redb 4.3.0

Rust Embedded DataBase
Documentation 
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

use crate::BackendError;
use crate::db::FULL_RANGE;
use crate::{DatabaseError, Result, StorageBackend};
use std::fs::{File, TryLockError};
use std::io;
use std::io::{Read, Seek, SeekFrom, Write};
use std::ops::Bound;
use std::sync::Mutex;
use std::sync::atomic::{AtomicBool, Ordering};

/// Stores a database as a file on-disk.
#[derive(Debug)]
pub struct FileBackend {
    whole_file_locked: AtomicBool,
    file: Mutex<File>,
}

impl FileBackend {
    /// Creates a new backend which stores data to the given file.
    pub fn new(file: File) -> Result<Self, DatabaseError> {
        Ok(Self {
            whole_file_locked: AtomicBool::new(false),
            file: Mutex::new(file),
        })
    }

    fn lock_whole_file(&self, shared: bool) -> Result<bool, io::Error> {
        let file = self.file.lock().unwrap();
        let result = if shared {
            file.try_lock_shared()
        } else {
            file.try_lock()
        };

        match result {
            Ok(()) => {
                self.whole_file_locked.store(true, Ordering::Release);
                Ok(true)
            }
            Err(TryLockError::WouldBlock) => Ok(false),
            Err(TryLockError::Error(err)) => Err(err),
        }
    }
}

/// This backend has no byte-range locks. Only the whole storage can be locked, which a whole-file
/// lock does, so that is the one range it supports.
impl StorageBackend for FileBackend {
    fn try_lock_range(&self, start: Bound<u64>, end: Bound<u64>) -> Result<bool, BackendError> {
        if matches!(start, Bound::Unbounded | Bound::Included(0)) && end == Bound::Unbounded {
            self.lock_whole_file(false).map_err(BackendError::from)
        } else {
            Err(BackendError::Unsupported)
        }
    }

    fn try_lock_shared_range(
        &self,
        start: Bound<u64>,
        end: Bound<u64>,
    ) -> Result<bool, BackendError> {
        if matches!(start, Bound::Unbounded | Bound::Included(0)) && end == Bound::Unbounded {
            self.lock_whole_file(true).map_err(BackendError::from)
        } else {
            Err(BackendError::Unsupported)
        }
    }

    fn unlock_range(&self, start: Bound<u64>, end: Bound<u64>) -> Result<(), BackendError> {
        if !matches!(start, Bound::Unbounded | Bound::Included(0)) || end != Bound::Unbounded {
            return Err(BackendError::Unsupported);
        }
        if self.whole_file_locked.swap(false, Ordering::AcqRel) {
            self.file.lock().unwrap().unlock()?;
        }

        Ok(())
    }

    fn lock_range(&self, _start: Bound<u64>, _end: Bound<u64>) -> Result<(), BackendError> {
        Err(BackendError::Unsupported)
    }

    fn lock_shared_range(&self, _start: Bound<u64>, _end: Bound<u64>) -> Result<(), BackendError> {
        Err(BackendError::Unsupported)
    }

    fn query_lock_range(&self, _start: Bound<u64>, _end: Bound<u64>) -> Result<bool, BackendError> {
        Err(BackendError::Unsupported)
    }

    fn close(&self) -> Result<(), io::Error> {
        self.unlock_range(FULL_RANGE.0, FULL_RANGE.1)
            .map_err(io::Error::from)
    }

    fn len(&self) -> Result<u64, io::Error> {
        Ok(self.file.lock().unwrap().metadata()?.len())
    }

    fn read(&self, offset: u64, out: &mut [u8]) -> Result<(), io::Error> {
        let mut file = self.file.lock().unwrap();
        file.seek(SeekFrom::Start(offset))?;
        file.read_exact(out)?;
        Ok(())
    }

    fn set_len(&self, len: u64) -> Result<(), io::Error> {
        self.file.lock().unwrap().set_len(len)
    }

    fn sync_data(&self) -> Result<(), io::Error> {
        self.file.lock().unwrap().sync_data()
    }

    fn write(&self, offset: u64, data: &[u8]) -> Result<(), io::Error> {
        let mut file = self.file.lock().unwrap();
        file.seek(SeekFrom::Start(offset))?;
        file.write_all(data)
    }
}