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package storage
import (
"path/filepath"
"sync"
"time"
"github.com/pkg/errors"
)
// A Locker represents a file lock where the file is used to cache an
// identifier of the last party that made changes to whatever's being protected
// by the lock.
type Locker interface {
// Acquire a writer lock.
Lock()
// Unlock the lock.
Unlock()
// Acquire a reader lock.
RLock()
// Touch records, for others sharing the lock, that the caller was the
// last writer. It should only be called with the lock held.
Touch() error
// Modified() checks if the most recent writer was a party other than the
// last recorded writer. It should only be called with the lock held.
Modified() (bool, error)
// TouchedSince() checks if the most recent writer modified the file (likely using Touch()) after the specified time.
TouchedSince(when time.Time) bool
// IsReadWrite() checks if the lock file is read-write
IsReadWrite() bool
// Locked() checks if lock is locked
Locked() bool
}
var (
lockfiles map[string]Locker
lockfilesLock sync.Mutex
)
// GetLockfile opens a read-write lock file, creating it if necessary. The
// Locker object may already be locked if the path has already been requested
// by the current process.
func GetLockfile(path string) (Locker, error) {
return getLockfile(path, false)
}
// GetROLockfile opens a read-only lock file, creating it if necessary. The
// Locker object may already be locked if the path has already been requested
// by the current process.
func GetROLockfile(path string) (Locker, error) {
return getLockfile(path, true)
}
// getLockfile is a helper for GetLockfile and GetROLockfile and returns Locker
// based on the path and read-only property.
func getLockfile(path string, ro bool) (Locker, error) {
lockfilesLock.Lock()
defer lockfilesLock.Unlock()
if lockfiles == nil {
lockfiles = make(map[string]Locker)
}
cleanPath := filepath.Clean(path)
if locker, ok := lockfiles[cleanPath]; ok {
if ro && locker.IsReadWrite() {
return nil, errors.Errorf("lock %q is not a read-only lock", cleanPath)
}
if !ro && !locker.IsReadWrite() {
return nil, errors.Errorf("lock %q is not a read-write lock", cleanPath)
}
return locker, nil
}
locker, err := getLockFile(path, ro) // platform dependent locker
if err != nil {
return nil, err
}
lockfiles[filepath.Clean(path)] = locker
return locker, nil
}
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