// Copyright 2023 The Jujutsu Authors//// Licensed under the Apache License, Version 2.0 (the "License");// you may not use this file except in compliance with the License.// You may obtain a copy of the License at//// https://www.apache.org/licenses/LICENSE-2.0//// Unless required by applicable law or agreed to in writing, software// distributed under the License is distributed on an "AS IS" BASIS,// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.// See the License for the specific language governing permissions and// limitations under the License. #![allow(missing_docs)] use std::fs::File;use std::path::PathBuf; use rustix::fs::FlockOperation;use tracing::instrument; use super::FileLockError; pub struct FileLock {    path: PathBuf,    file: File,} impl FileLock {    pub fn lock(path: PathBuf) -> Result<FileLock, FileLockError> {        loop {            // Create lockfile, or open pre-existing one            let file = File::create(&path).map_err(|err| FileLockError {                message: "Failed to open lock file",                path: path.clone(),                err,            })?;            // If the lock was already held, wait for it to be released            rustix::fs::flock(&file, FlockOperation::LockExclusive).map_err(|errno| {                FileLockError {                    message: "Failed to lock lock file",                    path: path.clone(),                    err: errno.into(),                }            })?;             let stat = rustix::fs::fstat(&file).map_err(|errno| FileLockError {                message: "failed to stat lock file",                path: path.clone(),                err: errno.into(),            })?;            if stat.st_nlink == 0 {                // Lockfile was deleted, probably by the previous holder's `Drop` impl; create a                // new one so our ownership is visible, rather than hidden in an                // unlinked file. Not always necessary, since the previous                // holder might have exited abruptly.                continue;            }             return Ok(Self { path, file });        }    }} impl Drop for FileLock {    #[instrument(skip_all)]    fn drop(&mut self) {        // Removing the file isn't strictly necessary, but reduces confusion.        _ = std::fs::remove_file(&self.path);        // Unblock any processes that tried to acquire the lock while we held it.        // They're responsible for creating and locking a new lockfile, since we        // just deleted this one.        _ = rustix::fs::flock(&self.file, FlockOperation::Unlock);    }}