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.
30 last_dtor_key: Option<TlsKey>,
34 pub struct TlsData<'tcx> {
35 /// The Key to use for the next thread-local allocation.
38 /// pthreads-style thread-local storage.
39 keys: BTreeMap<TlsKey, TlsEntry<'tcx>>,
41 /// A single per thread destructor of the thread local storage (that's how
42 /// things work on macOS) with a data argument.
43 thread_dtors: BTreeMap<ThreadId, (ty::Instance<'tcx>, Scalar<Tag>)>,
45 /// State for currently running TLS dtors. If this map contains a key for a
46 /// specific thread, it means that we are in the "destruct" phase, during
47 /// which some operations are UB.
48 dtors_running: FxHashMap<ThreadId, RunningDtorsState>,
51 impl<'tcx> Default for TlsData<'tcx> {
52 fn default() -> Self {
54 next_key: 1, // start with 1 as we must not use 0 on Windows
55 keys: Default::default(),
56 thread_dtors: Default::default(),
57 dtors_running: Default::default(),
62 impl<'tcx> TlsData<'tcx> {
63 /// Generate a new TLS key with the given destructor.
64 /// `max_size` determines the integer size the key has to fit in.
65 pub fn create_tls_key(&mut self, dtor: Option<ty::Instance<'tcx>>, max_size: Size) -> InterpResult<'tcx, TlsKey> {
66 let new_key = self.next_key;
68 self.keys.insert(new_key, TlsEntry { data: Default::default(), dtor }).unwrap_none();
69 trace!("New TLS key allocated: {} with dtor {:?}", new_key, dtor);
71 if max_size.bits() < 128 && new_key >= (1u128 << max_size.bits() as u128) {
72 throw_unsup_format!("we ran out of TLS key space");
77 pub fn delete_tls_key(&mut self, key: TlsKey) -> InterpResult<'tcx> {
78 match self.keys.remove(&key) {
80 trace!("TLS key {} removed", key);
83 None => throw_ub_format!("removing a non-existig TLS key: {}", key),
91 cx: &impl HasDataLayout,
92 ) -> InterpResult<'tcx, Scalar<Tag>> {
93 match self.keys.get(&key) {
94 Some(TlsEntry { data, .. }) => {
95 let value = data.get(&thread_id).copied();
96 trace!("TLS key {} for thread {:?} loaded: {:?}", key, thread_id, value);
97 Ok(value.unwrap_or_else(|| Scalar::null_ptr(cx).into()))
99 None => throw_ub_format!("loading from a non-existing TLS key: {}", key),
107 new_data: Option<Scalar<Tag>>
108 ) -> InterpResult<'tcx> {
109 match self.keys.get_mut(&key) {
110 Some(TlsEntry { data, .. }) => {
113 trace!("TLS key {} for thread {:?} stored: {:?}", key, thread_id, scalar);
114 data.insert(thread_id, scalar);
117 trace!("TLS key {} for thread {:?} removed", key, thread_id);
118 data.remove(&thread_id);
123 None => throw_ub_format!("storing to a non-existing TLS key: {}", key),
127 /// Set the thread wide destructor of the thread local storage for the given
128 /// thread. This function is used to implement `_tlv_atexit` shim on MacOS.
130 /// Thread wide dtors are available only on MacOS. There is one destructor
131 /// per thread as can be guessed from the following comment in the
133 /// implementation](https://github.com/opensource-apple/dyld/blob/195030646877261f0c8c7ad8b001f52d6a26f514/src/threadLocalVariables.c#L389):
135 /// // NOTE: this does not need locks because it only operates on current thread data
136 pub fn set_thread_dtor(
139 dtor: ty::Instance<'tcx>,
141 ) -> InterpResult<'tcx> {
142 if self.dtors_running.contains_key(&thread) {
143 // UB, according to libstd docs.
