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//! Background worker that watches over the cache.
//!
//! It cleans up old cache, updates statistics and optimizes the cache.
//! We allow losing some messages (it doesn't hurt) and some races,
//! but we guarantee eventual consistency and fault tolerancy.
//! Background tasks can be CPU intensive, but the worker thread has low priority.
use super::{fs_write_atomic, CacheConfig};
use log::{debug, info, trace, warn};
use serde::{Deserialize, Serialize};
use std::cmp;
use std::collections::HashMap;
use std::ffi::OsStr;
use std::fmt;
use std::fs;
use std::path::{Path, PathBuf};
use std::sync::mpsc::{sync_channel, Receiver, SyncSender};
#[cfg(test)]
use std::sync::{Arc, Condvar, Mutex};
use std::thread;
use std::time::Duration;
#[cfg(not(test))]
use std::time::SystemTime;
#[cfg(test)]
use tests::system_time_stub::SystemTimeStub as SystemTime;
#[derive(Clone)]
pub(super) struct Worker {
sender: SyncSender<CacheEvent>,
#[cfg(test)]
stats: Arc<(Mutex<WorkerStats>, Condvar)>,
}
struct WorkerThread {
receiver: Receiver<CacheEvent>,
cache_config: CacheConfig,
#[cfg(test)]
stats: Arc<(Mutex<WorkerStats>, Condvar)>,
}
#[cfg(test)]
#[derive(Default)]
struct WorkerStats {
dropped: u32,
sent: u32,
handled: u32,
}
#[derive(Debug, Clone)]
enum CacheEvent {
OnCacheGet(PathBuf),
OnCacheUpdate(PathBuf),
}
impl Worker {
pub(super) fn start_new(
cache_config: &CacheConfig,
init_file_per_thread_logger: Option<&'static str>,
) -> Self {
let queue_size = match cache_config.worker_event_queue_size() {
num if num <= usize::max_value() as u64 => num as usize,
_ => usize::max_value(),
};
let (tx, rx) = sync_channel(queue_size);
#[cfg(test)]
let stats = Arc::new((Mutex::new(WorkerStats::default()), Condvar::new()));
let worker_thread = WorkerThread {
receiver: rx,
cache_config: cache_config.clone(),
#[cfg(test)]
stats: stats.clone(),
};
// when self is dropped, sender will be dropped, what will cause the channel
// to hang, and the worker thread to exit -- it happens in the tests
// non-tests binary has only a static worker, so Rust doesn't drop it
thread::spawn(move || worker_thread.run(init_file_per_thread_logger));
Self {
sender: tx,
#[cfg(test)]
stats,
}
}
pub(super) fn on_cache_get_async(&self, path: impl AsRef<Path>) {
let event = CacheEvent::OnCacheGet(path.as_ref().to_path_buf());
self.send_cache_event(event);
}
pub(super) fn on_cache_update_async(&self, path: impl AsRef<Path>) {
let event = CacheEvent::OnCacheUpdate(path.as_ref().to_path_buf());
self.send_cache_event(event);
}
#[inline]
fn send_cache_event(&self, event: CacheEvent) {
let sent_event = self.sender.try_send(event.clone());
if let Err(ref err) = sent_event {
info!(
"Failed to send asynchronously message to worker thread, \
event: {:?}, error: {}",
event, err
);
}
#[cfg(test)]
{
let mut stats = self
.stats
.0
.lock()
.expect("Failed to acquire worker stats lock");
if sent_event.is_ok() {
stats.sent += 1;
} else {
stats.dropped += 1;
}
}
}
#[cfg(test)]
pub(super) fn events_dropped(&self) -> u32 {
let stats = self
.stats
.0
.lock()
