1 //! Implements threads.
3 use std::convert::TryInto;
4 use std::cell::RefCell;
5 use std::convert::TryFrom;
6 use std::num::NonZeroU32;
10 use rustc_data_structures::fx::FxHashMap;
11 use rustc_hir::def_id::DefId;
12 use rustc_index::vec::{Idx, IndexVec};
14 middle::codegen_fn_attrs::CodegenFnAttrFlags,
21 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
22 pub enum SchedulingAction {
23 /// Execute step on the active thread.
25 /// Execute destructors of the active thread.
31 /// A thread identifier.
32 #[derive(Clone, Copy, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
33 pub struct ThreadId(usize);
35 /// The main thread. When it terminates, the whole application terminates.
36 const MAIN_THREAD: ThreadId = ThreadId(0);
39 pub fn to_u128(self) -> u128 {
40 self.0.try_into().unwrap()
44 impl Idx for ThreadId {
45 fn new(idx: usize) -> Self {
48 fn index(self) -> usize {
53 impl From<u64> for ThreadId {
54 fn from(id: u64) -> Self {
55 Self(usize::try_from(id).unwrap())
59 impl From<u32> for ThreadId {
60 fn from(id: u32) -> Self {
61 Self(usize::try_from(id).unwrap())
66 pub fn to_u32_scalar<'tcx>(&self) -> Scalar<Tag> {
67 Scalar::from_u32(u32::try_from(self.0).unwrap())
71 /// An identifier of a set of blocked threads. 0 is used to indicate the absence
72 /// of a blockset identifier and, therefore, is not a valid identifier.
73 #[derive(Clone, Copy, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
74 pub struct BlockSetId(NonZeroU32);
76 impl From<u32> for BlockSetId {
77 fn from(id: u32) -> Self {
78 Self(NonZeroU32::new(id).expect("0 is not a valid blockset id"))
83 pub fn to_u32_scalar<'tcx>(&self) -> Scalar<Tag> {
84 Scalar::from_u32(self.0.get())
88 /// The state of a thread.
89 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
90 pub enum ThreadState {
91 /// The thread is enabled and can be executed.
93 /// The thread tried to join the specified thread and is blocked until that
94 /// thread terminates.
95 BlockedOnJoin(ThreadId),
96 /// The thread is blocked and belongs to the given blockset.
98 /// The thread has terminated its execution (we do not delete terminated
103 /// The join status of a thread.
104 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
105 enum ThreadJoinStatus {
106 /// The thread can be joined.
108 /// A thread is detached if its join handle was destroyed and no other
109 /// thread can join it.
111 /// The thread was already joined by some thread and cannot be joined again.
116 pub struct Thread<'mir, 'tcx> {
118 /// Name of the thread.
119 thread_name: Option<Vec<u8>>,
120 /// The virtual call stack.
121 stack: Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>>,
123 join_status: ThreadJoinStatus,
126 impl<'mir, 'tcx> Thread<'mir, 'tcx> {
127 /// Check if the thread is done executing (no more stack frames). If yes,
128 /// change the state to terminated and return `true`.
129 fn check_terminated(&mut self) -> bool {
130 if self.state == ThreadState::Enabled {
131 if self.stack.is_empty() {
132 self.state = ThreadState::Terminated;
140 impl<'mir, 'tcx> std::fmt::Debug for Thread<'mir, 'tcx> {
141 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
142 if let Some(ref name) = self.thread_name {
143 write!(f, "{}", String::from_utf8_lossy(name))?;
145 write!(f, "<unnamed>")?;
147 write!(f, "({:?}, {:?})", self.state, self.join_status)
151 impl<'mir, 'tcx> Default for Thread<'mir, 'tcx> {
152 fn default() -> Self {
154 state: ThreadState::Enabled,
157 join_status: ThreadJoinStatus::Joinable,
162 /// A set of threads.
164 pub struct ThreadManager<'mir, 'tcx> {
165 /// Identifier of the currently active thread.
