1 //! This module manages how the incremental compilation cache is represented in
4 //! Incremental compilation caches are managed according to a copy-on-write
5 //! strategy: Once a complete, consistent cache version is finalized, it is
6 //! never modified. Instead, when a subsequent compilation session is started,
7 //! the compiler will allocate a new version of the cache that starts out as
8 //! a copy of the previous version. Then only this new copy is modified and it
9 //! will not be visible to other processes until it is finalized. This ensures
10 //! that multiple compiler processes can be executed concurrently for the same
11 //! crate without interfering with each other or blocking each other.
13 //! More concretely this is implemented via the following protocol:
15 //! 1. For a newly started compilation session, the compiler allocates a
16 //! new `session` directory within the incremental compilation directory.
17 //! This session directory will have a unique name that ends with the suffix
18 //! "-working" and that contains a creation timestamp.
19 //! 2. Next, the compiler looks for the newest finalized session directory,
20 //! that is, a session directory from a previous compilation session that
21 //! has been marked as valid and consistent. A session directory is
22 //! considered finalized if the "-working" suffix in the directory name has
23 //! been replaced by the SVH of the crate.
24 //! 3. Once the compiler has found a valid, finalized session directory, it will
25 //! hard-link/copy its contents into the new "-working" directory. If all
26 //! goes well, it will have its own, private copy of the source directory and
27 //! subsequently not have to worry about synchronizing with other compiler
29 //! 4. Now the compiler can do its normal compilation process, which involves
30 //! reading and updating its private session directory.
31 //! 5. When compilation finishes without errors, the private session directory
32 //! will be in a state where it can be used as input for other compilation
33 //! sessions. That is, it will contain a dependency graph and cache artifacts
34 //! that are consistent with the state of the source code it was compiled
35 //! from, with no need to change them ever again. At this point, the compiler
36 //! finalizes and "publishes" its private session directory by renaming it
37 //! from "s-{timestamp}-{random}-working" to "s-{timestamp}-{SVH}".
38 //! 6. At this point the "old" session directory that we copied our data from
39 //! at the beginning of the session has become obsolete because we have just
40 //! published a more current version. Thus the compiler will delete it.
42 //! ## Garbage Collection
44 //! Naively following the above protocol might lead to old session directories
45 //! piling up if a compiler instance crashes for some reason before its able to
46 //! remove its private session directory. In order to avoid wasting disk space,
47 //! the compiler also does some garbage collection each time it is started in
48 //! incremental compilation mode. Specifically, it will scan the incremental
49 //! compilation directory for private session directories that are not in use
50 //! any more and will delete those. It will also delete any finalized session
51 //! directories for a given crate except for the most recent one.
53 //! ## Synchronization
55 //! There is some synchronization needed in order for the compiler to be able to
56 //! determine whether a given private session directory is not in used any more.
57 //! This is done by creating a lock file for each session directory and
58 //! locking it while the directory is still being used. Since file locks have
59 //! operating system support, we can rely on the lock being released if the
60 //! compiler process dies for some unexpected reason. Thus, when garbage
61 //! collecting private session directories, the collecting process can determine
62 //! whether the directory is still in use by trying to acquire a lock on the
63 //! file. If locking the file fails, the original process must still be alive.
64 //! If locking the file succeeds, we know that the owning process is not alive
65 //! any more and we can safely delete the directory.
66 //! There is still a small time window between the original process creating the
67 //! lock file and actually locking it. In order to minimize the chance that
68 //! another process tries to acquire the lock in just that instance, only
69 //! session directories that are older than a few seconds are considered for
70 //! garbage collection.
72 //! Another case that has to be considered is what happens if one process
73 //! deletes a finalized session directory that another process is currently
74 //! trying to copy from. This case is also handled via the lock file. Before
75 //! a process starts copying a finalized session directory, it will acquire a
76 //! shared lock on the directory's lock file. Any garbage collecting process,
77 //! on the other hand, will acquire an exclusive lock on the lock file.
78 //! Thus, if a directory is being collected, any reader process will fail
79 //! acquiring the shared lock and will leave the directory alone. Conversely,
80 //! if a collecting process can't acquire the exclusive lock because the
81 //! directory is currently being read from, it will leave collecting that
82 //! directory to another process at a later point in time.
