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thread.rs
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//! Implements threads.
use std::mem;
use std::sync::atomic::Ordering::Relaxed;
use std::task::Poll;
use std::time::{Duration, SystemTime};
use rand::seq::IteratorRandom;
use rustc_abi::ExternAbi;
use rustc_const_eval::CTRL_C_RECEIVED;
use rustc_data_structures::either::Either;
use rustc_data_structures::fx::FxHashMap;
use rustc_hir::def_id::DefId;
use rustc_index::{Idx, IndexVec};
use rustc_middle::mir::Mutability;
use rustc_middle::ty::layout::TyAndLayout;
use rustc_span::{DUMMY_SP, Span};
use rustc_target::spec::Os;
use crate::concurrency::GlobalDataRaceHandler;
use crate::shims::tls;
use crate::*;
#[derive(Clone, Copy, Debug, PartialEq)]
enum SchedulingAction {
/// Execute step on the active thread.
ExecuteStep,
/// Execute a callback on the active thread.
ExecuteCallback,
/// Wait for a bit, until there is a timeout to be called.
Sleep(Duration),
}
/// What to do with TLS allocations from terminated threads
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum TlsAllocAction {
/// Deallocate backing memory of thread-local statics as usual
Deallocate,
/// Skip deallocating backing memory of thread-local statics and consider all memory reachable
/// from them as "allowed to leak" (like global `static`s).
Leak,
}
/// The argument type for the "unblock" callback, indicating why the thread got unblocked.
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum UnblockKind {
/// Operation completed successfully, thread continues normal execution.
Ready,
/// The operation did not complete within its specified duration.
TimedOut,
}
/// Type alias for unblock callbacks, i.e. machine callbacks invoked when
/// a thread gets unblocked.
pub type DynUnblockCallback<'tcx> = DynMachineCallback<'tcx, UnblockKind>;
/// A thread identifier.
#[derive(Clone, Copy, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
pub struct ThreadId(u32);
impl ThreadId {
pub fn to_u32(self) -> u32 {
self.0
}
/// Create a new thread id from a `u32` without checking if this thread exists.
pub fn new_unchecked(id: u32) -> Self {
Self(id)
}
pub const MAIN_THREAD: ThreadId = ThreadId(0);
}
impl Idx for ThreadId {
fn new(idx: usize) -> Self {
ThreadId(u32::try_from(idx).unwrap())
}
fn index(self) -> usize {
usize::try_from(self.0).unwrap()
}
}
impl From<ThreadId> for u64 {
fn from(t: ThreadId) -> Self {
t.0.into()
}
}
/// Keeps track of what the thread is blocked on.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub enum BlockReason {
/// The thread tried to join the specified thread and is blocked until that
/// thread terminates.
Join(ThreadId),
/// Waiting for time to pass.
Sleep,
/// Blocked on a mutex.
Mutex,
/// Blocked on a condition variable.
Condvar,
/// Blocked on a reader-writer lock.
RwLock,
/// Blocked on a Futex variable.
Futex,
/// Blocked on an InitOnce.
InitOnce,
/// Blocked on epoll.
Epoll,
/// Blocked on eventfd.
Eventfd,
/// Blocked on unnamed_socket.
UnnamedSocket,
/// Blocked for any reason related to GenMC, such as `assume` statements (GenMC mode only).
/// Will be implicitly unblocked when GenMC schedules this thread again.
Genmc,
}
/// The state of a thread.
enum ThreadState<'tcx> {
/// The thread is enabled and can be executed.
Enabled,
/// The thread is enabled, but there is an unblock callback that needs to
/// be executed first.
Unblocked { kind: UnblockKind, callback: DynUnblockCallback<'tcx> },
/// The thread is blocked on something.
Blocked { reason: BlockReason, timeout: Option<Timeout>, callback: DynUnblockCallback<'tcx> },
/// The thread has terminated its execution. We do not delete terminated
/// threads (FIXME: why?).
