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
47 use option::{None, Option, Some};
48 use rt::task::{Task, LocalStorage};
49 use slice::{ImmutableVector, MutableVector};
53 * Indexes a task-local data slot. This pointer is used for comparison to
54 * differentiate keys from one another. The actual type `T` is not used anywhere
55 * as a member of this type, except that it is parameterized with it to define
56 * the type of each key's value.
58 * The value of each Key is of the singleton enum KeyValue. These also have the
59 * same name as `Key` and their purpose is to take up space in the programs data
60 * sections to ensure that each value of the `Key` type points to a unique
63 pub type Key<T> = &'static KeyValue<T>;
66 pub enum KeyValue<T> { Key }
70 impl<T: 'static> LocalData for T {}
72 // The task-local-map stores all TLS information for the currently running task.
73 // It is stored as an owned pointer into the runtime, and it's only allocated
74 // when TLS is used for the first time. This map must be very carefully
75 // constructed because it has many mutable loans unsoundly handed out on it to
76 // the various invocations of TLS requests.
78 // One of the most important operations is loaning a value via `get` to a
79 // caller. In doing so, the slot that the TLS entry is occupying cannot be
80 // invalidated because upon returning its loan state must be updated. Currently
81 // the TLS map is a vector, but this is possibly dangerous because the vector
82 // can be reallocated/moved when new values are pushed onto it.
84 // This problem currently isn't solved in a very elegant way. Inside the `get`
85 // function, it internally "invalidates" all references after the loan is
86 // finished and looks up into the vector again. In theory this will prevent
87 // pointers from being moved under our feet so long as LLVM doesn't go too crazy
88 // with the optimizations.
90 // n.b. If TLS is used heavily in future, this could be made more efficient with
93 pub type Map = Vec<Option<(*u8, TLSValue, LoanState)>>;
94 type TLSValue = ~LocalData:Send;
96 // Gets the map from the runtime. Lazily initialises if not done so already.
97 unsafe fn get_local_map() -> &mut Map {
100 let task: *mut Task = Local::unsafe_borrow();
101 match &mut (*task).storage {
102 // If the at_exit function is already set, then we just need to take
103 // a loan out on the TLS map stored inside
104 &LocalStorage(Some(ref mut map_ptr)) => {
107 // If this is the first time we've accessed TLS, perform similar
108 // actions to the oldsched way of doing things.
109 &LocalStorage(ref mut slot) => {
110 *slot = Some(vec!());
112 Some(ref mut map_ptr) => { return map_ptr }
121 NoLoan, ImmLoan, MutLoan
125 fn describe(&self) -> &'static str {
128 ImmLoan => "immutable",
134 fn key_to_key_value<T: 'static>(key: Key<T>) -> *u8 {
135 unsafe { cast::transmute(key) }
138 /// Removes a task-local value from task-local storage. This will return
139 /// Some(value) if the key was present in TLS, otherwise it will return None.
141 /// A runtime assertion will be triggered it removal of TLS value is attempted
142 /// while the value is still loaned out via `get` or `get_mut`.
143 pub fn pop<T: 'static>(key: Key<T>) -> Option<T> {
144 let map = unsafe { get_local_map() };
145 let key_value = key_to_key_value(key);
147 for entry in map.mut_iter() {
149 Some((k, _, loan)) if k == key_value => {
151 fail!("TLS value cannot be removed because it is currently \
152 borrowed as {}", loan.describe());
154 // Move the data out of the `entry` slot via prelude::replace.
155 // This is guaranteed to succeed because we already matched
157 let data = match replace(entry, None) {
158 Some((_, data, _)) => data,
162 // Move `data` into transmute to get out the memory that it
163 // owns, we must free it manually later.
164 let (_vtable, alloc): (uint, ~T) = unsafe {
165 cast::transmute(data)
168 // Now that we own `alloc`, we can just move out of it as we
169 // would with any other data.
178 /// Retrieves a value from TLS. The closure provided is yielded `Some` of a
179 /// reference to the value located in TLS if one exists, or `None` if the key
180 /// provided is not present in TLS currently.
182 /// It is considered a runtime error to attempt to get a value which is already
183 /// on loan via the `get_mut` method provided.
184 pub fn get<T: 'static, U>(key: Key<T>, f: |Option<&T>| -> U) -> U {
185 get_with(key, ImmLoan, f)
188 /// Retrieves a mutable value from TLS. The closure provided is yielded `Some`
189 /// of a reference to the mutable value located in TLS if one exists, or `None`
190 /// if the key provided is not present in TLS currently.
192 /// It is considered a runtime error to attempt to get a value which is already
193 /// on loan via this or the `get` methods.
