1 //! Implements threads.
3 use std::cell::RefCell;
4 use std::convert::TryFrom;
5 use std::num::NonZeroU32;
9 use rustc_data_structures::fx::FxHashMap;
10 use rustc_hir::def_id::DefId;
11 use rustc_index::vec::{Idx, IndexVec};
13 middle::codegen_fn_attrs::CodegenFnAttrFlags,
20 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
21 pub enum SchedulingAction {
22 /// Execute step on the active thread.
24 /// Execute destructors of the active thread.
30 /// A thread identifier.
31 #[derive(Clone, Copy, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
32 pub struct ThreadId(usize);
34 /// The main thread. When it terminates, the whole application terminates.
35 const MAIN_THREAD: ThreadId = ThreadId(0);
37 impl Idx for ThreadId {
38 fn new(idx: usize) -> Self {
41 fn index(self) -> usize {
46 impl From<u64> for ThreadId {
47 fn from(id: u64) -> Self {
48 Self(usize::try_from(id).unwrap())
52 impl From<u32> for ThreadId {
53 fn from(id: u32) -> Self {
54 Self(usize::try_from(id).unwrap())
59 pub fn to_u32_scalar<'tcx>(&self) -> Scalar<Tag> {
60 Scalar::from_u32(u32::try_from(self.0).unwrap())
64 /// An identifier of a set of blocked threads.
65 #[derive(Clone, Copy, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
66 pub struct BlockSetId(NonZeroU32);
68 impl From<u32> for BlockSetId {
69 fn from(id: u32) -> Self {
70 Self(NonZeroU32::new(id).expect("0 is not a valid blockset id"))
75 pub fn to_u32_scalar<'tcx>(&self) -> Scalar<Tag> {
76 Scalar::from_u32(self.0.get())
80 /// The state of a thread.
81 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
82 pub enum ThreadState {
83 /// The thread is enabled and can be executed.
85 /// The thread tried to join the specified thread and is blocked until that
86 /// thread terminates.
87 BlockedOnJoin(ThreadId),
88 /// The thread is blocked and belongs to the given blockset.
90 /// The thread has terminated its execution (we do not delete terminated
95 /// The join status of a thread.
96 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
97 enum ThreadJoinStatus {
98 /// The thread can be joined.
100 /// A thread is detached if its join handle was destroyed and no other
101 /// thread can join it.
103 /// The thread was already joined by some thread and cannot be joined again.
108 pub struct Thread<'mir, 'tcx> {
110 /// Name of the thread.
111 thread_name: Option<Vec<u8>>,
112 /// The virtual call stack.
113 stack: Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>>,
115 join_status: ThreadJoinStatus,
118 impl<'mir, 'tcx> Thread<'mir, 'tcx> {
119 /// Check if the thread terminated. If yes, change the state to terminated
120 /// and return `true`.
121 fn check_terminated(&mut self) -> bool {
122 if self.state == ThreadState::Enabled {
123 if self.stack.is_empty() {
124 self.state = ThreadState::Terminated;
132 impl<'mir, 'tcx> std::fmt::Debug for Thread<'mir, 'tcx> {
133 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
134 if let Some(ref name) = self.thread_name {
135 write!(f, "{}", String::from_utf8_lossy(name))?;
137 write!(f, "<unnamed>")?;
139 write!(f, "({:?}, {:?})", self.state, self.join_status)
143 impl<'mir, 'tcx> Default for Thread<'mir, 'tcx> {
144 fn default() -> Self {
146 state: ThreadState::Enabled,
149 join_status: ThreadJoinStatus::Joinable,
154 /// A set of threads.
156 pub struct ThreadManager<'mir, 'tcx> {
157 /// Identifier of the currently active thread.
158 active_thread: ThreadId,
159 /// Threads used in the program.
161 /// Note that this vector also contains terminated threads.
