1 //! Implements threads.
3 use std::cell::RefCell;
4 use std::collections::hash_map::Entry;
5 use std::convert::TryFrom;
6 use std::num::TryFromIntError;
7 use std::time::{Duration, Instant, SystemTime};
11 use rustc_data_structures::fx::FxHashMap;
12 use rustc_hir::def_id::DefId;
13 use rustc_index::vec::{Idx, IndexVec};
15 use crate::sync::SynchronizationState;
18 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
19 pub enum SchedulingAction {
20 /// Execute step on the active thread.
22 /// Execute a timeout callback.
23 ExecuteTimeoutCallback,
24 /// Execute destructors of the active thread.
30 /// Timeout callbacks can be created by synchronization primitives to tell the
31 /// scheduler that they should be called once some period of time passes.
32 type TimeoutCallback<'mir, 'tcx> =
33 Box<dyn FnOnce(&mut InterpCx<'mir, 'tcx, Evaluator<'mir, 'tcx>>) -> InterpResult<'tcx> + 'tcx>;
35 /// A thread identifier.
36 #[derive(Clone, Copy, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
37 pub struct ThreadId(u32);
39 /// The main thread. When it terminates, the whole application terminates.
40 const MAIN_THREAD: ThreadId = ThreadId(0);
43 pub fn to_u32(self) -> u32 {
48 impl Idx for ThreadId {
49 fn new(idx: usize) -> Self {
50 ThreadId(u32::try_from(idx).unwrap())
53 fn index(self) -> usize {
54 usize::try_from(self.0).unwrap()
58 impl TryFrom<u64> for ThreadId {
59 type Error = TryFromIntError;
60 fn try_from(id: u64) -> Result<Self, Self::Error> {
61 u32::try_from(id).map(|id_u32| Self(id_u32))
65 impl From<u32> for ThreadId {
66 fn from(id: u32) -> Self {
72 pub fn to_u32_scalar<'tcx>(&self) -> Scalar<Tag> {
73 Scalar::from_u32(u32::try_from(self.0).unwrap())
77 /// The state of a thread.
78 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
79 pub enum ThreadState {
80 /// The thread is enabled and can be executed.
82 /// The thread tried to join the specified thread and is blocked until that
83 /// thread terminates.
84 BlockedOnJoin(ThreadId),
85 /// The thread is blocked on some synchronization primitive. It is the
86 /// responsibility of the synchronization primitives to track threads that
87 /// are blocked by them.
89 /// The thread has terminated its execution. We do not delete terminated
90 /// threads (FIXME: why?).
94 /// The join status of a thread.
95 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
96 enum ThreadJoinStatus {
97 /// The thread can be joined.
99 /// A thread is detached if its join handle was destroyed and no other
100 /// thread can join it.
102 /// The thread was already joined by some thread and cannot be joined again.
107 pub struct Thread<'mir, 'tcx> {
109 /// Name of the thread.
110 thread_name: Option<Vec<u8>>,
111 /// The virtual call stack.
112 stack: Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>>,
114 join_status: ThreadJoinStatus,
117 impl<'mir, 'tcx> Thread<'mir, 'tcx> {
118 /// Check if the thread is done executing (no more stack frames). If yes,
119 /// change the state to terminated and return `true`.
120 fn check_terminated(&mut self) -> bool {
121 if self.state == ThreadState::Enabled {
122 if self.stack.is_empty() {
123 self.state = ThreadState::Terminated;
130 /// Get the name of the current thread, or `<unnamed>` if it was not set.
131 fn thread_name(&self) -> &[u8] {
132 if let Some(ref thread_name) = self.thread_name {
140 impl<'mir, 'tcx> std::fmt::Debug for Thread<'mir, 'tcx> {
141 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
142 write!(f, "{}({:?}, {:?})", String::from_utf8_lossy(self.thread_name()), self.state, self.join_status)
146 impl<'mir, 'tcx> Default for Thread<'mir, 'tcx> {
147 fn default() -> Self {
149 state: ThreadState::Enabled,
152 join_status: ThreadJoinStatus::Joinable,
157 /// A specific moment in time.
161 RealTime(SystemTime),
165 /// How long do we have to wait from now until the specified time?