166 active_thread: ThreadId,
167 /// Threads used in the program.
169 /// Note that this vector also contains terminated threads.
170 threads: IndexVec<ThreadId, Thread<'mir, 'tcx>>,
171 /// A counter used to generate unique identifiers for blocksets.
172 blockset_counter: u32,
173 /// A mapping from a thread-local static to an allocation id of a thread
174 /// specific allocation.
175 thread_local_alloc_ids: RefCell<FxHashMap<(DefId, ThreadId), AllocId>>,
176 /// A flag that indicates that we should change the active thread.
177 yield_active_thread: bool,
180 impl<'mir, 'tcx> Default for ThreadManager<'mir, 'tcx> {
181 fn default() -> Self {
182 let mut threads = IndexVec::new();
183 // Create the main thread and add it to the list of threads.
184 let mut main_thread = Thread::default();
185 // The main thread can *not* be joined on.
186 main_thread.join_status = ThreadJoinStatus::Detached;
187 threads.push(main_thread);
189 active_thread: ThreadId::new(0),
192 thread_local_alloc_ids: Default::default(),
193 yield_active_thread: false,
198 impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
199 /// Check if we have an allocation for the given thread local static for the
201 fn get_thread_local_alloc_id(&self, def_id: DefId) -> Option<AllocId> {
202 self.thread_local_alloc_ids.borrow().get(&(def_id, self.active_thread)).cloned()
205 /// Set the allocation id as the allocation id of the given thread local
206 /// static for the active thread.
208 /// Panics if a thread local is initialized twice for the same thread.
209 fn set_thread_local_alloc_id(&self, def_id: DefId, new_alloc_id: AllocId) {
210 self.thread_local_alloc_ids
212 .insert((def_id, self.active_thread), new_alloc_id)
216 /// Borrow the stack of the active thread.
217 fn active_thread_stack(&self) -> &[Frame<'mir, 'tcx, Tag, FrameData<'tcx>>] {
218 &self.threads[self.active_thread].stack
221 /// Mutably borrow the stack of the active thread.
222 fn active_thread_stack_mut(&mut self) -> &mut Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>> {
223 &mut self.threads[self.active_thread].stack
226 /// Create a new thread and returns its id.
227 fn create_thread(&mut self) -> ThreadId {
228 let new_thread_id = ThreadId::new(self.threads.len());
229 self.threads.push(Default::default());
233 /// Set an active thread and return the id of the thread that was active before.
234 fn set_active_thread_id(&mut self, id: ThreadId) -> ThreadId {
235 let active_thread_id = self.active_thread;
236 self.active_thread = id;
237 assert!(self.active_thread.index() < self.threads.len());
241 /// Get the id of the currently active thread.
242 fn get_active_thread_id(&self) -> ThreadId {
246 /// Get the total number of threads that were ever spawn by this program.
247 fn get_total_thread_count(&self) -> usize {
251 /// Has the given thread terminated?
252 fn has_terminated(&self, thread_id: ThreadId) -> bool {
253 self.threads[thread_id].state == ThreadState::Terminated
256 /// Enable the thread for execution. The thread must be terminated.
257 fn enable_thread(&mut self, thread_id: ThreadId) {
258 assert!(self.has_terminated(thread_id));
259 self.threads[thread_id].state = ThreadState::Enabled;
262 /// Get a mutable borrow of the currently active thread.
263 fn active_thread_mut(&mut self) -> &mut Thread<'mir, 'tcx> {
264 &mut self.threads[self.active_thread]
267 /// Get a shared borrow of the currently active thread.
268 fn active_thread_ref(&self) -> &Thread<'mir, 'tcx> {
269 &self.threads[self.active_thread]
272 /// Mark the thread as detached, which means that no other thread will try
273 /// to join it and the thread is responsible for cleaning up.
