1 //! Implement thread-local storage.
3 use std::collections::BTreeMap;
4 use std::collections::btree_map::Entry;
8 use rustc_data_structures::fx::FxHashMap;
10 use rustc_target::abi::{Size, HasDataLayout};
13 HelpersEvalContextExt, InterpResult, MPlaceTy, Scalar, StackPopCleanup, Tag, ThreadId,
14 ThreadsEvalContextExt,
17 pub type TlsKey = u128;
19 #[derive(Clone, Debug)]
20 pub struct TlsEntry<'tcx> {
21 /// The data for this key. None is used to represent NULL.
22 /// (We normalize this early to avoid having to do a NULL-ptr-test each time we access the data.)
23 data: BTreeMap<ThreadId, Scalar<Tag>>,
24 dtor: Option<ty::Instance<'tcx>>,
27 #[derive(Clone, Debug)]
28 struct RunningDtorsState {
29 /// The last TlsKey used to retrieve a TLS destructor. `None` means that we
30 /// have not tried to retrieve a TLS destructor yet or that we already tried
32 last_dtor_key: Option<TlsKey>,
36 pub struct TlsData<'tcx> {
37 /// The Key to use for the next thread-local allocation.
40 /// pthreads-style thread-local storage.
41 keys: BTreeMap<TlsKey, TlsEntry<'tcx>>,
43 /// A single per thread destructor of the thread local storage (that's how
44 /// things work on macOS) with a data argument.
45 macos_thread_dtors: BTreeMap<ThreadId, (ty::Instance<'tcx>, Scalar<Tag>)>,
47 /// State for currently running TLS dtors. If this map contains a key for a
48 /// specific thread, it means that we are in the "destruct" phase, during
49 /// which some operations are UB.
50 dtors_running: FxHashMap<ThreadId, RunningDtorsState>,
53 impl<'tcx> Default for TlsData<'tcx> {
54 fn default() -> Self {
56 next_key: 1, // start with 1 as we must not use 0 on Windows
57 keys: Default::default(),
58 macos_thread_dtors: Default::default(),
59 dtors_running: Default::default(),
64 impl<'tcx> TlsData<'tcx> {
65 /// Generate a new TLS key with the given destructor.
66 /// `max_size` determines the integer size the key has to fit in.
67 pub fn create_tls_key(&mut self, dtor: Option<ty::Instance<'tcx>>, max_size: Size) -> InterpResult<'tcx, TlsKey> {
68 let new_key = self.next_key;
70 self.keys.insert(new_key, TlsEntry { data: Default::default(), dtor }).unwrap_none();
71 trace!("New TLS key allocated: {} with dtor {:?}", new_key, dtor);
73 if max_size.bits() < 128 && new_key >= (1u128 << max_size.bits() as u128) {
74 throw_unsup_format!("we ran out of TLS key space");
79 pub fn delete_tls_key(&mut self, key: TlsKey) -> InterpResult<'tcx> {
80 match self.keys.remove(&key) {
82 trace!("TLS key {} removed", key);
85 None => throw_ub_format!("removing a non-existig TLS key: {}", key),
93 cx: &impl HasDataLayout,
94 ) -> InterpResult<'tcx, Scalar<Tag>> {
95 match self.keys.get(&key) {
96 Some(TlsEntry { data, .. }) => {
97 let value = data.get(&thread_id).copied();
98 trace!("TLS key {} for thread {:?} loaded: {:?}", key, thread_id, value);
99 Ok(value.unwrap_or_else(|| Scalar::null_ptr(cx).into()))
101 None => throw_ub_format!("loading from a non-existing TLS key: {}", key),
109 new_data: Option<Scalar<Tag>>
110 ) -> InterpResult<'tcx> {
111 match self.keys.get_mut(&key) {
112 Some(TlsEntry { data, .. }) => {
115 trace!("TLS key {} for thread {:?} stored: {:?}", key, thread_id, scalar);
116 data.insert(thread_id, scalar);
119 trace!("TLS key {} for thread {:?} removed", key, thread_id);
120 data.remove(&thread_id);
125 None => throw_ub_format!("storing to a non-existing TLS key: {}", key),
129 /// Set the thread wide destructor of the thread local storage for the given
130 /// thread. This function is used to implement `_tlv_atexit` shim on MacOS.
