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Flaky failure in query feeding on the parallel compiler: caller raced calls to put() #162316

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@Zalathar

Observed in a CI failure here: #162105 (comment)

thread 'rustc' (525478) panicked at compiler/rustc_data_structures/src/vec_cache.rs:179:23:
caller raced calls to put()
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: rustc_middle::query::calls::query_feed::<rustc_middle::query::caches::DefIdCache<rustc_middle::query::erase::ErasedData<[u8; 8]>>>
   3: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_const_arg
   4: <<dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_generic_args_of_path::{closure#0}::GenericArgsCtxt as rustc_hir_analysis::hir_ty_lowering::GenericArgsLowerer>::provided_kind
   5: rustc_hir_analysis::hir_ty_lowering::generics::lower_generic_args::<<dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_generic_args_of_path::{closure#0}::GenericArgsCtxt>
   6: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_generic_args_of_path
   7: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_poly_trait_ref
   8: <dyn rustc_hir_analysis::hir_ty_lowering::HirTyLowerer>::lower_bounds::<&[rustc_hir::hir::GenericBound]>
   9: rustc_hir_analysis::collect::clauses_of::implied_clauses_with_filter
  10: rustc_hir_analysis::collect::clauses_of::explicit_implied_clauses_of
      [... omitted 1 frame ...]
  11: rustc_hir_analysis::check::check::check_item_type
  12: rustc_hir_analysis::check::wfcheck::check_well_formed
      [... omitted 1 frame ...]
  13: rustc_middle::query::calls::query_ensure_result::<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::ErasedData<[u8; 1]>, rustc_middle::dep_graph::graph::DepNodeIndex>, ()>
  14: <rustc_data_structures::sync::parallel::ParallelGuard>::run::<(), rustc_data_structures::sync::parallel::par_slice<&rustc_hir::hir::ItemId, rustc_data_structures::sync::parallel::try_par_for_each_in<&[rustc_hir::hir::ItemId], rustc_span::ErrorGuaranteed, <rustc_middle::hir::ModuleItems>::par_items<rustc_hir_analysis::check::wfcheck::check_type_wf::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#1}::{closure#0}::{closure#0}>
  15: <rustc_thread_pool::scope::ScopeBase>::execute_job_closure::<<rustc_thread_pool::scope::Scope>::spawn<rustc_data_structures::sync::parallel::par_slice<&rustc_hir::hir::ItemId, rustc_data_structures::sync::parallel::try_par_for_each_in<&[rustc_hir::hir::ItemId], rustc_span::ErrorGuaranteed, <rustc_middle::hir::ModuleItems>::par_items<rustc_hir_analysis::check::wfcheck::check_type_wf::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#1}::{closure#0}>::{closure#0}::{closure#0}, ()>
  16: <rustc_thread_pool::job::HeapJob<<rustc_thread_pool::scope::Scope>::spawn<rustc_data_structures::sync::parallel::par_slice<&rustc_hir::hir::ItemId, rustc_data_structures::sync::parallel::try_par_for_each_in<&[rustc_hir::hir::ItemId], rustc_span::ErrorGuaranteed, <rustc_middle::hir::ModuleItems>::par_items<rustc_hir_analysis::check::wfcheck::check_type_wf::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#1}::{closure#0}>::{closure#0}> as rustc_thread_pool::job::Job>::execute
  17: <rustc_thread_pool::registry::WorkerThread>::wait_or_steal_until_cold
  18: <rustc_thread_pool::registry::ThreadBuilder>::run
  19: rustc_span::set_session_globals_then::<(), rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#5}::{closure#0}::{closure#0}::{closure#0}>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Normally it's OK to feed the same query twice as long as both values are the same. However, from looking at query_feed there might be a race condition when two query calls try to feed the same query at the same time, see that the cache is empty, and then both try to fill the cache entry without further coordination.

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    A-parallel-compilerArea: parallel compilerC-bugCategory: This is a bug.I-ICEIssue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

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