@Override public synchronized void prefetchDeltaSignerInfo(WaveletFederationProvider provider, ByteString signerId, WaveletName waveletName, HashedVersion deltaEndVersion, SignerInfoPrefetchResultListener callback) { ProtocolSignerInfo signerInfo = retrieveSignerInfo(signerId); if (signerInfo != null) { callback.onSuccess(signerInfo); } else { enqueueSignerInfoRequest(provider, signerId, waveletName, deltaEndVersion, callback); } }