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, OwnedVector};
52 * Indexes a task-local data slot. This pointer is used for comparison to
53 * differentiate keys from one another. The actual type `T` is not used anywhere
54 * as a member of this type, except that it is parameterized with it to define
55 * the type of each key's value.
57 * The value of each Key is of the singleton enum KeyValue. These also have the
58 * same name as `Key` and their purpose is to take up space in the programs data
59 * sections to ensure that each value of the `Key` type points to a unique
62 pub type Key<T> = &'static KeyValue<T>;
65 pub enum KeyValue<T> { Key }
69 impl<T: 'static> LocalData for T {}
71 // The task-local-map stores all TLS information for the currently running task.
72 // It is stored as an owned pointer into the runtime, and it's only allocated
73 // when TLS is used for the first time. This map must be very carefully
74 // constructed because it has many mutable loans unsoundly handed out on it to
75 // the various invocations of TLS requests.
77 // One of the most important operations is loaning a value via `get` to a
78 // caller. In doing so, the slot that the TLS entry is occupying cannot be
79 // invalidated because upon returning its loan state must be updated. Currently
80 // the TLS map is a vector, but this is possibly dangerous because the vector
81 // can be reallocated/moved when new values are pushed onto it.
83 // This problem currently isn't solved in a very elegant way. Inside the `get`
84 // function, it internally "invalidates" all references after the loan is
85 // finished and looks up into the vector again. In theory this will prevent
86 // pointers from being moved under our feet so long as LLVM doesn't go too crazy
87 // with the optimizations.
89 // n.b. If TLS is used heavily in future, this could be made more efficient with
92 pub type Map = ~[Option<(*u8, TLSValue, LoanState)>];
93 type TLSValue = ~LocalData:Send;
95 // Gets the map from the runtime. Lazily initialises if not done so already.
96 unsafe fn get_local_map() -> &mut Map {
99 let task: *mut Task = Local::unsafe_borrow();
100 match &mut (*task).storage {
101 // If the at_exit function is already set, then we just need to take
102 // a loan out on the TLS map stored inside
103 &LocalStorage(Some(ref mut map_ptr)) => {
106 // If this is the first time we've accessed TLS, perform similar
107 // actions to the oldsched way of doing things.
108 &LocalStorage(ref mut slot) => {
111 Some(ref mut map_ptr) => { return map_ptr }
120 NoLoan, ImmLoan, MutLoan
124 fn describe(&self) -> &'static str {
127 ImmLoan => "immutable",
133 fn key_to_key_value<T: 'static>(key: Key<T>) -> *u8 {
134 unsafe { cast::transmute(key) }
137 /// Removes a task-local value from task-local storage. This will return
138 /// Some(value) if the key was present in TLS, otherwise it will return None.
140 /// A runtime assertion will be triggered it removal of TLS value is attempted
141 /// while the value is still loaned out via `get` or `get_mut`.
142 pub fn pop<T: 'static>(key: Key<T>) -> Option<T> {
143 let map = unsafe { get_local_map() };
144 let key_value = key_to_key_value(key);
146 for entry in map.mut_iter() {
148 Some((k, _, loan)) if k == key_value => {
150 fail!("TLS value cannot be removed because it is currently \
151 borrowed as {}", loan.describe());
153 // Move the data out of the `entry` slot via prelude::replace.
154 // This is guaranteed to succeed because we already matched
156 let data = match replace(entry, None) {
157 Some((_, data, _)) => data,
161 // Move `data` into transmute to get out the memory that it
162 // owns, we must free it manually later.
163 let (_vtable, alloc): (uint, ~T) = unsafe {
164 cast::transmute(data)
167 // Now that we own `alloc`, we can just move out of it as we
168 // would with any other data.
177 /// Retrieves a value from TLS. The closure provided is yielded `Some` of a
178 /// reference to the value located in TLS if one exists, or `None` if the key
179 /// provided is not present in TLS currently.
181 /// It is considered a runtime error to attempt to get a value which is already
182 /// on loan via the `get_mut` method provided.
183 pub fn get<T: 'static, U>(key: Key<T>, f: |Option<&T>| -> U) -> U {
184 get_with(key, ImmLoan, f)
187 /// Retrieves a mutable value from TLS. The closure provided is yielded `Some`
188 /// of a reference to the mutable value located in TLS if one exists, or `None`
189 /// if the key provided is not present in TLS currently.
191 /// It is considered a runtime error to attempt to get a value which is already
192 /// on loan via this or the `get` methods.