194 pub fn get_mut<T: 'static, U>(key: Key<T>, f: |Option<&mut T>| -> U) -> U {
195 get_with(key, MutLoan, |x| {
198 // We're violating a lot of compiler guarantees with this
199 // invocation of `transmute`, but we're doing runtime checks to
200 // ensure that it's always valid (only one at a time).
202 // there is no need to be upset!
203 Some(x) => { f(Some(unsafe { cast::transmute::<&_, &mut _>(x) })) }
208 fn get_with<T:'static,
212 f: |Option<&T>| -> U)
214 // This function must be extremely careful. Because TLS can store owned
215 // values, and we must have some form of `get` function other than `pop`,
216 // this function has to give a `&` reference back to the caller.
218 // One option is to return the reference, but this cannot be sound because
219 // the actual lifetime of the object is not known. The slot in TLS could not
220 // be modified until the object goes out of scope, but the TLS code cannot
221 // know when this happens.
223 // For this reason, the reference is yielded to a specified closure. This
224 // way the TLS code knows exactly what the lifetime of the yielded pointer
225 // is, allowing callers to acquire references to owned data. This is also
226 // sound so long as measures are taken to ensure that while a TLS slot is
227 // loaned out to a caller, it's not modified recursively.
228 let map = unsafe { get_local_map() };
229 let key_value = key_to_key_value(key);
231 let pos = map.iter().position(|entry| {
233 Some((k, _, _)) if k == key_value => true, _ => false
237 None => { return f(None); }
240 let mut return_loan = false;
241 match *map.get_mut(i) {
242 Some((_, ref data, ref mut loan)) => {
243 match (state, *loan) {
248 (ImmLoan, ImmLoan) => {}
250 fail!("TLS slot cannot be borrowed as {} because \
251 it is already borrowed as {}",
252 want.describe(), cur.describe());
255 // data was created with `~T as ~LocalData`, so we extract
256 // pointer part of the trait, (as ~T), and then use
257 // compiler coercions to achieve a '&' pointer.
259 match *cast::transmute::<&TLSValue, &(uint, ~T)>(data){
260 (_vtable, ref alloc) => {
261 let value: &T = *alloc;
262 ret = f(Some(value));
270 // n.b. 'data' and 'loans' are both invalid pointers at the point
271 // 'f' returned because `f` could have appended more TLS items which
272 // in turn relocated the vector. Hence we do another lookup here to
275 match *map.get_mut(i) {
276 Some((_, _, ref mut loan)) => { *loan = NoLoan; }
287 unsafe { intrinsics::abort() }
290 /// Inserts a value into task local storage. If the key is already present in
291 /// TLS, then the previous value is removed and replaced with the provided data.
293 /// It is considered a runtime error to attempt to set a key which is currently
294 /// on loan via the `get` or `get_mut` methods.
295 pub fn set<T: 'static>(key: Key<T>, data: T) {
296 let map = unsafe { get_local_map() };
297 let keyval = key_to_key_value(key);
299 // When the task-local map is destroyed, all the data needs to be cleaned
300 // up. For this reason we can't do some clever tricks to store '~T' as a
301 // '*c_void' or something like that. To solve the problem, we cast
302 // everything to a trait (LocalData) which is then stored inside the map.
303 // Upon destruction of the map, all the objects will be destroyed and the
304 // traits have enough information about them to destroy themselves.
305 let data = box data as ~LocalData:;
307 fn insertion_position(map: &mut Map,
308 key: *u8) -> Option<uint> {
309 // First see if the map contains this key already
310 let curspot = map.iter().position(|entry| {
312 Some((ekey, _, loan)) if key == ekey => {
314 fail!("TLS value cannot be overwritten because it is
315 already borrowed as {}", loan.describe())
322 // If it doesn't contain the key, just find a slot that's None
325 None => map.iter().position(|entry| entry.is_none())
329 // The type of the local data map must ascribe to Send, so we do the
330 // transmute here to add the Send bound back on. This doesn't actually
331 // matter because TLS will always own the data (until its moved out) and
332 // we're not actually sending it to other schedulers or anything.
333 let data: ~LocalData:Send = unsafe { cast::transmute(data) };
334 match insertion_position(map, keyval) {
335 Some(i) => { *map.get_mut(i) = Some((keyval, data, NoLoan)); }
336 None => { map.push(Some((keyval, data, NoLoan))); }
340 /// Modifies a task-local value by temporarily removing it from task-local
341 /// storage and then re-inserting if `Some` is returned from the closure.
