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 if let Ok(name_str) = std::str::from_utf8(name) {
136 write!(f, "{}", name_str)?;
138 write!(f, "<invalid thread name>")?;
141 write!(f, "unnamed")?;
143 write!(f, "({:?}, {:?})", self.state, self.join_status)
147 impl<'mir, 'tcx> Default for Thread<'mir, 'tcx> {
148 fn default() -> Self {
150 state: ThreadState::Enabled,
153 join_status: ThreadJoinStatus::Joinable,
158 /// A set of threads.
160 pub struct ThreadManager<'mir, 'tcx> {
161 /// Identifier of the currently active thread.
162 active_thread: ThreadId,
163 /// Threads used in the program.
165 /// Note that this vector also contains terminated threads.
166 threads: IndexVec<ThreadId, Thread<'mir, 'tcx>>,
167 /// A counter used to generate unique identifiers for blocksets.
168 blockset_counter: u32,
169 /// A mapping from a thread-local static to an allocation id of a thread
170 /// specific allocation.
171 thread_local_alloc_ids: RefCell<FxHashMap<(DefId, ThreadId), AllocId>>,
172 /// A flag that indicates that we should change the active thread.
173 yield_active_thread: bool,
176 impl<'mir, 'tcx> Default for ThreadManager<'mir, 'tcx> {
177 fn default() -> Self {
178 let mut threads = IndexVec::new();
179 // Create the main thread and add it to the list of threads.
180 let mut main_thread = Thread::default();
181 main_thread.join_status = ThreadJoinStatus::Detached;
182 threads.push(main_thread);
184 active_thread: ThreadId::new(0),
187 thread_local_alloc_ids: Default::default(),
188 yield_active_thread: false,
193 impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
194 /// Check if we have an allocation for the given thread local static for the
196 fn get_thread_local_alloc_id(&self, def_id: DefId) -> Option<AllocId> {
197 self.thread_local_alloc_ids.borrow().get(&(def_id, self.active_thread)).cloned()
200 /// Set the allocation id as the allocation id of the given thread local
201 /// static for the active thread.
203 /// Panics if a thread local is initialized twice for the same thread.
204 fn set_thread_local_alloc_id(&self, def_id: DefId, new_alloc_id: AllocId) {
205 self.thread_local_alloc_ids
207 .insert((def_id, self.active_thread), new_alloc_id)
211 /// Borrow the stack of the active thread.
212 fn active_thread_stack(&self) -> &[Frame<'mir, 'tcx, Tag, FrameData<'tcx>>] {
213 &self.threads[self.active_thread].stack
216 /// Mutably borrow the stack of the active thread.
217 fn active_thread_stack_mut(&mut self) -> &mut Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>> {
218 &mut self.threads[self.active_thread].stack
221 /// Create a new thread and returns its id.
222 fn create_thread(&mut self) -> ThreadId {
223 let new_thread_id = ThreadId::new(self.threads.len());
224 self.threads.push(Default::default());
228 /// Set an active thread and return the id of the thread that was active before.
229 fn set_active_thread_id(&mut self, id: ThreadId) -> ThreadId {
230 let active_thread_id = self.active_thread;
231 self.active_thread = id;
232 assert!(self.active_thread.index() < self.threads.len());
236 /// Get the id of the currently active thread.
237 fn get_active_thread_id(&self) -> ThreadId {
241 /// Get the total number of threads that were ever spawn by this program.
242 fn get_total_thread_count(&self) -> usize {
246 /// Has the given thread terminated?
247 fn has_terminated(&self, thread_id: ThreadId) -> bool {
248 self.threads[thread_id].state == ThreadState::Terminated
251 /// Enable the thread for execution. The thread must be terminated.
252 fn enable_thread(&mut self, thread_id: ThreadId) {
253 assert!(self.has_terminated(thread_id));
254 self.threads[thread_id].state = ThreadState::Enabled;
257 /// Get a mutable borrow of the currently active thread.
258 fn active_thread_mut(&mut self) -> &mut Thread<'mir, 'tcx> {
259 &mut self.threads[self.active_thread]
262 /// Get a shared borrow of the currently active thread.