Terminated,
}
impl<'tcx> std::fmt::Debug for ThreadState<'tcx> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Self::Enabled => write!(f, "Enabled"),
Self::Unblocked { kind, .. } =>
f.debug_struct("Unblocked").field("kind", kind).finish(),
Self::Blocked { reason, timeout, .. } =>
f.debug_struct("Blocked").field("reason", reason).field("timeout", timeout).finish(),
Self::Terminated => write!(f, "Terminated"),
}
}
}
impl<'tcx> ThreadState<'tcx> {
fn is_enabled(&self) -> bool {
matches!(self, ThreadState::Enabled)
}
fn is_terminated(&self) -> bool {
matches!(self, ThreadState::Terminated)
}
fn is_blocked_on(&self, reason: BlockReason) -> bool {
matches!(*self, ThreadState::Blocked { reason: actual_reason, .. } if actual_reason == reason)
}
}
/// The join status of a thread.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
enum ThreadJoinStatus {
/// The thread can be joined.
Joinable,
/// A thread is detached if its join handle was destroyed and no other
/// thread can join it.
Detached,
/// The thread was already joined by some thread and cannot be joined again.
Joined,
}
/// A thread.
pub struct Thread<'tcx> {
state: ThreadState<'tcx>,
/// Name of the thread.
thread_name: Option<Vec<u8>>,
/// The virtual call stack.
stack: Vec<Frame<'tcx, Provenance, FrameExtra<'tcx>>>,
/// A span that explains where the thread (or more specifically, its current root
/// frame) "comes from".
pub(crate) origin_span: Span,
/// The function to call when the stack ran empty, to figure out what to do next.
/// Conceptually, this is the interpreter implementation of the things that happen 'after' the
/// Rust language entry point for this thread returns (usually implemented by the C or OS runtime).
/// (`None` is an error, it means the callback has not been set up yet or is actively running.)
pub(crate) on_stack_empty: Option<StackEmptyCallback<'tcx>>,
/// The index of the topmost user-relevant frame in `stack`. This field must contain
/// the value produced by `get_top_user_relevant_frame`.
/// This field is a cache to reduce how often we call that method. The cache is manually
/// maintained inside `MiriMachine::after_stack_push` and `MiriMachine::after_stack_pop`.
top_user_relevant_frame: Option<usize>,
/// The join status.
join_status: ThreadJoinStatus,
/// Stack of active unwind payloads for the current thread. Used for storing
/// the argument of the call to `miri_start_unwind` (the payload) when unwinding.
/// This is pointer-sized, and matches the `Payload` type in `src/libpanic_unwind/miri.rs`.
///
/// In real unwinding, the payload gets passed as an argument to the landing pad,
/// which then forwards it to 'Resume'. However this argument is implicit in MIR,
/// so we have to store it out-of-band. When there are multiple active unwinds,
/// the innermost one is always caught first, so we can store them as a stack.
pub(crate) unwind_payloads: Vec<ImmTy<'tcx>>,
/// Last OS error location in memory. It is a 32-bit integer.
pub(crate) last_error: Option<MPlaceTy<'tcx>>,
}
pub type StackEmptyCallback<'tcx> =
Box<dyn FnMut(&mut MiriInterpCx<'tcx>) -> InterpResult<'tcx, Poll<()>> + 'tcx>;
impl<'tcx> Thread<'tcx> {
/// Get the name of the current thread if it was set.
fn thread_name(&self) -> Option<&[u8]> {
self.thread_name.as_deref()
}
/// Return whether this thread is enabled or not.
pub fn is_enabled(&self) -> bool {
self.state.is_enabled()
}
/// Get the name of the current thread for display purposes; will include thread ID if not set.
fn thread_display_name(&self, id: ThreadId) -> String {
if let Some(ref thread_name) = self.thread_name {
String::from_utf8_lossy(thread_name).into_owned()
} else {
format!("unnamed-{}", id.index())
}
}
/// Return the top user-relevant frame, if there is one. `skip` indicates how many top frames
/// should be skipped.
/// Note that the choice to return `None` here when there is no user-relevant frame is part of
/// justifying the optimization that only pushes of user-relevant frames require updating the
/// `top_user_relevant_frame` field.
fn compute_top_user_relevant_frame(&self, skip: usize) -> Option<usize> {
// We are search for the frame with maximum relevance.
let mut best = None;
for (idx, frame) in self.stack.iter().enumerate().rev().skip(skip) {
let relevance = frame.extra.user_relevance;
if relevance == u8::MAX {
// We can short-circuit this search.
return Some(idx);
}
if best.is_none_or(|(_best_idx, best_relevance)| best_relevance < relevance) {
// The previous best frame has strictly worse relevance, so despite us being lower
// in the stack, we win.