166 fn get_wait_time(&self) -> Duration {
168 Time::Monotonic(instant) => instant.saturating_duration_since(Instant::now()),
169 Time::RealTime(time) =>
170 time.duration_since(SystemTime::now()).unwrap_or(Duration::new(0, 0)),
175 /// Callbacks are used to implement timeouts. For example, waiting on a
176 /// conditional variable with a timeout creates a callback that is called after
177 /// the specified time and unblocks the thread. If another thread signals on the
178 /// conditional variable, the signal handler deletes the callback.
179 struct TimeoutCallbackInfo<'mir, 'tcx> {
180 /// The callback should be called no earlier than this time.
182 /// The called function.
183 callback: TimeoutCallback<'mir, 'tcx>,
186 impl<'mir, 'tcx> std::fmt::Debug for TimeoutCallbackInfo<'mir, 'tcx> {
187 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
188 write!(f, "TimeoutCallback({:?})", self.call_time)
192 /// A set of threads.
194 pub struct ThreadManager<'mir, 'tcx> {
195 /// Identifier of the currently active thread.
196 active_thread: ThreadId,
197 /// Threads used in the program.
199 /// Note that this vector also contains terminated threads.
200 threads: IndexVec<ThreadId, Thread<'mir, 'tcx>>,
201 /// This field is pub(crate) because the synchronization primitives
202 /// (`crate::sync`) need a way to access it.
203 pub(crate) sync: SynchronizationState,
204 /// A mapping from a thread-local static to an allocation id of a thread
205 /// specific allocation.
206 thread_local_alloc_ids: RefCell<FxHashMap<(DefId, ThreadId), AllocId>>,
207 /// A flag that indicates that we should change the active thread.
208 yield_active_thread: bool,
209 /// Callbacks that are called once the specified time passes.
210 timeout_callbacks: FxHashMap<ThreadId, TimeoutCallbackInfo<'mir, 'tcx>>,
213 impl<'mir, 'tcx> Default for ThreadManager<'mir, 'tcx> {
214 fn default() -> Self {
215 let mut threads = IndexVec::new();
216 // Create the main thread and add it to the list of threads.
217 let mut main_thread = Thread::default();
218 // The main thread can *not* be joined on.
219 main_thread.join_status = ThreadJoinStatus::Detached;
220 threads.push(main_thread);
222 active_thread: ThreadId::new(0),
224 sync: SynchronizationState::default(),
225 thread_local_alloc_ids: Default::default(),
226 yield_active_thread: false,
227 timeout_callbacks: FxHashMap::default(),
232 impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
233 /// Check if we have an allocation for the given thread local static for the
235 fn get_thread_local_alloc_id(&self, def_id: DefId) -> Option<AllocId> {
236 self.thread_local_alloc_ids.borrow().get(&(def_id, self.active_thread)).cloned()
239 /// Set the allocation id as the allocation id of the given thread local
240 /// static for the active thread.
242 /// Panics if a thread local is initialized twice for the same thread.
243 fn set_thread_local_alloc_id(&self, def_id: DefId, new_alloc_id: AllocId) {
244 self.thread_local_alloc_ids
246 .insert((def_id, self.active_thread), new_alloc_id)
250 /// Borrow the stack of the active thread.
251 fn active_thread_stack(&self) -> &[Frame<'mir, 'tcx, Tag, FrameData<'tcx>>] {
252 &self.threads[self.active_thread].stack
255 /// Mutably borrow the stack of the active thread.
256 fn active_thread_stack_mut(&mut self) -> &mut Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>> {
257 &mut self.threads[self.active_thread].stack
260 /// Create a new thread and returns its id.
261 fn create_thread(&mut self) -> ThreadId {
262 let new_thread_id = ThreadId::new(self.threads.len());
263 self.threads.push(Default::default());
267 /// Set an active thread and return the id of the thread that was active before.
268 fn set_active_thread_id(&mut self, id: ThreadId) -> ThreadId {
269 let active_thread_id = self.active_thread;
270 self.active_thread = id;
271 assert!(self.active_thread.index() < self.threads.len());
275 /// Get the id of the currently active thread.
276 fn get_active_thread_id(&self) -> ThreadId {
280 /// Get the total number of threads that were ever spawn by this program.
281 fn get_total_thread_count(&self) -> usize {
285 /// Has the given thread terminated?
286 fn has_terminated(&self, thread_id: ThreadId) -> bool {
287 self.threads[thread_id].state == ThreadState::Terminated
290 /// Enable the thread for execution. The thread must be terminated.