263 fn active_thread_ref(&self) -> &Thread<'mir, 'tcx> {
264 &self.threads[self.active_thread]
267 /// Mark the thread as detached, which means that no other thread will try
268 /// to join it and the thread is responsible for cleaning up.
269 fn detach_thread(&mut self, id: ThreadId) -> InterpResult<'tcx> {
270 if self.threads[id].join_status != ThreadJoinStatus::Joinable {
271 throw_ub_format!("trying to detach thread that was already detached or joined");
273 self.threads[id].join_status = ThreadJoinStatus::Detached;
277 /// Mark that the active thread tries to join the thread with `joined_thread_id`.
278 fn join_thread(&mut self, joined_thread_id: ThreadId) -> InterpResult<'tcx> {
279 if self.threads[joined_thread_id].join_status != ThreadJoinStatus::Joinable {
280 throw_ub_format!("trying to join a detached or already joined thread");
282 if joined_thread_id == self.active_thread {
283 throw_ub_format!("trying to join itself");
288 .all(|thread| thread.state != ThreadState::BlockedOnJoin(joined_thread_id)),
289 "a joinable thread has threads waiting for its termination"
291 // Mark the joined thread as being joined so that we detect if other
292 // threads try to join it.
293 self.threads[joined_thread_id].join_status = ThreadJoinStatus::Joined;
294 if self.threads[joined_thread_id].state != ThreadState::Terminated {
295 // The joined thread is still running, we need to wait for it.
296 self.active_thread_mut().state = ThreadState::BlockedOnJoin(joined_thread_id);
298 "{:?} blocked on {:?} when trying to join",
306 /// Set the name of the active thread.
307 fn set_thread_name(&mut self, new_thread_name: Vec<u8>) {
308 self.active_thread_mut().thread_name = Some(new_thread_name);
311 /// Get the name of the active thread.
312 fn get_thread_name(&self) -> InterpResult<'tcx, &[u8]> {
313 if let Some(ref thread_name) = self.active_thread_ref().thread_name {
316 throw_ub_format!("thread {:?} has no name set", self.active_thread)
320 /// Allocate a new blockset id.
321 fn create_blockset(&mut self) -> BlockSetId {
322 self.blockset_counter = self.blockset_counter.checked_add(1).unwrap();
323 self.blockset_counter.into()
326 /// Block the currently active thread and put it into the given blockset.
327 fn block_active_thread(&mut self, set: BlockSetId) {
328 let state = &mut self.active_thread_mut().state;
329 assert_eq!(*state, ThreadState::Enabled);
330 *state = ThreadState::Blocked(set);
333 /// Unblock any one thread from the given blockset if it contains at least
334 /// one. Return the id of the unblocked thread.
335 fn unblock_some_thread(&mut self, set: BlockSetId) -> Option<ThreadId> {
336 for (id, thread) in self.threads.iter_enumerated_mut() {
337 if thread.state == ThreadState::Blocked(set) {
338 trace!("unblocking {:?} in blockset {:?}", id, set);
339 thread.state = ThreadState::Enabled;
346 /// Change the active thread to some enabled thread.
347 fn yield_active_thread(&mut self) {
348 self.yield_active_thread = true;
351 /// Decide which action to take next and on which thread.
353 /// The currently implemented scheduling policy is the one that is commonly
354 /// used in stateless model checkers such as Loom: run the active thread as
355 /// long as we can and switch only when we have to (the active thread was
356 /// blocked, terminated, or was explicitly asked to be preempted).
357 fn schedule(&mut self) -> InterpResult<'tcx, SchedulingAction> {
358 if self.threads[self.active_thread].check_terminated() {
359 // Check if we need to unblock any threads.
360 for (i, thread) in self.threads.iter_enumerated_mut() {
361 if thread.state == ThreadState::BlockedOnJoin(self.active_thread) {
362 trace!("unblocking {:?} because {:?} terminated", i, self.active_thread);
363 thread.state = ThreadState::Enabled;
366 return Ok(SchedulingAction::ExecuteDtors);
368 if self.threads[MAIN_THREAD].state == ThreadState::Terminated {
369 // The main thread terminated; stop the program.
