gix_lock/
acquire.rs

1use std::{
2    fmt,
3    path::{Path, PathBuf},
4    time::Duration,
5};
6
7use gix_tempfile::{AutoRemove, ContainingDirectory};
8
9use crate::{backoff, File, Marker, DOT_LOCK_SUFFIX};
10
11/// Describe what to do if a lock cannot be obtained as it's already held elsewhere.
12#[derive(Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
13pub enum Fail {
14    /// Fail after the first unsuccessful attempt of obtaining a lock.
15    #[default]
16    Immediately,
17    /// Retry after failure with exponentially longer sleep times to block the current thread.
18    /// Fail once the given duration is exceeded, similar to [Fail::Immediately]
19    AfterDurationWithBackoff(Duration),
20}
21
22impl fmt::Display for Fail {
23    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
24        match self {
25            Fail::Immediately => f.write_str("immediately"),
26            Fail::AfterDurationWithBackoff(duration) => {
27                write!(f, "after {:.02}s", duration.as_secs_f32())
28            }
29        }
30    }
31}
32
33impl From<Duration> for Fail {
34    fn from(value: Duration) -> Self {
35        if value.is_zero() {
36            Fail::Immediately
37        } else {
38            Fail::AfterDurationWithBackoff(value)
39        }
40    }
41}
42
43/// The error returned when acquiring a [`File`] or [`Marker`].
44#[derive(Debug, thiserror::Error)]
45#[allow(missing_docs)]
46pub enum Error {
47    #[error("Another IO error occurred while obtaining the lock")]
48    Io(#[from] std::io::Error),
49    #[error("The lock for resource '{resource_path}' could not be obtained {mode} after {attempts} attempt(s). The lockfile at '{resource_path}{}' might need manual deletion.", super::DOT_LOCK_SUFFIX)]
50    PermanentlyLocked {
51        resource_path: PathBuf,
52        mode: Fail,
53        attempts: usize,
54    },
55}
56
57impl File {
58    /// Create a writable lock file with failure `mode` whose content will eventually overwrite the given resource `at_path`.
59    ///
60    /// If `boundary_directory` is given, non-existing directories will be created automatically and removed in the case of
61    /// a rollback. Otherwise the containing directory is expected to exist, even though the resource doesn't have to.
62    ///
63    /// Note that permissions will be set to `0o666`, which usually results in `0o644` after passing a default umask, on Unix systems.
64    ///
65    /// ### Warning of potential resource leak
66    ///
67    /// Please note that the underlying file will remain if destructors don't run, as is the case when interrupting the application.
68    /// This results in the resource being locked permanently unless the lock file is removed by other means.
69    /// See [the crate documentation](crate) for more information.
70    pub fn acquire_to_update_resource(
71        at_path: impl AsRef<Path>,
72        mode: Fail,
73        boundary_directory: Option<PathBuf>,
74    ) -> Result<File, Error> {
75        let (lock_path, handle) = lock_with_mode(at_path.as_ref(), mode, boundary_directory, &|p, d, c| {
76            if let Some(permissions) = default_permissions() {
77                gix_tempfile::writable_at_with_permissions(p, d, c, permissions)
78            } else {
79                gix_tempfile::writable_at(p, d, c)
80            }
81        })?;
82        Ok(File {
83            inner: handle,
84            lock_path,
85        })
86    }
87
88    /// Like [`acquire_to_update_resource()`](File::acquire_to_update_resource), but allows to set filesystem permissions using `make_permissions`.
89    pub fn acquire_to_update_resource_with_permissions(
90        at_path: impl AsRef<Path>,
91        mode: Fail,
92        boundary_directory: Option<PathBuf>,
93        make_permissions: impl Fn() -> std::fs::Permissions,
94    ) -> Result<File, Error> {
95        let (lock_path, handle) = lock_with_mode(at_path.as_ref(), mode, boundary_directory, &|p, d, c| {
96            gix_tempfile::writable_at_with_permissions(p, d, c, make_permissions())
97        })?;
98        Ok(File {
99            inner: handle,
100            lock_path,
101        })
102    }
103}
104
105impl Marker {
106    /// Like [`acquire_to_update_resource()`](File::acquire_to_update_resource()) but _without_ the possibility to make changes
107    /// and commit them.
108    ///
109    /// If `boundary_directory` is given, non-existing directories will be created automatically and removed in the case of
110    /// a rollback.
111    ///
112    /// Note that permissions will be set to `0o666`, which usually results in `0o644` after passing a default umask, on Unix systems.
113    ///
114    /// ### Warning of potential resource leak
115    ///
116    /// Please note that the underlying file will remain if destructors don't run, as is the case when interrupting the application.
117    /// This results in the resource being locked permanently unless the lock file is removed by other means.
118    /// See [the crate documentation](crate) for more information.
