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Fix waiting on a query that panicked #115198

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merged 1 commit into from
Aug 26, 2023
Merged

Fix waiting on a query that panicked #115198

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13 changes: 12 additions & 1 deletion compiler/rustc_query_system/src/query/plumbing.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -300,7 +300,18 @@ where
match result {
Ok(()) => {
let Some((v, index)) = query.query_cache(qcx).lookup(&key) else {
cold_path(|| panic!("value must be in cache after waiting"))
cold_path(|| {
// We didn't find the query result in the query cache. Check if it was
// poisoned due to a panic instead.
let lock = query.query_state(qcx).active.get_shard_by_value(&key).lock();
match lock.get(&key) {
// The query we waited on panicked. Continue unwinding here.
Some(QueryResult::Poisoned) => FatalError.raise(),
_ => panic!(
"query result must in the cache or the query must be poisoned after a wait"
),
}
Comment on lines +304 to +313
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The only possible course of action is unwinding. Should we replace the match by an assertion?

Suggested change
// We didn't find the query result in the query cache. Check if it was
// poisoned due to a panic instead.
let lock = query.query_state(qcx).active.get_shard_by_value(&key).lock();
match lock.get(&key) {
// The query we waited on panicked. Continue unwinding here.
Some(QueryResult::Poisoned) => FatalError.raise(),
_ => panic!(
"query result must in the cache or the query must be poisoned after a wait"
),
}
// We didn't find the query result in the query cache. Check if it was
// poisoned due to a panic instead.
debug_assert!(
matches!(
query.query_state(qcx).active.get_shard_by_value(&key).lock().get(&key),
Some(QueryResult::Poisoned),
),
"query result must in the cache or the query must be poisoned after a wait",
);
// The query we waited on panicked. Continue unwinding here.
FatalError.raise()

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I feel like the current version makes it more clear that we should only call FatalError.raise() once we observe the QueryResult::Poisoned case. I don't think I want to downgrade to a debug_assert without some more testing of the parallel compiler. This path is also not terribly hot.

})
};

qcx.dep_context().profiler().query_cache_hit(index.into());
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