src/sync.rs

   1 use std::collections::{hash_map::Entry, HashMap, VecDeque};
   2 use std::convert::TryFrom;
   3 use std::num::NonZeroU32;
   4 use std::ops::Not;
   5
   6 use rustc_index::vec::{Idx, IndexVec};
   7
   8 use crate::*;
   9
  10 /// We cannot use the `newtype_index!` macro because we have to use 0 as a
  11 /// sentinel value meaning that the identifier is not assigned. This is because
  12 /// the pthreads static initializers initialize memory with zeros (see the
  13 /// `src/shims/sync.rs` file).
  14 macro_rules! declare_id {
  15     ($name: ident) => {
  16         /// 0 is used to indicate that the id was not yet assigned and,
  17         /// therefore, is not a valid identifier.
  18         #[derive(Clone, Copy, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
  19         pub struct $name(NonZeroU32);
  20
  21         impl $name {
  22             // Panics if `id == 0`.
  23             pub fn from_u32(id: u32) -> Self {
  24                 Self(NonZeroU32::new(id).unwrap())
  25             }
  26         }
  27
  28         impl Idx for $name {
  29             fn new(idx: usize) -> Self {
  30                 // We use 0 as a sentinel value (see the comment above) and,
  31                 // therefore, need to shift by one when converting from an index
  32                 // into a vector.
  33                 let shifted_idx = u32::try_from(idx).unwrap().checked_add(1).unwrap();
  34                 $name(NonZeroU32::new(shifted_idx).unwrap())
  35             }
  36             fn index(self) -> usize {
  37                 // See the comment in `Self::new`.
  38                 // (This cannot underflow because self is NonZeroU32.)
  39                 usize::try_from(self.0.get() - 1).unwrap()
  40             }
  41         }
  42
  43         impl $name {
  44             pub fn to_u32_scalar<'tcx>(&self) -> Scalar<Tag> {
  45                 Scalar::from_u32(self.0.get())
  46             }
  47         }
  48     };
  49 }
  50
  51 declare_id!(MutexId);
  52
  53 /// The mutex state.
  54 #[derive(Default, Debug)]
  55 struct Mutex {
  56     /// The thread that currently owns the lock.
  57     owner: Option<ThreadId>,
  58     /// How many times the mutex was locked by the owner.
  59     lock_count: usize,
  60     /// The queue of threads waiting for this mutex.
  61     queue: VecDeque<ThreadId>,
  62 }
  63
  64 declare_id!(RwLockId);
  65
  66 /// The read-write lock state.
  67 #[derive(Default, Debug)]
  68 struct RwLock {
  69     /// The writer thread that currently owns the lock.
  70     writer: Option<ThreadId>,
  71     /// The readers that currently own the lock and how many times they acquired
  72     /// the lock.
  73     readers: HashMap<ThreadId, usize>,
  74     /// The queue of writer threads waiting for this lock.
  75     writer_queue: VecDeque<ThreadId>,
  76     /// The queue of reader threads waiting for this lock.
  77     reader_queue: VecDeque<ThreadId>,
  78 }
  79
  80 declare_id!(CondvarId);
  81
  82 /// A thread waiting on a conditional variable.
  83 #[derive(Debug)]
  84 struct CondvarWaiter {
  85     /// The thread that is waiting on this variable.
  86     thread: ThreadId,
  87     /// The mutex on which the thread is waiting.
  88     mutex: MutexId,
  89 }
  90
  91 /// The conditional variable state.
  92 #[derive(Default, Debug)]
  93 struct Condvar {
  94     waiters: VecDeque<CondvarWaiter>,
  95 }
  96
  97 /// The state of all synchronization variables.
  98 #[derive(Default, Debug)]
  99 pub(super) struct SynchronizationState {
 100     mutexes: IndexVec<MutexId, Mutex>,
 101     rwlocks: IndexVec<RwLockId, RwLock>,
 102     condvars: IndexVec<CondvarId, Condvar>,
 103 }
 104
 105 // Public interface to synchronization primitives. Please note that in most
 106 // cases, the function calls are infallible and it is the client's (shim
 107 // implementation's) responsibility to detect and deal with erroneous
 108 // situations.
 109 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
 110 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
 111     #[inline]
 112     /// Create state for a new mutex.
 113     fn mutex_create(&mut self) -> MutexId {
 114         let this = self.eval_context_mut();
 115         this.machine.threads.sync.mutexes.push(Default::default())
 116     }
 117
 118     #[inline]
 119     /// Get the id of the thread that currently owns this lock.
 120     fn mutex_get_owner(&mut self, id: MutexId) -> ThreadId {
 121         let this = self.eval_context_ref();
 122         this.machine.threads.sync.mutexes[id].owner.unwrap()
 123     }
 124
 125     #[inline]
 126     /// Check if locked.
