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Drop the query result memmap before serializing it back.

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This commit is contained in:
Camille GILLOT 2021-03-17 22:49:16 +01:00
parent 6b47e1ece8
commit 98007e2ce6
4 changed files with 44 additions and 26 deletions
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11
compiler/rustc_incremental/src/persist/file_format.rs
View File

@ -52,7 +52,10 @@ where
// Delete the old file, if any.
// Note: It's important that we actually delete the old file and not just
// truncate and overwrite it, since it might be a shared hard-link, the
// underlying data of which we don't want to modify
// underlying data of which we don't want to modify.
//
// We have to ensure we have dropped the memory maps to this file
// before performing this removal.
match fs::remove_file(&path_buf) {
Ok(()) => {
debug!("save: remove old file");
@ -114,6 +117,12 @@ pub fn read_file(
Err(err) if err.kind() == io::ErrorKind::NotFound => return Ok(None),
Err(err) => return Err(err),
};
// SAFETY: This process must not modify nor remove the backing file while the memory map lives.
// For the dep-graph and the work product index, it is as soon as the decoding is done.
// For the query result cache, the memory map is dropped in save_dep_graph before calling
// save_in and trying to remove the backing file.
//
// There is no way to prevent another process from modifying this file.
let mmap = unsafe { Mmap::map(file) }?;
let mut file = io::Cursor::new(&*mmap);

5
compiler/rustc_incremental/src/persist/save.rs
View File

@ -42,6 +42,11 @@ pub fn save_dep_graph(tcx: TyCtxt<'_>) {
join(
move || {
sess.time("incr_comp_persist_result_cache", || {
// Drop the memory map so that we can remove the file and write to it.
if let Some(odc) = &tcx.on_disk_cache {
odc.drop_serialized_data(tcx);
}
file_format::save_in(sess, query_cache_path, "query cache", |e| {
encode_query_cache(tcx, e)
});

2
compiler/rustc_middle/src/ty/context.rs
View File

@ -101,6 +101,8 @@ pub trait OnDiskCache<'tcx>: rustc_data_structures::sync::Sync {
fn register_reused_dep_node(&self, tcx: TyCtxt<'tcx>, dep_node: &DepNode);
fn store_foreign_def_id_hash(&self, def_id: DefId, hash: DefPathHash);
fn drop_serialized_data(&self, tcx: TyCtxt<'tcx>);
fn serialize(&self, tcx: TyCtxt<'tcx>, encoder: &mut FileEncoder) -> FileEncodeResult;
}