83 //! The exact same scheme is also used when reading the metadata hashes file
84 //! from an extern crate. When a crate is compiled, the hash values of its
85 //! metadata are stored in a file in its session directory. When the
86 //! compilation session of another crate imports the first crate's metadata,
87 //! it also has to read in the accompanying metadata hashes. It thus will access
88 //! the finalized session directory of all crates it links to and while doing
89 //! so, it will also place a read lock on that the respective session directory
90 //! so that it won't be deleted while the metadata hashes are loaded.
94 //! This system relies on two features being available in the file system in
95 //! order to work really well: file locking and hard linking.
96 //! If hard linking is not available (like on FAT) the data in the cache
97 //! actually has to be copied at the beginning of each session.
98 //! If file locking does not work reliably (like on NFS), some of the
99 //! synchronization will go haywire.
100 //! In both cases we recommend to locate the incremental compilation directory
101 //! on a file system that supports these things.
102 //! It might be a good idea though to try and detect whether we are on an
103 //! unsupported file system and emit a warning in that case. This is not yet
106 use rustc_data_structures
::fx
::{FxHashMap, FxHashSet}
;
107 use rustc_data_structures
::svh
::Svh
;
108 use rustc_data_structures
::{base_n, flock}
;
109 use rustc_errors
::ErrorGuaranteed
;
110 use rustc_fs_util
::{link_or_copy, LinkOrCopy}
;
111 use rustc_session
::{Session, StableCrateId}
;
113 use std
::fs
as std_fs
;
114 use std
::io
::{self, ErrorKind}
;
116 use std
::path
::{Path, PathBuf}
;
117 use std
::time
::{Duration, SystemTime, UNIX_EPOCH}
;
119 use rand
::{thread_rng, RngCore}
;
124 const LOCK_FILE_EXT
: &str = ".lock";
125 const DEP_GRAPH_FILENAME
: &str = "dep-graph.bin";
126 const STAGING_DEP_GRAPH_FILENAME
: &str = "dep-graph.part.bin";
127 const WORK_PRODUCTS_FILENAME
: &str = "work-products.bin";
128 const QUERY_CACHE_FILENAME
: &str = "query-cache.bin";
130 // We encode integers using the following base, so they are shorter than decimal
131 // or hexadecimal numbers (we want short file and directory names). Since these
132 // numbers will be used in file names, we choose an encoding that is not
133 // case-sensitive (as opposed to base64, for example).
134 const INT_ENCODE_BASE
: usize = base_n
::CASE_INSENSITIVE
;
136 /// Returns the path to a session's dependency graph.
137 pub fn dep_graph_path(sess
: &Session
) -> PathBuf
{
138 in_incr_comp_dir_sess(sess
, DEP_GRAPH_FILENAME
)
140 /// Returns the path to a session's staging dependency graph.
142 /// On the difference between dep-graph and staging dep-graph,
143 /// see `build_dep_graph`.
144 pub fn staging_dep_graph_path(sess
: &Session
) -> PathBuf
{
145 in_incr_comp_dir_sess(sess
, STAGING_DEP_GRAPH_FILENAME
)
147 pub fn work_products_path(sess
: &Session
) -> PathBuf
{
148 in_incr_comp_dir_sess(sess
, WORK_PRODUCTS_FILENAME
)
150 /// Returns the path to a session's query cache.
151 pub fn query_cache_path(sess
: &Session
) -> PathBuf
{
152 in_incr_comp_dir_sess(sess
, QUERY_CACHE_FILENAME
)
155 /// Locks a given session directory.
156 pub fn lock_file_path(session_dir
: &Path
) -> PathBuf
{
157 let crate_dir
= session_dir
.parent().unwrap();
159 let directory_name
= session_dir
.file_name().unwrap().to_string_lossy();
160 assert_no_characters_lost(&directory_name
);
162 let dash_indices
: Vec
<_
> = directory_name
.match_indices('
-'
).map(|(idx
, _
)| idx
).collect();
163 if dash_indices
.len() != 3 {
165 "Encountered incremental compilation session directory with \
167 session_dir
.display()
171 crate_dir
.join(&directory_name
[0..dash_indices
[2]]).with_extension(&LOCK_FILE_EXT
[1..])
174 /// Returns the path for a given filename within the incremental compilation directory
175 /// in the current session.