.expect("Failed to acquire worker stats lock");
stats.dropped
}
#[cfg(test)]
pub(super) fn wait_for_all_events_handled(&self) {
let (stats, condvar) = &*self.stats;
let mut stats = stats.lock().expect("Failed to acquire worker stats lock");
while stats.handled != stats.sent {
stats = condvar
.wait(stats)
.expect("Failed to reacquire worker stats lock");
}
}
}
impl fmt::Debug for Worker {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Worker").finish()
}
}
#[derive(Serialize, Deserialize)]
struct ModuleCacheStatistics {
pub usages: u64,
#[serde(rename = "optimized-compression")]
pub compression_level: i32,
}
impl ModuleCacheStatistics {
fn default(cache_config: &CacheConfig) -> Self {
Self {
usages: 0,
compression_level: cache_config.baseline_compression_level(),
}
}
}
enum CacheEntry {
Recognized {
path: PathBuf,
mtime: SystemTime,
size: u64,
},
Unrecognized {
path: PathBuf,
is_dir: bool,
},
}
macro_rules! unwrap_or_warn {
($result:expr, $cont:stmt, $err_msg:expr, $path:expr) => {
match $result {
Ok(val) => val,
Err(err) => {
warn!("{}, path: {}, msg: {}", $err_msg, $path.display(), err);
$cont
}
}
};
}
impl WorkerThread {
fn run(self, init_file_per_thread_logger: Option<&'static str>) {
if let Some(prefix) = init_file_per_thread_logger {
file_per_thread_logger::initialize(prefix);
}
debug!("Cache worker thread started.");
Self::lower_thread_priority();
#[cfg(test)]
let (stats, condvar) = &*self.stats;
for event in self.receiver.iter() {
match event {
CacheEvent::OnCacheGet(path) => self.handle_on_cache_get(path),
CacheEvent::OnCacheUpdate(path) => self.handle_on_cache_update(path),
}
#[cfg(test)]
{
let mut stats = stats.lock().expect("Failed to acquire worker stats lock");
stats.handled += 1;
condvar.notify_all();
}
}
}
#[cfg(target_os = "fuchsia")]
fn lower_thread_priority() {
// TODO This needs to use Fuchsia thread profiles
// https://fuchsia.dev/fuchsia-src/reference/kernel_objects/profile
warn!(
"Lowering thread priority on Fuchsia is currently a noop. It might affect application performance."
);
}
#[cfg(target_os = "windows")]
fn lower_thread_priority() {
use windows_sys::Win32::System::Threading::*;
// https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-setthreadpriority
// https://docs.microsoft.com/en-us/windows/win32/procthread/scheduling-priorities
if unsafe {
SetThreadPriority(
GetCurrentThread(),
THREAD_MODE_BACKGROUND_BEGIN.try_into().unwrap(),
)
} == 0
{
warn!(
"Failed to lower worker thread priority. It might affect application performance."
);
}
}
#[cfg(not(any(target_os = "windows", target_os = "fuchsia")))]
fn lower_thread_priority() {
// http://man7.org/linux/man-pages/man7/sched.7.html
const NICE_DELTA_FOR_BACKGROUND_TASKS: i32 = 3;
match rustix::process::nice(NICE_DELTA_FOR_BACKGROUND_TASKS) {
Ok(current_nice) => {
debug!("New nice value of worker thread: {}", current_nice);
}
Err(err) => {
warn!(
"Failed to lower worker thread priority ({:?}). It might affect application performance.", err);
}
};
}
/// Increases the usage counter and recompresses the file
/// if the usage counter reached configurable treshold.