best = Some((idx, relevance));
}
}
best.map(|(idx, _relevance)| idx)
}
/// Re-compute the top user-relevant frame from scratch. `skip` indicates how many top frames
/// should be skipped.
pub fn recompute_top_user_relevant_frame(&mut self, skip: usize) {
self.top_user_relevant_frame = self.compute_top_user_relevant_frame(skip);
}
/// Set the top user-relevant frame to the given value. Must be equal to what
/// `get_top_user_relevant_frame` would return!
pub fn set_top_user_relevant_frame(&mut self, frame_idx: usize) {
debug_assert_eq!(Some(frame_idx), self.compute_top_user_relevant_frame(0));
self.top_user_relevant_frame = Some(frame_idx);
}
/// Returns the topmost frame that is considered user-relevant, or the
/// top of the stack if there is no such frame, or `None` if the stack is empty.
pub fn top_user_relevant_frame(&self) -> Option<usize> {
// This can be called upon creation of an allocation. We create allocations while setting up
// parts of the Rust runtime when we do not have any stack frames yet, so we need to handle
// empty stacks.
self.top_user_relevant_frame.or_else(|| self.stack.len().checked_sub(1))
}
pub fn current_user_relevance(&self) -> u8 {
self.top_user_relevant_frame()
.map(|frame_idx| self.stack[frame_idx].extra.user_relevance)
.unwrap_or(0)
}
pub fn current_user_relevant_span(&self) -> Span {
debug_assert_eq!(self.top_user_relevant_frame, self.compute_top_user_relevant_frame(0));
self.top_user_relevant_frame()
.map(|frame_idx| self.stack[frame_idx].current_span())
.unwrap_or(rustc_span::DUMMY_SP)
}
}
impl<'tcx> std::fmt::Debug for Thread<'tcx> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(
f,
"{}({:?}, {:?})",
String::from_utf8_lossy(self.thread_name().unwrap_or(b"<unnamed>")),
self.state,
self.join_status
)
}
}
impl<'tcx> Thread<'tcx> {
fn new(name: Option<&str>, on_stack_empty: Option<StackEmptyCallback<'tcx>>) -> Self {
Self {
state: ThreadState::Enabled,
thread_name: name.map(|name| Vec::from(name.as_bytes())),
stack: Vec::new(),
origin_span: DUMMY_SP,
top_user_relevant_frame: None,
join_status: ThreadJoinStatus::Joinable,
unwind_payloads: Vec::new(),
last_error: None,
on_stack_empty,
}
}
}
impl VisitProvenance for Thread<'_> {
fn visit_provenance(&self, visit: &mut VisitWith<'_>) {
let Thread {
unwind_payloads: panic_payload,
last_error,
stack,
origin_span: _,
top_user_relevant_frame: _,
state: _,
thread_name: _,
join_status: _,
on_stack_empty: _, // we assume the closure captures no GC-relevant state
} = self;
for payload in panic_payload {
payload.visit_provenance(visit);
}
last_error.visit_provenance(visit);
for frame in stack {
frame.visit_provenance(visit)
}
}
}
impl VisitProvenance for Frame<'_, Provenance, FrameExtra<'_>> {
fn visit_provenance(&self, visit: &mut VisitWith<'_>) {
let Frame {
return_place,
locals,
extra,
// There are some private fields we cannot access; they contain no tags.
..
} = self;
// Return place.
return_place.visit_provenance(visit);
// Locals.
for local in locals.iter() {
match local.as_mplace_or_imm() {
None => {}
Some(Either::Left((ptr, meta))) => {
ptr.visit_provenance(visit);
meta.visit_provenance(visit);
}
Some(Either::Right(imm)) => {
imm.visit_provenance(visit);
}
}
}
extra.visit_provenance(visit);
}
}
/// The moment in time when a blocked thread should be woken up.
#[derive(Debug)]
enum Timeout {
Monotonic(Instant),
RealTime(SystemTime),
}
impl Timeout {
/// How long do we have to wait from now until the specified time?
fn get_wait_time(&self, clock: &MonotonicClock) -> Duration {
match self {
Timeout::Monotonic(instant) => instant.duration_since(clock.now()),
Timeout::RealTime(time) =>
time.duration_since(SystemTime::now()).unwrap_or(Duration::ZERO),
}
}
/// Will try to add `duration`, but if that overflows it may add less.
fn add_lossy(&self, duration: Duration) -> Self {
match self {
Timeout::Monotonic(i) => Timeout::Monotonic(i.add_lossy(duration)),
Timeout::RealTime(s) => {
// If this overflows, try adding just 1h and assume that will not overflow.
