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//go:build linux
// +build linux
package lock
import (
"fmt"
"syscall"
"github.com/containers/podman/v4/libpod/lock/shm"
)
// 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
}
// AllocateAndRetrieveLock allocates the lock with the given ID and returns it.
// If the lock is already allocated, error.
func (m *SHMLockManager) AllocateAndRetrieveLock(id uint32) (Locker, error) {
lock := new(SHMLock)
lock.lockID = id
lock.manager = m
if id >= m.locks.GetMaxLocks() {
return nil, fmt.Errorf("lock ID %d is too large - max lock size is %d: %w",
id, m.locks.GetMaxLocks()-1, syscall.EINVAL)
}
if err := m.locks.AllocateGivenSemaphore(id); err != nil {
return nil, err
}
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, fmt.Errorf("lock ID %d is too large - max lock size is %d: %w",
id, m.locks.GetMaxLocks()-1, syscall.EINVAL)
}
return lock, nil
}
// FreeAllLocks frees all locks in the manager.
// This function is DANGEROUS. Please read the full comment in locks.go before
// trying to use it.
func (m *SHMLockManager) FreeAllLocks() error {
return m.locks.DeallocateAllSemaphores()
}
// 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)
}
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