343 /// This function will have the same runtime errors as generated from `pop` and
344 /// `set` (the key must not currently be on loan
345 pub fn modify<T: 'static>(key: Key<T>, f: |Option<T>| -> Option<T>) {
347 Some(next) => { set(key, next); }
360 fn test_tls_multitask() {
361 static my_key: Key<~str> = &Key;
362 set(my_key, "parent data".to_owned());
364 // TLS shouldn't carry over.
365 assert!(get(my_key, |k| k.map(|k| (*k).clone())).is_none());
366 set(my_key, "child data".to_owned());
367 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() ==
368 "child data".to_owned());
369 // should be cleaned up for us
371 // Must work multiple times
372 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() == "parent data".to_owned());
373 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() == "parent data".to_owned());
374 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() == "parent data".to_owned());
378 fn test_tls_overwrite() {
379 static my_key: Key<~str> = &Key;
380 set(my_key, "first data".to_owned());
381 set(my_key, "next data".to_owned()); // Shouldn't leak.
382 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() == "next data".to_owned());
387 static my_key: Key<~str> = &Key;
388 set(my_key, "weasel".to_owned());
389 assert!(pop(my_key).unwrap() == "weasel".to_owned());
390 // Pop must remove the data from the map.
391 assert!(pop(my_key).is_none());
395 fn test_tls_modify() {
396 static my_key: Key<~str> = &Key;
397 modify(my_key, |data| {
399 Some(ref val) => fail!("unwelcome value: {}", *val),
400 None => Some("first data".to_owned())
403 modify(my_key, |data| {
404 match data.as_ref().map(|s| s.as_slice()) {
405 Some("first data") => Some("next data".to_owned()),
406 Some(ref val) => fail!("wrong value: {}", *val),
407 None => fail!("missing value")
410 assert!(pop(my_key).unwrap() == "next data".to_owned());
414 fn test_tls_crust_automorestack_memorial_bug() {
415 // This might result in a stack-canary clobber if the runtime fails to
416 // set sp_limit to 0 when calling the cleanup extern - it might
417 // automatically jump over to the rust stack, which causes next_c_sp
418 // to get recorded as something within a rust stack segment. Then a
419 // subsequent upcall (esp. for logging, think vsnprintf) would run on
420 // a stack smaller than 1 MB.
421 static my_key: Key<~str> = &Key;
423 set(my_key, "hax".to_owned());
428 fn test_tls_multiple_types() {
429 static str_key: Key<~str> = &Key;
430 static box_key: Key<@()> = &Key;
431 static int_key: Key<int> = &Key;
433 set(str_key, "string data".to_owned());
441 fn test_tls_overwrite_multiple_types() {
442 static str_key: Key<~str> = &Key;
443 static box_key: Key<@()> = &Key;
444 static int_key: Key<int> = &Key;
446 set(str_key, "string data".to_owned());
447 set(str_key, "string data 2".to_owned());
451 // This could cause a segfault if overwriting-destruction is done
452 // with the crazy polymorphic transmute rather than the provided
460 fn test_tls_cleanup_on_failure() {
461 static str_key: Key<~str> = &Key;
462 static box_key: Key<@()> = &Key;
463 static int_key: Key<int> = &Key;
464 set(str_key, "parent data".to_owned());
468 set(str_key, "string data".to_owned());
473 // Not quite nondeterministic.
479 fn test_static_pointer() {
480 static key: Key<&'static int> = &Key;
481 static VALUE: int = 0;
482 let v: &'static int = &VALUE;
488 static key: Key<~int> = &Key;
494 assert_eq!(**v.unwrap(), 1);
496 assert_eq!(**v.unwrap(), 1);
498 assert_eq!(**v.unwrap(), 1);
502 assert_eq!(**v.unwrap(), 2);
508 static key: Key<int> = &Key;
516 assert_eq!(*v.unwrap(), 2);
521 fn test_same_key_type() {
522 static key1: Key<int> = &Key;
523 static key2: Key<int> = &Key;
524 static key3: Key<int> = &Key;
525 static key4: Key<int> = &Key;
526 static key5: Key<int> = &Key;
533 get(key1, |x| assert_eq!(*x.unwrap(), 1));
534 get(key2, |x| assert_eq!(*x.unwrap(), 2));
535 get(key3, |x| assert_eq!(*x.unwrap(), 3));
536 get(key4, |x| assert_eq!(*x.unwrap(), 4));
537 get(key5, |x| assert_eq!(*x.unwrap(), 5));
542 fn test_nested_get_set1() {
543 static key: Key<int> = &Key;
552 fn test_nested_get_mut2() {
553 static key: Key<int> = &Key;
562 fn test_nested_get_mut3() {
563 static key: Key<int> = &Key;
572 fn test_nested_get_mut4() {
573 static key: Key<int> = &Key;