162 threads: IndexVec<ThreadId, Thread<'mir, 'tcx>>,
163 /// A counter used to generate unique identifiers for blocksets.
164 blockset_counter: u32,
165 /// A mapping from a thread-local static to an allocation id of a thread
166 /// specific allocation.
167 thread_local_alloc_ids: RefCell<FxHashMap<(DefId, ThreadId), AllocId>>,
168 /// A flag that indicates that we should change the active thread.
169 yield_active_thread: bool,
172 impl<'mir, 'tcx> Default for ThreadManager<'mir, 'tcx> {
173 fn default() -> Self {
174 let mut threads = IndexVec::new();
175 // Create the main thread and add it to the list of threads.
176 let mut main_thread = Thread::default();
177 main_thread.join_status = ThreadJoinStatus::Detached;
178 threads.push(main_thread);
180 active_thread: ThreadId::new(0),
183 thread_local_alloc_ids: Default::default(),
184 yield_active_thread: false,
189 impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
190 /// Check if we have an allocation for the given thread local static for the
192 fn get_thread_local_alloc_id(&self, def_id: DefId) -> Option<AllocId> {
193 self.thread_local_alloc_ids.borrow().get(&(def_id, self.active_thread)).cloned()
196 /// Set the allocation id as the allocation id of the given thread local
197 /// static for the active thread.
199 /// Panics if a thread local is initialized twice for the same thread.
200 fn set_thread_local_alloc_id(&self, def_id: DefId, new_alloc_id: AllocId) {
201 self.thread_local_alloc_ids
203 .insert((def_id, self.active_thread), new_alloc_id)
207 /// Borrow the stack of the active thread.
208 fn active_thread_stack(&self) -> &[Frame<'mir, 'tcx, Tag, FrameData<'tcx>>] {
209 &self.threads[self.active_thread].stack
212 /// Mutably borrow the stack of the active thread.
213 fn active_thread_stack_mut(&mut self) -> &mut Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>> {
214 &mut self.threads[self.active_thread].stack
217 /// Create a new thread and returns its id.
218 fn create_thread(&mut self) -> ThreadId {
219 let new_thread_id = ThreadId::new(self.threads.len());
220 self.threads.push(Default::default());
224 /// Set an active thread and return the id of the thread that was active before.
225 fn set_active_thread_id(&mut self, id: ThreadId) -> ThreadId {
226 let active_thread_id = self.active_thread;
227 self.active_thread = id;
228 assert!(self.active_thread.index() < self.threads.len());
232 /// Get the id of the currently active thread.
233 fn get_active_thread_id(&self) -> ThreadId {
237 /// Get the total number of threads that were ever spawn by this program.
238 fn get_total_thread_count(&self) -> usize {
242 /// Has the given thread terminated?
243 fn has_terminated(&self, thread_id: ThreadId) -> bool {
244 self.threads[thread_id].state == ThreadState::Terminated
247 /// Enable the thread for execution. The thread must be terminated.
248 fn enable_thread(&mut self, thread_id: ThreadId) {
249 assert!(self.has_terminated(thread_id));
250 self.threads[thread_id].state = ThreadState::Enabled;
253 /// Get a mutable borrow of the currently active thread.
254 fn active_thread_mut(&mut self) -> &mut Thread<'mir, 'tcx> {
255 &mut self.threads[self.active_thread]
258 /// Get a shared borrow of the currently active thread.
259 fn active_thread_ref(&self) -> &Thread<'mir, 'tcx> {
260 &self.threads[self.active_thread]
263 /// Mark the thread as detached, which means that no other thread will try
264 /// to join it and the thread is responsible for cleaning up.
265 fn detach_thread(&mut self, id: ThreadId) -> InterpResult<'tcx> {
266 if self.threads[id].join_status != ThreadJoinStatus::Joinable {
267 throw_ub_format!("trying to detach thread that was already detached or joined");
269 self.threads[id].join_status = ThreadJoinStatus::Detached;
273 /// Mark that the active thread tries to join the thread with `joined_thread_id`.