52
compiler/rustc_query_impl/src/on_disk_cache.rs
View File

@ -1,7 +1,7 @@
use crate::QueryCtxt;
use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
use rustc_data_structures::memmap::Mmap;
use rustc_data_structures::sync::{HashMapExt, Lock, Lrc, OnceCell};
use rustc_data_structures::sync::{HashMapExt, Lock, Lrc, OnceCell, RwLock};
use rustc_data_structures::unhash::UnhashMap;
use rustc_hir::def_id::{CrateNum, DefId, DefIndex, LocalDefId, StableCrateId, LOCAL_CRATE};
use rustc_hir::definitions::DefPathHash;
@ -43,7 +43,7 @@ const TAG_EXPN_DATA: u8 = 1;
/// any side effects that have been emitted during a query.
pub struct OnDiskCache<'sess> {
// The complete cache data in serialized form.
serialized_data: Option<Mmap>,
serialized_data: RwLock<Option<Mmap>>,
// Collects all `QuerySideEffects` created during the current compilation
// session.
@ -206,7 +206,7 @@ impl<'sess> rustc_middle::ty::OnDiskCache<'sess> for OnDiskCache<'sess> {
};
Self {
serialized_data: Some(data),
serialized_data: RwLock::new(Some(data)),
file_index_to_stable_id: footer.file_index_to_stable_id,
file_index_to_file: Default::default(),
cnum_map: OnceCell::new(),
@ -227,7 +227,7 @@ impl<'sess> rustc_middle::ty::OnDiskCache<'sess> for OnDiskCache<'sess> {
fn new_empty(source_map: &'sess SourceMap) -> Self {
Self {
serialized_data: None,
serialized_data: RwLock::new(None),
file_index_to_stable_id: Default::default(),
file_index_to_file: Default::default(),
cnum_map: OnceCell::new(),
@ -246,7 +246,26 @@ impl<'sess> rustc_middle::ty::OnDiskCache<'sess> for OnDiskCache<'sess> {
}
}
fn serialize(&self, tcx: TyCtxt<'sess>, encoder: &mut FileEncoder) -> FileEncodeResult {
fn drop_serialized_data(&self, tcx: TyCtxt<'tcx>) {
// Register any dep nodes that we reused from the previous session,
// but didn't `DepNode::construct` in this session. This ensures
// that their `DefPathHash` to `RawDefId` mappings are registered
// in 'latest_foreign_def_path_hashes' if necessary, since that
// normally happens in `DepNode::construct`.
tcx.dep_graph.register_reused_dep_nodes(tcx);
// Load everything into memory so we can write it out to the on-disk
// cache. The vast majority of cacheable query results should already
// be in memory, so this should be a cheap operation.
// Do this *before* we clone 'latest_foreign_def_path_hashes', since
// loading existing queries may cause us to create new DepNodes, which
// may in turn end up invoking `store_foreign_def_id_hash`
tcx.dep_graph.exec_cache_promotions(QueryCtxt::from_tcx(tcx));
*self.serialized_data.write() = None;
}
fn serialize<'tcx>(&self, tcx: TyCtxt<'tcx>, encoder: &mut FileEncoder) -> FileEncodeResult {
// Serializing the `DepGraph` should not modify it.
tcx.dep_graph.with_ignore(|| {
// Allocate `SourceFileIndex`es.
@ -268,21 +287,6 @@ impl<'sess> rustc_middle::ty::OnDiskCache<'sess> for OnDiskCache<'sess> {
(file_to_file_index, file_index_to_stable_id)
};
// Register any dep nodes that we reused from the previous session,
// but didn't `DepNode::construct` in this session. This ensures
// that their `DefPathHash` to `RawDefId` mappings are registered
// in 'latest_foreign_def_path_hashes' if necessary, since that
// normally happens in `DepNode::construct`.
tcx.dep_graph.register_reused_dep_nodes(tcx);
// Load everything into memory so we can write it out to the on-disk
// cache. The vast majority of cacheable query results should already
// be in memory, so this should be a cheap operation.
// Do this *before* we clone 'latest_foreign_def_path_hashes', since
// loading existing queries may cause us to create new DepNodes, which
// may in turn end up invoking `store_foreign_def_id_hash`
tcx.dep_graph.exec_cache_promotions(QueryCtxt::from_tcx(tcx));
let latest_foreign_def_path_hashes = self.latest_foreign_def_path_hashes.lock().clone();
let hygiene_encode_context = HygieneEncodeContext::default();
@ -566,7 +570,7 @@ impl<'sess> OnDiskCache<'sess> {
})
}
fn with_decoder<'a, 'tcx, T, F: FnOnce(&mut CacheDecoder<'sess, 'tcx>) -> T>(
fn with_decoder<'a, 'tcx, T, F: for<'s> FnOnce(&mut CacheDecoder<'s, 'tcx>) -> T>(
&'sess self,
tcx: TyCtxt<'tcx>,
pos: AbsoluteBytePos,
@ -577,12 +581,10 @@ impl<'sess> OnDiskCache<'sess> {
{
let cnum_map = self.cnum_map.get_or_init(|| Self::compute_cnum_map(tcx));
let serialized_data = self.serialized_data.read();
let mut decoder = CacheDecoder {
tcx,
opaque: opaque::Decoder::new(
self.serialized_data.as_deref().unwrap_or(&[]),
pos.to_usize(),
),
opaque: opaque::Decoder::new(serialized_data.as_deref().unwrap_or(&[]), pos.to_usize()),
source_map: self.source_map,
cnum_map,
file_index_to_file: &self.file_index_to_file,