Timeout::RealTime(
s.checked_add(duration)
.unwrap_or_else(|| s.checked_add(Duration::from_secs(3600)).unwrap()),
)
}
}
}
}
/// The clock to use for the timeout you are asking for.
#[derive(Debug, Copy, Clone, PartialEq)]
pub enum TimeoutClock {
Monotonic,
RealTime,
}
/// Whether the timeout is relative or absolute.
#[derive(Debug, Copy, Clone)]
pub enum TimeoutAnchor {
Relative,
Absolute,
}
/// An error signaling that the requested thread doesn't exist.
#[derive(Debug, Copy, Clone)]
pub struct ThreadNotFound;
/// A set of threads.
#[derive(Debug)]
pub struct ThreadManager<'tcx> {
/// Identifier of the currently active thread.
active_thread: ThreadId,
/// Threads used in the program.
///
/// Note that this vector also contains terminated threads.
threads: IndexVec<ThreadId, Thread<'tcx>>,
/// A mapping from a thread-local static to the thread specific allocation.
thread_local_allocs: FxHashMap<(DefId, ThreadId), StrictPointer>,
/// A flag that indicates that we should change the active thread.
/// Completely ignored in GenMC mode.
yield_active_thread: bool,
/// A flag that indicates that we should do round robin scheduling of threads else randomized scheduling is used.
fixed_scheduling: bool,
}
impl VisitProvenance for ThreadManager<'_> {
fn visit_provenance(&self, visit: &mut VisitWith<'_>) {
let ThreadManager {
threads,
thread_local_allocs,
active_thread: _,
yield_active_thread: _,
fixed_scheduling: _,
} = self;
for thread in threads {
thread.visit_provenance(visit);
}
for ptr in thread_local_allocs.values() {
ptr.visit_provenance(visit);
}
}
}
impl<'tcx> ThreadManager<'tcx> {
pub(crate) fn new(config: &MiriConfig) -> Self {
let mut threads = IndexVec::new();
// Create the main thread and add it to the list of threads.
threads.push(Thread::new(Some("main"), None));
Self {
active_thread: ThreadId::MAIN_THREAD,
threads,
thread_local_allocs: Default::default(),
yield_active_thread: false,
fixed_scheduling: config.fixed_scheduling,
}
}
pub(crate) fn init(
ecx: &mut MiriInterpCx<'tcx>,
on_main_stack_empty: StackEmptyCallback<'tcx>,
) {
ecx.machine.threads.threads[ThreadId::MAIN_THREAD].on_stack_empty =
Some(on_main_stack_empty);
if ecx.tcx.sess.target.os != Os::Windows {
// The main thread can *not* be joined on except on windows.
ecx.machine.threads.threads[ThreadId::MAIN_THREAD].join_status =
ThreadJoinStatus::Detached;
}
}
pub fn thread_id_try_from(&self, id: impl TryInto<u32>) -> Result<ThreadId, ThreadNotFound> {
if let Ok(id) = id.try_into()
&& usize::try_from(id).is_ok_and(|id| id < self.threads.len())
{
Ok(ThreadId(id))
} else {
Err(ThreadNotFound)
}
}
/// Check if we have an allocation for the given thread local static for the
/// active thread.
fn get_thread_local_alloc_id(&self, def_id: DefId) -> Option<StrictPointer> {
self.thread_local_allocs.get(&(def_id, self.active_thread)).cloned()
}
/// Set the pointer for the allocation of the given thread local
/// static for the active thread.
///
/// Panics if a thread local is initialized twice for the same thread.
fn set_thread_local_alloc(&mut self, def_id: DefId, ptr: StrictPointer) {
self.thread_local_allocs.try_insert((def_id, self.active_thread), ptr).unwrap();
}
/// Borrow the stack of the active thread.
pub fn active_thread_stack(&self) -> &[Frame<'tcx, Provenance, FrameExtra<'tcx>>] {
&self.threads[self.active_thread].stack
}
/// Mutably borrow the stack of the active thread.
pub fn active_thread_stack_mut(
&mut self,
) -> &mut Vec<Frame<'tcx, Provenance, FrameExtra<'tcx>>> {
&mut self.threads[self.active_thread].stack
}
pub fn all_blocked_stacks(
&self,
) -> impl Iterator<Item = (ThreadId, &[Frame<'tcx, Provenance, FrameExtra<'tcx>>])> {
self.threads
.iter_enumerated()
.filter(|(_id, t)| matches!(t.state, ThreadState::Blocked { .. }))
.map(|(id, t)| (id, &t.stack[..]))