291 fn enable_thread(&mut self, thread_id: ThreadId) {
292 assert!(self.has_terminated(thread_id));
293 self.threads[thread_id].state = ThreadState::Enabled;
296 /// Get a mutable borrow of the currently active thread.
297 fn active_thread_mut(&mut self) -> &mut Thread<'mir, 'tcx> {
298 &mut self.threads[self.active_thread]
301 /// Get a shared borrow of the currently active thread.
302 fn active_thread_ref(&self) -> &Thread<'mir, 'tcx> {
303 &self.threads[self.active_thread]
306 /// Mark the thread as detached, which means that no other thread will try
307 /// to join it and the thread is responsible for cleaning up.
308 fn detach_thread(&mut self, id: ThreadId) -> InterpResult<'tcx> {
309 if self.threads[id].join_status != ThreadJoinStatus::Joinable {
310 throw_ub_format!("trying to detach thread that was already detached or joined");
312 self.threads[id].join_status = ThreadJoinStatus::Detached;
316 /// Mark that the active thread tries to join the thread with `joined_thread_id`.
317 fn join_thread(&mut self, joined_thread_id: ThreadId) -> InterpResult<'tcx> {
318 if self.threads[joined_thread_id].join_status != ThreadJoinStatus::Joinable {
319 throw_ub_format!("trying to join a detached or already joined thread");
321 if joined_thread_id == self.active_thread {
322 throw_ub_format!("trying to join itself");
327 .all(|thread| thread.state != ThreadState::BlockedOnJoin(joined_thread_id)),
328 "a joinable thread already has threads waiting for its termination"
330 // Mark the joined thread as being joined so that we detect if other
331 // threads try to join it.
332 self.threads[joined_thread_id].join_status = ThreadJoinStatus::Joined;
333 if self.threads[joined_thread_id].state != ThreadState::Terminated {
334 // The joined thread is still running, we need to wait for it.
335 self.active_thread_mut().state = ThreadState::BlockedOnJoin(joined_thread_id);
337 "{:?} blocked on {:?} when trying to join",
345 /// Set the name of the active thread.
346 fn set_thread_name(&mut self, new_thread_name: Vec<u8>) {
347 self.active_thread_mut().thread_name = Some(new_thread_name);
350 /// Get the name of the active thread.
351 fn get_thread_name(&self) -> &[u8] {
352 self.active_thread_ref().thread_name()
355 /// Put the thread into the blocked state.
356 fn block_thread(&mut self, thread: ThreadId) {
357 let state = &mut self.threads[thread].state;
358 assert_eq!(*state, ThreadState::Enabled);
359 *state = ThreadState::BlockedOnSync;
362 /// Put the blocked thread into the enabled state.
363 fn unblock_thread(&mut self, thread: ThreadId) {
364 let state = &mut self.threads[thread].state;
365 assert_eq!(*state, ThreadState::BlockedOnSync);
366 *state = ThreadState::Enabled;
369 /// Change the active thread to some enabled thread.
370 fn yield_active_thread(&mut self) {
371 // We do not yield immediately, as swapping out the current stack while executing a MIR statement
372 // could lead to all sorts of confusion.
373 // We should only switch stacks between steps.
374 self.yield_active_thread = true;
377 /// Register the given `callback` to be called once the `call_time` passes.
379 /// The callback will be called with `thread` being the active thread, and
380 /// the callback may not change the active thread.
381 fn register_timeout_callback(
385 callback: TimeoutCallback<'mir, 'tcx>,
387 self.timeout_callbacks
388 .insert(thread, TimeoutCallbackInfo { call_time, callback })
392 /// Unregister the callback for the `thread`.
393 fn unregister_timeout_callback_if_exists(&mut self, thread: ThreadId) {
394 self.timeout_callbacks.remove(&thread);
397 /// Get a callback that is ready to be called.
398 fn get_ready_callback(&mut self) -> Option<(ThreadId, TimeoutCallback<'mir, 'tcx>)> {
399 // We iterate over all threads in the order of their indices because
400 // this allows us to have a deterministic scheduler.
401 for thread in self.threads.indices() {
402 match self.timeout_callbacks.entry(thread) {
403 Entry::Occupied(entry) =>
404 if entry.get().call_time.get_wait_time() == Duration::new(0, 0) {
405 return Some((thread, entry.remove().callback));
407 Entry::Vacant(_) => {}
413 /// Decide which action to take next and on which thread.
