code: func (fc *DocumentsWriterFlushControl) setFlushPending(perThread *ThreadState) {
  	fc.Lock()
  	defer fc.Unlock()
  	fc._setFlushPending(perThread)
  }
docs: /*
  Sets flush pending state on the given ThreadState. The ThreadState
  must have indexed at least one Document and must not be already
  pending.
  */