}
/// Create a new thread and returns its id.
fn create_thread(&mut self, on_stack_empty: StackEmptyCallback<'tcx>) -> ThreadId {
let new_thread_id = ThreadId::new(self.threads.len());
self.threads.push(Thread::new(None, Some(on_stack_empty)));
new_thread_id
}
/// Set an active thread and return the id of the thread that was active before.
fn set_active_thread_id(&mut self, id: ThreadId) -> ThreadId {
assert!(id.index() < self.threads.len());
info!(
"---------- Now executing on thread `{}` (previous: `{}`) ----------------------------------------",
self.get_thread_display_name(id),
self.get_thread_display_name(self.active_thread)
);
std::mem::replace(&mut self.active_thread, id)
}
/// Get the id of the currently active thread.
pub fn active_thread(&self) -> ThreadId {
self.active_thread
}
/// Get the total number of threads that were ever spawn by this program.
pub fn get_total_thread_count(&self) -> usize {
self.threads.len()
}
/// Get the total of threads that are currently live, i.e., not yet terminated.
/// (They might be blocked.)
pub fn get_live_thread_count(&self) -> usize {
self.threads.iter().filter(|t| !t.state.is_terminated()).count()
}
/// Has the given thread terminated?
fn has_terminated(&self, thread_id: ThreadId) -> bool {
self.threads[thread_id].state.is_terminated()
}
/// Have all threads terminated?
fn have_all_terminated(&self) -> bool {
self.threads.iter().all(|thread| thread.state.is_terminated())
}
/// Enable the thread for execution. The thread must be terminated.
fn enable_thread(&mut self, thread_id: ThreadId) {
assert!(self.has_terminated(thread_id));
self.threads[thread_id].state = ThreadState::Enabled;
}
/// Get a mutable borrow of the currently active thread.
pub fn active_thread_mut(&mut self) -> &mut Thread<'tcx> {
&mut self.threads[self.active_thread]
}
/// Get a shared borrow of the currently active thread.
pub fn active_thread_ref(&self) -> &Thread<'tcx> {
&self.threads[self.active_thread]
}
pub fn thread_ref(&self, thread_id: ThreadId) -> &Thread<'tcx> {
&self.threads[thread_id]
}
/// Mark the thread as detached, which means that no other thread will try
/// to join it and the thread is responsible for cleaning up.
///
/// `allow_terminated_joined` allows detaching joined threads that have already terminated.
/// This matches Windows's behavior for `CloseHandle`.
///
/// See <https://docs.microsoft.com/en-us/windows/win32/procthread/thread-handles-and-identifiers>:
/// > The handle is valid until closed, even after the thread it represents has been terminated.
fn detach_thread(&mut self, id: ThreadId, allow_terminated_joined: bool) -> InterpResult<'tcx> {
// NOTE: In GenMC mode, we treat detached threads like regular threads that are never joined, so there is no special handling required here.
trace!("detaching {:?}", id);
let is_ub = if allow_terminated_joined && self.threads[id].state.is_terminated() {
// "Detached" in particular means "not yet joined". Redundant detaching is still UB.
self.threads[id].join_status == ThreadJoinStatus::Detached
} else {
self.threads[id].join_status != ThreadJoinStatus::Joinable
};
if is_ub {
throw_ub_format!("trying to detach thread that was already detached or joined");
}
self.threads[id].join_status = ThreadJoinStatus::Detached;
interp_ok(())
}
/// Set the name of the given thread.
pub fn set_thread_name(&mut self, thread: ThreadId, new_thread_name: Vec<u8>) {
self.threads[thread].thread_name = Some(new_thread_name);
}
/// Get the name of the given thread.
pub fn get_thread_name(&self, thread: ThreadId) -> Option<&[u8]> {
self.threads[thread].thread_name()
}
pub fn get_thread_display_name(&self, thread: ThreadId) -> String {
self.threads[thread].thread_display_name(thread)
}
/// Put the thread into the blocked state.
fn block_thread(
&mut self,
reason: BlockReason,
timeout: Option<Timeout>,
callback: DynUnblockCallback<'tcx>,
) {
let state = &mut self.threads[self.active_thread].state;
assert!(state.is_enabled());
*state = ThreadState::Blocked { reason, timeout, callback }
}
/// Change the active thread to some enabled thread.
fn yield_active_thread(&mut self) {
// We do not yield immediately, as swapping out the current stack while executing a MIR statement
// could lead to all sorts of confusion.
