1 //! Implements threads.
3 use std::cell::RefCell;
4 use std::convert::TryFrom;
5 use std::num::{NonZeroU32, TryFromIntError};
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(u32);
34 /// The main thread. When it terminates, the whole application terminates.
35 const MAIN_THREAD: ThreadId = ThreadId(0);
38 pub fn to_u32(self) -> u32 {
43 impl Idx for ThreadId {
44 fn new(idx: usize) -> Self {
45 ThreadId(u32::try_from(idx).unwrap())
48 fn index(self) -> usize {
49 usize::try_from(self.0).unwrap()
53 impl TryFrom<u64> for ThreadId {
54 type Error = TryFromIntError;
55 fn try_from(id: u64) -> Result<Self, Self::Error> {
56 u32::try_from(id).map(|id_u32| Self(id_u32))
60 impl From<u32> for ThreadId {
61 fn from(id: u32) -> Self {
67 pub fn to_u32_scalar<'tcx>(&self) -> Scalar<Tag> {
68 Scalar::from_u32(u32::try_from(self.0).unwrap())
72 /// An identifier of a set of blocked threads. 0 is used to indicate the absence
73 /// of a blockset identifier and, therefore, is not a valid identifier.
74 #[derive(Clone, Copy, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
75 pub struct BlockSetId(NonZeroU32);
78 /// Panics if `id` is 0.
79 pub fn new(id: u32) -> Self {
80 Self(NonZeroU32::new(id).expect("0 is not a valid blockset id"))
82 pub fn to_u32_scalar<'tcx>(&self) -> Scalar<Tag> {
83 Scalar::from_u32(self.0.get())
87 /// The state of a thread.
88 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
89 pub enum ThreadState {
90 /// The thread is enabled and can be executed.
92 /// The thread tried to join the specified thread and is blocked until that
93 /// thread terminates.
94 BlockedOnJoin(ThreadId),
95 /// The thread is blocked and belongs to the given blockset.
97 /// The thread has terminated its execution (we do not delete terminated
102 /// The join status of a thread.
103 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
104 enum ThreadJoinStatus {
105 /// The thread can be joined.
107 /// A thread is detached if its join handle was destroyed and no other
108 /// thread can join it.
110 /// The thread was already joined by some thread and cannot be joined again.
115 pub struct Thread<'mir, 'tcx> {
117 /// Name of the thread.
118 thread_name: Option<Vec<u8>>,
119 /// The virtual call stack.
120 stack: Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>>,
122 join_status: ThreadJoinStatus,
125 impl<'mir, 'tcx> Thread<'mir, 'tcx> {
126 /// Check if the thread is done executing (no more stack frames). If yes,
127 /// change the state to terminated and return `true`.
128 fn check_terminated(&mut self) -> bool {
129 if self.state == ThreadState::Enabled {
130 if self.stack.is_empty() {
131 self.state = ThreadState::Terminated;
139 impl<'mir, 'tcx> std::fmt::Debug for Thread<'mir, 'tcx> {
140 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
141 if let Some(ref name) = self.thread_name {
142 write!(f, "{}", String::from_utf8_lossy(name))?;
144 write!(f, "<unnamed>")?;
146 write!(f, "({:?}, {:?})", self.state, self.join_status)
150 impl<'mir, 'tcx> Default for Thread<'mir, 'tcx> {
151 fn default() -> Self {
153 state: ThreadState::Enabled,
156 join_status: ThreadJoinStatus::Joinable,
161 /// A set of threads.
163 pub struct ThreadManager<'mir, 'tcx> {
164 /// Identifier of the currently active thread.
165 active_thread: ThreadId,
166 /// Threads used in the program.
168 /// Note that this vector also contains terminated threads.
169 threads: IndexVec<ThreadId, Thread<'mir, 'tcx>>,
170 /// A counter used to generate unique identifiers for blocksets.
