fjall 3.1.5

Log-structured, embeddable key-value storage engine
Documentation 
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// Copyright (c) 2024-present, fjall-rs
// This source code is licensed under both the Apache 2.0 and MIT License
// (found in the LICENSE-* files in the repository)

use std::{
    fs::{File, OpenOptions},
    path::Path,
    sync::Arc,
};

struct LockedFileGuardInner(File);

impl Drop for LockedFileGuardInner {
    fn drop(&mut self) {
        log::debug!("Unlocking database lock");

        self.0
            .unlock()
            .inspect_err(|e| {
                log::warn!("Failed to unlock database lock: {e:?}");
            })
            .ok();
    }
}

#[derive(Clone)]
#[expect(unused)]
pub struct LockedFileGuard(Arc<LockedFileGuardInner>);

impl LockedFileGuard {
    pub fn create_new(path: &Path) -> crate::Result<Self> {
        log::debug!("Acquiring database lock at {}", path.display());

        let file = match File::create_new(path) {
            Ok(f) => f,
            Err(e) if e.kind() == std::io::ErrorKind::AlreadyExists => {
                OpenOptions::new().read(true).write(true).open(path)?
            }
            e => e?,
        };

        file.try_lock().map_err(|e| match e {
            std::fs::TryLockError::Error(e) => {
                log::error!("Failed to acquire database lock - if this is expected, you can try opening again (maybe wait a little)");
                crate::Error::Io(e)
            }
            std::fs::TryLockError::WouldBlock => crate::Error::Locked,
        })?;

        Ok(Self(Arc::new(LockedFileGuardInner(file))))
    }

    pub fn try_acquire(path: &Path) -> crate::Result<Self> {
        const RETRIES: usize = 3;

        log::debug!("Acquiring database lock at {}", path.display());

        let file = OpenOptions::new().read(true).write(true).open(path)?;

        for i in 1..=RETRIES {
            if let Err(e) = file.try_lock() {
                match e {
                    std::fs::TryLockError::Error(e) => {
                        log::error!("Failed to acquire database lock - if this is expected, you can try opening again (maybe wait a little)");
                        return Err(crate::Error::Io(e));
                    }
                    std::fs::TryLockError::WouldBlock => {
                        if i == RETRIES {
                            return Err(crate::Error::Locked);
                        }
                        std::thread::sleep(std::time::Duration::from_millis(100));
                    }
                }
            } else {
                // Success
                break;
            }
        }

        Ok(Self(Arc::new(LockedFileGuardInner(file))))
    }
}

#[cfg(test)]
mod tests {
    use super::LockedFileGuard;
    use std::fs::File;

    #[test]
    fn create_new_acquires_lock_when_file_already_exists() -> crate::Result<()> {
        let dir = tempfile::tempdir()?;
        let path = dir.path().join("lock");

        File::create(&path)?;

        let _guard = LockedFileGuard::create_new(&path)?;

        Ok(())
    }

    #[test]
    fn try_acquire_acquires_lock_on_existing_file() -> crate::Result<()> {
        let dir = tempfile::tempdir()?;
        let path = dir.path().join("lock");

        File::create(&path)?;

        let _guard = LockedFileGuard::try_acquire(&path)?;

        Ok(())
    }
}