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use crate::dep_graph::DepContext;
use crate::error::CycleStack;
use crate::query::plumbing::CycleError;
use crate::query::DepKind;
use crate::query::{QueryContext, QueryStackFrame};
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::{
Diagnostic, DiagnosticBuilder, ErrorGuaranteed, Handler, IntoDiagnostic, Level,
};
use rustc_hir::def::DefKind;
use rustc_session::Session;
use rustc_span::Span;
use std::hash::Hash;
use std::io::Write;
use std::num::NonZeroU64;
#[cfg(parallel_compiler)]
use {
parking_lot::{Condvar, Mutex},
rayon_core,
rustc_data_structures::fx::FxHashSet,
rustc_data_structures::{defer, jobserver},
rustc_span::DUMMY_SP,
std::iter,
std::process,
std::sync::Arc,
};
/// Represents a span and a query key.
#[derive(Clone, Debug)]
pub struct QueryInfo {
/// The span corresponding to the reason for which this query was required.
pub span: Span,
pub query: QueryStackFrame,
}
pub type QueryMap = FxHashMap<QueryJobId, QueryJobInfo>;
/// A value uniquely identifying an active query job.
#[derive(Copy, Clone, Eq, PartialEq, Hash)]
pub struct QueryJobId(pub NonZeroU64);
impl QueryJobId {
fn query(self, map: &QueryMap) -> QueryStackFrame {
map.get(&self).unwrap().query.clone()
}
#[cfg(parallel_compiler)]
fn span(self, map: &QueryMap) -> Span {
map.get(&self).unwrap().job.span
}
#[cfg(parallel_compiler)]
fn parent(self, map: &QueryMap) -> Option<QueryJobId> {
map.get(&self).unwrap().job.parent
}
#[cfg(parallel_compiler)]
fn latch(self, map: &QueryMap) -> Option<&QueryLatch> {
map.get(&self).unwrap().job.latch.as_ref()
}
}
#[derive(Clone)]
pub struct QueryJobInfo {
pub query: QueryStackFrame,
pub job: QueryJob,
}
/// Represents an active query job.
#[derive(Clone)]
pub struct QueryJob {
pub id: QueryJobId,
/// The span corresponding to the reason for which this query was required.
pub span: Span,
/// The parent query job which created this job and is implicitly waiting on it.
pub parent: Option<QueryJobId>,
/// The latch that is used to wait on this job.
#[cfg(parallel_compiler)]
latch: Option<QueryLatch>,
}
impl QueryJob {
/// Creates a new query job.
#[inline]
pub fn new(id: QueryJobId, span: Span, parent: Option<QueryJobId>) -> Self {
QueryJob {
id,
span,
parent,
#[cfg(parallel_compiler)]
latch: None,
}
}
#[cfg(parallel_compiler)]
pub(super) fn latch(&mut self) -> QueryLatch {
if self.latch.is_none() {
self.latch = Some(QueryLatch::new());
}
self.latch.as_ref().unwrap().clone()
}
/// Signals to waiters that the query is complete.