193 pub fn get_mut<T: 'static, U>(key: Key<T>, f: |Option<&mut T>| -> U) -> U {
194 get_with(key, MutLoan, |x| {
197 // We're violating a lot of compiler guarantees with this
198 // invocation of `transmute_mut`, but we're doing runtime checks to
199 // ensure that it's always valid (only one at a time).
201 // there is no need to be upset!
202 Some(x) => { f(Some(unsafe { cast::transmute_mut(x) })) }
207 fn get_with<T:'static,
211 f: |Option<&T>| -> U)
213 // This function must be extremely careful. Because TLS can store owned
214 // values, and we must have some form of `get` function other than `pop`,
215 // this function has to give a `&` reference back to the caller.
217 // One option is to return the reference, but this cannot be sound because
218 // the actual lifetime of the object is not known. The slot in TLS could not
219 // be modified until the object goes out of scope, but the TLS code cannot
220 // know when this happens.
222 // For this reason, the reference is yielded to a specified closure. This
223 // way the TLS code knows exactly what the lifetime of the yielded pointer
224 // is, allowing callers to acquire references to owned data. This is also
225 // sound so long as measures are taken to ensure that while a TLS slot is
226 // loaned out to a caller, it's not modified recursively.
227 let map = unsafe { get_local_map() };
228 let key_value = key_to_key_value(key);
230 let pos = map.iter().position(|entry| {
232 Some((k, _, _)) if k == key_value => true, _ => false
236 None => { return f(None); }
239 let mut return_loan = false;
241 Some((_, ref data, ref mut loan)) => {
242 match (state, *loan) {
247 (ImmLoan, ImmLoan) => {}
249 fail!("TLS slot cannot be borrowed as {} because \
250 it is already borrowed as {}",
251 want.describe(), cur.describe());
254 // data was created with `~T as ~LocalData`, so we extract
255 // pointer part of the trait, (as ~T), and then use
256 // compiler coercions to achieve a '&' pointer.
258 match *cast::transmute::<&TLSValue, &(uint, ~T)>(data){
259 (_vtable, ref alloc) => {
260 let value: &T = *alloc;
261 ret = f(Some(value));
269 // n.b. 'data' and 'loans' are both invalid pointers at the point
270 // 'f' returned because `f` could have appended more TLS items which
271 // in turn relocated the vector. Hence we do another lookup here to
275 Some((_, _, ref mut loan)) => { *loan = NoLoan; }
286 unsafe { intrinsics::abort() }
289 /// Inserts a value into task local storage. If the key is already present in
290 /// TLS, then the previous value is removed and replaced with the provided data.
292 /// It is considered a runtime error to attempt to set a key which is currently
293 /// on loan via the `get` or `get_mut` methods.
294 pub fn set<T: 'static>(key: Key<T>, data: T) {
295 let map = unsafe { get_local_map() };
296 let keyval = key_to_key_value(key);
298 // When the task-local map is destroyed, all the data needs to be cleaned
299 // up. For this reason we can't do some clever tricks to store '~T' as a
300 // '*c_void' or something like that. To solve the problem, we cast
301 // everything to a trait (LocalData) which is then stored inside the map.
302 // Upon destruction of the map, all the objects will be destroyed and the
303 // traits have enough information about them to destroy themselves.
304 let data = ~data as ~LocalData:;
306 fn insertion_position(map: &mut Map,
307 key: *u8) -> Option<uint> {
308 // First see if the map contains this key already
309 let curspot = map.iter().position(|entry| {
311 Some((ekey, _, loan)) if key == ekey => {
313 fail!("TLS value cannot be overwritten because it is
314 already borrowed as {}", loan.describe())
321 // If it doesn't contain the key, just find a slot that's None
324 None => map.iter().position(|entry| entry.is_none())
328 // The type of the local data map must ascribe to Send, so we do the
329 // transmute here to add the Send bound back on. This doesn't actually
330 // matter because TLS will always own the data (until its moved out) and
331 // we're not actually sending it to other schedulers or anything.
332 let data: ~LocalData:Send = unsafe { cast::transmute(data) };
333 match insertion_position(map, keyval) {
334 Some(i) => { map[i] = Some((keyval, data, NoLoan)); }
335 None => { map.push(Some((keyval, data, NoLoan))); }
339 /// Modifies a task-local value by temporarily removing it from task-local
340 /// storage and then re-inserting if `Some` is returned from the closure.