176 pub fn in_incr_comp_dir_sess(sess
: &Session
, file_name
: &str) -> PathBuf
{
177 in_incr_comp_dir(&sess
.incr_comp_session_dir(), file_name
)
180 /// Returns the path for a given filename within the incremental compilation directory,
181 /// not necessarily from the current session.
183 /// To ensure the file is part of the current session, use [`in_incr_comp_dir_sess`].
184 pub fn in_incr_comp_dir(incr_comp_session_dir
: &Path
, file_name
: &str) -> PathBuf
{
185 incr_comp_session_dir
.join(file_name
)
188 /// Allocates the private session directory.
190 /// If the result of this function is `Ok`, we have a valid incremental
191 /// compilation session directory. A valid session
192 /// directory is one that contains a locked lock file. It may or may not contain
193 /// a dep-graph and work products from a previous session.
195 /// This always attempts to load a dep-graph from the directory.
196 /// If loading fails for some reason, we fallback to a disabled `DepGraph`.
197 /// See [`rustc_interface::queries::dep_graph`].
199 /// If this function returns an error, it may leave behind an invalid session directory.
200 /// The garbage collection will take care of it.
202 /// [`rustc_interface::queries::dep_graph`]: ../../rustc_interface/struct.Queries.html#structfield.dep_graph
203 pub fn prepare_session_directory(
206 stable_crate_id
: StableCrateId
,
207 ) -> Result
<(), ErrorGuaranteed
> {
208 if sess
.opts
.incremental
.is_none() {
212 let _timer
= sess
.timer("incr_comp_prepare_session_directory");
214 debug
!("prepare_session_directory");
216 // {incr-comp-dir}/{crate-name-and-disambiguator}
217 let crate_dir
= crate_path(sess
, crate_name
, stable_crate_id
);
218 debug
!("crate-dir: {}", crate_dir
.display());
219 create_dir(sess
, &crate_dir
, "crate")?
;
221 // Hack: canonicalize the path *after creating the directory*
222 // because, on windows, long paths can cause problems;
223 // canonicalization inserts this weird prefix that makes windows
224 // tolerate long paths.
225 let crate_dir
= match crate_dir
.canonicalize() {
228 let reported
= sess
.err(&format
!(
229 "incremental compilation: error canonicalizing path `{}`: {}",
233 return Err(reported
);
237 let mut source_directories_already_tried
= FxHashSet
::default();
240 // Generate a session directory of the form:
242 // {incr-comp-dir}/{crate-name-and-disambiguator}/s-{timestamp}-{random}-working
243 let session_dir
= generate_session_dir_path(&crate_dir
);
244 debug
!("session-dir: {}", session_dir
.display());
246 // Lock the new session directory. If this fails, return an
247 // error without retrying
248 let (directory_lock
, lock_file_path
) = lock_directory(sess
, &session_dir
)?
;
250 // Now that we have the lock, we can actually create the session
252 create_dir(sess
, &session_dir
, "session")?
;
254 // Find a suitable source directory to copy from. Ignore those that we
255 // have already tried before.
256 let source_directory
= find_source_directory(&crate_dir
, &source_directories_already_tried
);
258 let Some(source_directory
) = source_directory
else {
259 // There's nowhere to copy from, we're done
261 "no source directory found. Continuing with empty session \
265 sess
.init_incr_comp_session(session_dir
, directory_lock
, false);
269 debug
!("attempting to copy data from source: {}", source_directory
.display());
271 // Try copying over all files from the source directory
272 if let Ok(allows_links
) = copy_files(sess
, &session_dir
, &source_directory
) {
273 debug
!("successfully copied data from: {}", source_directory
.display());
277 "Hard linking files in the incremental \
278 compilation cache failed. Copying files \
279 instead. Consider moving the cache \
280 directory to a file system which supports \
281 hard linking in session dir `{}`",
282 session_dir
.display()
286 sess
.init_incr_comp_session(session_dir
, directory_lock
, true);
289 debug
!("copying failed - trying next directory");
291 // Something went wrong while trying to copy/link files from the
292 // source directory. Try again with a different one.
293 source_directories_already_tried
.insert(source_directory
);
295 // Try to remove the session directory we just allocated. We don't
296 // know if there's any garbage in it from the failed copy action.