370 if self.threads.iter().any(|thread| thread.state != ThreadState::Terminated) {
371 // FIXME: This check should be either configurable or just emit
372 // a warning. For example, it seems normal for a program to
373 // terminate without waiting for its detached threads to
374 // terminate. However, this case is not trivial to support
375 // because we also probably do not want to consider the memory
376 // owned by these threads as leaked.
377 throw_unsup_format!("the main thread terminated without waiting for other threads");
379 return Ok(SchedulingAction::Stop);
381 if self.threads[self.active_thread].state == ThreadState::Enabled
382 && !self.yield_active_thread
384 // The currently active thread is still enabled, just continue with it.
385 return Ok(SchedulingAction::ExecuteStep);
387 // We need to pick a new thread for execution.
388 for (id, thread) in self.threads.iter_enumerated() {
389 if thread.state == ThreadState::Enabled {
390 if !self.yield_active_thread || id != self.active_thread {
391 self.active_thread = id;
396 self.yield_active_thread = false;
397 if self.threads[self.active_thread].state == ThreadState::Enabled {
398 return Ok(SchedulingAction::ExecuteStep);
400 // We have not found a thread to execute.
401 if self.threads.iter().all(|thread| thread.state == ThreadState::Terminated) {
404 throw_machine_stop!(TerminationInfo::Deadlock);
409 // Public interface to thread management.
410 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
411 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
412 /// A workaround for thread-local statics until
413 /// https://github.com/rust-lang/rust/issues/70685 is fixed: change the
414 /// thread-local allocation id with a freshly generated allocation id for
415 /// the currently active thread.
416 fn remap_thread_local_alloc_ids(
418 val: &mut mir::interpret::ConstValue<'tcx>,
419 ) -> InterpResult<'tcx> {
420 let this = self.eval_context_ref();
422 mir::interpret::ConstValue::Scalar(Scalar::Ptr(ref mut ptr)) => {
423 let alloc_id = ptr.alloc_id;
424 let alloc = this.tcx.alloc_map.lock().get(alloc_id);
426 let is_thread_local = |def_id| {
427 tcx.codegen_fn_attrs(def_id).flags.contains(CodegenFnAttrFlags::THREAD_LOCAL)
430 Some(GlobalAlloc::Static(def_id)) if is_thread_local(def_id) => {
431 ptr.alloc_id = this.get_or_create_thread_local_alloc_id(def_id)?;
437 // FIXME: Handling only `Scalar` seems to work for now, but at
438 // least in principle thread-locals could be in any constant, so
439 // we should also consider other cases. However, once
440 // https://github.com/rust-lang/rust/issues/70685 gets fixed,
441 // this code will have to be rewritten anyway.
447 /// Get a thread-specific allocation id for the given thread-local static.
448 /// If needed, allocate a new one.
450 /// FIXME: This method should be replaced as soon as
451 /// https://github.com/rust-lang/rust/issues/70685 gets fixed.
452 fn get_or_create_thread_local_alloc_id(&self, def_id: DefId) -> InterpResult<'tcx, AllocId> {
453 let this = self.eval_context_ref();
455 if let Some(new_alloc_id) = this.machine.threads.get_thread_local_alloc_id(def_id) {
456 // We already have a thread-specific allocation id for this
457 // thread-local static.
460 // We need to allocate a thread-specific allocation id for this
461 // thread-local static.
463 // At first, we invoke the `const_eval_raw` query and extract the
464 // allocation from it. Unfortunately, we have to duplicate the code
465 // from `Memory::get_global_alloc` that does this.
467 // Then we store the retrieved allocation back into the `alloc_map`
468 // to get a fresh allocation id, which we can use as a
469 // thread-specific allocation id for the thread-local static.
470 if tcx.is_foreign_item(def_id) {
471 throw_unsup_format!("foreign thread-local statics are not supported");
473 // Invoke the `const_eval_raw` query.
