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