171 blockset_counter: u32,
172 /// A mapping from a thread-local static to an allocation id of a thread
173 /// specific allocation.
174 thread_local_alloc_ids: RefCell<FxHashMap<(DefId, ThreadId), AllocId>>,
175 /// A flag that indicates that we should change the active thread.
176 yield_active_thread: bool,
179 impl<'mir, 'tcx> Default for ThreadManager<'mir, 'tcx> {
180 fn default() -> Self {
181 let mut threads = IndexVec::new();
182 // Create the main thread and add it to the list of threads.
183 let mut main_thread = Thread::default();
184 // The main thread can *not* be joined on.
185 main_thread.join_status = ThreadJoinStatus::Detached;
186 threads.push(main_thread);
188 active_thread: ThreadId::new(0),
191 thread_local_alloc_ids: Default::default(),
192 yield_active_thread: false,
197 impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
198 /// Check if we have an allocation for the given thread local static for the
200 fn get_thread_local_alloc_id(&self, def_id: DefId) -> Option<AllocId> {
201 self.thread_local_alloc_ids.borrow().get(&(def_id, self.active_thread)).cloned()
204 /// Set the allocation id as the allocation id of the given thread local
205 /// static for the active thread.
207 /// Panics if a thread local is initialized twice for the same thread.
208 fn set_thread_local_alloc_id(&self, def_id: DefId, new_alloc_id: AllocId) {
209 self.thread_local_alloc_ids
211 .insert((def_id, self.active_thread), new_alloc_id)
215 /// Borrow the stack of the active thread.
216 fn active_thread_stack(&self) -> &[Frame<'mir, 'tcx, Tag, FrameData<'tcx>>] {
217 &self.threads[self.active_thread].stack
220 /// Mutably borrow the stack of the active thread.
221 fn active_thread_stack_mut(&mut self) -> &mut Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>> {
222 &mut self.threads[self.active_thread].stack
225 /// Create a new thread and returns its id.
226 fn create_thread(&mut self) -> ThreadId {
227 let new_thread_id = ThreadId::new(self.threads.len());
228 self.threads.push(Default::default());
232 /// Set an active thread and return the id of the thread that was active before.
233 fn set_active_thread_id(&mut self, id: ThreadId) -> ThreadId {
234 let active_thread_id = self.active_thread;
235 self.active_thread = id;
236 assert!(self.active_thread.index() < self.threads.len());
240 /// Get the id of the currently active thread.
241 fn get_active_thread_id(&self) -> ThreadId {
245 /// Get the total number of threads that were ever spawn by this program.
246 fn get_total_thread_count(&self) -> usize {
250 /// Has the given thread terminated?
251 fn has_terminated(&self, thread_id: ThreadId) -> bool {
252 self.threads[thread_id].state == ThreadState::Terminated
255 /// Enable the thread for execution. The thread must be terminated.
256 fn enable_thread(&mut self, thread_id: ThreadId) {
257 assert!(self.has_terminated(thread_id));
258 self.threads[thread_id].state = ThreadState::Enabled;
261 /// Get a mutable borrow of the currently active thread.
262 fn active_thread_mut(&mut self) -> &mut Thread<'mir, 'tcx> {
263 &mut self.threads[self.active_thread]
266 /// Get a shared borrow of the currently active thread.
267 fn active_thread_ref(&self) -> &Thread<'mir, 'tcx> {
268 &self.threads[self.active_thread]
271 /// Mark the thread as detached, which means that no other thread will try
272 /// to join it and the thread is responsible for cleaning up.
273 fn detach_thread(&mut self, id: ThreadId) -> InterpResult<'tcx> {
274 if self.threads[id].join_status != ThreadJoinStatus::Joinable {
275 throw_ub_format!("trying to detach thread that was already detached or joined");
277 self.threads[id].join_status = ThreadJoinStatus::Detached;
281 /// Mark that the active thread tries to join the thread with `joined_thread_id`.
