rust/src/sync.rs

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use std::collections::{hash_map::Entry, HashMap, VecDeque};
use std::num::NonZeroU32;
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use std::ops::Not;
use log::trace;
use rustc_index::vec::{Idx, IndexVec};
use crate::*;
/// We cannot use the `newtype_index!` macro because we have to use 0 as a
/// sentinel value meaning that the identifier is not assigned. This is because
/// the pthreads static initializers initialize memory with zeros (see the
/// `src/shims/sync.rs` file).
macro_rules! declare_id {
($name: ident) => {
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/// 0 is used to indicate that the id was not yet assigned and,
/// therefore, is not a valid identifier.
#[derive(Clone, Copy, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
pub struct $name(NonZeroU32);
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impl $name {
// Panics if `id == 0`.
pub fn from_u32(id: u32) -> Self {
Self(NonZeroU32::new(id).unwrap())
}
}
impl Idx for $name {
fn new(idx: usize) -> Self {
// We use 0 as a sentinel value (see the comment above) and,
// therefore, need to shift by one when converting from an index
// into a vector.
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let shifted_idx = u32::try_from(idx).unwrap().checked_add(1).unwrap();
$name(NonZeroU32::new(shifted_idx).unwrap())
}
fn index(self) -> usize {
// See the comment in `Self::new`.
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// (This cannot underflow because self is NonZeroU32.)
usize::try_from(self.0.get() - 1).unwrap()
}
}
impl $name {
pub fn to_u32_scalar<'tcx>(&self) -> Scalar<Tag> {
Scalar::from_u32(self.0.get())
}
}
};
}
declare_id!(MutexId);
/// The mutex state.
#[derive(Default, Debug)]
struct Mutex {
/// The thread that currently owns the lock.
owner: Option<ThreadId>,
/// How many times the mutex was locked by the owner.
lock_count: usize,
/// The queue of threads waiting for this mutex.
queue: VecDeque<ThreadId>,
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/// Data race handle, this tracks the happens-before
/// relationship between each mutex access. It is
/// released to during unlock and acquired from during
/// locking, and therefore stores the clock of the last
/// thread to release this mutex.
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data_race: VClock,
}
declare_id!(RwLockId);
/// The read-write lock state.
#[derive(Default, Debug)]
struct RwLock {
/// The writer thread that currently owns the lock.
writer: Option<ThreadId>,
/// The readers that currently own the lock and how many times they acquired
/// the lock.
readers: HashMap<ThreadId, usize>,
/// The queue of writer threads waiting for this lock.
writer_queue: VecDeque<ThreadId>,
/// The queue of reader threads waiting for this lock.
reader_queue: VecDeque<ThreadId>,
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/// Data race handle for writers, tracks the happens-before
/// ordering between each write access to a rwlock and is updated
/// after a sequence of concurrent readers to track the happens-
/// before ordering between the set of previous readers and
/// the current writer.
/// Contains the clock of the last thread to release a writer
/// lock or the joined clock of the set of last threads to release
/// shared reader locks.
data_race: VClock,
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/// Data race handle for readers, this is temporary storage
/// for the combined happens-before ordering for between all
/// concurrent readers and the next writer, and the value
/// is stored to the main data_race variable once all
/// readers are finished.
/// Has to be stored separately since reader lock acquires
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/// must load the clock of the last write and must not
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/// add happens-before orderings between shared reader
/// locks.
data_race_reader: VClock,
}
declare_id!(CondvarId);
/// A thread waiting on a conditional variable.
#[derive(Debug)]
struct CondvarWaiter {
/// The thread that is waiting on this variable.
thread: ThreadId,
/// The mutex on which the thread is waiting.
mutex: MutexId,
}
/// The conditional variable state.
#[derive(Default, Debug)]
struct Condvar {
waiters: VecDeque<CondvarWaiter>,
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/// Tracks the happens-before relationship
/// between a cond-var signal and a cond-var
/// wait during a non-suprious signal event.
