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poll.rs
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poll.rs
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//! Generic Watcher implementation based on polling
//!
//! Checks the `watch`ed paths periodically to detect changes. This implementation only uses
//! Rust stdlib APIs and should work on all of the platforms it supports.
use super::event::*;
use super::{Error, EventHandler, RecursiveMode, Result, Watcher};
use filetime::FileTime;
use std::collections::hash_map::RandomState;
use std::collections::HashMap;
use std::fmt::Debug;
use std::fs::Metadata;
use std::hash::BuildHasher;
use std::hash::Hasher;
use std::io::{ErrorKind, Read};
use std::path::{Path, PathBuf};
use std::sync::{
atomic::{AtomicBool, Ordering},
Arc, Mutex,
};
use std::thread;
use std::time::{Duration, Instant};
use std::{fs, io};
use walkdir::WalkDir;
#[derive(Debug, Clone)]
struct PathData {
mtime: i64,
hash: Option<u64>,
last_check: Instant,
}
#[derive(Debug)]
struct WatchData {
is_recursive: bool,
paths: HashMap<PathBuf, PathData>,
}
/// Polling based `Watcher` implementation
pub struct PollWatcher {
event_handler: Arc<Mutex<dyn EventHandler>>,
watches: Arc<Mutex<HashMap<PathBuf, WatchData>>>,
open: Arc<AtomicBool>,
delay: Duration,
compare_contents: bool,
}
/// General purpose configuration for [`PollWatcher`] specifically. Can be used to tune
/// this watcher differently than the other platform specific ones.
#[derive(Debug, Clone)]
pub struct PollWatcherConfig {
/// Interval between each rescan attempt. This can be extremely expensive for large
/// file trees so it is recommended to measure and tune accordingly.
pub poll_interval: Duration,
/// Optional feature that will evaluate the contents of changed files to determine if
/// they have indeed changed using a fast hashing algorithm. This is especially important
/// for pseudo filesystems like those on Linux under /sys and /proc which are not obligated
/// to respect any other filesystem norms such as modification timestamps, file sizes, etc.
/// By enabling this feature, performance will be significantly impacted as all files will
/// need to be read and hashed at each `poll_interval`.
pub compare_contents: bool,
}
impl Default for PollWatcherConfig {
fn default() -> Self {
Self {
poll_interval: Duration::from_secs(30),
compare_contents: false,
}
}
}
impl Debug for PollWatcher {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("PollWatcher")
.field("event_handler", &Arc::as_ptr(&self.watches))
.field("watches", &self.watches)
.field("open", &self.open)
.field("delay", &self.delay)
.field("compare_contents", &self.compare_contents)
.finish()
}
}
fn emit_event(event_handler: &Mutex<dyn EventHandler>, res: Result<Event>) {
if let Ok(mut guard) = event_handler.lock() {
let f: &mut dyn EventHandler = &mut *guard;
f.handle_event(res);
}
}
impl PathData {
pub fn collect<BH: BuildHasher>(
path: &Path,
metadata: &Metadata,
build_hasher: Option<&BH>,
last_check: Instant,
) -> Self {
let mtime = FileTime::from_last_modification_time(metadata).seconds();
let hash = metadata
.is_file()
.then(|| build_hasher.and_then(|bh| Self::hash_file(path, bh).ok()))
.flatten();
Self {
mtime,
hash,
last_check,
}
}
fn hash_file<P: AsRef<Path>, BH: BuildHasher>(path: P, build_hasher: &BH) -> io::Result<u64> {
let mut hasher = build_hasher.build_hasher();
let mut file = fs::File::open(path)?;
let mut buf = [0; 512];
loop {
let n = match file.read(&mut buf) {
Ok(0) => break,
Ok(len) => len,
Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
Err(e) => return Err(e),
};
hasher.write(&buf[..n]);
}
Ok(hasher.finish())
}
pub fn detect_change(&self, other: &PathData) -> Option<EventKind> {
if self.mtime > other.mtime {
Some(EventKind::Modify(ModifyKind::Metadata(
MetadataKind::WriteTime,
)))
} else if self.hash != other.hash {
Some(EventKind::Modify(ModifyKind::Data(DataChange::Any)))
} else {
None
}
}
}
impl PollWatcher {
/// Create a new [PollWatcher], configured as needed.
pub fn with_config<F: EventHandler>(
event_handler: F,
config: PollWatcherConfig,
) -> Result<PollWatcher> {
let mut p = PollWatcher {
event_handler: Arc::new(Mutex::new(event_handler)),
watches: Arc::new(Mutex::new(HashMap::new())),
open: Arc::new(AtomicBool::new(true)),
delay: config.poll_interval,
compare_contents: config.compare_contents,
};
p.run();
Ok(p)
}
fn run(&mut self) {
let watches = self.watches.clone();
let open = self.open.clone();
let delay = self.delay;
let build_hasher = self.compare_contents.then(RandomState::default);
let event_handler = self.event_handler.clone();
let event_handler = move |res| emit_event(&event_handler, res);
let _ = thread::Builder::new()
.name("notify-rs poll loop".to_string())
.spawn(move || {
// In order of priority:
// TODO: handle metadata events
// TODO: handle renames
// TODO: DRY it up
loop {
if !open.load(Ordering::SeqCst) {
break;
}
if let Ok(mut watches) = watches.lock() {
let current_time = Instant::now();
for (
watch,
&mut WatchData {
is_recursive,
ref mut paths,
},
) in watches.iter_mut()
{
match fs::metadata(watch) {
Err(e) => {
let err = Err(Error::io(e).add_path(watch.clone()));
event_handler(err);
continue;
}
Ok(metadata) => {
// this is a file type watching point
if !metadata.is_dir() {
let path_data = PathData::collect(
watch,
&metadata,
build_hasher.as_ref(),
current_time,
);
// Update `path_data` for this watching point. In file
// type watching point, only has single one path need
// to update.