// We should only switch stacks between steps.
self.yield_active_thread = true;
}
/// Unblocks all blocked threads whose timeout has occurred. Returns the
/// wait time until the earliest non-elapsed timeout.
fn process_timeouts(&mut self, clock: &MonotonicClock) -> Option<Duration> {
let mut shortest_wait = None;
for thread in &mut self.threads {
match &thread.state {
ThreadState::Blocked { timeout: Some(timeout), .. } => {
let wait_time = timeout.get_wait_time(clock);
if wait_time == Duration::ZERO {
let ThreadState::Blocked { callback, .. } =
mem::replace(&mut thread.state, ThreadState::Enabled)
else {
unreachable!("just checked that the thread is blocked")
};
// The timeout has occurred. Unblock the thread.
thread.state =
ThreadState::Unblocked { kind: UnblockKind::TimedOut, callback };
} else {
shortest_wait = if shortest_wait.is_some_and(|t| t < wait_time) {
shortest_wait
} else {
Some(wait_time)
};
}
}
_ => {}
}
}
shortest_wait
}
}
impl<'tcx> EvalContextPrivExt<'tcx> for MiriInterpCx<'tcx> {}
trait EvalContextPrivExt<'tcx>: MiriInterpCxExt<'tcx> {
/// Execute the callback scheduled for the currently active thread.
#[inline]
fn run_callback(&mut self) -> InterpResult<'tcx> {
let this = self.eval_context_mut();
let active_thread = this.active_thread_mut();
let ThreadState::Unblocked { kind, callback } =
mem::replace(&mut active_thread.state, ThreadState::Enabled)
else {
bug!("tried to execute a callback on a thread that didn't have a callback scheduled");
};
callback.call(this, kind)
}
#[inline]
fn run_on_stack_empty(&mut self) -> InterpResult<'tcx, Poll<()>> {
let this = self.eval_context_mut();
let active_thread = this.active_thread_mut();
active_thread.origin_span = DUMMY_SP; // reset, the old value no longer applied
let mut callback = active_thread
.on_stack_empty
.take()
.expect("`on_stack_empty` not set up, or already running");
let res = callback(this)?;
this.active_thread_mut().on_stack_empty = Some(callback);
interp_ok(res)
}
/// Decide which action to take next and on which thread.
///
/// The currently implemented scheduling policy is the one that is commonly
/// used in stateless model checkers such as Loom: run the active thread as
/// long as we can and switch only when we have to (the active thread was
/// blocked, terminated, or has explicitly asked to be preempted).
///
/// If GenMC mode is active, the scheduling is instead handled by GenMC.
fn schedule(&mut self) -> InterpResult<'tcx, SchedulingAction> {
let this = self.eval_context_mut();
// In GenMC mode, we let GenMC do the scheduling.
if this.machine.data_race.as_genmc_ref().is_some() {
loop {
let genmc_ctx = this.machine.data_race.as_genmc_ref().unwrap();
let Some(next_thread_id) = genmc_ctx.schedule_thread(this)? else {
return interp_ok(SchedulingAction::ExecuteStep);
};
// If a thread is blocked on GenMC, we have to implicitly unblock it when it gets scheduled again.
if this.machine.threads.threads[next_thread_id]
.state
.is_blocked_on(BlockReason::Genmc)
{
info!(
"GenMC: scheduling blocked thread {next_thread_id:?}, so we unblock it now."
);
this.unblock_thread(next_thread_id, BlockReason::Genmc)?;
}
// The thread we just unblocked may have been blocked again during the unblocking callback.