282 fn join_thread(&mut self, joined_thread_id: ThreadId) -> InterpResult<'tcx> {
283 if self.threads[joined_thread_id].join_status != ThreadJoinStatus::Joinable {
284 throw_ub_format!("trying to join a detached or already joined thread");
286 if joined_thread_id == self.active_thread {
287 throw_ub_format!("trying to join itself");
292 .all(|thread| thread.state != ThreadState::BlockedOnJoin(joined_thread_id)),
293 "a joinable thread already has threads waiting for its termination"
295 // Mark the joined thread as being joined so that we detect if other
296 // threads try to join it.
297 self.threads[joined_thread_id].join_status = ThreadJoinStatus::Joined;
298 if self.threads[joined_thread_id].state != ThreadState::Terminated {
299 // The joined thread is still running, we need to wait for it.
300 self.active_thread_mut().state = ThreadState::BlockedOnJoin(joined_thread_id);
302 "{:?} blocked on {:?} when trying to join",
310 /// Set the name of the active thread.
311 fn set_thread_name(&mut self, new_thread_name: Vec<u8>) {
312 self.active_thread_mut().thread_name = Some(new_thread_name);
315 /// Get the name of the active thread.
316 fn get_thread_name(&self) -> &[u8] {
317 if let Some(ref thread_name) = self.active_thread_ref().thread_name {
324 /// Allocate a new blockset id.
325 fn create_blockset(&mut self) -> BlockSetId {
326 self.blockset_counter = self.blockset_counter.checked_add(1).unwrap();
327 BlockSetId::new(self.blockset_counter)
330 /// Block the currently active thread and put it into the given blockset.
331 fn block_active_thread(&mut self, set: BlockSetId) {
332 let state = &mut self.active_thread_mut().state;
333 assert_eq!(*state, ThreadState::Enabled);
334 *state = ThreadState::Blocked(set);
337 /// Unblock any one thread from the given blockset if it contains at least
338 /// one. Return the id of the unblocked thread.
339 fn unblock_some_thread(&mut self, set: BlockSetId) -> Option<ThreadId> {
340 for (id, thread) in self.threads.iter_enumerated_mut() {
341 if thread.state == ThreadState::Blocked(set) {
342 trace!("unblocking {:?} in blockset {:?}", id, set);
343 thread.state = ThreadState::Enabled;
350 /// Change the active thread to some enabled thread.
351 fn yield_active_thread(&mut self) {
352 self.yield_active_thread = true;
355 /// Decide which action to take next and on which thread.
357 /// The currently implemented scheduling policy is the one that is commonly
358 /// used in stateless model checkers such as Loom: run the active thread as
359 /// long as we can and switch only when we have to (the active thread was
360 /// blocked, terminated, or has explicitly asked to be preempted).
361 fn schedule(&mut self) -> InterpResult<'tcx, SchedulingAction> {
362 // Check whether the thread has **just** terminated (`check_terminated`
363 // checks whether the thread has popped all its stack and if yes, sets
364 // the thread state to terminated).
365 if self.threads[self.active_thread].check_terminated() {
366 // Check if we need to unblock any threads.
367 for (i, thread) in self.threads.iter_enumerated_mut() {
368 if thread.state == ThreadState::BlockedOnJoin(self.active_thread) {
369 trace!("unblocking {:?} because {:?} terminated", i, self.active_thread);
370 thread.state = ThreadState::Enabled;
373 return Ok(SchedulingAction::ExecuteDtors);
375 if self.threads[MAIN_THREAD].state == ThreadState::Terminated {
376 // The main thread terminated; stop the program.
377 if self.threads.iter().any(|thread| thread.state != ThreadState::Terminated) {
378 // FIXME: This check should be either configurable or just emit
379 // a warning. For example, it seems normal for a program to
380 // terminate without waiting for its detached threads to
381 // terminate. However, this case is not trivial to support
382 // because we also probably do not want to consider the memory
383 // owned by these threads as leaked.