297 if let Err(err
) = safe_remove_dir_all(&session_dir
) {
299 "Failed to delete partly initialized \
300 session dir `{}`: {}",
301 session_dir
.display(),
306 delete_session_dir_lock_file(sess
, &lock_file_path
);
307 mem
::drop(directory_lock
);
312 /// This function finalizes and thus 'publishes' the session directory by
313 /// renaming it to `s-{timestamp}-{svh}` and releasing the file lock.
314 /// If there have been compilation errors, however, this function will just
315 /// delete the presumably invalid session directory.
316 pub fn finalize_session_directory(sess
: &Session
, svh
: Svh
) {
317 if sess
.opts
.incremental
.is_none() {
321 let _timer
= sess
.timer("incr_comp_finalize_session_directory");
323 let incr_comp_session_dir
: PathBuf
= sess
.incr_comp_session_dir().clone();
325 if sess
.has_errors_or_delayed_span_bugs() {
326 // If there have been any errors during compilation, we don't want to
327 // publish this session directory. Rather, we'll just delete it.
330 "finalize_session_directory() - invalidating session directory: {}",
331 incr_comp_session_dir
.display()
334 if let Err(err
) = safe_remove_dir_all(&*incr_comp_session_dir
) {
336 "Error deleting incremental compilation \
337 session directory `{}`: {}",
338 incr_comp_session_dir
.display(),
343 let lock_file_path
= lock_file_path(&*incr_comp_session_dir
);
344 delete_session_dir_lock_file(sess
, &lock_file_path
);
345 sess
.mark_incr_comp_session_as_invalid();
348 debug
!("finalize_session_directory() - session directory: {}", incr_comp_session_dir
.display());
350 let old_sub_dir_name
= incr_comp_session_dir
.file_name().unwrap().to_string_lossy();
351 assert_no_characters_lost(&old_sub_dir_name
);
353 // Keep the 's-{timestamp}-{random-number}' prefix, but replace the
354 // '-working' part with the SVH of the crate
355 let dash_indices
: Vec
<_
> = old_sub_dir_name
.match_indices('
-'
).map(|(idx
, _
)| idx
).collect();
356 if dash_indices
.len() != 3 {
358 "Encountered incremental compilation session directory with \
360 incr_comp_session_dir
.display()
364 // State: "s-{timestamp}-{random-number}-"
365 let mut new_sub_dir_name
= String
::from(&old_sub_dir_name
[..=dash_indices
[2]]);
368 base_n
::push_str(svh
.as_u64() as u128
, INT_ENCODE_BASE
, &mut new_sub_dir_name
);
370 // Create the full path
371 let new_path
= incr_comp_session_dir
.parent().unwrap().join(new_sub_dir_name
);
372 debug
!("finalize_session_directory() - new path: {}", new_path
.display());
374 match rename_path_with_retry(&*incr_comp_session_dir
, &new_path
, 3) {
376 debug
!("finalize_session_directory() - directory renamed successfully");
378 // This unlocks the directory
379 sess
.finalize_incr_comp_session(new_path
);
382 // Warn about the error. However, no need to abort compilation now.
384 "Error finalizing incremental compilation \
385 session directory `{}`: {}",
386 incr_comp_session_dir
.display(),
390 debug
!("finalize_session_directory() - error, marking as invalid");
391 // Drop the file lock, so we can garage collect
392 sess
.mark_incr_comp_session_as_invalid();
396 let _
= garbage_collect_session_directories(sess
);
399 pub fn delete_all_session_dir_contents(sess
: &Session
) -> io
::Result
<()> {
400 let sess_dir_iterator
= sess
.incr_comp_session_dir().read_dir()?
;
401 for entry
in sess_dir_iterator
{
403 safe_remove_file(&entry
.path())?
408 fn copy_files(sess
: &Session
, target_dir
: &Path
, source_dir
: &Path
) -> Result
<bool
, ()> {
409 // We acquire a shared lock on the lock file of the directory, so that
410 // nobody deletes it out from under us while we are reading from it.
