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
|
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package filelock provides a platform-independent API for advisory file
// locking. Calls to functions in this package on platforms that do not support
// advisory locks will return errors for which IsNotSupported returns true.
package filelock
import (
"errors"
"os"
)
// A File provides the minimal set of methods required to lock an open file.
// File implementations must be usable as map keys.
// The usual implementation is *os.File.
type File interface {
// Name returns the name of the file.
Name() string
// Fd returns a valid file descriptor.
// (If the File is an *os.File, it must not be closed.)
Fd() uintptr
// Stat returns the FileInfo structure describing file.
Stat() (os.FileInfo, error)
}
// Lock places an advisory write lock on the file, blocking until it can be
// locked.
//
// If Lock returns nil, no other process will be able to place a read or write
// lock on the file until this process exits, closes f, or calls Unlock on it.
//
// If f's descriptor is already read- or write-locked, the behavior of Lock is
// unspecified.
//
// Closing the file may or may not release the lock promptly. Callers should
// ensure that Unlock is always called when Lock succeeds.
func Lock(f File) error {
return lock(f, writeLock)
}
// RLock places an advisory read lock on the file, blocking until it can be locked.
//
// If RLock returns nil, no other process will be able to place a write lock on
// the file until this process exits, closes f, or calls Unlock on it.
//
// If f is already read- or write-locked, the behavior of RLock is unspecified.
//
// Closing the file may or may not release the lock promptly. Callers should
// ensure that Unlock is always called if RLock succeeds.
func RLock(f File) error {
return lock(f, readLock)
}
// Unlock removes an advisory lock placed on f by this process.
//
// The caller must not attempt to unlock a file that is not locked.
func Unlock(f File) error {
return unlock(f)
}
// String returns the name of the function corresponding to lt
// (Lock, RLock, or Unlock).
func (lt lockType) String() string {
switch lt {
case readLock:
return "RLock"
case writeLock:
return "Lock"
default:
return "Unlock"
}
}
// IsNotSupported returns a boolean indicating whether the error is known to
// report that a function is not supported (possibly for a specific input).
// It is satisfied by ErrNotSupported as well as some syscall errors.
func IsNotSupported(err error) bool {
return isNotSupported(underlyingError(err))
}
var ErrNotSupported = errors.New("operation not supported")
// underlyingError returns the underlying error for known os error types.
func underlyingError(err error) error {
switch err := err.(type) {
case *os.PathError:
return err.Err
case *os.LinkError:
return err.Err
case *os.SyscallError:
return err.Err
}
return err
}
|