384 throw_unsup_format!("the main thread terminated without waiting for other threads");
386 return Ok(SchedulingAction::Stop);
388 if self.threads[self.active_thread].state == ThreadState::Enabled
389 && !self.yield_active_thread
391 // The currently active thread is still enabled, just continue with it.
392 return Ok(SchedulingAction::ExecuteStep);
394 // We need to pick a new thread for execution.
395 for (id, thread) in self.threads.iter_enumerated() {
396 if thread.state == ThreadState::Enabled {
397 if !self.yield_active_thread || id != self.active_thread {
398 self.active_thread = id;
403 self.yield_active_thread = false;
404 if self.threads[self.active_thread].state == ThreadState::Enabled {
405 return Ok(SchedulingAction::ExecuteStep);
407 // We have not found a thread to execute.
408 if self.threads.iter().all(|thread| thread.state == ThreadState::Terminated) {
411 throw_machine_stop!(TerminationInfo::Deadlock);
416 // Public interface to thread management.
417 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
418 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
419 /// A workaround for thread-local statics until
420 /// https://github.com/rust-lang/rust/issues/70685 is fixed: change the
421 /// thread-local allocation id with a freshly generated allocation id for
422 /// the currently active thread.
423 fn remap_thread_local_alloc_ids(
425 val: &mut mir::interpret::ConstValue<'tcx>,
426 ) -> InterpResult<'tcx> {
427 let this = self.eval_context_ref();
429 mir::interpret::ConstValue::Scalar(Scalar::Ptr(ref mut ptr)) => {
430 let alloc_id = ptr.alloc_id;
431 let alloc = this.tcx.alloc_map.lock().get(alloc_id);
433 let is_thread_local = |def_id| {
434 tcx.codegen_fn_attrs(def_id).flags.contains(CodegenFnAttrFlags::THREAD_LOCAL)
437 Some(GlobalAlloc::Static(def_id)) if is_thread_local(def_id) => {
438 ptr.alloc_id = this.get_or_create_thread_local_alloc_id(def_id)?;
444 // FIXME: Handling only `Scalar` seems to work for now, but at
445 // least in principle thread-locals could be in any constant, so
446 // we should also consider other cases. However, once
447 // https://github.com/rust-lang/rust/issues/70685 gets fixed,
448 // this code will have to be rewritten anyway.
454 /// Get a thread-specific allocation id for the given thread-local static.
455 /// If needed, allocate a new one.
457 /// FIXME: This method should be replaced as soon as
458 /// https://github.com/rust-lang/rust/issues/70685 gets fixed.
459 fn get_or_create_thread_local_alloc_id(&self, def_id: DefId) -> InterpResult<'tcx, AllocId> {
460 let this = self.eval_context_ref();
462 if let Some(new_alloc_id) = this.machine.threads.get_thread_local_alloc_id(def_id) {
463 // We already have a thread-specific allocation id for this
464 // thread-local static.
467 // We need to allocate a thread-specific allocation id for this
468 // thread-local static.
470 // At first, we invoke the `const_eval_raw` query and extract the
471 // allocation from it. Unfortunately, we have to duplicate the code
472 // from `Memory::get_global_alloc` that does this.
474 // Then we store the retrieved allocation back into the `alloc_map`
475 // to get a fresh allocation id, which we can use as a
476 // thread-specific allocation id for the thread-local static.
477 if tcx.is_foreign_item(def_id) {
478 throw_unsup_format!("foreign thread-local statics are not supported");
480 // Invoke the `const_eval_raw` query.
481 let instance = Instance::mono(tcx.tcx, def_id);
482 let gid = GlobalId { instance, promoted: None };
484 tcx.const_eval_raw(ty::ParamEnv::reveal_all().and(gid)).map_err(|err| {
485 // no need to report anything, the const_eval call takes care of that
487 assert!(tcx.is_static(def_id));
490 let id = raw_const.alloc_id;
491 // Extract the allocation from the query result.