411 let lock_file_path
= lock_file_path(source_dir
);
414 let Ok(_lock
) = flock
::Lock
::new(
416 false, // don't wait,
417 false, // don't create
420 // Could not acquire the lock, don't try to copy from here
424 let Ok(source_dir_iterator
) = source_dir
.read_dir() else {
428 let mut files_linked
= 0;
429 let mut files_copied
= 0;
431 for entry
in source_dir_iterator
{
434 let file_name
= entry
.file_name();
436 let target_file_path
= target_dir
.join(file_name
);
437 let source_path
= entry
.path();
439 debug
!("copying into session dir: {}", source_path
.display());
440 match link_or_copy(source_path
, target_file_path
) {
441 Ok(LinkOrCopy
::Link
) => files_linked
+= 1,
442 Ok(LinkOrCopy
::Copy
) => files_copied
+= 1,
443 Err(_
) => return Err(()),
446 Err(_
) => return Err(()),
450 if sess
.opts
.debugging_opts
.incremental_info
{
452 "[incremental] session directory: \
453 {} files hard-linked",
457 "[incremental] session directory: \
463 Ok(files_linked
> 0 || files_copied
== 0)
466 /// Generates unique directory path of the form:
467 /// {crate_dir}/s-{timestamp}-{random-number}-working
468 fn generate_session_dir_path(crate_dir
: &Path
) -> PathBuf
{
469 let timestamp
= timestamp_to_string(SystemTime
::now());
470 debug
!("generate_session_dir_path: timestamp = {}", timestamp
);
471 let random_number
= thread_rng().next_u32();
472 debug
!("generate_session_dir_path: random_number = {}", random_number
);
474 let directory_name
= format
!(
477 base_n
::encode(random_number
as u128
, INT_ENCODE_BASE
)
479 debug
!("generate_session_dir_path: directory_name = {}", directory_name
);
480 let directory_path
= crate_dir
.join(directory_name
);
481 debug
!("generate_session_dir_path: directory_path = {}", directory_path
.display());
485 fn create_dir(sess
: &Session
, path
: &Path
, dir_tag
: &str) -> Result
<(), ErrorGuaranteed
> {
486 match std_fs
::create_dir_all(path
) {
488 debug
!("{} directory created successfully", dir_tag
);
492 let reported
= sess
.err(&format
!(
493 "Could not create incremental compilation {} \
504 /// Allocate the lock-file and lock it.
508 ) -> Result
<(flock
::Lock
, PathBuf
), ErrorGuaranteed
> {
509 let lock_file_path
= lock_file_path(session_dir
);
510 debug
!("lock_directory() - lock_file: {}", lock_file_path
.display());
512 match flock
::Lock
::new(
515 true, // create the lock file
518 // the lock should be exclusive
519 Ok(lock
) => Ok((lock
, lock_file_path
)),
521 let mut err
= sess
.struct_err(&format
!(
522 "incremental compilation: could not create \
523 session directory lock file: {}",
526 if flock
::Lock
::error_unsupported(&lock_err
) {
528 "the filesystem for the incremental path at {} \
529 does not appear to support locking, consider changing the \
530 incremental path to a filesystem that supports locking \
531 or disable incremental compilation",
532 session_dir
.display()
534 if std
::env
::var_os("CARGO").is_some() {
536 "incremental compilation can be disabled by setting the \
537 environment variable CARGO_INCREMENTAL=0 (see \
538 https://doc.rust-lang.org/cargo/reference/profiles.html#incremental)",
541 "the entire build directory can be changed to a different \
542 filesystem by setting the environment variable CARGO_TARGET_DIR \
543 to a different path (see \
544 https://doc.rust-lang.org/cargo/reference/config.html#buildtarget-dir)",
553 fn delete_session_dir_lock_file(sess
: &Session
, lock_file_path
: &Path
) {
554 if let Err(err
) = safe_remove_file(&lock_file_path
) {
556 "Error deleting lock file for incremental \
557 compilation session directory `{}`: {}",
558 lock_file_path
.display(),
564 /// Finds the most recent published session directory that is not in the
566 fn find_source_directory(
568 source_directories_already_tried
: &FxHashSet
<PathBuf
>,
569 ) -> Option
<PathBuf
> {
573 .filter_map(|e
| e
.ok().map(|e
| e
.path()));
