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Change prefetch to avoid deadlock #118488

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Dec 5, 2023
Merged

Change prefetch to avoid deadlock #118488

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23 changes: 7 additions & 16 deletions compiler/rustc_metadata/src/rmeta/encoder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -658,8 +658,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
let debugger_visualizers =
stat!("debugger-visualizers", || self.encode_debugger_visualizers());

// Encode exported symbols info. This is prefetched in `encode_metadata` so we encode
// this as late as possible to give the prefetching as much time as possible to complete.
// Encode exported symbols info. This is prefetched in `encode_metadata`.
let exported_symbols = stat!("exported-symbols", || {
self.encode_exported_symbols(tcx.exported_symbols(LOCAL_CRATE))
});
Expand Down Expand Up @@ -2193,21 +2192,13 @@ pub fn encode_metadata(tcx: TyCtxt<'_>, path: &Path) {
// there's no need to do dep-graph tracking for any of it.
tcx.dep_graph.assert_ignored();

join(
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I would strongly prefer this be changed to use disabled::join so it could be easily reverted.

|| encode_metadata_impl(tcx, path),
|| {
if tcx.sess.threads() == 1 {
return;
}
// Prefetch some queries used by metadata encoding.
// This is not necessary for correctness, but is only done for performance reasons.
// It can be removed if it turns out to cause trouble or be detrimental to performance.
join(|| prefetch_mir(tcx), || tcx.exported_symbols(LOCAL_CRATE));
},
);
}
if tcx.sess.threads() != 1 {
// Prefetch some queries used by metadata encoding.
// This is not necessary for correctness, but is only done for performance reasons.
// It can be removed if it turns out to cause trouble or be detrimental to performance.
join(|| prefetch_mir(tcx), || tcx.exported_symbols(LOCAL_CRATE));
}

fn encode_metadata_impl(tcx: TyCtxt<'_>, path: &Path) {
let mut encoder = opaque::FileEncoder::new(path)
.unwrap_or_else(|err| tcx.sess.emit_fatal(FailCreateFileEncoder { err }));
encoder.emit_raw_bytes(METADATA_HEADER);
Expand Down
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