// In that case, we need to ask for a different thread to run next.
let thread_manager = &mut this.machine.threads;
if thread_manager.threads[next_thread_id].state.is_enabled() {
// Set the new active thread.
thread_manager.active_thread = next_thread_id;
return interp_ok(SchedulingAction::ExecuteStep);
}
}
}
// We are not in GenMC mode, so we control the scheduling.
let thread_manager = &mut this.machine.threads;
let clock = &this.machine.monotonic_clock;
let rng = this.machine.rng.get_mut();
// If no reschedule was requested, try to continue with the currently active thread.
if !thread_manager.yield_active_thread {
match thread_manager.threads[thread_manager.active_thread].state {
// The currently active thread is still enabled, just continue with it.
ThreadState::Enabled => return interp_ok(SchedulingAction::ExecuteStep),
// The currently active thread is enabled, but a callback needs to be run first.
ThreadState::Unblocked { .. } =>
return interp_ok(SchedulingAction::ExecuteCallback),
_ => {}
}
}
// The active thread is blocked or terminated. Let's see if there are
// any timeouts to take care of. This may unblock some threads, so we
// need to check before choosing the next thread to prevent deadlocks.
let potential_sleep_time = thread_manager.process_timeouts(clock);
// Search for another enabled thread. We build the list of threads by
// starting with the threads after the current one, followed by the
// threads before the current one and then the current thread itself
// (i.e., this iterator acts like
// `threads.rotate_left(self.active_thread.index() + 1)`.
// This ensures that if we pick the first eligible thread, we do regular
// round-robin scheduling, and all threads get a chance to take a step.
let mut threads_iter = thread_manager
.threads
.iter_enumerated()
.skip(thread_manager.active_thread.index() + 1)
.chain(
thread_manager
.threads
.iter_enumerated()
.take(thread_manager.active_thread.index() + 1),
)
.filter_map(|(id, thread)| {
match thread.state {
ThreadState::Enabled => Some((id, SchedulingAction::ExecuteStep)),
ThreadState::Unblocked { .. } => Some((id, SchedulingAction::ExecuteCallback)),
_ => None,
}
});
// Pick a new thread, and switch to it.
let new_thread = if thread_manager.fixed_scheduling {
threads_iter.next()
} else {
threads_iter.choose(rng)
};
// This completes the `yield`, if any was requested.
thread_manager.yield_active_thread = false;
if let Some((id, action)) = new_thread {
if thread_manager.active_thread != id {
info!(
"---------- Now executing on thread `{}` (previous: `{}`) ----------------------------------------",
thread_manager.get_thread_display_name(id),
thread_manager.get_thread_display_name(thread_manager.active_thread)
);
thread_manager.active_thread = id;
}
interp_ok(action)
} else {
// We have not found a thread to execute.
if thread_manager.threads.iter().all(|thread| thread.state.is_terminated()) {
unreachable!("all threads terminated without the main thread terminating?!");
} else if let Some(sleep_time) = potential_sleep_time {
// All threads are currently blocked, but we have unexecuted
// timeout_callbacks, which may unblock some of the threads. Hence,
// sleep until the first callback.
interp_ok(SchedulingAction::Sleep(sleep_time))
} else {
throw_machine_stop!(TerminationInfo::GlobalDeadlock);
}
}
}
}
// Public interface to thread management.
impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
#[inline]
fn thread_id_try_from(&self, id: impl TryInto<u32>) -> Result<ThreadId, ThreadNotFound> {
self.eval_context_ref().machine.threads.thread_id_try_from(id)
}
/// Get a thread-specific allocation id for the given thread-local static.
/// If needed, allocate a new one.
fn get_or_create_thread_local_alloc(
&mut self,
def_id: DefId,
) -> InterpResult<'tcx, StrictPointer> {
let this = self.eval_context_mut();
let tcx = this.tcx;
if let Some(old_alloc) = this.machine.threads.get_thread_local_alloc_id(def_id) {
// We already have a thread-specific allocation id for this
// thread-local static.
interp_ok(old_alloc)
} else {
// We need to allocate a thread-specific allocation id for this
// thread-local static.