///
/// This does nothing for single threaded rustc,
/// as there are no concurrent jobs which could be waiting on us
#[inline]
pub fn signal_complete(self) {
#[cfg(parallel_compiler)]
{
if let Some(latch) = self.latch {
latch.set();
}
}
}
}
impl QueryJobId {
pub(super) fn find_cycle_in_stack(
&self,
query_map: QueryMap,
current_job: &Option<QueryJobId>,
span: Span,
) -> CycleError {
// Find the waitee amongst `current_job` parents
let mut cycle = Vec::new();
let mut current_job = Option::clone(current_job);
while let Some(job) = current_job {
let info = query_map.get(&job).unwrap();
cycle.push(QueryInfo { span: info.job.span, query: info.query.clone() });
if job == *self {
cycle.reverse();
// This is the end of the cycle
// The span entry we included was for the usage
// of the cycle itself, and not part of the cycle
// Replace it with the span which caused the cycle to form
cycle[0].span = span;
// Find out why the cycle itself was used
let usage = info
.job
.parent
.as_ref()
.map(|parent| (info.job.span, parent.query(&query_map)));
return CycleError { usage, cycle };
}
current_job = info.job.parent;
}
panic!("did not find a cycle")
}
#[cold]
#[inline(never)]
pub fn try_find_layout_root(
&self,
query_map: QueryMap,
layout_of_kind: DepKind,
) -> Option<(QueryJobInfo, usize)> {
let mut last_layout = None;
let mut current_id = Some(*self);
let mut depth = 0;
while let Some(id) = current_id {
let info = query_map.get(&id).unwrap();
if info.query.dep_kind == layout_of_kind {
depth += 1;
last_layout = Some((info.clone(), depth));
}
current_id = info.job.parent;
}
last_layout
}
}
#[cfg(parallel_compiler)]
struct QueryWaiter {
query: Option<QueryJobId>,
condvar: Condvar,
span: Span,
cycle: Mutex<Option<CycleError>>,
}
#[cfg(parallel_compiler)]
impl QueryWaiter {
fn notify(&self, registry: &rayon_core::Registry) {
rayon_core::mark_unblocked(registry);
self.condvar.notify_one();
}
}
#[cfg(parallel_compiler)]
struct QueryLatchInfo {
complete: bool,
waiters: Vec<Arc<QueryWaiter>>,
}
#[cfg(parallel_compiler)]
#[derive(Clone)]
pub(super) struct QueryLatch {
info: Arc<Mutex<QueryLatchInfo>>,
}
#[cfg(parallel_compiler)]
impl QueryLatch {
fn new() -> Self {
QueryLatch {
info: Arc::new(Mutex::new(QueryLatchInfo { complete: false, waiters: Vec::new() })),
}
}
/// Awaits for the query job to complete.
pub(super) fn wait_on(&self, query: Option<QueryJobId>, span: Span) -> Result<(), CycleError> {
let waiter =
Arc::new(QueryWaiter { query, span, cycle: Mutex::new(None), condvar: Condvar::new() });
self.wait_on_inner(&waiter);
// FIXME: Get rid of this lock. We have ownership of the QueryWaiter
// although another thread may still have a Arc reference so we cannot
// use Arc::get_mut
let mut cycle = waiter.cycle.lock();
match cycle.take() {
None => Ok(()),
Some(cycle) => Err(cycle),
}
}
/// Awaits the caller on this latch by blocking the current thread.
fn wait_on_inner(&self, waiter: &Arc<QueryWaiter>) {
let mut info = self.info.lock();
if !info.complete {
// We push the waiter on to the `waiters` list. It can be accessed inside
// the `wait` call below, by 1) the `set` method or 2) by deadlock detection.
// Both of these will remove it from the `waiters` list before resuming
// this thread.
info.waiters.push(waiter.clone());
// If this detects a deadlock and the deadlock handler wants to resume this thread
// we have to be in the `wait` call. This is ensured by the deadlock handler
// getting the self.info lock.
rayon_core::mark_blocked();
jobserver::release_thread();
waiter.condvar.wait(&mut info);
// Release the lock before we potentially block in `acquire_thread`
drop(info);
jobserver::acquire_thread();
}
}
/// Sets the latch and resumes all waiters on it
fn set(&self) {
let mut info = self.info.lock();
debug_assert!(!info.complete);
info.complete = true;
let registry = rayon_core::Registry::current();
for waiter in info.waiters.drain(..) {
waiter.notify(®istry);
}
}
/// Removes a single waiter from the list of waiters.
/// This is used to break query cycles.
fn extract_waiter(&self, waiter: usize) -> Arc<QueryWaiter> {
let mut info = self.info.lock();
debug_assert!(!info.complete);
// Remove the waiter from the list of waiters
info.waiters.remove(waiter)
}
}
/// A resumable waiter of a query. The usize is the index into waiters in the query's latch
#[cfg(parallel_compiler)]
type Waiter = (QueryJobId, usize);
/// Visits all the non-resumable and resumable waiters of a query.