274 fn detach_thread(&mut self, id: ThreadId) -> InterpResult<'tcx> {
275 if self.threads[id].join_status != ThreadJoinStatus::Joinable {
276 throw_ub_format!("trying to detach thread that was already detached or joined");
278 self.threads[id].join_status = ThreadJoinStatus::Detached;
282 /// Mark that the active thread tries to join the thread with `joined_thread_id`.
283 fn join_thread(&mut self, joined_thread_id: ThreadId) -> InterpResult<'tcx> {
284 if self.threads[joined_thread_id].join_status != ThreadJoinStatus::Joinable {
285 throw_ub_format!("trying to join a detached or already joined thread");
287 if joined_thread_id == self.active_thread {
288 throw_ub_format!("trying to join itself");
293 .all(|thread| thread.state != ThreadState::BlockedOnJoin(joined_thread_id)),
294 "a joinable thread already has threads waiting for its termination"
296 // Mark the joined thread as being joined so that we detect if other
297 // threads try to join it.
298 self.threads[joined_thread_id].join_status = ThreadJoinStatus::Joined;
299 if self.threads[joined_thread_id].state != ThreadState::Terminated {
300 // The joined thread is still running, we need to wait for it.
301 self.active_thread_mut().state = ThreadState::BlockedOnJoin(joined_thread_id);
303 "{:?} blocked on {:?} when trying to join",
311 /// Set the name of the active thread.
312 fn set_thread_name(&mut self, new_thread_name: Vec<u8>) {
313 self.active_thread_mut().thread_name = Some(new_thread_name);
316 /// Get the name of the active thread.
317 fn get_thread_name(&self) -> InterpResult<'tcx, &[u8]> {
318 if let Some(ref thread_name) = self.active_thread_ref().thread_name {
321 throw_ub_format!("thread {:?} has no name set", self.active_thread)
325 /// Allocate a new blockset id.
326 fn create_blockset(&mut self) -> BlockSetId {
327 self.blockset_counter = self.blockset_counter.checked_add(1).unwrap();
328 self.blockset_counter.into()
331 /// Block the currently active thread and put it into the given blockset.
332 fn block_active_thread(&mut self, set: BlockSetId) {
333 let state = &mut self.active_thread_mut().state;
334 assert_eq!(*state, ThreadState::Enabled);
335 *state = ThreadState::Blocked(set);
338 /// Unblock any one thread from the given blockset if it contains at least
339 /// one. Return the id of the unblocked thread.
340 fn unblock_some_thread(&mut self, set: BlockSetId) -> Option<ThreadId> {
341 for (id, thread) in self.threads.iter_enumerated_mut() {
342 if thread.state == ThreadState::Blocked(set) {
343 trace!("unblocking {:?} in blockset {:?}", id, set);
344 thread.state = ThreadState::Enabled;
351 /// Change the active thread to some enabled thread.
352 fn yield_active_thread(&mut self) {
353 self.yield_active_thread = true;
356 /// Decide which action to take next and on which thread.
358 /// The currently implemented scheduling policy is the one that is commonly
359 /// used in stateless model checkers such as Loom: run the active thread as
360 /// long as we can and switch only when we have to (the active thread was
361 /// blocked, terminated, or has explicitly asked to be preempted).
362 fn schedule(&mut self) -> InterpResult<'tcx, SchedulingAction> {
363 if self.threads[self.active_thread].check_terminated() {
364 // Check if we need to unblock any threads.
365 for (i, thread) in self.threads.iter_enumerated_mut() {
366 if thread.state == ThreadState::BlockedOnJoin(self.active_thread) {
367 trace!("unblocking {:?} because {:?} terminated", i, self.active_thread);
368 thread.state = ThreadState::Enabled;
371 return Ok(SchedulingAction::ExecuteDtors);
373 if self.threads[MAIN_THREAD].state == ThreadState::Terminated {
374 // The main thread terminated; stop the program.
