 @@ pub struct Handler<T, U> {
pub struct Condition<'self, T, U> {
name: &'static str,
key: local_data::LocalDataKey<'self, Handler<T, U>>
key: local_data::LocalDataKey<'self, @Handler<T, U>>
}
impl<'self, T, U> Condition<'self, T, U> {

18
src/libstd/local_data.rs
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@@ -46,33 +46,27 @@ use task::local_data_priv::{local_get, local_pop, local_set, Handle};
*
* These two cases aside, the interface is safe.
*/
pub type LocalDataKey<'self,T> = &'self fn:Copy(v: @T);
pub type LocalDataKey<'self,T> = &'self fn:Copy(v: T);
/**
* Remove a task-local data value from the table, returning the
* reference that was originally created to insert it.
*/
pub unsafe fn local_data_pop<T: 'static>(
key: LocalDataKey<T>) -> Option<@T> {
pub unsafe fn local_data_pop<T: 'static>(key: LocalDataKey<T>) -> Option<T> {
local_pop(Handle::new(), key)
}
/**
* Retrieve a task-local data value. It will also be kept alive in the
* table until explicitly removed.
*/
pub unsafe fn local_data_get<T: 'static>(
key: LocalDataKey<T>) -> Option<@T> {
local_get(Handle::new(), key)
pub unsafe fn local_data_get<T: 'static>(key: LocalDataKey<@T>) -> Option<@T> {
local_get(Handle::new(), key, |loc| loc.map(|&x| *x))
}
/**
* Store a value in task-local data. If this key already has a value,
* that value is overwritten (and its destructor is run).
*/
pub unsafe fn local_data_set<T: 'static>(
key: LocalDataKey<T>, data: @T) {
pub unsafe fn local_data_set<T: 'static>(key: LocalDataKey<@T>, data: @T) {
local_set(Handle::new(), key, data)
}
/**
@@ -80,7 +74,7 @@ pub unsafe fn local_data_set<T: 'static>(
* data is removed (and its reference dropped).
*/
pub unsafe fn local_data_modify<T: 'static>(
key: LocalDataKey<T>,
key: LocalDataKey<@T>,
modify_fn: &fn(Option<@T>) -> Option<@T>) {
let cur = local_data_pop(key);