274 fn join_thread(&mut self, joined_thread_id: ThreadId) -> InterpResult<'tcx> {
275 if self.threads[joined_thread_id].join_status != ThreadJoinStatus::Joinable {
276 throw_ub_format!("trying to join a detached or already joined thread");
278 if joined_thread_id == self.active_thread {
279 throw_ub_format!("trying to join itself");
284 .all(|thread| thread.state != ThreadState::BlockedOnJoin(joined_thread_id)),
285 "a joinable thread has threads waiting for its termination"
287 // Mark the joined thread as being joined so that we detect if other
288 // threads try to join it.
289 self.threads[joined_thread_id].join_status = ThreadJoinStatus::Joined;
290 if self.threads[joined_thread_id].state != ThreadState::Terminated {
291 // The joined thread is still running, we need to wait for it.
292 self.active_thread_mut().state = ThreadState::BlockedOnJoin(joined_thread_id);
294 "{:?} blocked on {:?} when trying to join",
302 /// Set the name of the active thread.
303 fn set_thread_name(&mut self, new_thread_name: Vec<u8>) {
304 self.active_thread_mut().thread_name = Some(new_thread_name);
307 /// Get the name of the active thread.
308 fn get_thread_name(&self) -> InterpResult<'tcx, &[u8]> {
309 if let Some(ref thread_name) = self.active_thread_ref().thread_name {
312 throw_ub_format!("thread {:?} has no name set", self.active_thread)
316 /// Allocate a new blockset id.
317 fn create_blockset(&mut self) -> BlockSetId {
318 self.blockset_counter = self.blockset_counter.checked_add(1).unwrap();
319 self.blockset_counter.into()
322 /// Block the currently active thread and put it into the given blockset.
323 fn block_active_thread(&mut self, set: BlockSetId) {
324 let state = &mut self.active_thread_mut().state;
325 assert_eq!(*state, ThreadState::Enabled);
326 *state = ThreadState::Blocked(set);
329 /// Unblock any one thread from the given blockset if it contains at least
330 /// one. Return the id of the unblocked thread.
331 fn unblock_some_thread(&mut self, set: BlockSetId) -> Option<ThreadId> {
332 for (id, thread) in self.threads.iter_enumerated_mut() {
333 if thread.state == ThreadState::Blocked(set) {
334 trace!("unblocking {:?} in blockset {:?}", id, set);
335 thread.state = ThreadState::Enabled;
342 /// Change the active thread to some enabled thread.
343 fn yield_active_thread(&mut self) {
344 self.yield_active_thread = true;
347 /// Decide which action to take next and on which thread.
349 /// The currently implemented scheduling policy is the one that is commonly
350 /// used in stateless model checkers such as Loom: run the active thread as
351 /// long as we can and switch only when we have to (the active thread was
352 /// blocked, terminated, or was explicitly asked to be preempted).
353 fn schedule(&mut self) -> InterpResult<'tcx, SchedulingAction> {
354 if self.threads[self.active_thread].check_terminated() {
355 // Check if we need to unblock any threads.
356 for (i, thread) in self.threads.iter_enumerated_mut() {
357 if thread.state == ThreadState::BlockedOnJoin(self.active_thread) {
358 trace!("unblocking {:?} because {:?} terminated", i, self.active_thread);
359 thread.state = ThreadState::Enabled;
362 return Ok(SchedulingAction::ExecuteDtors);
364 if self.threads[MAIN_THREAD].state == ThreadState::Terminated {
365 // The main thread terminated; stop the program.
366 if self.threads.iter().any(|thread| thread.state != ThreadState::Terminated) {
367 // FIXME: This check should be either configurable or just emit
368 // a warning. For example, it seems normal for a program to
369 // terminate without waiting for its detached threads to
370 // terminate. However, this case is not trivial to support
371 // because we also probably do not want to consider the memory
372 // owned by these threads as leaked.