375 if self.threads.iter().any(|thread| thread.state != ThreadState::Terminated) {
376 // FIXME: This check should be either configurable or just emit
377 // a warning. For example, it seems normal for a program to
378 // terminate without waiting for its detached threads to
379 // terminate. However, this case is not trivial to support
380 // because we also probably do not want to consider the memory
381 // owned by these threads as leaked.
382 throw_unsup_format!("the main thread terminated without waiting for other threads");
384 return Ok(SchedulingAction::Stop);
386 if self.threads[self.active_thread].state == ThreadState::Enabled
387 && !self.yield_active_thread
389 // The currently active thread is still enabled, just continue with it.
390 return Ok(SchedulingAction::ExecuteStep);
392 // We need to pick a new thread for execution.
393 for (id, thread) in self.threads.iter_enumerated() {
394 if thread.state == ThreadState::Enabled {
395 if !self.yield_active_thread || id != self.active_thread {
396 self.active_thread = id;
401 self.yield_active_thread = false;
402 if self.threads[self.active_thread].state == ThreadState::Enabled {
403 return Ok(SchedulingAction::ExecuteStep);
405 // We have not found a thread to execute.
406 if self.threads.iter().all(|thread| thread.state == ThreadState::Terminated) {
409 throw_machine_stop!(TerminationInfo::Deadlock);
414 // Public interface to thread management.
415 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
416 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
417 /// A workaround for thread-local statics until
418 /// https://github.com/rust-lang/rust/issues/70685 is fixed: change the
419 /// thread-local allocation id with a freshly generated allocation id for
420 /// the currently active thread.
421 fn remap_thread_local_alloc_ids(
423 val: &mut mir::interpret::ConstValue<'tcx>,
424 ) -> InterpResult<'tcx> {
425 let this = self.eval_context_ref();
427 mir::interpret::ConstValue::Scalar(Scalar::Ptr(ref mut ptr)) => {
428 let alloc_id = ptr.alloc_id;
429 let alloc = this.tcx.alloc_map.lock().get(alloc_id);
431 let is_thread_local = |def_id| {
432 tcx.codegen_fn_attrs(def_id).flags.contains(CodegenFnAttrFlags::THREAD_LOCAL)
435 Some(GlobalAlloc::Static(def_id)) if is_thread_local(def_id) => {
436 ptr.alloc_id = this.get_or_create_thread_local_alloc_id(def_id)?;
442 // FIXME: Handling only `Scalar` seems to work for now, but at
443 // least in principle thread-locals could be in any constant, so
444 // we should also consider other cases. However, once
445 // https://github.com/rust-lang/rust/issues/70685 gets fixed,
446 // this code will have to be rewritten anyway.
452 /// Get a thread-specific allocation id for the given thread-local static.
453 /// If needed, allocate a new one.
455 /// FIXME: This method should be replaced as soon as
456 /// https://github.com/rust-lang/rust/issues/70685 gets fixed.
457 fn get_or_create_thread_local_alloc_id(&self, def_id: DefId) -> InterpResult<'tcx, AllocId> {
458 let this = self.eval_context_ref();
460 if let Some(new_alloc_id) = this.machine.threads.get_thread_local_alloc_id(def_id) {
461 // We already have a thread-specific allocation id for this
462 // thread-local static.
465 // We need to allocate a thread-specific allocation id for this
466 // thread-local static.
468 // At first, we invoke the `const_eval_raw` query and extract the
469 // allocation from it. Unfortunately, we have to duplicate the code
470 // from `Memory::get_global_alloc` that does this.
472 // Then we store the retrieved allocation back into the `alloc_map`
473 // to get a fresh allocation id, which we can use as a
474 // thread-specific allocation id for the thread-local static.
475 if tcx.is_foreign_item(def_id) {
476 throw_unsup_format!("foreign thread-local statics are not supported");
478 // Invoke the `const_eval_raw` query.