144 throw_ub_format!("setting thread's local storage destructor while destructors are already running");
146 if self.thread_dtors.insert(thread, (dtor, data)).is_some() {
147 throw_unsup_format!("setting more than one thread local storage destructor for the same thread is not supported");
152 /// Returns a dtor, its argument and its index, if one is supposed to run.
153 /// `key` is the last dtors that was run; we return the *next* one after that.
155 /// An optional destructor function may be associated with each key value.
156 /// At thread exit, if a key value has a non-NULL destructor pointer,
157 /// and the thread has a non-NULL value associated with that key,
158 /// the value of the key is set to NULL, and then the function pointed
159 /// to is called with the previously associated value as its sole argument.
160 /// The order of destructor calls is unspecified if more than one destructor
161 /// exists for a thread when it exits.
163 /// If, after all the destructors have been called for all non-NULL values
164 /// with associated destructors, there are still some non-NULL values with
165 /// associated destructors, then the process is repeated.
166 /// If, after at least {PTHREAD_DESTRUCTOR_ITERATIONS} iterations of destructor
167 /// calls for outstanding non-NULL values, there are still some non-NULL values
168 /// with associated destructors, implementations may stop calling destructors,
169 /// or they may continue calling destructors until no non-NULL values with
170 /// associated destructors exist, even though this might result in an infinite loop.
175 ) -> Option<(ty::Instance<'tcx>, Scalar<Tag>, TlsKey)> {
176 use std::collections::Bound::*;
178 let thread_local = &mut self.keys;
179 let start = match key {
180 Some(key) => Excluded(key),
183 for (&key, TlsEntry { data, dtor }) in
184 thread_local.range_mut((start, Unbounded))
186 match data.entry(thread_id) {
187 Entry::Occupied(entry) => {
188 if let Some(dtor) = dtor {
189 let data_scalar = entry.remove();
190 let ret = Some((*dtor, data_scalar, key));
194 Entry::Vacant(_) => {}
200 /// Set that dtors are running for `thread`. It is guaranteed not to change
201 /// the existing values stored in `dtors_running` for this thread. Returns
202 /// `true` if dtors for `thread` are already running.
203 fn set_dtors_running_for_thread(&mut self, thread: ThreadId) -> bool {
204 if self.dtors_running.contains_key(&thread) {
207 self.dtors_running.insert(
209 RunningDtorsState { last_dtor_key: None }
215 /// Delete all TLS entries for the given thread. This function should be
216 /// called after all TLS destructors have already finished.
217 fn delete_all_thread_tls(&mut self, thread_id: ThreadId) {
218 for TlsEntry { data, .. } in self.keys.values_mut() {
219 data.remove(&thread_id);
224 impl<'mir, 'tcx: 'mir> EvalContextPrivExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
225 trait EvalContextPrivExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
226 /// Schedule TLS destructors for the main thread on Windows. The
227 /// implementation assumes that we do not support concurrency on Windows
229 fn schedule_windows_tls_dtors(&mut self) -> InterpResult<'tcx> {
230 let this = self.eval_context_mut();
231 let active_thread = this.get_active_thread()?;
232 assert_eq!(this.get_total_thread_count()?, 1, "concurrency on Windows not supported");
233 // Windows has a special magic linker section that is run on certain events.
234 // Instead of searching for that section and supporting arbitrary hooks in there
235 // (that would be basically https://github.com/rust-lang/miri/issues/450),
236 // we specifically look up the static in libstd that we know is placed
238 let thread_callback = this.eval_path_scalar(&["std", "sys", "windows", "thread_local", "p_thread_callback"])?;
239 let thread_callback = this.memory.get_fn(thread_callback.not_undef()?)?.as_instance()?;
241 // The signature of this function is `unsafe extern "system" fn(h: c::LPVOID, dwReason: c::DWORD, pv: c::LPVOID)`.