/// Only waiters in a query are visited.
/// `visit` is called for every waiter and is passed a query waiting on `query_ref`
/// and a span indicating the reason the query waited on `query_ref`.
/// If `visit` returns Some, this function returns.
/// For visits of non-resumable waiters it returns the return value of `visit`.
/// For visits of resumable waiters it returns Some(Some(Waiter)) which has the
/// required information to resume the waiter.
/// If all `visit` calls returns None, this function also returns None.
#[cfg(parallel_compiler)]
fn visit_waiters<F>(query_map: &QueryMap, query: QueryJobId, mut visit: F) -> Option<Option<Waiter>>
where
F: FnMut(Span, QueryJobId) -> Option<Option<Waiter>>,
{
// Visit the parent query which is a non-resumable waiter since it's on the same stack
if let Some(parent) = query.parent(query_map) {
if let Some(cycle) = visit(query.span(query_map), parent) {
return Some(cycle);
}
}
// Visit the explicit waiters which use condvars and are resumable
if let Some(latch) = query.latch(query_map) {
for (i, waiter) in latch.info.lock().waiters.iter().enumerate() {
if let Some(waiter_query) = waiter.query {
if visit(waiter.span, waiter_query).is_some() {
// Return a value which indicates that this waiter can be resumed
return Some(Some((query, i)));
}
}
}
}
None
}
/// Look for query cycles by doing a depth first search starting at `query`.
/// `span` is the reason for the `query` to execute. This is initially DUMMY_SP.
/// If a cycle is detected, this initial value is replaced with the span causing
/// the cycle.
#[cfg(parallel_compiler)]
fn cycle_check(
query_map: &QueryMap,
query: QueryJobId,
span: Span,
stack: &mut Vec<(Span, QueryJobId)>,
visited: &mut FxHashSet<QueryJobId>,
) -> Option<Option<Waiter>> {
if !visited.insert(query) {
return if let Some(p) = stack.iter().position(|q| q.1 == query) {
// We detected a query cycle, fix up the initial span and return Some
// Remove previous stack entries
stack.drain(0..p);
// Replace the span for the first query with the cycle cause
stack[0].0 = span;
Some(None)
} else {
None
};
}
// Query marked as visited is added it to the stack
stack.push((span, query));
// Visit all the waiters
let r = visit_waiters(query_map, query, |span, successor| {
cycle_check(query_map, successor, span, stack, visited)
});
// Remove the entry in our stack if we didn't find a cycle
if r.is_none() {
stack.pop();
}
r
}
/// Finds out if there's a path to the compiler root (aka. code which isn't in a query)
/// from `query` without going through any of the queries in `visited`.
/// This is achieved with a depth first search.
#[cfg(parallel_compiler)]
fn connected_to_root(
query_map: &QueryMap,
query: QueryJobId,
visited: &mut FxHashSet<QueryJobId>,
) -> bool {
// We already visited this or we're deliberately ignoring it
if !visited.insert(query) {
return false;
}
// This query is connected to the root (it has no query parent), return true
if query.parent(query_map).is_none() {
return true;
}
visit_waiters(query_map, query, |_, successor| {
connected_to_root(query_map, successor, visited).then_some(None)
})
.is_some()
}
// Deterministically pick an query from a list
#[cfg(parallel_compiler)]
fn pick_query<'a, T, F>(query_map: &QueryMap, queries: &'a [T], f: F) -> &'a T
where
F: Fn(&T) -> (Span, QueryJobId),
{
// Deterministically pick an entry point
// FIXME: Sort this instead
queries
.iter()
.min_by_key(|v| {
let (span, query) = f(v);
let hash = query.query(query_map).hash;
// Prefer entry points which have valid spans for nicer error messages
// We add an integer to the tuple ensuring that entry points
// with valid spans are picked first
let span_cmp = if span == DUMMY_SP { 1 } else { 0 };
(span_cmp, hash)
})
.unwrap()
}
/// Looks for query cycles starting from the last query in `jobs`.