575 find_source_directory_in_iter(iter
, source_directories_already_tried
)
578 fn find_source_directory_in_iter
<I
>(
580 source_directories_already_tried
: &FxHashSet
<PathBuf
>,
583 I
: Iterator
<Item
= PathBuf
>,
585 let mut best_candidate
= (UNIX_EPOCH
, None
);
587 for session_dir
in iter
{
588 debug
!("find_source_directory_in_iter - inspecting `{}`", session_dir
.display());
590 let directory_name
= session_dir
.file_name().unwrap().to_string_lossy();
591 assert_no_characters_lost(&directory_name
);
593 if source_directories_already_tried
.contains(&session_dir
)
594 || !is_session_directory(&directory_name
)
595 || !is_finalized(&directory_name
)
597 debug
!("find_source_directory_in_iter - ignoring");
601 let timestamp
= extract_timestamp_from_session_dir(&directory_name
).unwrap_or_else(|_
| {
602 bug
!("unexpected incr-comp session dir: {}", session_dir
.display())
605 if timestamp
> best_candidate
.0 {
606 best_candidate
= (timestamp
, Some(session_dir
.clone()));
613 fn is_finalized(directory_name
: &str) -> bool
{
614 !directory_name
.ends_with("-working")
617 fn is_session_directory(directory_name
: &str) -> bool
{
618 directory_name
.starts_with("s-") && !directory_name
.ends_with(LOCK_FILE_EXT
)
621 fn is_session_directory_lock_file(file_name
: &str) -> bool
{
622 file_name
.starts_with("s-") && file_name
.ends_with(LOCK_FILE_EXT
)
625 fn extract_timestamp_from_session_dir(directory_name
: &str) -> Result
<SystemTime
, ()> {
626 if !is_session_directory(directory_name
) {
630 let dash_indices
: Vec
<_
> = directory_name
.match_indices('
-'
).map(|(idx
, _
)| idx
).collect();
631 if dash_indices
.len() != 3 {
635 string_to_timestamp(&directory_name
[dash_indices
[0] + 1..dash_indices
[1]])
638 fn timestamp_to_string(timestamp
: SystemTime
) -> String
{
639 let duration
= timestamp
.duration_since(UNIX_EPOCH
).unwrap();
640 let micros
= duration
.as_secs() * 1_000_000 + (duration
.subsec_nanos() as u64) / 1000;
641 base_n
::encode(micros
as u128
, INT_ENCODE_BASE
)
644 fn string_to_timestamp(s
: &str) -> Result
<SystemTime
, ()> {
645 let micros_since_unix_epoch
= u64::from_str_radix(s
, INT_ENCODE_BASE
as u32);
647 if micros_since_unix_epoch
.is_err() {
651 let micros_since_unix_epoch
= micros_since_unix_epoch
.unwrap();
653 let duration
= Duration
::new(
654 micros_since_unix_epoch
/ 1_000_000,
655 1000 * (micros_since_unix_epoch
% 1_000_000) as u32,
657 Ok(UNIX_EPOCH
+ duration
)
660 fn crate_path(sess
: &Session
, crate_name
: &str, stable_crate_id
: StableCrateId
) -> PathBuf
{
661 let incr_dir
= sess
.opts
.incremental
.as_ref().unwrap().clone();
663 let stable_crate_id
= base_n
::encode(stable_crate_id
.to_u64() as u128
, INT_ENCODE_BASE
);
665 let crate_name
= format
!("{}-{}", crate_name
, stable_crate_id
);
666 incr_dir
.join(crate_name
)
669 fn assert_no_characters_lost(s
: &str) {
670 if s
.contains('
\u{FFFD}'
) {
671 bug
!("Could not losslessly convert '{}'.", s
)
675 fn is_old_enough_to_be_collected(timestamp
: SystemTime
) -> bool
{
676 timestamp
< SystemTime
::now() - Duration
::from_secs(10)
679 /// Runs garbage collection for the current session.
680 pub fn garbage_collect_session_directories(sess
: &Session
) -> io
::Result
<()> {
681 debug
!("garbage_collect_session_directories() - begin");
683 let session_directory
= sess
.incr_comp_session_dir();
685 "garbage_collect_session_directories() - session directory: {}",
686 session_directory
.display()
689 let crate_directory
= session_directory
.parent().unwrap();
691 "garbage_collect_session_directories() - crate directory: {}",
692 crate_directory
.display()
695 // First do a pass over the crate directory, collecting lock files and
696 // session directories
697 let mut session_directories
= FxHashSet
::default();
698 let mut lock_files
= FxHashSet
::default();
700 for dir_entry
in crate_directory
.read_dir()?