 127     fn mutex_is_locked(&mut self, id: MutexId) -> bool {
 128         let this = self.eval_context_mut();
 129         this.machine.threads.sync.mutexes[id].owner.is_some()
 130     }
 131
 132     /// Lock by setting the mutex owner and increasing the lock count.
 133     fn mutex_lock(&mut self, id: MutexId, thread: ThreadId) {
 134         let this = self.eval_context_mut();
 135         let mutex = &mut this.machine.threads.sync.mutexes[id];
 136         if let Some(current_owner) = mutex.owner {
 137             assert_eq!(thread, current_owner, "mutex already locked by another thread");
 138             assert!(
 139                 mutex.lock_count > 0,
 140                 "invariant violation: lock_count == 0 iff the thread is unlocked"
 141             );
 142         } else {
 143             mutex.owner = Some(thread);
 144         }
 145         mutex.lock_count = mutex.lock_count.checked_add(1).unwrap();
 146     }
 147
 148     /// Try unlocking by decreasing the lock count and returning the old owner
 149     /// and the old lock count. If the lock count reaches 0, release the lock
 150     /// and potentially give to a new owner. If the lock was not locked, return
 151     /// `None`.
 152     ///
 153     /// Note: It is the caller's responsibility to check that the thread that
 154     /// unlocked the lock actually is the same one, which owned it.
 155     fn mutex_unlock(
 156         &mut self,
 157         id: MutexId,
 158         expected_owner: ThreadId,
 159     ) -> InterpResult<'tcx, Option<usize>> {
 160         let this = self.eval_context_mut();
 161         let mutex = &mut this.machine.threads.sync.mutexes[id];
 162         if let Some(current_owner) = mutex.owner {
 163             // Mutex is locked.
 164             if current_owner != expected_owner {
 165                 // Only the owner can unlock the mutex.
 166                 return Ok(None);
 167             }
 168             let old_lock_count = mutex.lock_count;
 169             mutex.lock_count = old_lock_count
 170                 .checked_sub(1)
 171                 .expect("invariant violation: lock_count == 0 iff the thread is unlocked");
 172             if mutex.lock_count == 0 {
 173                 mutex.owner = None;
 174                 // The mutex is completely unlocked. Try transfering ownership
 175                 // to another thread.
 176                 if let Some(new_owner) = this.mutex_dequeue(id) {
 177                     this.mutex_lock(id, new_owner);
 178                     this.unblock_thread(new_owner)?;
 179                 }
 180             }
 181             Ok(Some(old_lock_count))
 182         } else {
 183             // Mutex is unlocked.
 184             Ok(None)
 185         }
 186     }
 187
 188     #[inline]
 189     /// Put the thread into the queue waiting for the lock.
 190     fn mutex_enqueue(&mut self, id: MutexId, thread: ThreadId) {
 191         let this = self.eval_context_mut();
 192         assert!(this.mutex_is_locked(id), "queing on unlocked mutex");
 193         this.machine.threads.sync.mutexes[id].queue.push_back(thread);
 194     }
 195
 196     #[inline]
 197     /// Take a thread out of the queue waiting for the lock.
 198     fn mutex_dequeue(&mut self, id: MutexId) -> Option<ThreadId> {
 199         let this = self.eval_context_mut();
 200         this.machine.threads.sync.mutexes[id].queue.pop_front()
 201     }
 202
 203     #[inline]
 204     /// Create state for a new read write lock.
 205     fn rwlock_create(&mut self) -> RwLockId {
 206         let this = self.eval_context_mut();
 207         this.machine.threads.sync.rwlocks.push(Default::default())
 208     }
 209
 210     #[inline]
 211     /// Check if locked.
 212     fn rwlock_is_locked(&mut self, id: RwLockId) -> bool {
 213         let this = self.eval_context_mut();
 214         this.machine.threads.sync.rwlocks[id].writer.is_some()
 215             || this.machine.threads.sync.rwlocks[id].readers.is_empty().not()
 216     }
 217
 218     #[inline]
 219     /// Check if write locked.
 220     fn rwlock_is_write_locked(&mut self, id: RwLockId) -> bool {
 221         let this = self.eval_context_mut();
 222         this.machine.threads.sync.rwlocks[id].writer.is_some()
 223     }
 224
 225     /// Read-lock the lock by adding the `reader` the list of threads that own
 226     /// this lock.
 227     fn rwlock_reader_lock(&mut self, id: RwLockId, reader: ThreadId) {
 228         let this = self.eval_context_mut();
 229         assert!(!this.rwlock_is_write_locked(id), "the lock is write locked");
 230         let count = this.machine.threads.sync.rwlocks[id].readers.entry(reader).or_insert(0);
 231         *count = count.checked_add(1).expect("the reader counter overflowed");
 232     }
 233
 234     /// Try read-unlock the lock for `reader`. Returns `true` if succeeded,
 235     /// `false` if this `reader` did not hold the lock.
