1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
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::{env, thread};
use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
use super::*;
#[test]
fn lock_basic() {
let number: u32 = rand::random();
let lock_path = env::temp_dir().join(format!("test-{}.lock", number));
assert!(!lock_path.exists());
{
let _lock = FileLock::lock(lock_path.clone());
assert!(lock_path.exists());
}
assert!(!lock_path.exists());
}
#[test]
fn lock_concurrent() {
let number: u32 = rand::random();
let data_path = env::temp_dir().join(format!("test-{}", number));
let lock_path = env::temp_dir().join(format!("test-{}.lock", number));
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);
}
}