474 let instance = Instance::mono(tcx.tcx, def_id);
475 let gid = GlobalId { instance, promoted: None };
477 tcx.const_eval_raw(ty::ParamEnv::reveal_all().and(gid)).map_err(|err| {
478 // no need to report anything, the const_eval call takes care of that
480 assert!(tcx.is_static(def_id));
483 let id = raw_const.alloc_id;
484 // Extract the allocation from the query result.
485 let mut alloc_map = tcx.alloc_map.lock();
486 let allocation = alloc_map.unwrap_memory(id);
487 // Create a new allocation id for the same allocation in this hacky
488 // way. Internally, `alloc_map` deduplicates allocations, but this
489 // is fine because Miri will make a copy before a first mutable
491 let new_alloc_id = alloc_map.create_memory_alloc(allocation);
492 this.machine.threads.set_thread_local_alloc_id(def_id, new_alloc_id);
498 fn create_thread(&mut self) -> InterpResult<'tcx, ThreadId> {
499 let this = self.eval_context_mut();
500 Ok(this.machine.threads.create_thread())
504 fn detach_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx> {
505 let this = self.eval_context_mut();
506 this.machine.threads.detach_thread(thread_id)
510 fn join_thread(&mut self, joined_thread_id: ThreadId) -> InterpResult<'tcx> {
511 let this = self.eval_context_mut();
512 this.machine.threads.join_thread(joined_thread_id)
516 fn set_active_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx, ThreadId> {
517 let this = self.eval_context_mut();
518 Ok(this.machine.threads.set_active_thread_id(thread_id))
522 fn get_active_thread(&self) -> InterpResult<'tcx, ThreadId> {
523 let this = self.eval_context_ref();
524 Ok(this.machine.threads.get_active_thread_id())
528 fn get_total_thread_count(&self) -> InterpResult<'tcx, usize> {
529 let this = self.eval_context_ref();
530 Ok(this.machine.threads.get_total_thread_count())
534 fn has_terminated(&self, thread_id: ThreadId) -> InterpResult<'tcx, bool> {
535 let this = self.eval_context_ref();
536 Ok(this.machine.threads.has_terminated(thread_id))
540 fn enable_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx> {
541 let this = self.eval_context_mut();
542 this.machine.threads.enable_thread(thread_id);
547 fn active_thread_stack(&self) -> &[Frame<'mir, 'tcx, Tag, FrameData<'tcx>>] {
548 let this = self.eval_context_ref();
549 this.machine.threads.active_thread_stack()
553 fn active_thread_stack_mut(&mut self) -> &mut Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>> {
554 let this = self.eval_context_mut();
555 this.machine.threads.active_thread_stack_mut()
559 fn set_active_thread_name(&mut self, new_thread_name: Vec<u8>) -> InterpResult<'tcx, ()> {
560 let this = self.eval_context_mut();
561 Ok(this.machine.threads.set_thread_name(new_thread_name))
565 fn get_active_thread_name<'c>(&'c self) -> InterpResult<'tcx, &'c [u8]>
569 let this = self.eval_context_ref();
570 this.machine.threads.get_thread_name()
574 fn create_blockset(&mut self) -> InterpResult<'tcx, BlockSetId> {
575 let this = self.eval_context_mut();
576 Ok(this.machine.threads.create_blockset())
580 fn block_active_thread(&mut self, set: BlockSetId) -> InterpResult<'tcx> {
581 let this = self.eval_context_mut();
582 Ok(this.machine.threads.block_active_thread(set))
586 fn unblock_some_thread(&mut self, set: BlockSetId) -> InterpResult<'tcx, Option<ThreadId>> {
587 let this = self.eval_context_mut();
588 Ok(this.machine.threads.unblock_some_thread(set))
592 fn yield_active_thread(&mut self) -> InterpResult<'tcx> {
593 let this = self.eval_context_mut();
594 this.machine.threads.yield_active_thread();
598 /// Decide which action to take next and on which thread.
600 fn schedule(&mut self) -> InterpResult<'tcx, SchedulingAction> {
601 let this = self.eval_context_mut();
602 this.machine.threads.schedule()