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package lock
import (
"fmt"
"math"
"strconv"
"syscall"
"github.com/pkg/errors"
)
// SHMLockManager manages shared memory locks.
type SHMLockManager struct {
locks *SHMLocks
}
// NewSHMLockManager makes a new SHMLockManager with the given number of locks.
func NewSHMLockManager(numLocks uint32) (Manager, error) {
locks, err := CreateSHMLock(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(numLocks uint32) (LockManager, error) {
locks, err := OpenSHMLock(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 string) (Locker, error) {
intID, err := strconv.ParseInt(id, 16, 64)
if err != nil {
return errors.Wrapf(err, "given ID %q is not a valid SHMLockManager ID - cannot be parsed as int", id)
}
if intID < 0 {
return errors.Wrapf(syscall.EINVAL, "given ID %q is not a valid SHMLockManager ID - must be positive", id)
}
if intID > math.MaxUint32 {
return errors.Wrapf(syscall.EINVAL, "given ID %q is not a valid SHMLockManager ID - too large", id)
}
var u32ID uint32 = uint32(intID)
if u32ID >= m.locks.maxLocks {
return errors.Wrapf(syscall.EINVAL, "given ID %q is not a valid SHMLockManager ID - too large to fit", id)
}
lock := new(SHMLock)
lock.lockID = u32ID
lock.manager = m
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() string {
return fmt.Sprintf("%x", l.lockID)
}
// Lock acquires the lock.
func (l *SHMLock) Lock() error {
return l.manager.locks.LockSemaphore(l.lockID)
}
// Unlock releases the lock.
func (l *SHMLock) Unlock() error {
return l.manager.locks.UnlockSemaphore(l.lockID)
}
// 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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