/// Contains the clock of the last thread to
/// perform a futex-signal.
data_race: VClock,
}
/// The futex state.
#[derive(Default, Debug)]
struct Futex {
waiters: VecDeque<FutexWaiter>,
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/// Tracks the happens-before relationship
/// between a futex-wake and a futex-wait
/// during a non-spurious wake event.
/// Contains the clock of the last thread to
/// perform a futex-wake.
data_race: VClock,
}
/// A thread waiting on a futex.
#[derive(Debug)]
struct FutexWaiter {
/// The thread that is waiting on this futex.
thread: ThreadId,
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/// The bitset used by FUTEX_*_BITSET, or u32::MAX for other operations.
bitset: u32,
}
/// The state of all synchronization variables.
#[derive(Default, Debug)]
pub(super) struct SynchronizationState {
mutexes: IndexVec<MutexId, Mutex>,
rwlocks: IndexVec<RwLockId, RwLock>,
condvars: IndexVec<CondvarId, Condvar>,
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futexes: HashMap<u64, Futex>,
}
// Private extension trait for local helper methods
impl<'mir, 'tcx: 'mir> EvalContextExtPriv<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
trait EvalContextExtPriv<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
/// Take a reader out of the queue waiting for the lock.
/// Returns `true` if some thread got the rwlock.
#[inline]
fn rwlock_dequeue_and_lock_reader(&mut self, id: RwLockId) -> bool {
let this = self.eval_context_mut();
if let Some(reader) = this.machine.threads.sync.rwlocks[id].reader_queue.pop_front() {
this.unblock_thread(reader);
this.rwlock_reader_lock(id, reader);
true
} else {
false
}
}
/// Take the writer out of the queue waiting for the lock.
/// Returns `true` if some thread got the rwlock.
#[inline]
fn rwlock_dequeue_and_lock_writer(&mut self, id: RwLockId) -> bool {
let this = self.eval_context_mut();
if let Some(writer) = this.machine.threads.sync.rwlocks[id].writer_queue.pop_front() {
this.unblock_thread(writer);
this.rwlock_writer_lock(id, writer);
true
} else {
false
}
}
/// Take a thread out of the queue waiting for the mutex, and lock
/// the mutex for it. Returns `true` if some thread has the mutex now.
#[inline]
fn mutex_dequeue_and_lock(&mut self, id: MutexId) -> bool {
let this = self.eval_context_mut();
if let Some(thread) = this.machine.threads.sync.mutexes[id].queue.pop_front() {
this.unblock_thread(thread);
this.mutex_lock(id, thread);
true
} else {
false
}
}
}
// Public interface to synchronization primitives. Please note that in most
// cases, the function calls are infallible and it is the client's (shim
// implementation's) responsibility to detect and deal with erroneous
// situations.
impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
#[inline]
/// Peek the id of the next mutex
fn mutex_next_id(&self) -> MutexId {
let this = self.eval_context_ref();
this.machine.threads.sync.mutexes.next_index()
}
#[inline]
/// Create state for a new mutex.
fn mutex_create(&mut self) -> MutexId {
let this = self.eval_context_mut();
this.machine.threads.sync.mutexes.push(Default::default())
}
#[inline]
/// Get the id of the thread that currently owns this lock.
fn mutex_get_owner(&mut self, id: MutexId) -> ThreadId {
let this = self.eval_context_ref();
this.machine.threads.sync.mutexes[id].owner.unwrap()
}
#[inline]
/// Check if locked.
fn mutex_is_locked(&self, id: MutexId) -> bool {
let this = self.eval_context_ref();
this.machine.threads.sync.mutexes[id].owner.is_some()
}
/// Lock by setting the mutex owner and increasing the lock count.