373 throw_unsup_format!("the main thread terminated without waiting for other threads");
375 return Ok(SchedulingAction::Stop);
377 if self.threads[self.active_thread].state == ThreadState::Enabled
378 && !self.yield_active_thread
380 // The currently active thread is still enabled, just continue with it.
381 return Ok(SchedulingAction::ExecuteStep);
383 // We need to pick a new thread for execution.
384 for (id, thread) in self.threads.iter_enumerated() {
385 if thread.state == ThreadState::Enabled {
386 if !self.yield_active_thread || id != self.active_thread {
387 self.active_thread = id;
392 self.yield_active_thread = false;
393 if self.threads[self.active_thread].state == ThreadState::Enabled {
394 return Ok(SchedulingAction::ExecuteStep);
396 // We have not found a thread to execute.
397 if self.threads.iter().all(|thread| thread.state == ThreadState::Terminated) {
400 throw_machine_stop!(TerminationInfo::Deadlock);
405 // Public interface to thread management.
406 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
407 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
408 /// A workaround for thread-local statics until
409 /// https://github.com/rust-lang/rust/issues/70685 is fixed: change the
410 /// thread-local allocation id with a freshly generated allocation id for
411 /// the currently active thread.
412 fn remap_thread_local_alloc_ids(
414 val: &mut mir::interpret::ConstValue<'tcx>,
415 ) -> InterpResult<'tcx> {
416 let this = self.eval_context_ref();
418 mir::interpret::ConstValue::Scalar(Scalar::Ptr(ref mut ptr)) => {
419 let alloc_id = ptr.alloc_id;
420 let alloc = this.tcx.alloc_map.lock().get(alloc_id);
422 let is_thread_local = |def_id| {
423 tcx.codegen_fn_attrs(def_id).flags.contains(CodegenFnAttrFlags::THREAD_LOCAL)
426 Some(GlobalAlloc::Static(def_id)) if is_thread_local(def_id) => {
427 ptr.alloc_id = this.get_or_create_thread_local_alloc_id(def_id)?;
433 // FIXME: Handling only `Scalar` seems to work for now, but at
434 // least in principle thread-locals could be in any constant, so
435 // we should also consider other cases. However, once
436 // https://github.com/rust-lang/rust/issues/70685 gets fixed,
437 // this code will have to be rewritten anyway.
443 /// Get a thread-specific allocation id for the given thread-local static.
444 /// If needed, allocate a new one.
446 /// FIXME: This method should be replaced as soon as
447 /// https://github.com/rust-lang/rust/issues/70685 gets fixed.
448 fn get_or_create_thread_local_alloc_id(&self, def_id: DefId) -> InterpResult<'tcx, AllocId> {
449 let this = self.eval_context_ref();
451 if let Some(new_alloc_id) = this.machine.threads.get_thread_local_alloc_id(def_id) {
452 // We already have a thread-specific allocation id for this
453 // thread-local static.
456 // We need to allocate a thread-specific allocation id for this
457 // thread-local static.
459 // At first, we invoke the `const_eval_raw` query and extract the
460 // allocation from it. Unfortunately, we have to duplicate the code
461 // from `Memory::get_global_alloc` that does this.
463 // Then we store the retrieved allocation back into the `alloc_map`
464 // to get a fresh allocation id, which we can use as a
465 // thread-specific allocation id for the thread-local static.
466 if tcx.is_foreign_item(def_id) {
467 throw_unsup_format!("foreign thread-local statics are not supported");
469 // Invoke the `const_eval_raw` query.
470 let instance = Instance::mono(tcx.tcx, def_id);
471 let gid = GlobalId { instance, promoted: None };
473 tcx.const_eval_raw(ty::ParamEnv::reveal_all().and(gid)).map_err(|err| {
474 // no need to report anything, the const_eval call takes care of that
476 assert!(tcx.is_static(def_id));
479 let id = raw_const.alloc_id;
480 // Extract the allocation from the query result.