415 /// The currently implemented scheduling policy is the one that is commonly
416 /// used in stateless model checkers such as Loom: run the active thread as
417 /// long as we can and switch only when we have to (the active thread was
418 /// blocked, terminated, or has explicitly asked to be preempted).
419 fn schedule(&mut self) -> InterpResult<'tcx, SchedulingAction> {
420 // Check whether the thread has **just** terminated (`check_terminated`
421 // checks whether the thread has popped all its stack and if yes, sets
422 // the thread state to terminated).
423 if self.threads[self.active_thread].check_terminated() {
424 // Check if we need to unblock any threads.
425 for (i, thread) in self.threads.iter_enumerated_mut() {
426 if thread.state == ThreadState::BlockedOnJoin(self.active_thread) {
427 trace!("unblocking {:?} because {:?} terminated", i, self.active_thread);
428 thread.state = ThreadState::Enabled;
431 return Ok(SchedulingAction::ExecuteDtors);
433 if self.threads[MAIN_THREAD].state == ThreadState::Terminated {
434 // The main thread terminated; stop the program.
435 if self.threads.iter().any(|thread| thread.state != ThreadState::Terminated) {
436 // FIXME: This check should be either configurable or just emit
437 // a warning. For example, it seems normal for a program to
438 // terminate without waiting for its detached threads to
439 // terminate. However, this case is not trivial to support
440 // because we also probably do not want to consider the memory
441 // owned by these threads as leaked.
442 throw_unsup_format!("the main thread terminated without waiting for other threads");
444 return Ok(SchedulingAction::Stop);
446 // At least for `pthread_cond_timedwait` we need to report timeout when
447 // the function is called already after the specified time even if a
448 // signal is received before the thread gets scheduled. Therefore, we
449 // need to schedule all timeout callbacks before we continue regular
453 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_cond_timedwait.html#
454 let potential_sleep_time =
455 self.timeout_callbacks.values().map(|info| info.call_time.get_wait_time()).min();
456 if potential_sleep_time == Some(Duration::new(0, 0)) {
457 return Ok(SchedulingAction::ExecuteTimeoutCallback);
459 // No callbacks scheduled, pick a regular thread to execute.
460 if self.threads[self.active_thread].state == ThreadState::Enabled
461 && !self.yield_active_thread
463 // The currently active thread is still enabled, just continue with it.
464 return Ok(SchedulingAction::ExecuteStep);
466 // We need to pick a new thread for execution.
467 for (id, thread) in self.threads.iter_enumerated() {
468 if thread.state == ThreadState::Enabled {
469 if !self.yield_active_thread || id != self.active_thread {
470 self.active_thread = id;
475 self.yield_active_thread = false;
476 if self.threads[self.active_thread].state == ThreadState::Enabled {
477 return Ok(SchedulingAction::ExecuteStep);
479 // We have not found a thread to execute.
480 if self.threads.iter().all(|thread| thread.state == ThreadState::Terminated) {
481 unreachable!("all threads terminated without the main thread terminating?!");
482 } else if let Some(sleep_time) = potential_sleep_time {
483 // All threads are currently blocked, but we have unexecuted
484 // timeout_callbacks, which may unblock some of the threads. Hence,
485 // sleep until the first callback.
486 std::thread::sleep(sleep_time);
487 Ok(SchedulingAction::ExecuteTimeoutCallback)
489 throw_machine_stop!(TerminationInfo::Deadlock);
494 // Public interface to thread management.
495 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
496 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
497 /// Get a thread-specific allocation id for the given thread-local static.
498 /// If needed, allocate a new one.
499 fn get_or_create_thread_local_alloc_id(&self, def_id: DefId) -> InterpResult<'tcx, AllocId> {
500 let this = self.eval_context_ref();
502 if let Some(new_alloc_id) = this.machine.threads.get_thread_local_alloc_id(def_id) {
503 // We already have a thread-specific allocation id for this
504 // thread-local static.
507 // We need to allocate a thread-specific allocation id for this
508 // thread-local static.
510 // At first, we compute the initial value for this static.
511 // Then we store the retrieved allocation back into the `alloc_map`
512 // to get a fresh allocation id, which we can use as a
513 // thread-specific allocation id for the thread-local static.
514 // On first access to that allocation, it will be copied over to the machine memory.