fn mutex_lock(&mut self, id: MutexId, thread: ThreadId) {
let this = self.eval_context_mut();
let mutex = &mut this.machine.threads.sync.mutexes[id];
if let Some(current_owner) = mutex.owner {
assert_eq!(thread, current_owner, "mutex already locked by another thread");
assert!(
mutex.lock_count > 0,
"invariant violation: lock_count == 0 iff the thread is unlocked"
);
} else {
mutex.owner = Some(thread);
}
mutex.lock_count = mutex.lock_count.checked_add(1).unwrap();
if let Some(data_race) = &this.machine.data_race {
data_race.validate_lock_acquire(&mutex.data_race, thread);
}
}
/// Try unlocking by decreasing the lock count and returning the old lock
/// count. If the lock count reaches 0, release the lock and potentially
/// give to a new owner. If the lock was not locked by `expected_owner`,
/// return `None`.
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fn mutex_unlock(&mut self, id: MutexId, expected_owner: ThreadId) -> Option<usize> {
let this = self.eval_context_mut();
let mutex = &mut this.machine.threads.sync.mutexes[id];
if let Some(current_owner) = mutex.owner {
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// Mutex is locked.
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if current_owner != expected_owner {
// Only the owner can unlock the mutex.
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return None;
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}
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let old_lock_count = mutex.lock_count;
mutex.lock_count = old_lock_count
.checked_sub(1)
.expect("invariant violation: lock_count == 0 iff the thread is unlocked");
if mutex.lock_count == 0 {
mutex.owner = None;
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// The mutex is completely unlocked. Try transfering ownership
// to another thread.
if let Some(data_race) = &this.machine.data_race {
data_race.validate_lock_release(&mut mutex.data_race, current_owner);
}
this.mutex_dequeue_and_lock(id);
}
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Some(old_lock_count)
} else {
// Mutex is not locked.
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None
}
}
#[inline]
/// Put the thread into the queue waiting for the mutex.
fn mutex_enqueue_and_block(&mut self, id: MutexId, thread: ThreadId) {
let this = self.eval_context_mut();
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assert!(this.mutex_is_locked(id), "queing on unlocked mutex");
this.machine.threads.sync.mutexes[id].queue.push_back(thread);
this.block_thread(thread);
}
#[inline]
/// Peek the id of the next read write lock
fn rwlock_next_id(&self) -> RwLockId {
let this = self.eval_context_ref();
this.machine.threads.sync.rwlocks.next_index()
}
#[inline]
/// Create state for a new read write lock.
fn rwlock_create(&mut self) -> RwLockId {
let this = self.eval_context_mut();
this.machine.threads.sync.rwlocks.push(Default::default())
}
#[inline]
/// Check if locked.
fn rwlock_is_locked(&self, id: RwLockId) -> bool {
let this = self.eval_context_ref();
let rwlock = &this.machine.threads.sync.rwlocks[id];
trace!(
"rwlock_is_locked: {:?} writer is {:?} and there are {} reader threads (some of which could hold multiple read locks)",
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id,
rwlock.writer,
rwlock.readers.len(),
);
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rwlock.writer.is_some() || rwlock.readers.is_empty().not()
}
#[inline]
/// Check if write locked.
fn rwlock_is_write_locked(&self, id: RwLockId) -> bool {
let this = self.eval_context_ref();
let rwlock = &this.machine.threads.sync.rwlocks[id];
trace!("rwlock_is_write_locked: {:?} writer is {:?}", id, rwlock.writer);
rwlock.writer.is_some()
}
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/// Read-lock the lock by adding the `reader` the list of threads that own
/// this lock.
fn rwlock_reader_lock(&mut self, id: RwLockId, reader: ThreadId) {
let this = self.eval_context_mut();
assert!(!this.rwlock_is_write_locked(id), "the lock is write locked");
trace!("rwlock_reader_lock: {:?} now also held (one more time) by {:?}", id, reader);
let rwlock = &mut this.machine.threads.sync.rwlocks[id];
let count = rwlock.readers.entry(reader).or_insert(0);
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*count = count.checked_add(1).expect("the reader counter overflowed");
if let Some(data_race) = &this.machine.data_race {
data_race.validate_lock_acquire(&rwlock.data_race, reader);
}
}
/// Try read-unlock the lock for `reader` and potentially give the lock to a new owner.
