summaryrefslogtreecommitdiff
path: root/libpod/lock/shm_lock_manager_linux.go
blob: 94dfd7dd733b6af92d3b1815676f41eb0106e553 (plain)
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
// +build linux

package lock

import (
	"syscall"

	"github.com/containers/libpod/libpod/lock/shm"
	"github.com/pkg/errors"
)

// SHMLockManager manages shared memory locks.
type SHMLockManager struct {
	locks *shm.SHMLocks
}

// NewSHMLockManager makes a new SHMLockManager with the given number of locks.
// Due to the underlying implementation, the exact number of locks created may
// be greater than the number given here.
func NewSHMLockManager(path string, numLocks uint32) (Manager, error) {
	locks, err := shm.CreateSHMLock(path, numLocks)
	if err != nil {
		return nil, err
	}

	manager := new(SHMLockManager)
	manager.locks = locks

	return manager, nil
}

// OpenSHMLockManager opens an existing SHMLockManager with the given number of
// locks.
func OpenSHMLockManager(path string, numLocks uint32) (Manager, error) {
	locks, err := shm.OpenSHMLock(path, numLocks)
	if err != nil {
		return nil, err
	}

	manager := new(SHMLockManager)
	manager.locks = locks

	return manager, nil
}

// AllocateLock allocates a new lock from the manager.
func (m *SHMLockManager) AllocateLock() (Locker, error) {
	semIndex, err := m.locks.AllocateSemaphore()
	if err != nil {
		return nil, err
	}

	lock := new(SHMLock)
	lock.lockID = semIndex
	lock.manager = m

	return lock, nil
}

// RetrieveLock retrieves a lock from the manager given its ID.
func (m *SHMLockManager) RetrieveLock(id uint32) (Locker, error) {
	lock := new(SHMLock)
	lock.lockID = id
	lock.manager = m

	if id >= m.locks.GetMaxLocks() {
		return nil, errors.Wrapf(syscall.EINVAL, "lock ID %d is too large - max lock size is %d",
			id, m.locks.GetMaxLocks()-1)
	}

	return lock, nil
}

// SHMLock is an individual shared memory lock.
type SHMLock struct {
	lockID  uint32
	manager *SHMLockManager
}

// ID returns the ID of the lock.
func (l *SHMLock) ID() uint32 {
	return l.lockID
}

// Lock acquires the lock.
func (l *SHMLock) Lock() {
	if err := l.manager.locks.LockSemaphore(l.lockID); err != nil {
		panic(err.Error())
	}
}

// Unlock releases the lock.
func (l *SHMLock) Unlock() {
	if err := l.manager.locks.UnlockSemaphore(l.lockID); err != nil {
		panic(err.Error())
	}
}

// Free releases the lock, allowing it to be reused.
func (l *SHMLock) Free() error {
	return l.manager.locks.DeallocateSemaphore(l.lockID)
}