515 if tcx.is_foreign_item(def_id) {
516 throw_unsup_format!("foreign thread-local statics are not supported");
518 let allocation = interpret::get_static(*tcx, def_id)?;
519 // Create a new allocation id for the same allocation in this hacky
520 // way. Internally, `alloc_map` deduplicates allocations, but this
521 // is fine because Miri will make a copy before a first mutable
523 let new_alloc_id = tcx.create_memory_alloc(allocation);
524 this.machine.threads.set_thread_local_alloc_id(def_id, new_alloc_id);
530 fn create_thread(&mut self) -> ThreadId {
531 let this = self.eval_context_mut();
532 this.machine.threads.create_thread()
536 fn detach_thread(&mut self, thread_id: ThreadId) -> InterpResult<'tcx> {
537 let this = self.eval_context_mut();
538 this.machine.threads.detach_thread(thread_id)
542 fn join_thread(&mut self, joined_thread_id: ThreadId) -> InterpResult<'tcx> {
543 let this = self.eval_context_mut();
544 this.machine.threads.join_thread(joined_thread_id)
548 fn set_active_thread(&mut self, thread_id: ThreadId) -> ThreadId {
549 let this = self.eval_context_mut();
550 this.machine.threads.set_active_thread_id(thread_id)
554 fn get_active_thread(&self) -> ThreadId {
555 let this = self.eval_context_ref();
556 this.machine.threads.get_active_thread_id()
560 fn get_total_thread_count(&self) -> usize {
561 let this = self.eval_context_ref();
562 this.machine.threads.get_total_thread_count()
566 fn has_terminated(&self, thread_id: ThreadId) -> bool {
567 let this = self.eval_context_ref();
568 this.machine.threads.has_terminated(thread_id)
572 fn enable_thread(&mut self, thread_id: ThreadId) {
573 let this = self.eval_context_mut();
574 this.machine.threads.enable_thread(thread_id);
578 fn active_thread_stack(&self) -> &[Frame<'mir, 'tcx, Tag, FrameData<'tcx>>] {
579 let this = self.eval_context_ref();
580 this.machine.threads.active_thread_stack()
584 fn active_thread_stack_mut(&mut self) -> &mut Vec<Frame<'mir, 'tcx, Tag, FrameData<'tcx>>> {
585 let this = self.eval_context_mut();
586 this.machine.threads.active_thread_stack_mut()
590 fn set_active_thread_name(&mut self, new_thread_name: Vec<u8>) {
591 let this = self.eval_context_mut();
592 this.machine.threads.set_thread_name(new_thread_name);
596 fn get_active_thread_name<'c>(&'c self) -> &'c [u8]
600 let this = self.eval_context_ref();
601 this.machine.threads.get_thread_name()
605 fn block_thread(&mut self, thread: ThreadId) {
606 let this = self.eval_context_mut();
607 this.machine.threads.block_thread(thread);
611 fn unblock_thread(&mut self, thread: ThreadId) {
612 let this = self.eval_context_mut();
613 this.machine.threads.unblock_thread(thread);
617 fn yield_active_thread(&mut self) {
618 let this = self.eval_context_mut();
619 this.machine.threads.yield_active_thread();
623 fn register_timeout_callback(
627 callback: TimeoutCallback<'mir, 'tcx>,
629 let this = self.eval_context_mut();
630 this.machine.threads.register_timeout_callback(thread, call_time, callback);
634 fn unregister_timeout_callback_if_exists(&mut self, thread: ThreadId) {
635 let this = self.eval_context_mut();
636 this.machine.threads.unregister_timeout_callback_if_exists(thread);
639 /// Execute a timeout callback on the callback's thread.
641 fn run_timeout_callback(&mut self) -> InterpResult<'tcx> {
642 let this = self.eval_context_mut();
643 let (thread, callback) =
644 this.machine.threads.get_ready_callback().expect("no callback found");
645 // This back-and-forth with `set_active_thread` is here because of two
647 // 1. Make the caller and not the callback responsible for changing
649 // 2. Make the scheduler the only place that can change the active
651 let old_thread = this.set_active_thread(thread);
653 this.set_active_thread(old_thread);
657 /// Decide which action to take next and on which thread.
659 fn schedule(&mut self) -> InterpResult<'tcx, SchedulingAction> {
660 let this = self.eval_context_mut();
661 this.machine.threads.schedule()