fn handle_on_cache_get(&self, path: PathBuf) {
trace!("handle_on_cache_get() for path: {}", path.display());
// construct .stats file path
let filename = path.file_name().unwrap().to_str().unwrap();
let stats_path = path.with_file_name(format!("{}.stats", filename));
// load .stats file (default if none or error)
let mut stats = read_stats_file(stats_path.as_ref())
.unwrap_or_else(|| ModuleCacheStatistics::default(&self.cache_config));
// step 1: update the usage counter & write to the disk
// it's racy, but it's fine (the counter will be just smaller,
// sometimes will retrigger recompression)
stats.usages += 1;
if !write_stats_file(stats_path.as_ref(), &stats) {
return;
}
// step 2: recompress if there's a need
let opt_compr_lvl = self.cache_config.optimized_compression_level();
if stats.compression_level >= opt_compr_lvl
|| stats.usages
< self
.cache_config
.optimized_compression_usage_counter_threshold()
{
return;
}
let lock_path = if let Some(p) = acquire_task_fs_lock(
path.as_ref(),
self.cache_config.optimizing_compression_task_timeout(),
self.cache_config
.allowed_clock_drift_for_files_from_future(),
) {
p
} else {
return;
};
trace!("Trying to recompress file: {}", path.display());
// recompress, write to other file, rename (it's atomic file content exchange)
// and update the stats file
let compressed_cache_bytes = unwrap_or_warn!(
fs::read(&path),
return,
"Failed to read old cache file",
path
);
let cache_bytes = unwrap_or_warn!(
zstd::decode_all(&compressed_cache_bytes[..]),
return,
"Failed to decompress cached code",
path
);
let recompressed_cache_bytes = unwrap_or_warn!(
zstd::encode_all(&cache_bytes[..], opt_compr_lvl),
return,
"Failed to compress cached code",
path
);
unwrap_or_warn!(
fs::write(&lock_path, &recompressed_cache_bytes),
return,
"Failed to write recompressed cache",
lock_path
);
unwrap_or_warn!(
fs::rename(&lock_path, &path),
{
if let Err(error) = fs::remove_file(&lock_path) {
warn!(
"Failed to clean up (remove) recompressed cache, path {}, err: {}",
lock_path.display(),
error
);
}
return;
},
"Failed to rename recompressed cache",
lock_path
);
// update stats file (reload it! recompression can take some time)
if let Some(mut new_stats) = read_stats_file(stats_path.as_ref()) {
if new_stats.compression_level >= opt_compr_lvl {
// Rare race:
// two instances with different opt_compr_lvl: we don't know in which order they updated
// the cache file and the stats file (they are not updated together atomically)
// Possible solution is to use directories per cache entry, but it complicates the system
// and is not worth it.
debug!(
"DETECTED task did more than once (or race with new file): \
recompression of {}. Note: if optimized compression level setting \
has changed in the meantine, the stats file might contain \
inconsistent compression level due to race.",
path.display()
);
} else {
new_stats.compression_level = opt_compr_lvl;
let _ = write_stats_file(stats_path.as_ref(), &new_stats);
}
if new_stats.usages < stats.usages {
debug!(
"DETECTED lower usage count (new file or race with counter \
increasing): file {}",
path.display()
);
}
} else {
debug!(
"Can't read stats file again to update compression level (it might got \
cleaned up): file {}",
stats_path.display()
);
}
trace!("Task finished: recompress file: {}", path.display());
}
fn handle_on_cache_update(&self, path: PathBuf) {
trace!("handle_on_cache_update() for path: {}", path.display());
// ---------------------- step 1: create .stats file
// construct .stats file path
let filename = path
.file_name()
.expect("Expected valid cache file name")
.to_str()
.expect("Expected valid cache file name");
let stats_path = path.with_file_name(format!("{}.stats", filename));
// create and write stats file
let mut stats = ModuleCacheStatistics::default(&self.cache_config);
stats.usages += 1;
write_stats_file(&stats_path, &stats);
// ---------------------- step 2: perform cleanup task if needed
// acquire lock for cleanup task
// Lock is a proof of recent cleanup task, so we don't want to delete them.
// Expired locks will be deleted by the cleanup task.