/// If a cycle is found, all queries in the cycle is removed from `jobs` and
/// the function return true.
/// If a cycle was not found, the starting query is removed from `jobs` and
/// the function returns false.
#[cfg(parallel_compiler)]
fn remove_cycle(
query_map: &QueryMap,
jobs: &mut Vec<QueryJobId>,
wakelist: &mut Vec<Arc<QueryWaiter>>,
) -> bool {
let mut visited = FxHashSet::default();
let mut stack = Vec::new();
// Look for a cycle starting with the last query in `jobs`
if let Some(waiter) =
cycle_check(query_map, jobs.pop().unwrap(), DUMMY_SP, &mut stack, &mut visited)
{
// The stack is a vector of pairs of spans and queries; reverse it so that
// the earlier entries require later entries
let (mut spans, queries): (Vec<_>, Vec<_>) = stack.into_iter().rev().unzip();
// Shift the spans so that queries are matched with the span for their waitee
spans.rotate_right(1);
// Zip them back together
let mut stack: Vec<_> = iter::zip(spans, queries).collect();
// Remove the queries in our cycle from the list of jobs to look at
for r in &stack {
if let Some(pos) = jobs.iter().position(|j| j == &r.1) {
jobs.remove(pos);
}
}
// Find the queries in the cycle which are
// connected to queries outside the cycle
let entry_points = stack
.iter()
.filter_map(|&(span, query)| {
if query.parent(query_map).is_none() {
// This query is connected to the root (it has no query parent)
Some((span, query, None))
} else {
let mut waiters = Vec::new();
// Find all the direct waiters who lead to the root
visit_waiters(query_map, query, |span, waiter| {
// Mark all the other queries in the cycle as already visited
let mut visited = FxHashSet::from_iter(stack.iter().map(|q| q.1));
if connected_to_root(query_map, waiter, &mut visited) {
waiters.push((span, waiter));
}
None
});
if waiters.is_empty() {
None
} else {
// Deterministically pick one of the waiters to show to the user
let waiter = *pick_query(query_map, &waiters, |s| *s);
Some((span, query, Some(waiter)))
}
}
})
.collect::<Vec<(Span, QueryJobId, Option<(Span, QueryJobId)>)>>();
// Deterministically pick an entry point
let (_, entry_point, usage) = pick_query(query_map, &entry_points, |e| (e.0, e.1));
// Shift the stack so that our entry point is first
let entry_point_pos = stack.iter().position(|(_, query)| query == entry_point);
if let Some(pos) = entry_point_pos {
stack.rotate_left(pos);
}
let usage = usage.as_ref().map(|(span, query)| (*span, query.query(query_map)));
// Create the cycle error
let error = CycleError {
usage,
cycle: stack
.iter()
.map(|&(s, ref q)| QueryInfo { span: s, query: q.query(query_map) })
.collect(),
};
// We unwrap `waiter` here since there must always be one
// edge which is resumable / waited using a query latch
let (waitee_query, waiter_idx) = waiter.unwrap();
// Extract the waiter we want to resume
let waiter = waitee_query.latch(query_map).unwrap().extract_waiter(waiter_idx);
// Set the cycle error so it will be picked up when resumed
*waiter.cycle.lock() = Some(error);
// Put the waiter on the list of things to resume
wakelist.push(waiter);
true
} else {
false
}
}
/// Detects query cycles by using depth first search over all active query jobs.
/// If a query cycle is found it will break the cycle by finding an edge which
/// uses a query latch and then resuming that waiter.
/// There may be multiple cycles involved in a deadlock, so this searches
/// all active queries for cycles before finally resuming all the waiters at once.