// First, we compute the initial value for this static.
if tcx.is_foreign_item(def_id) {
throw_unsup_format!("foreign thread-local statics are not supported");
}
let params = this.machine.get_default_alloc_params();
let alloc = this.ctfe_query(|tcx| tcx.eval_static_initializer(def_id))?;
// We make a full copy of this allocation.
let mut alloc = alloc.inner().adjust_from_tcx(
&this.tcx,
|bytes, align| {
interp_ok(MiriAllocBytes::from_bytes(
std::borrow::Cow::Borrowed(bytes),
align,
params,
))
},
|ptr| this.global_root_pointer(ptr),
)?;
// This allocation will be deallocated when the thread dies, so it is not in read-only memory.
alloc.mutability = Mutability::Mut;
// Create a fresh allocation with this content.
let ptr = this.insert_allocation(alloc, MiriMemoryKind::Tls.into())?;
this.machine.threads.set_thread_local_alloc(def_id, ptr);
interp_ok(ptr)
}
}
/// Start a regular (non-main) thread.
#[inline]
fn start_regular_thread(
&mut self,
thread: Option<MPlaceTy<'tcx>>,
start_routine: Pointer,
start_abi: ExternAbi,
func_arg: ImmTy<'tcx>,
ret_layout: TyAndLayout<'tcx>,
) -> InterpResult<'tcx, ThreadId> {
let this = self.eval_context_mut();
// Create the new thread
let current_span = this.machine.current_user_relevant_span();
let new_thread_id = this.machine.threads.create_thread({
let mut state = tls::TlsDtorsState::default();
Box::new(move |m| state.on_stack_empty(m))
});
match &mut this.machine.data_race {
GlobalDataRaceHandler::None => {}
GlobalDataRaceHandler::Vclocks(data_race) =>
data_race.thread_created(&this.machine.threads, new_thread_id, current_span),
GlobalDataRaceHandler::Genmc(genmc_ctx) =>
genmc_ctx.handle_thread_create(
&this.machine.threads,
start_routine,
&func_arg,
new_thread_id,
)?,
}
// Write the current thread-id, switch to the next thread later
// to treat this write operation as occurring on the current thread.
if let Some(thread_info_place) = thread {
this.write_scalar(
Scalar::from_uint(new_thread_id.to_u32(), thread_info_place.layout.size),
&thread_info_place,
)?;
}
// Finally switch to new thread so that we can push the first stackframe.
// After this all accesses will be treated as occurring in the new thread.
let old_thread_id = this.machine.threads.set_active_thread_id(new_thread_id);
// The child inherits its parent's cpu affinity.
if let Some(cpuset) = this.machine.thread_cpu_affinity.get(&old_thread_id).cloned() {
this.machine.thread_cpu_affinity.insert(new_thread_id, cpuset);
}
// Perform the function pointer load in the new thread frame.
let instance = this.get_ptr_fn(start_routine)?.as_instance()?;
// Note: the returned value is currently ignored (see the FIXME in
// pthread_join in shims/unix/thread.rs) because the Rust standard library does not use
// it.
let ret_place = this.allocate(ret_layout, MiriMemoryKind::Machine.into())?;
this.call_thread_root_function(
instance,
start_abi,
&[func_arg],
Some(&ret_place),
current_span,
)?;
// Restore the old active thread frame.
this.machine.threads.set_active_thread_id(old_thread_id);
interp_ok(new_thread_id)
}
/// Handles thread termination of the active thread: wakes up threads joining on this one,
/// and deals with the thread's thread-local statics according to `tls_alloc_action`.
///
/// This is called by the eval loop when a thread's on_stack_empty returns `Ready`.
fn terminate_active_thread(&mut self, tls_alloc_action: TlsAllocAction) -> InterpResult<'tcx> {
let this = self.eval_context_mut();
// Mark thread as terminated.
let thread = this.active_thread_mut();
assert!(thread.stack.is_empty(), "only threads with an empty stack can be terminated");
thread.state = ThreadState::Terminated;
// Deallocate TLS.
let gone_thread = this.active_thread();
{
let mut free_tls_statics = Vec::new();
this.machine.threads.thread_local_allocs.retain(|&(_def_id, thread), &mut alloc_id| {
if thread != gone_thread {
// A different thread, keep this static around.
return true;
}
// Delete this static from the map and from memory.
// We cannot free directly here as we cannot use `?` in this context.
free_tls_statics.push(alloc_id);
false
});
// Now free the TLS statics.
for ptr in free_tls_statics {
match tls_alloc_action {
TlsAllocAction::Deallocate =>
this.deallocate_ptr(ptr.into(), None, MiriMemoryKind::Tls.into())?,
TlsAllocAction::Leak =>