dgraph-io/badger · error

Throttle Do Done mismatch

Error message

Throttle Do Done mismatch

What it means

This is a panic raised inside Throttle.Done (y/y.go) when the internal channel is empty at Done time. Throttle pairs each Do() call with exactly one Done(); the select-with-default detects that Done was invoked more times than outstanding Do calls — an API-misuse bug in the worker goroutine (extra Done, or Done called outside the throttle's lifecycle). Since it is a panic, not an error return, it crashes the goroutine and typically the process; there is no recovery path inside Badger.

Source

Thrown at y/y.go:229

			return nil
		case err := <-t.errCh:
			if err != nil {
				return err
			}
		}
	}
}

// Done should be called by workers when they finish working. They can also
// pass the error status of work done.
func (t *Throttle) Done(err error) {
	if err != nil {
		t.errCh <- err
	}
	select {
	case <-t.ch:
	default:
		panic("Throttle Do Done mismatch")
	}
	t.wg.Done()
}

// Finish waits until all workers have finished working. It would return any error passed by Done.
// If Finish is called multiple time, it will wait for workers to finish only once(first time).
// From next calls, it will return same error as found on first call.
func (t *Throttle) Finish() error {
	t.once.Do(func() {
		t.wg.Wait()
		close(t.ch)
		close(t.errCh)
		for err := range t.errCh {
			if err != nil {
				t.finishErr = err
				return
			}
		}

View on GitHub (pinned to 2a001d466f)

Solutions

1. Audit the code calling Throttle.Done: every call site must correspond to exactly one successful Throttle.Do on the same instance
2. Ensure error paths do not call Done twice (e.g. once in the worker and once in a deferred cleanup)
3. Wrap critical goroutines with recover if third-party code misuses the throttle, and log the stack to find the extra Done
4. Add unit tests that pair Do/Done under error conditions to prevent regression

When it happens

Trigger: Thrown at y/y.go:229 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of dgraph-io/badger@2a001d466f (2026-09-05). Data as JSON: /api/errors/87a428aa8933f25e. Report an issue: GitHub.