1 // Copyright 2012-2013 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.
13 Task local data management
15 Allows storing arbitrary types inside task-local-storage (TLS), to be accessed
16 anywhere within a task, keyed by a global pointer parameterized over the type of
17 the TLS slot. Useful for dynamic variables, singletons, and interfacing with
18 foreign code with bad callback interfaces.
20 To declare a new key for storing local data of a particular type, use the
21 `local_data_key!` macro. This macro will expand to a `static` item appropriately
22 named and annotated. This name is then passed to the functions in this module to
23 modify/read the slot specified by the key.
28 local_data_key!(key_int: int)
29 local_data_key!(key_vector: ~[int])
31 local_data::set(key_int, 3);
32 local_data::get(key_int, |opt| assert_eq!(opt.map(|x| *x), Some(3)));
34 local_data::set(key_vector, ~[4]);
35 local_data::get(key_vector, |opt| assert_eq!(*opt.unwrap(), ~[4]));
40 // Casting 'Arcane Sight' reveals an overwhelming aura of Transmutation
45 use rt::task::{Task, LocalStorage};
49 * Indexes a task-local data slot. This pointer is used for comparison to
50 * differentiate keys from one another. The actual type `T` is not used anywhere
51 * as a member of this type, except that it is parameterized with it to define
52 * the type of each key's value.
54 * The value of each Key is of the singleton enum KeyValue. These also have the
55 * same name as `Key` and their purpose is to take up space in the programs data
56 * sections to ensure that each value of the `Key` type points to a unique
59 pub type Key<T> = &'static KeyValue<T>;
62 pub enum KeyValue<T> { Key }
66 impl<T: 'static> LocalData for T {}
68 // The task-local-map stores all TLS information for the currently running task.
69 // It is stored as an owned pointer into the runtime, and it's only allocated
70 // when TLS is used for the first time. This map must be very carefully
71 // constructed because it has many mutable loans unsoundly handed out on it to
72 // the various invocations of TLS requests.
74 // One of the most important operations is loaning a value via `get` to a
75 // caller. In doing so, the slot that the TLS entry is occupying cannot be
76 // invalidated because upon returning its loan state must be updated. Currently
77 // the TLS map is a vector, but this is possibly dangerous because the vector
78 // can be reallocated/moved when new values are pushed onto it.
80 // This problem currently isn't solved in a very elegant way. Inside the `get`
81 // function, it internally "invalidates" all references after the loan is
82 // finished and looks up into the vector again. In theory this will prevent
83 // pointers from being moved under our feet so long as LLVM doesn't go too crazy
84 // with the optimizations.
86 // n.b. If TLS is used heavily in future, this could be made more efficient with
89 pub type Map = ~[Option<(*u8, TLSValue, LoanState)>];
90 type TLSValue = ~LocalData;
92 // Gets the map from the runtime. Lazily initialises if not done so already.
93 unsafe fn get_local_map() -> &mut Map {
96 let task: *mut Task = Local::unsafe_borrow();
97 match &mut (*task).storage {
98 // If the at_exit function is already set, then we just need to take
99 // a loan out on the TLS map stored inside
100 &LocalStorage(Some(ref mut map_ptr)) => {
103 // If this is the first time we've accessed TLS, perform similar
104 // actions to the oldsched way of doing things.
105 &LocalStorage(ref mut slot) => {
108 Some(ref mut map_ptr) => { return map_ptr }
117 NoLoan, ImmLoan, MutLoan
121 fn describe(&self) -> &'static str {
124 ImmLoan => "immutable",
130 fn key_to_key_value<T: 'static>(key: Key<T>) -> *u8 {
131 unsafe { cast::transmute(key) }
134 /// Removes a task-local value from task-local storage. This will return
135 /// Some(value) if the key was present in TLS, otherwise it will return None.
137 /// A runtime assertion will be triggered it removal of TLS value is attempted
138 /// while the value is still loaned out via `get` or `get_mut`.
139 pub fn pop<T: 'static>(key: Key<T>) -> Option<T> {
140 let map = unsafe { get_local_map() };
141 let key_value = key_to_key_value(key);
143 for entry in map.mut_iter() {
145 Some((k, _, loan)) if k == key_value => {
147 fail!("TLS value cannot be removed because it is currently \
148 borrowed as {}", loan.describe());
150 // Move the data out of the `entry` slot via util::replace.
151 // This is guaranteed to succeed because we already matched
153 let data = match replace(entry, None) {
154 Some((_, data, _)) => data,
158 // Move `data` into transmute to get out the memory that it
159 // owns, we must free it manually later.
160 let (_vtable, alloc): (uint, ~T) = unsafe {
161 cast::transmute(data)
164 // Now that we own `alloc`, we can just move out of it as we
165 // would with any other data.
