containerd/content/locks.go

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package content
import (
"sync"
"github.com/nightlyone/lockfile"
"github.com/pkg/errors"
)
// In addition to providing inter-process locks for content ingest, we also
// define a global in process lock to prevent two goroutines writing to the
// same file.
//
// This is pretty unsophisticated for now. In the future, we'd probably like to
// have more information about who is holding which locks, as well as better
// error reporting.
var (
errLocked = errors.New("key is locked")
// locks lets us lock in process, as well as output of process.
locks = map[lockfile.Lockfile]struct{}{}
locksMu sync.Mutex
)
func tryLock(lock lockfile.Lockfile) error {
locksMu.Lock()
defer locksMu.Unlock()
if _, ok := locks[lock]; ok {
return errLocked
}
if err := lock.TryLock(); err != nil {
if errors.Cause(err) == lockfile.ErrBusy {
return errLocked
}
return errors.Wrapf(err, "lock.TryLock() encountered an error")
}
locks[lock] = struct{}{}
return nil
}
func unlock(lock lockfile.Lockfile) error {
locksMu.Lock()
defer locksMu.Unlock()
if _, ok := locks[lock]; !ok {
return nil
}
delete(locks, lock)
return lock.Unlock()
}