Add Release function for flock

pkg/flock/flock_other.go

@@ -19,6 +19,11 @@ limitations under the License.
 package flock
 
 // Acquire is not implemented on non-unix systems.
-func Acquire(path string) error {
+func Acquire(path string) (int, error) {
+	return -1, nil
+}
+
+// Release is not implemented on non-unix systems.
+func Release(lock int) error {
 	return nil
 }

pkg/flock/flock_unix.go

@@ -20,16 +20,17 @@ package flock
 
 import "golang.org/x/sys/unix"
 
-// Acquire acquires a lock on a file for the duration of the process. This method
-// is reentrant.
-func Acquire(path string) error {
-	fd, err := unix.Open(path, unix.O_CREAT|unix.O_RDWR|unix.O_CLOEXEC, 0600)
+// Acquire creates an exclusive lock on a file for the duration of the process, or until Release(d).
+// This method is reentrant.
+func Acquire(path string) (int, error) {
+	lock, err := unix.Open(path, unix.O_CREAT|unix.O_RDWR|unix.O_CLOEXEC, 0600)
 	if err != nil {
-		return err
+		return -1, err
 	}
-
-	// We don't need to close the fd since we should hold
-	// it until the process exits.
-
-	return unix.Flock(fd, unix.LOCK_EX)
+	return lock, unix.Flock(lock, unix.LOCK_EX)
+}
+
+// Release removes an existing lock held by this process.
+func Release(lock int) error {
+	return unix.Flock(lock, unix.LOCK_UN)
 }