174 /// Retrieves a value from TLS. The closure provided is yielded `Some` of a
175 /// reference to the value located in TLS if one exists, or `None` if the key
176 /// provided is not present in TLS currently.
178 /// It is considered a runtime error to attempt to get a value which is already
179 /// on loan via the `get_mut` method provided.
180 pub fn get<T: 'static, U>(key: Key<T>, f: |Option<&T>| -> U) -> U {
181 get_with(key, ImmLoan, f)
184 /// Retrieves a mutable value from TLS. The closure provided is yielded `Some`
185 /// of a reference to the mutable value located in TLS if one exists, or `None`
186 /// if the key provided is not present in TLS currently.
188 /// It is considered a runtime error to attempt to get a value which is already
189 /// on loan via this or the `get` methods.
190 pub fn get_mut<T: 'static, U>(key: Key<T>, f: |Option<&mut T>| -> U) -> U {
191 get_with(key, MutLoan, |x| {
194 // We're violating a lot of compiler guarantees with this
195 // invocation of `transmute_mut`, but we're doing runtime checks to
196 // ensure that it's always valid (only one at a time).
198 // there is no need to be upset!
199 Some(x) => { f(Some(unsafe { cast::transmute_mut(x) })) }
204 fn get_with<T:'static,
208 f: |Option<&T>| -> U)
210 // This function must be extremely careful. Because TLS can store owned
211 // values, and we must have some form of `get` function other than `pop`,
212 // this function has to give a `&` reference back to the caller.
214 // One option is to return the reference, but this cannot be sound because
215 // the actual lifetime of the object is not known. The slot in TLS could not
216 // be modified until the object goes out of scope, but the TLS code cannot
217 // know when this happens.
219 // For this reason, the reference is yielded to a specified closure. This
220 // way the TLS code knows exactly what the lifetime of the yielded pointer
221 // is, allowing callers to acquire references to owned data. This is also
222 // sound so long as measures are taken to ensure that while a TLS slot is
223 // loaned out to a caller, it's not modified recursively.
224 let map = unsafe { get_local_map() };
225 let key_value = key_to_key_value(key);
227 let pos = map.iter().position(|entry| {
229 Some((k, _, _)) if k == key_value => true, _ => false
233 None => { return f(None); }
236 let mut return_loan = false;
238 Some((_, ref data, ref mut loan)) => {
239 match (state, *loan) {
244 (ImmLoan, ImmLoan) => {}
246 fail!("TLS slot cannot be borrowed as {} because \
247 it is already borrowed as {}",
248 want.describe(), cur.describe());
251 // data was created with `~T as ~LocalData`, so we extract
252 // pointer part of the trait, (as ~T), and then use
253 // compiler coercions to achieve a '&' pointer.
255 match *cast::transmute::<&TLSValue, &(uint, ~T)>(data){
256 (_vtable, ref alloc) => {
257 let value: &T = *alloc;
258 ret = f(Some(value));
266 // n.b. 'data' and 'loans' are both invalid pointers at the point
267 // 'f' returned because `f` could have appended more TLS items which
268 // in turn relocated the vector. Hence we do another lookup here to
272 Some((_, _, ref mut loan)) => { *loan = NoLoan; }
282 use std::unstable::intrinsics;
283 unsafe { intrinsics::abort() }
286 /// Inserts a value into task local storage. If the key is already present in
287 /// TLS, then the previous value is removed and replaced with the provided data.
289 /// It is considered a runtime error to attempt to set a key which is currently
290 /// on loan via the `get` or `get_mut` methods.
291 pub fn set<T: 'static>(key: Key<T>, data: T) {
292 let map = unsafe { get_local_map() };
293 let keyval = key_to_key_value(key);
295 // When the task-local map is destroyed, all the data needs to be cleaned
296 // up. For this reason we can't do some clever tricks to store '~T' as a
297 // '*c_void' or something like that. To solve the problem, we cast
298 // everything to a trait (LocalData) which is then stored inside the map.
299 // Upon destruction of the map, all the objects will be destroyed and the
300 // traits have enough information about them to destroy themselves.
301 let data = ~data as ~LocalData:;
303 fn insertion_position(map: &mut Map,
304 key: *u8) -> Option<uint> {
305 // First see if the map contains this key already
306 let curspot = map.iter().position(|entry| {
308 Some((ekey, _, loan)) if key == ekey => {
310 fail!("TLS value cannot be overwritten because it is
311 already borrowed as {}", loan.describe())
318 // If it doesn't contain the key, just find a slot that's None
321 None => map.iter().position(|entry| entry.is_none())
325 // The type of the local data map must ascribe to Send, so we do the
326 // transmute here to add the Send bound back on. This doesn't actually
327 // matter because TLS will always own the data (until its moved out) and
328 // we're not actually sending it to other schedulers or anything.