492 let mut alloc_map = tcx.alloc_map.lock();
493 let allocation = alloc_map.unwrap_memory(id);
494 // Create a new allocation id for the same allocation in this hacky
495 // way. Internally, `alloc_map` deduplicates allocations, but this
496 // is fine because Miri will make a copy before a first mutable
498 let new_alloc_id = alloc_map.create_memory_alloc(allocation);
499 this.machine.threads.set_thread_local_alloc_id(def_id, new_alloc_id);
505 fn create_thread(&mut self) -> InterpResult<'tcx, ThreadId> {
506 let this = self.eval_context_mut();
507 Ok(this.machine.threads.create_thread())
511 fn detach_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx> {
512 let this = self.eval_context_mut();
513 this.machine.threads.detach_thread(thread_id)
517 fn join_thread(&mut self, joined_thread_id: ThreadId) -> InterpResult<'tcx> {
518 let this = self.eval_context_mut();
519 this.machine.threads.join_thread(joined_thread_id)
523 fn set_active_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx, ThreadId> {
524 let this = self.eval_context_mut();
525 Ok(this.machine.threads.set_active_thread_id(thread_id))
529 fn get_active_thread(&self) -> InterpResult<'tcx, ThreadId> {
530 let this = self.eval_context_ref();
531 Ok(this.machine.threads.get_active_thread_id())
535 fn get_total_thread_count(&self) -> InterpResult<'tcx, usize> {
536 let this = self.eval_context_ref();
537 Ok(this.machine.threads.get_total_thread_count())
541 fn has_terminated(&self, thread_id: ThreadId) -> InterpResult<'tcx, bool> {
542 let this = self.eval_context_ref();
543 Ok(this.machine.threads.has_terminated(thread_id))
547 fn enable_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx> {
548 let this = self.eval_context_mut();
549 this.machine.threads.enable_thread(thread_id);
554 fn active_thread_stack(&self) -> &[Frame<'mir, 'tcx, Tag, FrameData<'tcx>>] {
555 let this = self.eval_context_ref();
556 this.machine.threads.active_thread_stack()
560 fn active_thread_stack_mut(&mut self) -> &mut Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>> {
561 let this = self.eval_context_mut();
562 this.machine.threads.active_thread_stack_mut()
566 fn set_active_thread_name(&mut self, new_thread_name: Vec<u8>) -> InterpResult<'tcx, ()> {
567 let this = self.eval_context_mut();
568 Ok(this.machine.threads.set_thread_name(new_thread_name))
572 fn get_active_thread_name<'c>(&'c self) -> InterpResult<'tcx, &'c [u8]>
576 let this = self.eval_context_ref();
577 Ok(this.machine.threads.get_thread_name())
581 fn create_blockset(&mut self) -> InterpResult<'tcx, BlockSetId> {
582 let this = self.eval_context_mut();
583 Ok(this.machine.threads.create_blockset())
587 fn block_active_thread(&mut self, set: BlockSetId) -> InterpResult<'tcx> {
588 let this = self.eval_context_mut();
589 Ok(this.machine.threads.block_active_thread(set))
593 fn unblock_some_thread(&mut self, set: BlockSetId) -> InterpResult<'tcx, Option<ThreadId>> {
594 let this = self.eval_context_mut();
595 Ok(this.machine.threads.unblock_some_thread(set))
599 fn yield_active_thread(&mut self) -> InterpResult<'tcx> {
600 let this = self.eval_context_mut();
601 this.machine.threads.yield_active_thread();
605 /// Decide which action to take next and on which thread.
607 fn schedule(&mut self) -> InterpResult<'tcx, SchedulingAction> {
608 let this = self.eval_context_mut();
609 this.machine.threads.schedule()