119    pub fn acquire_to_hold_resource(
120        at_path: impl AsRef<Path>,
121        mode: Fail,
122        boundary_directory: Option<PathBuf>,
123    ) -> Result<Marker, Error> {
124        let (lock_path, handle) = lock_with_mode(at_path.as_ref(), mode, boundary_directory, &|p, d, c| {
125            if let Some(permissions) = default_permissions() {
126                gix_tempfile::mark_at_with_permissions(p, d, c, permissions)
127            } else {
128                gix_tempfile::mark_at(p, d, c)
129            }
130        })?;
131        Ok(Marker {
132            created_from_file: false,
133            inner: handle,
134            lock_path,
135        })
136    }
137
138    /// Like [`acquire_to_hold_resource()`](Marker::acquire_to_hold_resource), but allows to set filesystem permissions using `make_permissions`.
139    pub fn acquire_to_hold_resource_with_permissions(
140        at_path: impl AsRef<Path>,
141        mode: Fail,
142        boundary_directory: Option<PathBuf>,
143        make_permissions: impl Fn() -> std::fs::Permissions,
144    ) -> Result<Marker, Error> {
145        let (lock_path, handle) = lock_with_mode(at_path.as_ref(), mode, boundary_directory, &|p, d, c| {
146            gix_tempfile::mark_at_with_permissions(p, d, c, make_permissions())
147        })?;
148        Ok(Marker {
149            created_from_file: false,
150            inner: handle,
151            lock_path,
152        })
153    }
154}
155
156fn dir_cleanup(boundary: Option<PathBuf>) -> (ContainingDirectory, AutoRemove) {
157    match boundary {
158        None => (ContainingDirectory::Exists, AutoRemove::Tempfile),
159        Some(boundary_directory) => (
160            ContainingDirectory::CreateAllRaceProof(Default::default()),
161            AutoRemove::TempfileAndEmptyParentDirectoriesUntil { boundary_directory },
162        ),
163    }
164}
165
166fn lock_with_mode<T>(
167    resource: &Path,
168    mode: Fail,
169    boundary_directory: Option<PathBuf>,
170    try_lock: &dyn Fn(&Path, ContainingDirectory, AutoRemove) -> std::io::Result<T>,
171) -> Result<(PathBuf, T), Error> {
172    use std::io::ErrorKind::*;
173    let (directory, cleanup) = dir_cleanup(boundary_directory);
174    let lock_path = add_lock_suffix(resource);
175    let mut attempts = 1;
176    match mode {
177        Fail::Immediately => try_lock(&lock_path, directory, cleanup),
178        Fail::AfterDurationWithBackoff(time) => {
179            for wait in backoff::Exponential::default_with_random().until_no_remaining(time) {
180                attempts += 1;
181                match try_lock(&lock_path, directory, cleanup.clone()) {
182                    Ok(v) => return Ok((lock_path, v)),
183                    #[cfg(windows)]
184                    Err(err) if err.kind() == AlreadyExists || err.kind() == PermissionDenied => {
185                        std::thread::sleep(wait);
186                        continue;
187                    }
188                    #[cfg(not(windows))]
189                    Err(err) if err.kind() == AlreadyExists => {
190                        std::thread::sleep(wait);
191                        continue;
192                    }
193                    Err(err) => return Err(Error::from(err)),
194                }
195            }
196            try_lock(&lock_path, directory, cleanup)
197        }
198    }
199    .map(|v| (lock_path, v))
200    .map_err(|err| match err.kind() {
201        AlreadyExists => Error::PermanentlyLocked {
202            resource_path: resource.into(),
203            mode,
204            attempts,
205        },
206        _ => Error::Io(err),
207    })
208}
209
210fn add_lock_suffix(resource_path: &Path) -> PathBuf {
211    resource_path.with_extension(resource_path.extension().map_or_else(
212        || DOT_LOCK_SUFFIX.chars().skip(1).collect(),
213        |ext| format!("{}{}", ext.to_string_lossy(), DOT_LOCK_SUFFIX),
214    ))
215}
216
217fn default_permissions() -> Option<std::fs::Permissions> {
218    #[cfg(unix)]
219    {
220        use std::os::unix::fs::PermissionsExt;
221        Some(std::fs::Permissions::from_mode(0o666))
222    }
223    #[cfg(not(unix))]
224    {
225        None
226    }
227}
228
229#[cfg(test)]
230mod tests {
231    use super::*;
232
233    #[test]
234    fn add_lock_suffix_to_file_with_extension() {
235        assert_eq!(add_lock_suffix(Path::new("hello.ext")), Path::new("hello.ext.lock"));
236    }
237
238    #[test]
239    fn add_lock_suffix_to_file_without_extension() {
240        assert_eq!(add_lock_suffix(Path::new("hello")), Path::new("hello.lock"));
241    }
242}
gix_lock/acquire.rs

gix_lock/
acquire.rs