match paths.insert(watch.clone(), path_data.clone()) {
// `old_path_data` not exists, this is a new path
None => {
let kind = EventKind::Create(CreateKind::Any);
let ev = Event::new(kind).add_path(watch.clone());
event_handler(Ok(ev));
}
// path already exists, need further check to see
// what's the difference.
Some(old_path_data) => {
if let Some(kind) =
path_data.detect_change(&old_path_data)
{
let ev =
Event::new(kind).add_path(watch.clone());
event_handler(Ok(ev));
}
}
}
// this is a dir type watching point
} else {
let depth =
if is_recursive { usize::max_value() } else { 1 };
for entry in WalkDir::new(watch)
.follow_links(true)
.max_depth(depth)
.into_iter()
.filter_map(|e| e.ok())
{
let path = entry.path();
// TODO: duplicate logic, considering refactor following lines to a function.
match entry.metadata() {
Err(e) => {
let err = Error::io(e.into())
.add_path(path.to_path_buf());
event_handler(Err(err));
}
Ok(m) => {
let path_data = PathData::collect(
path,
&m,
build_hasher.as_ref(),
current_time,
);
match paths.insert(
path.to_path_buf(),
path_data.clone(),
) {
None => {
let kind =
EventKind::Create(CreateKind::Any);
let ev = Event::new(kind)
.add_path(path.to_path_buf());
event_handler(Ok(ev));
}
Some(old_path_data) => {
if let Some(kind) = path_data
.detect_change(&old_path_data)
{
// TODO add new mtime as attr
let ev = Event::new(kind)
.add_path(path.to_path_buf());
event_handler(Ok(ev));
}
}
}
}
}
}
}
}
}
}
// clear out all paths which not updated by this round.
for (_, &mut WatchData { ref mut paths, .. }) in watches.iter_mut() {
// find which paths should be removed in this watching point.
let mut removed = Vec::new();
for (path, &PathData { last_check, .. }) in paths.iter() {
if last_check < current_time {
let ev = Event::new(EventKind::Remove(RemoveKind::Any))
.add_path(path.clone());
event_handler(Ok(ev));
removed.push(path.clone());
}
}
// remove actually.
for path in removed {
(*paths).remove(&path);
}
}
}
thread::sleep(delay);
}
});
}
fn watch_inner(&mut self, path: &Path, recursive_mode: RecursiveMode) -> Result<()> {
let build_hasher = self.compare_contents.then(RandomState::default);
if let Ok(mut watches) = self.watches.lock() {
let current_time = Instant::now();
let watch = path.to_owned();
match fs::metadata(path) {
Err(e) => {
let err = Error::io(e).add_path(watch);
emit_event(&self.event_handler, Err(err));
}
Ok(metadata) => {
let mut paths = HashMap::new();
if !metadata.is_dir() {
let path_data =
PathData::collect(path, &metadata, build_hasher.as_ref(), current_time);
paths.insert(watch.clone(), path_data);
} else {
let depth = if recursive_mode.is_recursive() {
usize::max_value()
} else {
1
};
for entry in WalkDir::new(watch.clone())
.follow_links(true)
.max_depth(depth)
.into_iter()
.filter_map(|e| e.ok())
{
let path = entry.path();
match entry.metadata() {
Err(e) => {
let err = Error::io(e.into()).add_path(path.to_path_buf());
emit_event(&self.event_handler, Err(err));
}
Ok(m) => {
let path_data = PathData::collect(
path,
&m,
build_hasher.as_ref(),
current_time,
);
paths.insert(path.to_path_buf(), path_data);
}
}
}
}
watches.insert(
watch,
WatchData {
is_recursive: recursive_mode.is_recursive(),
paths,
},
);
}
}
}
Ok(())
}
fn unwatch_inner(&mut self, path: &Path) -> Result<()> {
if (*self.watches).lock().unwrap().remove(path).is_some() {
Ok(())
} else {
Err(Error::watch_not_found())
}
}
}
impl Watcher for PollWatcher {
/// Create a new [PollWatcher].
///
/// The default poll frequency is 30 seconds.
/// Use [with_config] to manually set the poll frequency.
fn new<F: EventHandler>(event_handler: F) -> Result<Self> {
Self::with_config(event_handler, PollWatcherConfig::default())
}
fn watch(&mut self, path: &Path, recursive_mode: RecursiveMode) -> Result<()> {
self.watch_inner(path, recursive_mode)
}
fn unwatch(&mut self, path: &Path) -> Result<()> {
self.unwatch_inner(path)
}
fn kind() -> crate::WatcherKind {
crate::WatcherKind::PollWatcher
}
}
impl Drop for PollWatcher {
fn drop(&mut self) {
self.open.store(false, Ordering::Relaxed);
}
}
#[test]
fn poll_watcher_is_send_and_sync() {
fn check<T: Send + Sync>() {}
check::<PollWatcher>();
}