 236     fn rwlock_reader_unlock(&mut self, id: RwLockId, reader: ThreadId) -> bool {
 237         let this = self.eval_context_mut();
 238         match this.machine.threads.sync.rwlocks[id].readers.entry(reader) {
 239             Entry::Occupied(mut entry) => {
 240                 let count = entry.get_mut();
 241                 assert!(*count > 0, "rwlock locked with count == 0");
 242                 *count -= 1;
 243                 if *count == 0 {
 244                     entry.remove();
 245                 }
 246                 true
 247             }
 248             Entry::Vacant(_) => false,
 249         }
 250     }
 251
 252     #[inline]
 253     /// Put the reader in the queue waiting for the lock and block it.
 254     fn rwlock_enqueue_and_block_reader(
 255         &mut self,
 256         id: RwLockId,
 257         reader: ThreadId,
 258     ) -> InterpResult<'tcx> {
 259         let this = self.eval_context_mut();
 260         assert!(this.rwlock_is_write_locked(id), "queueing on not write locked lock");
 261         this.machine.threads.sync.rwlocks[id].reader_queue.push_back(reader);
 262         this.block_thread(reader)
 263     }
 264
 265     #[inline]
 266     /// Take a reader out the queue waiting for the lock.
 267     fn rwlock_dequeue_reader(&mut self, id: RwLockId) -> Option<ThreadId> {
 268         let this = self.eval_context_mut();
 269         this.machine.threads.sync.rwlocks[id].reader_queue.pop_front()
 270     }
 271
 272     #[inline]
 273     /// Lock by setting the writer that owns the lock.
 274     fn rwlock_writer_lock(&mut self, id: RwLockId, writer: ThreadId) {
 275         let this = self.eval_context_mut();
 276         assert!(!this.rwlock_is_locked(id), "the lock is already locked");
 277         this.machine.threads.sync.rwlocks[id].writer = Some(writer);
 278     }
 279
 280     #[inline]
 281     /// Try to unlock by removing the writer.
 282     fn rwlock_writer_unlock(&mut self, id: RwLockId) -> Option<ThreadId> {
 283         let this = self.eval_context_mut();
 284         this.machine.threads.sync.rwlocks[id].writer.take()
 285     }
 286
 287     #[inline]
 288     /// Put the writer in the queue waiting for the lock.
 289     fn rwlock_enqueue_and_block_writer(
 290         &mut self,
 291         id: RwLockId,
 292         writer: ThreadId,
 293     ) -> InterpResult<'tcx> {
 294         let this = self.eval_context_mut();
 295         assert!(this.rwlock_is_locked(id), "queueing on unlocked lock");
 296         this.machine.threads.sync.rwlocks[id].writer_queue.push_back(writer);
 297         this.block_thread(writer)
 298     }
 299
 300     #[inline]
 301     /// Take the writer out the queue waiting for the lock.
 302     fn rwlock_dequeue_writer(&mut self, id: RwLockId) -> Option<ThreadId> {
 303         let this = self.eval_context_mut();
 304         this.machine.threads.sync.rwlocks[id].writer_queue.pop_front()
 305     }
 306
 307     #[inline]
 308     /// Create state for a new conditional variable.
 309     fn condvar_create(&mut self) -> CondvarId {
 310         let this = self.eval_context_mut();
 311         this.machine.threads.sync.condvars.push(Default::default())
 312     }
 313
 314     #[inline]
 315     /// Is the conditional variable awaited?
 316     fn condvar_is_awaited(&mut self, id: CondvarId) -> bool {
 317         let this = self.eval_context_mut();
 318         !this.machine.threads.sync.condvars[id].waiters.is_empty()
 319     }
 320
 321     /// Mark that the thread is waiting on the conditional variable.
 322     fn condvar_wait(&mut self, id: CondvarId, thread: ThreadId, mutex: MutexId) {
 323         let this = self.eval_context_mut();
 324         let waiters = &mut this.machine.threads.sync.condvars[id].waiters;
 325         assert!(waiters.iter().all(|waiter| waiter.thread != thread), "thread is already waiting");
 326         waiters.push_back(CondvarWaiter { thread, mutex });
 327     }
 328
 329     /// Wake up some thread (if there is any) sleeping on the conditional
 330     /// variable.
 331     fn condvar_signal(&mut self, id: CondvarId) -> Option<(ThreadId, MutexId)> {
 332         let this = self.eval_context_mut();
 333         this.machine.threads.sync.condvars[id]
 334             .waiters
 335             .pop_front()
 336             .map(|waiter| (waiter.thread, waiter.mutex))
 337     }
 338
 339     #[inline]
 340     /// Remove the thread from the queue of threads waiting on this conditional variable.
 341     fn condvar_remove_waiter(&mut self, id: CondvarId, thread: ThreadId) {
 342         let this = self.eval_context_mut();
 343         this.machine.threads.sync.condvars[id].waiters.retain(|waiter| waiter.thread != thread);
 344     }
 345 }