479 let instance = Instance::mono(tcx.tcx, def_id);
480 let gid = GlobalId { instance, promoted: None };
482 tcx.const_eval_raw(ty::ParamEnv::reveal_all().and(gid)).map_err(|err| {
483 // no need to report anything, the const_eval call takes care of that
485 assert!(tcx.is_static(def_id));
488 let id = raw_const.alloc_id;
489 // Extract the allocation from the query result.
490 let mut alloc_map = tcx.alloc_map.lock();
491 let allocation = alloc_map.unwrap_memory(id);
492 // Create a new allocation id for the same allocation in this hacky
493 // way. Internally, `alloc_map` deduplicates allocations, but this
494 // is fine because Miri will make a copy before a first mutable
496 let new_alloc_id = alloc_map.create_memory_alloc(allocation);
497 this.machine.threads.set_thread_local_alloc_id(def_id, new_alloc_id);
503 fn create_thread(&mut self) -> InterpResult<'tcx, ThreadId> {
504 let this = self.eval_context_mut();
505 Ok(this.machine.threads.create_thread())
509 fn detach_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx> {
510 let this = self.eval_context_mut();
511 this.machine.threads.detach_thread(thread_id)
515 fn join_thread(&mut self, joined_thread_id: ThreadId) -> InterpResult<'tcx> {
516 let this = self.eval_context_mut();
517 this.machine.threads.join_thread(joined_thread_id)
521 fn set_active_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx, ThreadId> {
522 let this = self.eval_context_mut();
523 Ok(this.machine.threads.set_active_thread_id(thread_id))
527 fn get_active_thread(&self) -> InterpResult<'tcx, ThreadId> {
528 let this = self.eval_context_ref();
529 Ok(this.machine.threads.get_active_thread_id())
533 fn get_total_thread_count(&self) -> InterpResult<'tcx, usize> {
534 let this = self.eval_context_ref();
535 Ok(this.machine.threads.get_total_thread_count())
539 fn has_terminated(&self, thread_id: ThreadId) -> InterpResult<'tcx, bool> {
540 let this = self.eval_context_ref();
541 Ok(this.machine.threads.has_terminated(thread_id))
545 fn enable_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx> {
546 let this = self.eval_context_mut();
547 this.machine.threads.enable_thread(thread_id);
552 fn active_thread_stack(&self) -> &[Frame<'mir, 'tcx, Tag, FrameData<'tcx>>] {
553 let this = self.eval_context_ref();
554 this.machine.threads.active_thread_stack()
558 fn active_thread_stack_mut(&mut self) -> &mut Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>> {
559 let this = self.eval_context_mut();
560 this.machine.threads.active_thread_stack_mut()
564 fn set_active_thread_name(&mut self, new_thread_name: Vec<u8>) -> InterpResult<'tcx, ()> {
565 let this = self.eval_context_mut();
566 Ok(this.machine.threads.set_thread_name(new_thread_name))
570 fn get_active_thread_name<'c>(&'c self) -> InterpResult<'tcx, &'c [u8]>
574 let this = self.eval_context_ref();
575 this.machine.threads.get_thread_name()
579 fn create_blockset(&mut self) -> InterpResult<'tcx, BlockSetId> {
580 let this = self.eval_context_mut();
581 Ok(this.machine.threads.create_blockset())
585 fn block_active_thread(&mut self, set: BlockSetId) -> InterpResult<'tcx> {
586 let this = self.eval_context_mut();
587 Ok(this.machine.threads.block_active_thread(set))
591 fn unblock_some_thread(&mut self, set: BlockSetId) -> InterpResult<'tcx, Option<ThreadId>> {
592 let this = self.eval_context_mut();
593 Ok(this.machine.threads.unblock_some_thread(set))
597 fn yield_active_thread(&mut self) -> InterpResult<'tcx> {
598 let this = self.eval_context_mut();
599 this.machine.threads.yield_active_thread();
603 /// Decide which action to take next and on which thread.
605 fn schedule(&mut self) -> InterpResult<'tcx, SchedulingAction> {
606 let this = self.eval_context_mut();
607 this.machine.threads.schedule()