seata clientID 及channel选择

seata TC 给每个客户端(TM及RM)都会编一个ID,这个ID是在TC端根据RPC context来设置的，无法自行设置，具体相关代码如下：

private static String buildClientId(String applicationId, Channel channel) {
        return applicationId + Constants.CLIENT_ID_SPLIT_CHAR + getAddressFromChannel(channel);
    }

private static RpcContext buildChannelHolder(NettyPoolKey.TransactionRole clientRole, String version, String applicationId,
                                                 String txServiceGroup, String dbkeys, Channel channel) {
        RpcContext holder = new RpcContext();
        holder.setClientRole(clientRole);
        holder.setVersion(version);
        holder.setClientId(buildClientId(applicationId, channel));
        holder.setApplicationId(applicationId);
        holder.setTransactionServiceGroup(txServiceGroup);
        holder.addResources(dbKeytoSet(dbkeys));
        holder.setChannel(channel);
        return holder;
    }

    }

如果客户端在branch 报告成功后异常退出，可能出现如下错误：

java.lang.RuntimeException: rm client is not connected. dbkey:TccActionOne,clientId:tcc-sample:127.0.0.1:61605
	at io.seata.core.rpc.netty.RpcServer.sendSyncRequest(RpcServer.java:217)
	at io.seata.core.rpc.netty.RpcServer.sendSyncRequest(RpcServer.java:236)
	at io.seata.server.coordinator.DefaultCoordinator.branchRollback(DefaultCoordinator.java:258)
	at io.seata.server.coordinator.DefaultCore.doGlobalRollback(DefaultCore.java:309)
	at io.seata.server.coordinator.DefaultCoordinator.handleRetryRollbacking(DefaultCoordinator.java:336)
	at io.seata.server.coordinator.DefaultCoordinator.lambda$1(DefaultCoordinator.java:436)
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
	at java.util.concurrent.FutureTask.runAndReset(Unknown Source)
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(Unknown Source)
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.lang.Thread.run(Unknown Source)

这个错误其实不用担心，重新启动client（或者有相同resourceId-rm branch名称相同） 会自动rollback，有关处理逻辑可以看public class DefaultCore的doGlobalRollback函数，如何选择channel（及RM client）的逻辑为，依次选择：

• 原有IP及端口
• 原有IP上相同应用（application ID）及相同resourceId（RMCLIENT）
• 其它IP上相同应用（application ID）及相同resourceId（RMCLIENT）
• 其它IP上其它应用（application ID）及相同resourceId（RMCLIENT）

具体见如下代码

 /**
     * Gets get channel.
     *
     * @param resourceId Resource ID
     * @param clientId   Client ID - ApplicationId:IP:Port
     * @return Corresponding channel, NULL if not found.
     */
    public static Channel getChannel(String resourceId, String clientId) {
        Channel resultChannel = null;

        String[] clientIdInfo = readClientId(clientId);

        if (clientIdInfo == null || clientIdInfo.length != 3) {
            throw new FrameworkException("Invalid Client ID: " + clientId);
        }

        String targetApplicationId = clientIdInfo[0];
        String targetIP = clientIdInfo[1];
        int targetPort = Integer.parseInt(clientIdInfo[2]);

        ConcurrentMap<String, ConcurrentMap<String, ConcurrentMap<Integer,
            RpcContext>>> applicationIdMap = RM_CHANNELS.get(resourceId);

        if (targetApplicationId == null || applicationIdMap == null ||  applicationIdMap.isEmpty()) {
            if (LOGGER.isInfoEnabled()) {
                LOGGER.info("No channel is available for resource[" + resourceId + "]");
            }
            return null;
        }

        ConcurrentMap<String, ConcurrentMap<Integer, RpcContext>> ipMap = applicationIdMap.get(targetApplicationId);

        if (null != ipMap && !ipMap.isEmpty()) {

            // Firstly, try to find the original channel through which the branch was registered.
            ConcurrentMap<Integer, RpcContext> portMapOnTargetIP = ipMap.get(targetIP);
            if (portMapOnTargetIP != null && !portMapOnTargetIP.isEmpty()) {

                RpcContext exactRpcContext = portMapOnTargetIP.get(targetPort);
                if (exactRpcContext != null) {
                    Channel channel = exactRpcContext.getChannel();
                    if (channel.isActive()) {
                        resultChannel = channel;
                        if (LOGGER.isDebugEnabled()) {
                            LOGGER.debug("Just got exactly the one " + channel + " for " + clientId);
                        }
                    } else {
                        if (portMapOnTargetIP.remove(targetPort, exactRpcContext)) {
                            if (LOGGER.isInfoEnabled()) {
                                LOGGER.info("Removed inactive " + channel);
                            }
                        }
                    }
                }

                // The original channel was broken, try another one.
                if (resultChannel == null) {
                    for (ConcurrentMap.Entry<Integer, RpcContext> portMapOnTargetIPEntry : portMapOnTargetIP
                        .entrySet()) {
                        Channel channel = portMapOnTargetIPEntry.getValue().getChannel();

                        if (channel.isActive()) {
                            resultChannel = channel;
                            if (LOGGER.isInfoEnabled()) {
                                LOGGER.info(
                                    "Choose " + channel + " on the same IP[" + targetIP + "]  as alternative of "
                                        + clientId);
                            }
                            break;
                        } else {
                            if (portMapOnTargetIP.remove(portMapOnTargetIPEntry.getKey(),
                                portMapOnTargetIPEntry.getValue())) {
                                if (LOGGER.isInfoEnabled()) {
                                    LOGGER.info("Removed inactive " + channel);
                                }
                            }
                        }
                    }
                }
            }

            // No channel on the this app node, try another one.
            if (resultChannel == null) {
                for (ConcurrentMap.Entry<String, ConcurrentMap<Integer, RpcContext>> ipMapEntry : ipMap
                    .entrySet()) {
                    if (ipMapEntry.getKey().equals(targetIP)) { continue; }

                    ConcurrentMap<Integer, RpcContext> portMapOnOtherIP = ipMapEntry.getValue();
                    if (portMapOnOtherIP == null || portMapOnOtherIP.isEmpty()) {
                        continue;
                    }

                    for (ConcurrentMap.Entry<Integer, RpcContext> portMapOnOtherIPEntry : portMapOnOtherIP.entrySet()) {
                        Channel channel = portMapOnOtherIPEntry.getValue().getChannel();

                        if (channel.isActive()) {
                            resultChannel = channel;
                            if (LOGGER.isInfoEnabled()) {
                                LOGGER.info("Choose " + channel + " on the same application[" + targetApplicationId
                                    + "] as alternative of "
                                    + clientId);
                            }
                            break;
                        } else {
                            if (portMapOnOtherIP.remove(portMapOnOtherIPEntry.getKey(),
                                portMapOnOtherIPEntry.getValue())) {
                                if (LOGGER.isInfoEnabled()) {
                                    LOGGER.info("Removed inactive " + channel);
                                }
                            }
                        }
                    }
                    if (resultChannel != null) { break; }
                }
            }
        }

        if (resultChannel == null) {
            resultChannel = tryOtherApp(applicationIdMap, targetApplicationId);

            if (resultChannel == null) {
                if (LOGGER.isInfoEnabled()) {
                    LOGGER.info("No channel is available for resource[" + resourceId
                        + "]  as alternative of "
                        + clientId);
                }
            } else {
                if (LOGGER.isInfoEnabled()) {
                    LOGGER.info("Choose " + resultChannel + " on the same resource[" + resourceId
                        + "]  as alternative of "
                        + clientId);
                }
            }
        }

        return resultChannel;

    }