342 /// This function will have the same runtime errors as generated from `pop` and
343 /// `set` (the key must not currently be on loan
344 pub fn modify<T: 'static>(key: Key<T>, f: |Option<T>| -> Option<T>) {
346 Some(next) => { set(key, next); }
358 fn test_tls_multitask() {
359 static my_key: Key<~str> = &Key;
360 set(my_key, ~"parent data");
362 // TLS shouldn't carry over.
363 assert!(get(my_key, |k| k.map(|k| (*k).clone())).is_none());
364 set(my_key, ~"child data");
365 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() ==
367 // should be cleaned up for us
369 // Must work multiple times
370 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() == ~"parent data");
371 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() == ~"parent data");
372 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() == ~"parent data");
376 fn test_tls_overwrite() {
377 static my_key: Key<~str> = &Key;
378 set(my_key, ~"first data");
379 set(my_key, ~"next data"); // Shouldn't leak.
380 assert!(get(my_key, |k| k.map(|k| (*k).clone())).unwrap() == ~"next data");
385 static my_key: Key<~str> = &Key;
386 set(my_key, ~"weasel");
387 assert!(pop(my_key).unwrap() == ~"weasel");
388 // Pop must remove the data from the map.
389 assert!(pop(my_key).is_none());
393 fn test_tls_modify() {
394 static my_key: Key<~str> = &Key;
395 modify(my_key, |data| {
397 Some(ref val) => fail!("unwelcome value: {}", *val),
398 None => Some(~"first data")
401 modify(my_key, |data| {
402 match data.as_ref().map(|s| s.as_slice()) {
403 Some("first data") => Some(~"next data"),
404 Some(ref val) => fail!("wrong value: {}", *val),
405 None => fail!("missing value")
408 assert!(pop(my_key).unwrap() == ~"next data");
412 fn test_tls_crust_automorestack_memorial_bug() {
413 // This might result in a stack-canary clobber if the runtime fails to
414 // set sp_limit to 0 when calling the cleanup extern - it might
415 // automatically jump over to the rust stack, which causes next_c_sp
416 // to get recorded as something within a rust stack segment. Then a
417 // subsequent upcall (esp. for logging, think vsnprintf) would run on
418 // a stack smaller than 1 MB.
419 static my_key: Key<~str> = &Key;
426 fn test_tls_multiple_types() {
427 static str_key: Key<~str> = &Key;
428 static box_key: Key<@()> = &Key;
429 static int_key: Key<int> = &Key;
431 set(str_key, ~"string data");
439 fn test_tls_overwrite_multiple_types() {
440 static str_key: Key<~str> = &Key;
441 static box_key: Key<@()> = &Key;
442 static int_key: Key<int> = &Key;
444 set(str_key, ~"string data");
445 set(str_key, ~"string data 2");
449 // This could cause a segfault if overwriting-destruction is done
450 // with the crazy polymorphic transmute rather than the provided
458 fn test_tls_cleanup_on_failure() {
459 static str_key: Key<~str> = &Key;
460 static box_key: Key<@()> = &Key;
461 static int_key: Key<int> = &Key;
462 set(str_key, ~"parent data");
466 set(str_key, ~"string data");
471 // Not quite nondeterministic.
477 fn test_static_pointer() {
478 static key: Key<&'static int> = &Key;
479 static VALUE: int = 0;
480 let v: &'static int = &VALUE;
486 static key: Key<~int> = &Key;
492 assert_eq!(**v.unwrap(), 1);
494 assert_eq!(**v.unwrap(), 1);
496 assert_eq!(**v.unwrap(), 1);
500 assert_eq!(**v.unwrap(), 2);
506 static key: Key<int> = &Key;
514 assert_eq!(*v.unwrap(), 2);
519 fn test_same_key_type() {
520 static key1: Key<int> = &Key;
521 static key2: Key<int> = &Key;
522 static key3: Key<int> = &Key;
523 static key4: Key<int> = &Key;
524 static key5: Key<int> = &Key;
531 get(key1, |x| assert_eq!(*x.unwrap(), 1));
532 get(key2, |x| assert_eq!(*x.unwrap(), 2));
533 get(key3, |x| assert_eq!(*x.unwrap(), 3));
534 get(key4, |x| assert_eq!(*x.unwrap(), 4));
535 get(key5, |x| assert_eq!(*x.unwrap(), 5));
540 fn test_nested_get_set1() {
541 static key: Key<int> = &Key;
550 fn test_nested_get_mut2() {
551 static key: Key<int> = &Key;
560 fn test_nested_get_mut3() {
561 static key: Key<int> = &Key;
570 fn test_nested_get_mut4() {
571 static key: Key<int> = &Key;