#[cfg(parallel_compiler)]
pub fn deadlock(query_map: QueryMap, registry: &rayon_core::Registry) {
let on_panic = defer(|| {
eprintln!("deadlock handler panicked, aborting process");
process::abort();
});
let mut wakelist = Vec::new();
let mut jobs: Vec<QueryJobId> = query_map.keys().cloned().collect();
let mut found_cycle = false;
while jobs.len() > 0 {
if remove_cycle(&query_map, &mut jobs, &mut wakelist) {
found_cycle = true;
}
}
// Check that a cycle was found. It is possible for a deadlock to occur without
// a query cycle if a query which can be waited on uses Rayon to do multithreading
// internally. Such a query (X) may be executing on 2 threads (A and B) and A may
// wait using Rayon on B. Rayon may then switch to executing another query (Y)
// which in turn will wait on X causing a deadlock. We have a false dependency from
// X to Y due to Rayon waiting and a true dependency from Y to X. The algorithm here
// only considers the true dependency and won't detect a cycle.
if !found_cycle {
panic!("deadlock detected");
}
// FIXME: Ensure this won't cause a deadlock before we return
for waiter in wakelist.into_iter() {
waiter.notify(registry);
}
on_panic.disable();
}
#[inline(never)]
#[cold]
pub(crate) fn report_cycle<'a>(
sess: &'a Session,
CycleError { usage, cycle: stack }: &CycleError,
) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
assert!(!stack.is_empty());
let span = stack[0].query.default_span(stack[1 % stack.len()].span);
let mut cycle_stack = Vec::new();
use crate::error::StackCount;
let stack_count = if stack.len() == 1 { StackCount::Single } else { StackCount::Multiple };
for i in 1..stack.len() {
let query = &stack[i].query;
let span = query.default_span(stack[(i + 1) % stack.len()].span);
cycle_stack.push(CycleStack { span, desc: query.description.to_owned() });
}
let mut cycle_usage = None;
if let Some((span, ref query)) = *usage {
cycle_usage = Some(crate::error::CycleUsage {
span: query.default_span(span),
usage: query.description.to_string(),
});
}
let alias = if stack.iter().all(|entry| matches!(entry.query.def_kind, Some(DefKind::TyAlias)))
{
Some(crate::error::Alias::Ty)
} else if stack.iter().all(|entry| entry.query.def_kind == Some(DefKind::TraitAlias)) {
Some(crate::error::Alias::Trait)
} else {
None
};
let cycle_diag = crate::error::Cycle {
span,
cycle_stack,
stack_bottom: stack[0].query.description.to_owned(),
alias,
cycle_usage: cycle_usage,
stack_count,
note_span: (),
};
cycle_diag.into_diagnostic(&sess.parse_sess.span_diagnostic)
}
pub fn print_query_stack<Qcx: QueryContext>(
qcx: Qcx,
mut current_query: Option<QueryJobId>,
handler: &Handler,
num_frames: Option<usize>,
mut file: Option<std::fs::File>,
) -> usize {
// Be careful relying on global state here: this code is called from
// a panic hook, which means that the global `Handler` may be in a weird
// state if it was responsible for triggering the panic.
let mut count_printed = 0;
let mut count_total = 0;
let query_map = qcx.try_collect_active_jobs();
if let Some(ref mut file) = file {
let _ = writeln!(file, "\n\nquery stack during panic:");
}
while let Some(query) = current_query {
let Some(query_info) = query_map.as_ref().and_then(|map| map.get(&query)) else {
break;
};
if Some(count_printed) < num_frames || num_frames.is_none() {
// Only print to stderr as many stack frames as `num_frames` when present.
let mut diag = Diagnostic::new(
Level::FailureNote,
format!(
"#{} [{:?}] {}",
count_printed, query_info.query.dep_kind, query_info.query.description
),
);
diag.span = query_info.job.span.into();
handler.force_print_diagnostic(diag);
count_printed += 1;
}
if let Some(ref mut file) = file {
let _ = writeln!(
file,
"#{} [{}] {}",
count_total,
qcx.dep_context().dep_kind_info(query_info.query.dep_kind).name,
query_info.query.description
);
}
current_query = query_info.job.parent;
count_total += 1;
}
if let Some(ref mut file) = file {
let _ = writeln!(file, "end of query stack");
}
count_printed
}