let cleanup_file = self.cache_config.directory().join(".cleanup"); // some non existing marker file
if acquire_task_fs_lock(
&cleanup_file,
self.cache_config.cleanup_interval(),
self.cache_config
.allowed_clock_drift_for_files_from_future(),
)
.is_none()
{
return;
}
trace!("Trying to clean up cache");
let mut cache_index = self.list_cache_contents();
let future_tolerance = SystemTime::now()
.checked_add(
self.cache_config
.allowed_clock_drift_for_files_from_future(),
)
.expect("Brace your cache, the next Big Bang is coming (time overflow)");
cache_index.sort_unstable_by(|lhs, rhs| {
// sort by age
use CacheEntry::*;
match (lhs, rhs) {
(Recognized { mtime: lhs_mt, .. }, Recognized { mtime: rhs_mt, .. }) => {
match (*lhs_mt > future_tolerance, *rhs_mt > future_tolerance) {
// later == younger
(false, false) => rhs_mt.cmp(lhs_mt),
// files from far future are treated as oldest recognized files
// we want to delete them, so the cache keeps track of recent files
// however, we don't delete them uncodintionally,
// because .stats file can be overwritten with a meaningful mtime
(true, false) => cmp::Ordering::Greater,
(false, true) => cmp::Ordering::Less,
(true, true) => cmp::Ordering::Equal,
}
}
// unrecognized is kind of infinity
(Recognized { .. }, Unrecognized { .. }) => cmp::Ordering::Less,
(Unrecognized { .. }, Recognized { .. }) => cmp::Ordering::Greater,
(Unrecognized { .. }, Unrecognized { .. }) => cmp::Ordering::Equal,
}
});
// find "cut" boundary:
// - remove unrecognized files anyway,
// - remove some cache files if some quota has been exceeded
let mut total_size = 0u64;
let mut start_delete_idx = None;
let mut start_delete_idx_if_deleting_recognized_items: Option<usize> = None;
let total_size_limit = self.cache_config.files_total_size_soft_limit();
let file_count_limit = self.cache_config.file_count_soft_limit();
let tsl_if_deleting = total_size_limit
.checked_mul(
self.cache_config
.files_total_size_limit_percent_if_deleting() as u64,
)
.unwrap()
/ 100;
let fcl_if_deleting = file_count_limit
.checked_mul(self.cache_config.file_count_limit_percent_if_deleting() as u64)
.unwrap()
/ 100;
for (idx, item) in cache_index.iter().enumerate() {
let size = if let CacheEntry::Recognized { size, .. } = item {
size
} else {
start_delete_idx = Some(idx);
break;
};
total_size += size;
if start_delete_idx_if_deleting_recognized_items.is_none()
&& (total_size > tsl_if_deleting || (idx + 1) as u64 > fcl_if_deleting)
{
start_delete_idx_if_deleting_recognized_items = Some(idx);
}
if total_size > total_size_limit || (idx + 1) as u64 > file_count_limit {
start_delete_idx = start_delete_idx_if_deleting_recognized_items;
break;
}
}
if let Some(idx) = start_delete_idx {
for item in &cache_index[idx..] {
let (result, path, entity) = match item {
CacheEntry::Recognized { path, .. }
| CacheEntry::Unrecognized {
path,
is_dir: false,
} => (fs::remove_file(path), path, "file"),
CacheEntry::Unrecognized { path, is_dir: true } => {
(fs::remove_dir_all(path), path, "directory")
}
};
if let Err(err) = result {
warn!(
"Failed to remove {} during cleanup, path: {}, err: {}",
entity,
path.display(),
err
);
}
}
}
trace!("Task finished: clean up cache");
}
// Be fault tolerant: list as much as you can, and ignore the rest
fn list_cache_contents(&self) -> Vec<CacheEntry> {
fn enter_dir(
vec: &mut Vec<CacheEntry>,
dir_path: &Path,
level: u8,
cache_config: &CacheConfig,
) {
macro_rules! add_unrecognized {
(file: $path:expr) => {
add_unrecognized!(false, $path)
};
(dir: $path:expr) => {
add_unrecognized!(true, $path)
};
($is_dir:expr, $path:expr) => {
vec.push(CacheEntry::Unrecognized {
path: $path.to_path_buf(),
is_dir: $is_dir,
})
};
}
macro_rules! add_unrecognized_and {
([ $( $ty:ident: $path:expr ),* ], $cont:stmt) => {{
$( add_unrecognized!($ty: $path); )*
$cont
}};
}
macro_rules! unwrap_or {
($result:expr, $cont:stmt, $err_msg:expr) => {
unwrap_or!($result, $cont, $err_msg, dir_path)
};
($result:expr, $cont:stmt, $err_msg:expr, $path:expr) => {
unwrap_or_warn!(
$result,
$cont,
format!("{}, level: {}", $err_msg, level),
$path
)
};
}
// If we fail to list a directory, something bad is happening anyway
// (something touches our cache or we have disk failure)
// Try to delete it, so we can stay within soft limits of the cache size.