/// Returns `true` if succeeded, `false` if this `reader` did not hold the lock.
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fn rwlock_reader_unlock(&mut self, id: RwLockId, reader: ThreadId) -> bool {
let this = self.eval_context_mut();
let rwlock = &mut this.machine.threads.sync.rwlocks[id];
match rwlock.readers.entry(reader) {
Entry::Occupied(mut entry) => {
let count = entry.get_mut();
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assert!(*count > 0, "rwlock locked with count == 0");
*count -= 1;
if *count == 0 {
trace!("rwlock_reader_unlock: {:?} no longer held by {:?}", id, reader);
entry.remove();
} else {
trace!("rwlock_reader_unlock: {:?} held one less time by {:?}", id, reader);
}
}
Entry::Vacant(_) => return false, // we did not even own this lock
}
if let Some(data_race) = &this.machine.data_race {
data_race.validate_lock_release_shared(&mut rwlock.data_race_reader, reader);
}
// The thread was a reader. If the lock is not held any more, give it to a writer.
if this.rwlock_is_locked(id).not() {
// All the readers are finished, so set the writer data-race handle to the value
// of the union of all reader data race handles, since the set of readers
// happen-before the writers
let rwlock = &mut this.machine.threads.sync.rwlocks[id];
rwlock.data_race.clone_from(&rwlock.data_race_reader);
this.rwlock_dequeue_and_lock_writer(id);
}
true
}
#[inline]
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/// Put the reader in the queue waiting for the lock and block it.
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fn rwlock_enqueue_and_block_reader(&mut self, id: RwLockId, reader: ThreadId) {
let this = self.eval_context_mut();
assert!(this.rwlock_is_write_locked(id), "read-queueing on not write locked rwlock");
this.machine.threads.sync.rwlocks[id].reader_queue.push_back(reader);
this.block_thread(reader);
}
#[inline]
/// Lock by setting the writer that owns the lock.
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fn rwlock_writer_lock(&mut self, id: RwLockId, writer: ThreadId) {
let this = self.eval_context_mut();
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assert!(!this.rwlock_is_locked(id), "the rwlock is already locked");
trace!("rwlock_writer_lock: {:?} now held by {:?}", id, writer);
let rwlock = &mut this.machine.threads.sync.rwlocks[id];
rwlock.writer = Some(writer);
if let Some(data_race) = &this.machine.data_race {
data_race.validate_lock_acquire(&rwlock.data_race, writer);
}
}
#[inline]
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/// Try to unlock by removing the writer.
fn rwlock_writer_unlock(&mut self, id: RwLockId, expected_writer: ThreadId) -> bool {
let this = self.eval_context_mut();
let rwlock = &mut this.machine.threads.sync.rwlocks[id];
if let Some(current_writer) = rwlock.writer {
if current_writer != expected_writer {
// Only the owner can unlock the rwlock.
return false;
}
rwlock.writer = None;
trace!("rwlock_writer_unlock: {:?} unlocked by {:?}", id, expected_writer);
// Release memory to both reader and writer vector clocks
// since this writer happens-before both the union of readers once they are finished
// and the next writer
if let Some(data_race) = &this.machine.data_race {
data_race.validate_lock_release(&mut rwlock.data_race, current_writer);
data_race.validate_lock_release(&mut rwlock.data_race_reader, current_writer);
}
// The thread was a writer.
//
// We are prioritizing writers here against the readers. As a
// result, not only readers can starve writers, but also writers can
// starve readers.
if this.rwlock_dequeue_and_lock_writer(id) {
// Someone got the write lock, nice.
} else {
// Give the lock to all readers.
while this.rwlock_dequeue_and_lock_reader(id) {
// Rinse and repeat.
}
}
true
} else {
false
}
}
#[inline]
/// Put the writer in the queue waiting for the lock.