132 /// Thread wide dtors are available only on MacOS. There is one destructor
133 /// per thread as can be guessed from the following comment in the
135 /// implementation](https://github.com/opensource-apple/dyld/blob/195030646877261f0c8c7ad8b001f52d6a26f514/src/threadLocalVariables.c#L389):
137 /// // NOTE: this does not need locks because it only operates on current thread data
138 pub fn set_thread_dtor(
141 dtor: ty::Instance<'tcx>,
143 ) -> InterpResult<'tcx> {
144 if self.dtors_running.contains_key(&thread) {
145 // UB, according to libstd docs.
146 throw_ub_format!("setting thread's local storage destructor while destructors are already running");
148 if self.macos_thread_dtors.insert(thread, (dtor, data)).is_some() {
149 throw_unsup_format!("setting more than one thread local storage destructor for the same thread is not supported");
154 /// Returns a dtor, its argument and its index, if one is supposed to run.
155 /// `key` is the last dtors that was run; we return the *next* one after that.
157 /// An optional destructor function may be associated with each key value.
158 /// At thread exit, if a key value has a non-NULL destructor pointer,
159 /// and the thread has a non-NULL value associated with that key,
160 /// the value of the key is set to NULL, and then the function pointed
161 /// to is called with the previously associated value as its sole argument.
162 /// The order of destructor calls is unspecified if more than one destructor
163 /// exists for a thread when it exits.
165 /// If, after all the destructors have been called for all non-NULL values
166 /// with associated destructors, there are still some non-NULL values with
167 /// associated destructors, then the process is repeated.
168 /// If, after at least {PTHREAD_DESTRUCTOR_ITERATIONS} iterations of destructor
169 /// calls for outstanding non-NULL values, there are still some non-NULL values
170 /// with associated destructors, implementations may stop calling destructors,
171 /// or they may continue calling destructors until no non-NULL values with
172 /// associated destructors exist, even though this might result in an infinite loop.
177 ) -> Option<(ty::Instance<'tcx>, Scalar<Tag>, TlsKey)> {
178 use std::collections::Bound::*;
180 let thread_local = &mut self.keys;
181 let start = match key {
182 Some(key) => Excluded(key),
185 for (&key, TlsEntry { data, dtor }) in
186 thread_local.range_mut((start, Unbounded))
188 match data.entry(thread_id) {
189 Entry::Occupied(entry) => {
190 if let Some(dtor) = dtor {
191 // Set TLS data to NULL, and call dtor with old value.
192 let data_scalar = entry.remove();
193 let ret = Some((*dtor, data_scalar, key));
197 Entry::Vacant(_) => {}
203 /// Set that dtors are running for `thread`. It is guaranteed not to change
204 /// the existing values stored in `dtors_running` for this thread. Returns
205 /// `true` if dtors for `thread` are already running.
206 fn set_dtors_running_for_thread(&mut self, thread: ThreadId) -> bool {
207 if self.dtors_running.contains_key(&thread) {
210 // We need to guard this `insert` with a check because otherwise we
211 // would risk to overwrite `last_dtor_key` with `None`.
212 self.dtors_running.insert(
214 RunningDtorsState { last_dtor_key: None }
220 /// Delete all TLS entries for the given thread. This function should be
221 /// called after all TLS destructors have already finished.
222 fn delete_all_thread_tls(&mut self, thread_id: ThreadId) {
223 for TlsEntry { data, .. } in self.keys.values_mut() {
224 data.remove(&thread_id);
229 impl<'mir, 'tcx: 'mir> EvalContextPrivExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
230 trait EvalContextPrivExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
231 /// Schedule TLS destructors for the main thread on Windows. The
232 /// implementation assumes that we do not support concurrency on Windows
234 fn schedule_windows_tls_dtors(&mut self) -> InterpResult<'tcx> {
235 let this = self.eval_context_mut();
236 let active_thread = this.get_active_thread()?;
237 assert_eq!(this.get_total_thread_count()?, 1, "concurrency on Windows not supported");
238 // Windows has a special magic linker section that is run on certain events.
239 // Instead of searching for that section and supporting arbitrary hooks in there
240 // (that would be basically https://github.com/rust-lang/miri/issues/450),
241 // we specifically look up the static in libstd that we know is placed
243 let thread_callback = this.eval_path_scalar(&["std", "sys", "windows", "thread_local", "p_thread_callback"])?;
244 let thread_callback = this.memory.get_fn(thread_callback.not_undef()?)?.as_instance()?;
246 // The signature of this function is `unsafe extern "system" fn(h: c::LPVOID, dwReason: c::DWORD, pv: c::LPVOID)`.