// This comment applies later in this function, too.
let it = unwrap_or!(
fs::read_dir(dir_path),
add_unrecognized_and!([dir: dir_path], return),
"Failed to list cache directory, deleting it"
);
let mut cache_files = HashMap::new();
for entry in it {
// read_dir() returns an iterator over results - in case some of them are errors
// we don't know their names, so we can't delete them. We don't want to delete
// the whole directory with good entries too, so we just ignore the erroneous entries.
let entry = unwrap_or!(
entry,
continue,
"Failed to read a cache dir entry (NOT deleting it, it still occupies space)"
);
let path = entry.path();
match (level, path.is_dir()) {
(0..=1, true) => enter_dir(vec, &path, level + 1, cache_config),
(0..=1, false) => {
if level == 0
&& path.file_stem() == Some(OsStr::new(".cleanup"))
&& path.extension().is_some()
// assume it's cleanup lock
&& !is_fs_lock_expired(
Some(&entry),
&path,
cache_config.cleanup_interval(),
cache_config.allowed_clock_drift_for_files_from_future(),
)
{
continue; // skip active lock
}
add_unrecognized!(file: path);
}
(2, false) => {
match path.extension().and_then(OsStr::to_str) {
// mod or stats file
None | Some("stats") => {
cache_files.insert(path, entry);
}
Some(ext) => {
// check if valid lock
let recognized = ext.starts_with("wip-")
&& !is_fs_lock_expired(
Some(&entry),
&path,
cache_config.optimizing_compression_task_timeout(),
cache_config.allowed_clock_drift_for_files_from_future(),
);
if !recognized {
add_unrecognized!(file: path);
}
}
}
}
(_, is_dir) => add_unrecognized!(is_dir, path),
}
}
// associate module with its stats & handle them
// assumption: just mods and stats
for (path, entry) in cache_files.iter() {
let path_buf: PathBuf;
let (mod_, stats_, is_mod) = match path.extension() {
Some(_) => {
path_buf = path.with_extension("");
(
cache_files.get(&path_buf).map(|v| (&path_buf, v)),
Some((path, entry)),
false,
)
}
None => {
path_buf = path.with_extension("stats");
(
Some((path, entry)),
cache_files.get(&path_buf).map(|v| (&path_buf, v)),
true,
)
}
};
// construct a cache entry
match (mod_, stats_, is_mod) {
(Some((mod_path, mod_entry)), Some((stats_path, stats_entry)), true) => {
let mod_metadata = unwrap_or!(
mod_entry.metadata(),
add_unrecognized_and!([file: stats_path, file: mod_path], continue),
"Failed to get metadata, deleting BOTH module cache and stats files",
mod_path
);
let stats_mtime = unwrap_or!(
stats_entry.metadata().and_then(|m| m.modified()),
add_unrecognized_and!(
[file: stats_path],
unwrap_or!(
mod_metadata.modified(),
add_unrecognized_and!(
[file: stats_path, file: mod_path],
continue
),
"Failed to get mtime, deleting BOTH module cache and stats \
files",
mod_path
)
),
"Failed to get metadata/mtime, deleting the file",
stats_path
);
// .into() called for the SystemTimeStub if cfg(test)
#[allow(clippy::identity_conversion)]
vec.push(CacheEntry::Recognized {
path: mod_path.to_path_buf(),
mtime: stats_mtime.into(),
size: mod_metadata.len(),
})
}
(Some(_), Some(_), false) => (), // was or will be handled by previous branch
(Some((mod_path, mod_entry)), None, _) => {
let (mod_metadata, mod_mtime) = unwrap_or!(
mod_entry
.metadata()
.and_then(|md| md.modified().map(|mt| (md, mt))),
add_unrecognized_and!([file: mod_path], continue),
"Failed to get metadata/mtime, deleting the file",
mod_path
);
// .into() called for the SystemTimeStub if cfg(test)
#[allow(clippy::identity_conversion)]
vec.push(CacheEntry::Recognized {
path: mod_path.to_path_buf(),
mtime: mod_mtime.into(),
size: mod_metadata.len(),
})
}
(None, Some((stats_path, _stats_entry)), _) => {
debug!("Found orphaned stats file: {}", stats_path.display());
add_unrecognized!(file: stats_path);
}
_ => unreachable!(),
}
}
}
let mut vec = Vec::new();
enter_dir(
&mut vec,
self.cache_config.directory(),
0,
&self.cache_config,
);
vec
}
}
fn read_stats_file(path: &Path) -> Option<ModuleCacheStatistics> {
fs::read(path)
.map_err(|err| {
trace!(
"Failed to read stats file, path: {}, err: {}",
path.display(),
err
)
})
.and_then(|bytes| {
toml::from_slice::<ModuleCacheStatistics>(&bytes[..]).map_err(|err| {
trace!(
"Failed to parse stats file, path: {}, err: {}",
path.display(),
err,
)
})
})
.ok()
}
fn write_stats_file(path: &Path, stats: &ModuleCacheStatistics) -> bool {
toml::to_string_pretty(&stats)
.map_err(|err| {
warn!(
"Failed to serialize stats file, path: {}, err: {}",
path.display(),
err
)
})
.and_then(|serialized| {
if fs_write_atomic(path, "stats", serialized.as_bytes()) {
Ok(())
} else {
Err(())
}
})
.is_ok()
}
/// Tries to acquire a lock for specific task.
