| package config | |
| import ( | |
| "os" | |
| "path/filepath" | |
| "time" | |
| ) | |
| // atomicWriteFile writes data to a file atomically by writing to a unique | |
| // temporary file in the same directory and renaming it into place. This | |
| // prevents concurrent readers from observing a partially-written file. | |
| func atomicWriteFile(path string, data []byte, perm os.FileMode) error { | |
| path = filepath.Clean(path) | |
| dir := filepath.Dir(path) | |
| f, err := os.CreateTemp(dir, filepath.Base(path)+".*.tmp") | |
| if err != nil { | |
| return err | |
| } | |
| tmp := f.Name() | |
| if _, err := f.Write(data); err != nil { | |
| f.Close() | |
| os.Remove(tmp) | |
| return err | |
| } | |
| if err := f.Chmod(perm); err != nil { | |
| f.Close() | |
| os.Remove(tmp) | |
| return err | |
| } | |
| if err := f.Close(); err != nil { | |
| os.Remove(tmp) | |
| return err | |
| } | |
| if err := renameFile(tmp, path); err != nil { | |
| os.Remove(tmp) | |
| return err | |
| } | |
| return nil | |
| } | |
| // renameRetryBudget bounds how long renameFile keeps retrying transient | |
| // failures before giving up and returning the error. | |
| const renameRetryBudget = 2 * time.Second | |
| // renameFile renames tmp over path. On Windows the rename fails with | |
| // ERROR_ACCESS_DENIED or ERROR_SHARING_VIOLATION while another process | |
| // (antivirus, search indexer) or a concurrent reader briefly holds a | |
| // handle on the destination, so transient failures are retried with | |
| // backoff. On other platforms isTransientRenameError is always false | |
| // and this is a plain os.Rename. | |
| func renameFile(tmp, path string) error { | |
| var slept time.Duration | |
| delay := time.Millisecond | |
| for { | |
| err := os.Rename(tmp, path) | |
| if err == nil || !isTransientRenameError(err) || slept >= renameRetryBudget { | |
| return err | |
| } | |
| time.Sleep(delay) | |
| slept += delay | |
| delay = min(delay*2, 50*time.Millisecond) | |
| } | |
| } | |