1// Copyright 2022 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package os
6
7// File locking support for Plan 9. This uses fdMutex from the
8// internal/poll package.
9
10// incref adds a reference to the file. It returns an error if the file
11// is already closed. This method is on File so that we can incorporate
12// a nil test.
13func (f *File) incref(op string) (err error) {
14	if f == nil {
15		return ErrInvalid
16	}
17	if !f.fdmu.Incref() {
18		err = ErrClosed
19		if op != "" {
20			err = &PathError{Op: op, Path: f.name, Err: err}
21		}
22	}
23	return err
24}
25
26// decref removes a reference to the file. If this is the last
27// remaining reference, and the file has been marked to be closed,
28// then actually close it.
29func (file *file) decref() error {
30	if file.fdmu.Decref() {
31		return file.destroy()
32	}
33	return nil
34}
35
36// readLock adds a reference to the file and locks it for reading.
37// It returns an error if the file is already closed.
38func (file *file) readLock() error {
39	if !file.fdmu.ReadLock() {
40		return ErrClosed
41	}
42	return nil
43}
44
45// readUnlock removes a reference from the file and unlocks it for reading.
46// It also closes the file if it marked as closed and there is no remaining
47// reference.
48func (file *file) readUnlock() {
49	if file.fdmu.ReadUnlock() {
50		file.destroy()
51	}
52}
53
54// writeLock adds a reference to the file and locks it for writing.
55// It returns an error if the file is already closed.
56func (file *file) writeLock() error {
57	if !file.fdmu.WriteLock() {
58		return ErrClosed
59	}
60	return nil
61}
62
63// writeUnlock removes a reference from the file and unlocks it for writing.
64// It also closes the file if it is marked as closed and there is no remaining
65// reference.
66func (file *file) writeUnlock() {
67	if file.fdmu.WriteUnlock() {
68		file.destroy()
69	}
70}
71