///
/// Returns Some(path) to the lock if succeeds. The task path must not
/// contain any extension and have file stem.
///
/// To release a lock you need either manually rename or remove it,
/// or wait until it expires and cleanup task removes it.
///
/// Note: this function is racy. Main idea is: be fault tolerant and
/// never block some task. The price is that we rarely do some task
/// more than once.
fn acquire_task_fs_lock(
task_path: &Path,
timeout: Duration,
allowed_future_drift: Duration,
) -> Option<PathBuf> {
assert!(task_path.extension().is_none());
assert!(task_path.file_stem().is_some());
// list directory
let dir_path = task_path.parent()?;
let it = fs::read_dir(dir_path)
.map_err(|err| {
warn!(
"Failed to list cache directory, path: {}, err: {}",
dir_path.display(),
err
)
})
.ok()?;
// look for existing locks
for entry in it {
let entry = entry
.map_err(|err| {
warn!(
"Failed to list cache directory, path: {}, err: {}",
dir_path.display(),
err
)
})
.ok()?;
let path = entry.path();
if path.is_dir() || path.file_stem() != task_path.file_stem() {
continue;
}
// check extension and mtime
match path.extension() {
None => continue,
Some(ext) => {
if let Some(ext_str) = ext.to_str() {
// if it's None, i.e. not valid UTF-8 string, then that's not our lock for sure
if ext_str.starts_with("wip-")
&& !is_fs_lock_expired(Some(&entry), &path, timeout, allowed_future_drift)
{
return None;
}
}
}
}
}
// create the lock
let lock_path = task_path.with_extension(format!("wip-{}", std::process::id()));
let _file = fs::OpenOptions::new()
.create_new(true)
.write(true)
.open(&lock_path)
.map_err(|err| {
warn!(
"Failed to create lock file (note: it shouldn't exists): path: {}, err: {}",
lock_path.display(),
err
)
})
.ok()?;
Some(lock_path)
}
// we have either both, or just path; dir entry is desirable since on some platforms we can get
// metadata without extra syscalls
// futhermore: it's better to get a path if we have it instead of allocating a new one from the dir entry
fn is_fs_lock_expired(
entry: Option<&fs::DirEntry>,
path: &PathBuf,
threshold: Duration,
allowed_future_drift: Duration,
) -> bool {
let mtime = match entry
.map_or_else(|| path.metadata(), |e| e.metadata())
.and_then(|metadata| metadata.modified())
{
Ok(mt) => mt,
Err(err) => {
warn!(
"Failed to get metadata/mtime, treating as an expired lock, path: {}, err: {}",
path.display(),
err
);
return true; // can't read mtime, treat as expired, so this task will not be starved
}
};
// DON'T use: mtime.elapsed() -- we must call SystemTime directly for the tests to be deterministic
match SystemTime::now().duration_since(mtime) {
Ok(elapsed) => elapsed >= threshold,
Err(err) => {
trace!(
"Found mtime in the future, treating as a not expired lock, path: {}, err: {}",
path.display(),
err
);
// the lock is expired if the time is too far in the future
// it is fine to have network share and not synchronized clocks,
// but it's not good when user changes time in their system clock
err.duration() > allowed_future_drift
}
}
}
#[cfg(test)]
mod tests;