code: func (sc *DocumentsWriterStallControl) waitIfStalled() {
  	sc.Lock()
  	defer sc.Unlock()
  	if sc.stalled { // react on the first wake up call!
  		// don't loop here, higher level logic will re-stall
  		assert(sc.incWaiters())
  		sc.Wait()
  		assert(sc.decWaiters())
  	}
  }
docs: /* Blocks if documents writing is currently in a stalled state. */