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helpers.go
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/
helpers.go
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/*
Copyright 2018 Gravitational, Inc.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package backend
import (
"context"
"path/filepath"
"time"
"github.com/gravitational/trace"
)
const locksPrefix = ".locks"
// AcquireLock grabs a lock that will be released automatically in TTL
func AcquireLock(ctx context.Context, backend Backend, lockName string, ttl time.Duration) (err error) {
if lockName == "" {
return trace.BadParameter("missing parameter lock name")
}
key := []byte(filepath.Join(locksPrefix, lockName))
for {
// Get will clear TTL on a lock
backend.Get(ctx, key)
// CreateVal is atomic:
_, err = backend.Create(ctx, Item{Key: key, Value: []byte{1}, Expires: backend.Clock().Now().UTC().Add(ttl)})
if err == nil {
break // success
}
if trace.IsAlreadyExists(err) { // locked? wait and repeat:
backend.Clock().Sleep(250 * time.Millisecond)
continue
}
return trace.ConvertSystemError(err)
}
return nil
}
// ReleaseLock forces lock release
func ReleaseLock(ctx context.Context, backend Backend, lockName string) error {
if lockName == "" {
return trace.BadParameter("missing parameter lockName")
}
key := []byte(filepath.Join(locksPrefix, lockName))
if err := backend.Delete(ctx, key); err != nil {
return trace.Wrap(err)
}
return nil
}