178
src/libstd/task/local_data_priv.rs
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@@ -13,9 +13,13 @@
use cast;
use libc;
use local_data::LocalDataKey;
use managed::raw::BoxRepr;
use prelude::*;
use ptr;
use sys;
use task::rt;
use unstable::intrinsics;
use util;
use super::rt::rust_task;
use rt::task::{Task, LocalStorage};
@@ -47,15 +51,24 @@ trait LocalData {}
impl<T: 'static> LocalData for T {}
// The task-local-map actuall stores all TLS information. Right now it's a list
// of key-value pairs. Each value is an actual Rust type so that when the map is
// destroyed all of the contents are destroyed. Each of the keys are actually
// addresses which don't need to be destroyed.
// of triples of (key, value, loans). The key is a code pointer (right now at
// least), the value is a trait so destruction can work, and the loans value
// is a count of the number of times the value is currently on loan via
// `local_data_get`.
//
// TLS is designed to be able to store owned data, so `local_data_get` must
// return a borrowed pointer to this data. In order to have a proper lifetime, a
// borrowed pointer is insted yielded to a closure specified to the `get`
// function. As a result, it would be unsound to perform `local_data_set` on the
// same key inside of a `local_data_get`, so we ensure at runtime that this does
// not happen.
//
// n.b. Has to be a pointer at outermost layer; the foreign call returns void *.
//
// n.b. If TLS is used heavily in future, this could be made more efficient with
// a proper map.
type TaskLocalMap = ~[Option<(*libc::c_void, @LocalData)>];
type TaskLocalMap = ~[Option<(*libc::c_void, TLSValue, uint)>];
type TLSValue = @LocalData;
fn cleanup_task_local_map(map_ptr: *libc::c_void) {
unsafe {
@@ -123,35 +136,65 @@ unsafe fn key_to_key_value<T: 'static>(key: LocalDataKey<T>) -> *libc::c_void {
return pair.code as *libc::c_void;
}
// If returning Some(..), returns with @T with the map's reference. Careful!
unsafe fn local_data_lookup<T: 'static>(map: &TaskLocalMap,
key: LocalDataKey<T>)
-> Option<(uint, @T)>
{
use managed::raw::BoxRepr;
unsafe fn transmute_back<'a, T>(data: &'a TLSValue) -> (*BoxRepr, &'a T) {
// Currently, a TLSValue is an '@Trait' instance which means that its actual
// representation is a pair of (vtable, box). Also, because of issue #7673
// the box actually points to another box which has the data. Hence, to get
// a pointer to the actual value that we're interested in, we decode the
// trait pointer and pass through one layer of boxes to get to the actual
// data we're interested in.
//
// The reference count of the containing @Trait box is already taken care of
// because the TLSValue is owned by the containing TLS map which means that
// the reference count is at least one. Extra protections are then added at
// runtime to ensure that once a loan on a value in TLS has been given out,
// the value isn't modified by another user.
let (_vt, box) = *cast::transmute::<&TLSValue, &(uint, *BoxRepr)>(data);
return (box, cast::transmute(&(*box).data));
}
pub unsafe fn local_pop<T: 'static>(handle: Handle,
key: LocalDataKey<T>) -> Option<T> {
// If you've never seen horrendously unsafe code written in rust before,
// just feel free to look a bit farther...
let map = get_local_map(handle);
let key_value = key_to_key_value(key);
for map.iter().enumerate().advance |(i, entry)| {
for map.mut_iter().advance |entry| {
match *entry {
Some((k, ref data)) if k == key_value => {
// We now have the correct 'data' as type @LocalData which we
// need to somehow transmute this back to @T. This was
// originally stored into the map as:
//
// let data = @T;
// let element = @data as @LocalData;
// insert(key, element);
//
// This means that the element stored is a 2-word pair (because
// it's a trait). The second element is the vtable (we don't
// need it), and the first element is actually '@@T'. Not only
// is this @@T, but it's a pointer to the base of the @@T (box
// and all), so we have to traverse this to find the actual
// pointer that we want.
let (_vtable, box) =
*cast::transmute::<&@LocalData, &(uint, *BoxRepr)>(data);
let ptr: &@T = cast::transmute(&(*box).data);
return Some((i, *ptr));
Some((k, _, loans)) if k == key_value => {
if loans != 0 {
fail!("TLS value has been loaned via get already");
}
// Move the data out of the `entry` slot via util::replace. This
// is guaranteed to succeed because we already matched on `Some`
// above.
let data = match util::replace(entry, None) {
Some((_, data, _)) => data,
None => libc::abort(),
};
// First, via some various cheats/hacks, we extract the value
// contained within the TLS box. This leaves a big chunk of
// memory which needs to be deallocated now.
let (chunk, inside) = transmute_back(&data);
let inside = cast::transmute_mut(inside);
let ret = ptr::read_ptr(inside);
// Forget the trait box because we're about to manually
// deallocate the other box. And for my next trick (kids don't
// try this at home), transmute the chunk of @ memory from the
// @-trait box to a pointer to a zero-sized '@' block which will
// then cause it to get properly deallocated, but it won't touch
// any of the uninitialized memory beyond the end.
cast::forget(data);
let chunk: *mut BoxRepr = cast::transmute(chunk);
(*chunk).header.type_desc =
cast::transmute(intrinsics::get_tydesc::<()>());
let _: @() = cast::transmute(chunk);
return Some(ret);
}
_ => {}
}
@@ -159,28 +202,32 @@ unsafe fn local_data_lookup<T: 'static>(map: &TaskLocalMap,
return None;
}
pub unsafe fn local_pop<T: 'static>(handle: Handle,
key: LocalDataKey<T>) -> Option<@T> {
let map = get_local_map(handle);
match local_data_lookup(map, key) {
Some((index, data)) => {
map[index] = None;
Some(data)
}
None => None
}
}
pub unsafe fn local_get<T: 'static>(handle: Handle,
key: LocalDataKey<T>) -> Option<@T> {
match local_data_lookup(get_local_map(handle), key) {
Some((_, data)) => Some(data),
None => None
}
}
pub unsafe fn local_set<T: 'static>(handle: Handle,
pub unsafe fn local_get<T: 'static, U>(handle: Handle,
key: LocalDataKey<T>,
f: &fn(Option<&T>) -> U) -> U {
// This does in theory take multiple mutable loans on the tls map, but the
// references returned are never removed because the map is only increasing
// in size (it never shrinks).
let map = get_local_map(handle);
let key_value = key_to_key_value(key);
for map.mut_iter().advance |entry| {
match *entry {
Some((k, ref data, ref mut loans)) if k == key_value => {
*loans = *loans + 1;
let (_, val) = transmute_back(data);
let ret = f(Some(val));
*loans = *loans - 1;
return ret;
}
_ => {}
}
}
return f(None);
}
// FIXME(#7673): This shouldn't require '@', it should use '~'
pub unsafe fn local_set<T: 'static>(handle: Handle,
key: LocalDataKey<@T>,
data: @T) {
let map = get_local_map(handle);
let keyval = key_to_key_value(key);
@@ -191,16 +238,31 @@ pub unsafe fn local_set<T: 'static>(handle: Handle,
// everything to a trait (LocalData) which is then stored inside the map.
// Upon destruction of the map, all the objects will be destroyed and the
// traits have enough information about them to destroy themselves.
let entry = Some((keyval, @data as @LocalData));
let data = @data as @LocalData;
match local_data_lookup(map, key) {
Some((index, _)) => { map[index] = entry; }
// First, try to insert it if we already have it.
for map.mut_iter().advance |entry| {
match *entry {
Some((key, ref mut value, loans)) if key == keyval => {
if loans != 0 {
fail!("TLS value has been loaned via get already");
}
util::replace(value, data);
return;
}
_ => {}
}
}
// Next, search for an open spot
for map.mut_iter().advance |entry| {
match *entry {
Some(*) => {}
None => {
// Find an empty slot. If not, grow the vector.
match map.iter().position(|x| x.is_none()) {
Some(empty_index) => { map[empty_index] = entry; }
None => { map.push(entry); }
*entry = Some((keyval, data, 0));
return;
}
}
}
// Finally push it on the end of the list
map.push(Some((keyval, data, 0)));
}

6
src/libstd/task/spawn.rs
View File

@@ -477,7 +477,8 @@ fn gen_child_taskgroup(linked: bool, supervised: bool)
* Step 1. Get spawner's taskgroup info.
*##################################################################*/
let spawner_group: @@mut TCB =
match local_get(OldHandle(spawner), taskgroup_key!()) {
do local_get(OldHandle(spawner), taskgroup_key!()) |group| {
match group {
None => {
// Main task, doing first spawn ever. Lazily initialise
// here.
@@ -496,7 +497,8 @@ fn gen_child_taskgroup(linked: bool, supervised: bool)
local_set(OldHandle(spawner), taskgroup_key!(), group);
group
}
Some(group) => group
Some(&group) => group
}
};
let spawner_group: &mut TCB = *spawner_group;