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fn rwlock_enqueue_and_block_writer(&mut self, id: RwLockId, writer: ThreadId) {
let this = self.eval_context_mut();
assert!(this.rwlock_is_locked(id), "write-queueing on unlocked rwlock");
this.machine.threads.sync.rwlocks[id].writer_queue.push_back(writer);
this.block_thread(writer);
}
#[inline]
/// Peek the id of the next Condvar
fn condvar_next_id(&self) -> CondvarId {
let this = self.eval_context_ref();
this.machine.threads.sync.condvars.next_index()
}
#[inline]
/// Create state for a new conditional variable.
fn condvar_create(&mut self) -> CondvarId {
let this = self.eval_context_mut();
this.machine.threads.sync.condvars.push(Default::default())
}
#[inline]
/// Is the conditional variable awaited?
fn condvar_is_awaited(&mut self, id: CondvarId) -> bool {
let this = self.eval_context_mut();
!this.machine.threads.sync.condvars[id].waiters.is_empty()
}
/// Mark that the thread is waiting on the conditional variable.
fn condvar_wait(&mut self, id: CondvarId, thread: ThreadId, mutex: MutexId) {
let this = self.eval_context_mut();
let waiters = &mut this.machine.threads.sync.condvars[id].waiters;
assert!(waiters.iter().all(|waiter| waiter.thread != thread), "thread is already waiting");
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waiters.push_back(CondvarWaiter { thread, mutex });
}
/// Wake up some thread (if there is any) sleeping on the conditional
/// variable.
fn condvar_signal(&mut self, id: CondvarId) -> Option<(ThreadId, MutexId)> {
let this = self.eval_context_mut();
let current_thread = this.get_active_thread();
let condvar = &mut this.machine.threads.sync.condvars[id];
let data_race = &this.machine.data_race;
// Each condvar signal happens-before the end of the condvar wake
if let Some(data_race) = data_race {
data_race.validate_lock_release(&mut condvar.data_race, current_thread);
}
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condvar.waiters.pop_front().map(|waiter| {
if let Some(data_race) = data_race {
data_race.validate_lock_acquire(&condvar.data_race, waiter.thread);
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}
(waiter.thread, waiter.mutex)
})
}
#[inline]
/// Remove the thread from the queue of threads waiting on this conditional variable.
fn condvar_remove_waiter(&mut self, id: CondvarId, thread: ThreadId) {
let this = self.eval_context_mut();
this.machine.threads.sync.condvars[id].waiters.retain(|waiter| waiter.thread != thread);
}
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fn futex_wait(&mut self, addr: u64, thread: ThreadId, bitset: u32) {
let this = self.eval_context_mut();
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let futex = &mut this.machine.threads.sync.futexes.entry(addr).or_default();
let waiters = &mut futex.waiters;
assert!(waiters.iter().all(|waiter| waiter.thread != thread), "thread is already waiting");
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waiters.push_back(FutexWaiter { thread, bitset });
}
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fn futex_wake(&mut self, addr: u64, bitset: u32) -> Option<ThreadId> {
let this = self.eval_context_mut();
let current_thread = this.get_active_thread();
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let futex = &mut this.machine.threads.sync.futexes.get_mut(&addr)?;
let data_race = &this.machine.data_race;
// Each futex-wake happens-before the end of the futex wait
if let Some(data_race) = data_race {
data_race.validate_lock_release(&mut futex.data_race, current_thread);
}
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// Wake up the first thread in the queue that matches any of the bits in the bitset.
futex.waiters.iter().position(|w| w.bitset & bitset != 0).map(|i| {
let waiter = futex.waiters.remove(i).unwrap();
if let Some(data_race) = data_race {
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data_race.validate_lock_acquire(&futex.data_race, waiter.thread);
}
waiter.thread
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})
}
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fn futex_remove_waiter(&mut self, addr: u64, thread: ThreadId) {
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let this = self.eval_context_mut();
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if let Some(futex) = this.machine.threads.sync.futexes.get_mut(&addr) {
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futex.waiters.retain(|waiter| waiter.thread != thread);
}
}
}