247 let reason = this.eval_path_scalar(&["std", "sys", "windows", "c", "DLL_THREAD_DETACH"])?;
248 let ret_place = MPlaceTy::dangling(this.machine.layouts.unit, this).into();
251 &[Scalar::null_ptr(this).into(), reason.into(), Scalar::null_ptr(this).into()],
253 StackPopCleanup::None { cleanup: true },
256 this.enable_thread(active_thread)?;
260 /// Schedule the MacOS thread destructor of the thread local storage to be
261 /// executed. Returns `true` if scheduled.
263 /// Note: It is safe to call this function also on other Unixes.
264 fn schedule_macos_tls_dtor(&mut self) -> InterpResult<'tcx, bool> {
265 let this = self.eval_context_mut();
266 let thread_id = this.get_active_thread()?;
267 if let Some((instance, data)) = this.machine.tls.macos_thread_dtors.remove(&thread_id) {
268 trace!("Running macos dtor {:?} on {:?} at {:?}", instance, data, thread_id);
270 let ret_place = MPlaceTy::dangling(this.machine.layouts.unit, this).into();
275 StackPopCleanup::None { cleanup: true },
278 // Enable the thread so that it steps through the destructor which
279 // we just scheduled. Since we deleted the destructor, it is
280 // guaranteed that we will schedule it again. The `dtors_running`
281 // flag will prevent the code from adding the destructor again.
282 this.enable_thread(thread_id)?;
289 /// Schedule a pthread TLS destructor. Returns `true` if found
290 /// a destructor to schedule, and `false` otherwise.
291 fn schedule_next_pthread_tls_dtor(&mut self) -> InterpResult<'tcx, bool> {
292 let this = self.eval_context_mut();
293 let active_thread = this.get_active_thread()?;
295 assert!(this.has_terminated(active_thread)?, "running TLS dtors for non-terminated thread");
296 // Fetch next dtor after `key`.
297 let last_key = this.machine.tls.dtors_running[&active_thread].last_dtor_key.clone();
298 let dtor = match this.machine.tls.fetch_tls_dtor(last_key, active_thread) {
299 dtor @ Some(_) => dtor,
300 // We ran each dtor once, start over from the beginning.
302 this.machine.tls.fetch_tls_dtor(None, active_thread)
305 if let Some((instance, ptr, key)) = dtor {
306 this.machine.tls.dtors_running.get_mut(&active_thread).unwrap().last_dtor_key = Some(key);
307 trace!("Running TLS dtor {:?} on {:?} at {:?}", instance, ptr, active_thread);
308 assert!(!this.is_null(ptr).unwrap(), "data can't be NULL when dtor is called!");
310 let ret_place = MPlaceTy::dangling(this.machine.layouts.unit, this).into();
315 StackPopCleanup::None { cleanup: true },
318 this.enable_thread(active_thread)?;
321 this.machine.tls.dtors_running.get_mut(&active_thread).unwrap().last_dtor_key = None;
327 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
328 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
330 /// Schedule an active thread's TLS destructor to run on the active thread.
331 /// Note that this function does not run the destructors itself, it just
332 /// schedules them one by one each time it is called and reenables the
333 /// thread so that it can be executed normally by the main execution loop.
335 /// FIXME: we do not support yet deallocation of thread local statics.
336 /// Issue: https://github.com/rust-lang/miri/issues/1369
338 /// Note: we consistently run TLS destructors for all threads, including the
339 /// main thread. However, it is not clear that we should run the TLS
340 /// destructors for the main thread. See issue:
341 /// https://github.com/rust-lang/rust/issues/28129.
342 fn schedule_next_tls_dtor_for_active_thread(&mut self) -> InterpResult<'tcx> {
343 let this = self.eval_context_mut();
344 let active_thread = this.get_active_thread()?;
346 if this.machine.tls.set_dtors_running_for_thread(active_thread) {
347 // This is the first time we got asked to schedule a destructor. The
348 // Windows schedule destructor function must be called exactly once,
349 // this is why it is in this block.
350 if this.tcx.sess.target.target.target_os == "windows" {
351 // On Windows, we signal that the thread quit by starting the
352 // relevant function, reenabling the thread, and going back to
354 this.schedule_windows_tls_dtors()?;
358 // The macOS thread wide destructor runs "before any TLS slots get
359 // freed", so do that first.
360 if this.schedule_macos_tls_dtor()? {
361 // We have scheduled a MacOS dtor to run on the thread. Execute it
362 // to completion and come back here. Scheduling a destructor
363 // destroys it, so we will not enter this branch again.
366 if this.schedule_next_pthread_tls_dtor()? {
367 // We have scheduled a pthread destructor and removed it from the
368 // destructors list. Run it to completion and come back here.
373 this.machine.tls.delete_all_thread_tls(active_thread);