{
701 let Ok(dir_entry
) = dir_entry
else {
706 let entry_name
= dir_entry
.file_name();
707 let entry_name
= entry_name
.to_string_lossy();
709 if is_session_directory_lock_file(&entry_name
) {
710 assert_no_characters_lost(&entry_name
);
711 lock_files
.insert(entry_name
.into_owned());
712 } else if is_session_directory(&entry_name
) {
713 assert_no_characters_lost(&entry_name
);
714 session_directories
.insert(entry_name
.into_owned());
716 // This is something we don't know, leave it alone
720 // Now map from lock files to session directories
721 let lock_file_to_session_dir
: FxHashMap
<String
, Option
<String
>> = lock_files
723 .map(|lock_file_name
| {
724 assert
!(lock_file_name
.ends_with(LOCK_FILE_EXT
));
725 let dir_prefix_end
= lock_file_name
.len() - LOCK_FILE_EXT
.len();
727 let dir_prefix
= &lock_file_name
[0..dir_prefix_end
];
728 session_directories
.iter().find(|dir_name
| dir_name
.starts_with(dir_prefix
))
730 (lock_file_name
, session_dir
.map(String
::clone
))
734 // Delete all lock files, that don't have an associated directory. They must
735 // be some kind of leftover
736 for (lock_file_name
, directory_name
) in &lock_file_to_session_dir
{
737 if directory_name
.is_none() {
738 let Ok(timestamp
) = extract_timestamp_from_session_dir(lock_file_name
) else {
740 "found lock-file with malformed timestamp: {}",
741 crate_directory
.join(&lock_file_name
).display()
747 let lock_file_path
= crate_directory
.join(&**lock_file_name
);
749 if is_old_enough_to_be_collected(timestamp
) {
751 "garbage_collect_session_directories() - deleting \
752 garbage lock file: {}",
753 lock_file_path
.display()
755 delete_session_dir_lock_file(sess
, &lock_file_path
);
758 "garbage_collect_session_directories() - lock file with \
759 no session dir not old enough to be collected: {}",
760 lock_file_path
.display()
766 // Filter out `None` directories
767 let lock_file_to_session_dir
: FxHashMap
<String
, String
> = lock_file_to_session_dir
769 .filter_map(|(lock_file_name
, directory_name
)| directory_name
.map(|n
| (lock_file_name
, n
)))
772 // Delete all session directories that don't have a lock file.
773 for directory_name
in session_directories
{
774 if !lock_file_to_session_dir
.values().any(|dir
| *dir
== directory_name
) {
775 let path
= crate_directory
.join(directory_name
);
776 if let Err(err
) = safe_remove_dir_all(&path
) {
778 "Failed to garbage collect invalid incremental \
779 compilation session directory `{}`: {}",
787 // Now garbage collect the valid session directories.
788 let mut deletion_candidates
= vec
![];
790 for (lock_file_name
, directory_name
) in &lock_file_to_session_dir
{
791 debug
!("garbage_collect_session_directories() - inspecting: {}", directory_name
);
793 let Ok(timestamp
) = extract_timestamp_from_session_dir(directory_name
) else {
795 "found session-dir with malformed timestamp: {}",
796 crate_directory
.join(directory_name
).display()
802 if is_finalized(directory_name
) {
803 let lock_file_path
= crate_directory
.join(lock_file_name
);
804 match flock
::Lock
::new(
807 false, // don't create the lock-file
810 // get an exclusive lock
813 "garbage_collect_session_directories() - \
814 successfully acquired lock"
817 "garbage_collect_session_directories() - adding \
818 deletion candidate: {}",
822 // Note that we are holding on to the lock
823 deletion_candidates
.push((
825 crate_directory
.join(directory_name
),
831 "garbage_collect_session_directories() - \
832 not collecting, still in use"
836 } else if is_old_enough_to_be_collected(timestamp
) {
837 // When cleaning out "-working" session directories, i.e.
838 // session directories that might still be in use by another
839 // compiler instance, we only look a directories that are
840 // at least ten seconds old. This is supposed to reduce the
841 // chance of deleting a directory in the time window where
842 // the process has allocated the directory but has not yet
843 // acquired the file-lock on it.