242 let reason = this.eval_path_scalar(&["std", "sys", "windows", "c", "DLL_THREAD_DETACH"])?;
243 let ret_place = MPlaceTy::dangling(this.machine.layouts.unit, this).into();
246 &[Scalar::null_ptr(this).into(), reason.into(), Scalar::null_ptr(this).into()],
248 StackPopCleanup::None { cleanup: true },
251 this.enable_thread(active_thread)?;
255 /// Schedule the MacOS thread destructor of the thread local storage to be
258 /// Note: It is safe to call this function also on other Unixes.
259 fn schedule_macos_tls_dtor(&mut self) -> InterpResult<'tcx> {
260 let this = self.eval_context_mut();
261 let thread_id = this.get_active_thread()?;
262 if let Some((instance, data)) = this.machine.tls.thread_dtors.remove(&thread_id) {
263 trace!("Running macos dtor {:?} on {:?} at {:?}", instance, data, thread_id);
265 let ret_place = MPlaceTy::dangling(this.machine.layouts.unit, this).into();
270 StackPopCleanup::None { cleanup: true },
273 // Enable the thread so that it steps through the destructor which
274 // we just scheduled. Since we deleted the destructor, it is
275 // guaranteed that we will schedule it again. The `dtors_running`
276 // flag will prevent the code from adding the destructor again.
277 this.enable_thread(thread_id)?;
282 /// Schedule a pthread TLS destructor. Returns `true` if found
283 /// a destructor to schedule, and `false` otherwise.
284 fn schedule_pthread_tls_dtors(&mut self) -> InterpResult<'tcx, bool> {
285 let this = self.eval_context_mut();
286 let active_thread = this.get_active_thread()?;
288 assert!(this.has_terminated(active_thread)?, "running TLS dtors for non-terminated thread");
289 // Fetch next dtor after `key`.
290 let last_key = this.machine.tls.dtors_running[&active_thread].last_dtor_key.clone();
291 let dtor = match this.machine.tls.fetch_tls_dtor(last_key, active_thread) {
292 dtor @ Some(_) => dtor,
293 // We ran each dtor once, start over from the beginning.
295 this.machine.tls.fetch_tls_dtor(None, active_thread)
298 if let Some((instance, ptr, key)) = dtor {
299 this.machine.tls.dtors_running.get_mut(&active_thread).unwrap().last_dtor_key = Some(key);
300 trace!("Running TLS dtor {:?} on {:?} at {:?}", instance, ptr, active_thread);
301 assert!(!this.is_null(ptr).unwrap(), "data can't be NULL when dtor is called!");
303 let ret_place = MPlaceTy::dangling(this.machine.layouts.unit, this).into();
308 StackPopCleanup::None { cleanup: true },
311 this.enable_thread(active_thread)?;
314 this.machine.tls.dtors_running.get_mut(&active_thread).unwrap().last_dtor_key = None;
320 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
321 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
323 /// Schedule an active thread's TLS destructor to run on the active thread.
324 /// Note that this function does not run the destructors itself, it just
325 /// schedules them one by one each time it is called and reenables the
326 /// thread so that it can be executed normally by the main execution loop.
328 /// FIXME: we do not support yet deallocation of thread local statics.
329 /// Issue: https://github.com/rust-lang/miri/issues/1369
330 fn schedule_next_tls_dtor_for_active_thread(&mut self) -> InterpResult<'tcx> {
331 let this = self.eval_context_mut();
332 let active_thread = this.get_active_thread()?;
334 let finished = if this.tcx.sess.target.target.target_os == "windows" {
335 if !this.machine.tls.set_dtors_running_for_thread(active_thread) {
336 this.schedule_windows_tls_dtors()?;
340 this.machine.tls.set_dtors_running_for_thread(active_thread);
341 // The macOS thread wide destructor runs "before any TLS slots get
342 // freed", so do that first.
343 this.schedule_macos_tls_dtor()?;
344 this.schedule_pthread_tls_dtors()?
348 this.machine.tls.delete_all_thread_tls(active_thread);