use std::fs::{File, OpenOptions};
use std::path::PathBuf;
use std::time::Duration;
use backoff::{retry, ExponentialBackoff};
pub struct FileLock {
path: PathBuf,
_file: File,
}
impl FileLock {
pub fn lock(path: PathBuf) -> FileLock {
let mut options = OpenOptions::new();
options.create_new(true);
options.write(true);
let try_write_lock_file = || match options.open(&path) {
Ok(file) => Ok(FileLock {
path: path.clone(),
_file: file,
}),
Err(err) if err.kind() == std::io::ErrorKind::AlreadyExists => {
Err(backoff::Error::Transient {
err,
retry_after: None,
})
}
Err(err) if cfg!(windows) && err.kind() == std::io::ErrorKind::PermissionDenied => {
Err(backoff::Error::Transient {
err,
retry_after: None,
})
}
Err(err) => Err(backoff::Error::Permanent(err)),
};
let backoff = ExponentialBackoff {
initial_interval: Duration::from_millis(1),
max_elapsed_time: Some(Duration::from_secs(10)),
..Default::default()
};
match retry(backoff, try_write_lock_file) {
Err(err) => panic!(
"failed to create lock file {}: {}",
path.to_string_lossy(),
err
),
Ok(file_lock) => file_lock,
}
}
}
impl Drop for FileLock {
fn drop(&mut self) {
std::fs::remove_file(&self.path).expect("failed to delete lock file");
}
}
#[cfg(test)]
mod tests {
use std::cmp::max;
use std::thread;
use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
use super::*;
#[test]
fn lock_basic() {
let temp_dir = testutils::new_temp_dir();
let lock_path = temp_dir.path().join("test.lock");
assert!(!lock_path.exists());
{
let _lock = FileLock::lock(lock_path.clone());
assert!(lock_path.exists());
}
assert!(!lock_path.exists());
}
#[test]
fn lock_concurrent() {
let temp_dir = testutils::new_temp_dir();
let data_path = temp_dir.path().join("test");
let lock_path = temp_dir.path().join("test.lock");
let mut data_file = OpenOptions::new()
.create(true)
.write(true)
.open(data_path.clone())
.unwrap();
data_file.write_u32::<LittleEndian>(0).unwrap();
let num_threads = max(num_cpus::get(), 4);
let mut threads = vec![];
for _ in 0..num_threads {
let data_path = data_path.clone();
let lock_path = lock_path.clone();
let handle = thread::spawn(move || {
let _lock = FileLock::lock(lock_path);
let mut data_file = OpenOptions::new()
.read(true)
.open(data_path.clone())
.unwrap();
let value = data_file.read_u32::<LittleEndian>().unwrap();
thread::sleep(Duration::from_millis(1));
let mut data_file = OpenOptions::new().write(true).open(data_path).unwrap();
data_file.write_u32::<LittleEndian>(value + 1).unwrap();
});
threads.push(handle);
}
for thread in threads {
thread.join().ok().unwrap();
}
let mut data_file = OpenOptions::new().read(true).open(data_path).unwrap();
let value = data_file.read_u32::<LittleEndian>().unwrap();
assert_eq!(value, num_threads as u32);
}
}