329 let data: ~LocalData = unsafe { cast::transmute(data) };
330 match insertion_position(map, keyval) {
331 Some(i) => { map[i] = Some((keyval, data, NoLoan)); }
332 None => { map.push(Some((keyval, data, NoLoan))); }
336 /// Modifies a task-local value by temporarily removing it from task-local
337 /// storage and then re-inserting if `Some` is returned from the closure.
339 /// This function will have the same runtime errors as generated from `pop` and
340 /// `set` (the key must not currently be on loan
341 pub fn modify<T: 'static>(key: Key<T>, f: |Option<T>| -> Option<T>) {
343 Some(next) => { set(key, next); }
355 fn test_tls_multitask() {
356 static my_key: Key<~str> = &Key;
357 set(my_key, ~"parent data");
359 // TLS shouldn't carry over.
360 assert!(get(my_key, |k| k.map(|k| (*k).clone())).is_none());
361 set(my_key, ~"child data");
362 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() ==
364 // should be cleaned up for us
366 // Must work multiple times
367 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() == ~"parent data");
368 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() == ~"parent data");
369 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() == ~"parent data");
373 fn test_tls_overwrite() {
374 static my_key: Key<~str> = &Key;
375 set(my_key, ~"first data");
376 set(my_key, ~"next data"); // Shouldn't leak.
377 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() == ~"next data");
382 static my_key: Key<~str> = &Key;
383 set(my_key, ~"weasel");
384 assert!(pop(my_key).unwrap() == ~"weasel");
385 // Pop must remove the data from the map.
386 assert!(pop(my_key).is_none());
390 fn test_tls_modify() {
391 static my_key: Key<~str> = &Key;
392 modify(my_key, |data| {
394 Some(ref val) => fail!("unwelcome value: {}", *val),
395 None => Some(~"first data")
398 modify(my_key, |data| {
400 Some(~"first data") => Some(~"next data"),
401 Some(ref val) => fail!("wrong value: {}", *val),
402 None => fail!("missing value")
405 assert!(pop(my_key).unwrap() == ~"next data");
409 fn test_tls_crust_automorestack_memorial_bug() {
410 // This might result in a stack-canary clobber if the runtime fails to
411 // set sp_limit to 0 when calling the cleanup extern - it might
412 // automatically jump over to the rust stack, which causes next_c_sp
413 // to get recorded as something within a rust stack segment. Then a
414 // subsequent upcall (esp. for logging, think vsnprintf) would run on
415 // a stack smaller than 1 MB.
416 static my_key: Key<~str> = &Key;
423 fn test_tls_multiple_types() {
424 static str_key: Key<~str> = &Key;
425 static box_key: Key<@()> = &Key;
426 static int_key: Key<int> = &Key;
428 set(str_key, ~"string data");
436 fn test_tls_overwrite_multiple_types() {
437 static str_key: Key<~str> = &Key;
438 static box_key: Key<@()> = &Key;
439 static int_key: Key<int> = &Key;
441 set(str_key, ~"string data");
442 set(str_key, ~"string data 2");
446 // This could cause a segfault if overwriting-destruction is done
447 // with the crazy polymorphic transmute rather than the provided
455 fn test_tls_cleanup_on_failure() {
456 static str_key: Key<~str> = &Key;
457 static box_key: Key<@()> = &Key;
458 static int_key: Key<int> = &Key;
459 set(str_key, ~"parent data");
463 set(str_key, ~"string data");
468 // Not quite nondeterministic.
474 fn test_static_pointer() {
475 static key: Key<&'static int> = &Key;
476 static VALUE: int = 0;
477 let v: &'static int = &VALUE;
483 static key: Key<~int> = &Key;
489 assert_eq!(**v.unwrap(), 1);
491 assert_eq!(**v.unwrap(), 1);
493 assert_eq!(**v.unwrap(), 1);
497 assert_eq!(**v.unwrap(), 2);
503 static key: Key<int> = &Key;
511 assert_eq!(*v.unwrap(), 2);
516 fn test_same_key_type() {
517 static key1: Key<int> = &Key;
518 static key2: Key<int> = &Key;
519 static key3: Key<int> = &Key;
520 static key4: Key<int> = &Key;
521 static key5: Key<int> = &Key;
528 get(key1, |x| assert_eq!(*x.unwrap(), 1));
529 get(key2, |x| assert_eq!(*x.unwrap(), 2));
530 get(key3, |x| assert_eq!(*x.unwrap(), 3));
531 get(key4, |x| assert_eq!(*x.unwrap(), 4));
532 get(key5, |x| assert_eq!(*x.unwrap(), 5));
537 fn test_nested_get_set1() {
538 static key: Key<int> = &Key;
547 fn test_nested_get_mut2() {
548 static key: Key<int> = &Key;
557 fn test_nested_get_mut3() {
558 static key: Key<int> = &Key;
567 fn test_nested_get_mut4() {
568 static key: Key<int> = &Key;