845 // Try to acquire the directory lock. If we can't, it
846 // means that the owning process is still alive and we
847 // leave this directory alone.
848 let lock_file_path
= crate_directory
.join(lock_file_name
);
849 match flock
::Lock
::new(
852 false, // don't create the lock-file
855 // get an exclusive lock
858 "garbage_collect_session_directories() - \
859 successfully acquired lock"
862 delete_old(sess
, &crate_directory
.join(directory_name
));
864 // Let's make it explicit that the file lock is released at this point,
865 // or rather, that we held on to it until here
870 "garbage_collect_session_directories() - \
871 not collecting, still in use"
877 "garbage_collect_session_directories() - not finalized, not \
883 // Delete all but the most recent of the candidates
884 for (path
, lock
) in all_except_most_recent(deletion_candidates
) {
885 debug
!("garbage_collect_session_directories() - deleting `{}`", path
.display());
887 if let Err(err
) = safe_remove_dir_all(&path
) {
889 "Failed to garbage collect finalized incremental \
890 compilation session directory `{}`: {}",
895 delete_session_dir_lock_file(sess
, &lock_file_path(&path
));
898 // Let's make it explicit that the file lock is released at this point,
899 // or rather, that we held on to it until here
906 fn delete_old(sess
: &Session
, path
: &Path
) {
907 debug
!("garbage_collect_session_directories() - deleting `{}`", path
.display());
909 if let Err(err
) = safe_remove_dir_all(&path
) {
911 "Failed to garbage collect incremental compilation session directory `{}`: {}",
916 delete_session_dir_lock_file(sess
, &lock_file_path(&path
));
920 fn all_except_most_recent(
921 deletion_candidates
: Vec
<(SystemTime
, PathBuf
, Option
<flock
::Lock
>)>,
922 ) -> FxHashMap
<PathBuf
, Option
<flock
::Lock
>> {
923 let most_recent
= deletion_candidates
.iter().map(|&(timestamp
, ..)| timestamp
).max();
925 if let Some(most_recent
) = most_recent
{
928 .filter(|&(timestamp
, ..)| timestamp
!= most_recent
)
929 .map(|(_
, path
, lock
)| (path
, lock
))
936 /// Since paths of artifacts within session directories can get quite long, we
937 /// need to support deleting files with very long paths. The regular
938 /// WinApi functions only support paths up to 260 characters, however. In order
939 /// to circumvent this limitation, we canonicalize the path of the directory
940 /// before passing it to std::fs::remove_dir_all(). This will convert the path
941 /// into the '\\?\' format, which supports much longer paths.
942 fn safe_remove_dir_all(p
: &Path
) -> io
::Result
<()> {
943 let canonicalized
= match std_fs
::canonicalize(p
) {
944 Ok(canonicalized
) => canonicalized
,
945 Err(err
) if err
.kind() == io
::ErrorKind
::NotFound
=> return Ok(()),
946 Err(err
) => return Err(err
),
949 std_fs
::remove_dir_all(canonicalized
)
952 fn safe_remove_file(p
: &Path
) -> io
::Result
<()> {
953 let canonicalized
= match std_fs
::canonicalize(p
) {
954 Ok(canonicalized
) => canonicalized
,
955 Err(err
) if err
.kind() == io
::ErrorKind
::NotFound
=> return Ok(()),
956 Err(err
) => return Err(err
),
959 match std_fs
::remove_file(canonicalized
) {
960 Err(err
) if err
.kind() == io
::ErrorKind
::NotFound
=> Ok(()),
965 // On Windows the compiler would sometimes fail to rename the session directory because
966 // the OS thought something was still being accessed in it. So we retry a few times to give
967 // the OS time to catch up.
968 // See https://github.com/rust-lang/rust/issues/86929.
969 fn rename_path_with_retry(from
: &Path
, to
: &Path
, mut retries_left
: usize) -> std
::io
::Result
<()> {
971 match std_fs
::rename(from
, to
) {
972 Ok(()) => return Ok(()),
974 if retries_left
> 0 && e
.kind() == ErrorKind
::PermissionDenied
{
975 // Try again after a short waiting period.
976 std
::thread
::sleep(Duration
::from_millis(50));