481 let mut alloc_map = tcx.alloc_map.lock();
482 let allocation = alloc_map.unwrap_memory(id);
483 // Create a new allocation id for the same allocation in this hacky
484 // way. Internally, `alloc_map` deduplicates allocations, but this
485 // is fine because Miri will make a copy before a first mutable
487 let new_alloc_id = alloc_map.create_memory_alloc(allocation);
488 this.machine.threads.set_thread_local_alloc_id(def_id, new_alloc_id);
494 fn create_thread(&mut self) -> InterpResult<'tcx, ThreadId> {
495 let this = self.eval_context_mut();
496 Ok(this.machine.threads.create_thread())
500 fn detach_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx> {
501 let this = self.eval_context_mut();
502 this.machine.threads.detach_thread(thread_id)
506 fn join_thread(&mut self, joined_thread_id: ThreadId) -> InterpResult<'tcx> {
507 let this = self.eval_context_mut();
508 this.machine.threads.join_thread(joined_thread_id)
512 fn set_active_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx, ThreadId> {
513 let this = self.eval_context_mut();
514 Ok(this.machine.threads.set_active_thread_id(thread_id))
518 fn get_active_thread(&self) -> InterpResult<'tcx, ThreadId> {
519 let this = self.eval_context_ref();
520 Ok(this.machine.threads.get_active_thread_id())
524 fn get_total_thread_count(&self) -> InterpResult<'tcx, usize> {
525 let this = self.eval_context_ref();
526 Ok(this.machine.threads.get_total_thread_count())
530 fn has_terminated(&self, thread_id: ThreadId) -> InterpResult<'tcx, bool> {
531 let this = self.eval_context_ref();
532 Ok(this.machine.threads.has_terminated(thread_id))
536 fn enable_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx> {
537 let this = self.eval_context_mut();
538 this.machine.threads.enable_thread(thread_id);
543 fn active_thread_stack(&self) -> &[Frame<'mir, 'tcx, Tag, FrameData<'tcx>>] {
544 let this = self.eval_context_ref();
545 this.machine.threads.active_thread_stack()
549 fn active_thread_stack_mut(&mut self) -> &mut Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>> {
550 let this = self.eval_context_mut();
551 this.machine.threads.active_thread_stack_mut()
555 fn set_active_thread_name(&mut self, new_thread_name: Vec<u8>) -> InterpResult<'tcx, ()> {
556 let this = self.eval_context_mut();
557 Ok(this.machine.threads.set_thread_name(new_thread_name))
561 fn get_active_thread_name<'c>(&'c self) -> InterpResult<'tcx, &'c [u8]>
565 let this = self.eval_context_ref();
566 this.machine.threads.get_thread_name()
570 fn create_blockset(&mut self) -> InterpResult<'tcx, BlockSetId> {
571 let this = self.eval_context_mut();
572 Ok(this.machine.threads.create_blockset())
576 fn block_active_thread(&mut self, set: BlockSetId) -> InterpResult<'tcx> {
577 let this = self.eval_context_mut();
578 Ok(this.machine.threads.block_active_thread(set))
582 fn unblock_some_thread(&mut self, set: BlockSetId) -> InterpResult<'tcx, Option<ThreadId>> {
583 let this = self.eval_context_mut();
584 Ok(this.machine.threads.unblock_some_thread(set))
588 fn yield_active_thread(&mut self) -> InterpResult<'tcx> {
589 let this = self.eval_context_mut();
590 this.machine.threads.yield_active_thread();
594 /// Decide which action to take next and on which thread.
596 fn schedule(&mut self) -> InterpResult<'tcx, SchedulingAction> {
597 let this = self.eval_context_mut();
598 this.machine.threads.schedule()