public void run()

in zookeeper-server/src/main/java/org/apache/zookeeper/server/quorum/QuorumPeer.java [1487:1657]
147 lines of code
26 McCabe index (conditional complexity)

    public void run() {
        updateThreadName();

        LOG.debug("Starting quorum peer");
        try {
            jmxQuorumBean = new QuorumBean(this);
            MBeanRegistry.getInstance().register(jmxQuorumBean, null);
            for (QuorumServer s : getView().values()) {
                ZKMBeanInfo p;
                if (getMyId() == s.id) {
                    p = jmxLocalPeerBean = new LocalPeerBean(this);
                    try {
                        MBeanRegistry.getInstance().register(p, jmxQuorumBean);
                    } catch (Exception e) {
                        LOG.warn("Failed to register with JMX", e);
                        jmxLocalPeerBean = null;
                    }
                } else {
                    RemotePeerBean rBean = new RemotePeerBean(this, s);
                    try {
                        MBeanRegistry.getInstance().register(rBean, jmxQuorumBean);
                        jmxRemotePeerBean.put(s.id, rBean);
                    } catch (Exception e) {
                        LOG.warn("Failed to register with JMX", e);
                    }
                }
            }
        } catch (Exception e) {
            LOG.warn("Failed to register with JMX", e);
            jmxQuorumBean = null;
        }

        try {
            /*
             * Main loop
             */
            while (running) {
                if (unavailableStartTime == 0) {
                    unavailableStartTime = Time.currentElapsedTime();
                }

                switch (getPeerState()) {
                case LOOKING:
                    LOG.info("LOOKING");
                    ServerMetrics.getMetrics().LOOKING_COUNT.add(1);

                    if (Boolean.getBoolean("readonlymode.enabled")) {
                        LOG.info("Attempting to start ReadOnlyZooKeeperServer");

                        // Create read-only server but don't start it immediately
                        final ReadOnlyZooKeeperServer roZk = new ReadOnlyZooKeeperServer(logFactory, this, this.zkDb);

                        // Instead of starting roZk immediately, wait some grace
                        // period before we decide we're partitioned.
                        //
                        // Thread is used here because otherwise it would require
                        // changes in each of election strategy classes which is
                        // unnecessary code coupling.
                        Thread roZkMgr = new Thread() {
                            public void run() {
                                try {
                                    // lower-bound grace period to 2 secs
                                    sleep(Math.max(2000, tickTime));
                                    if (ServerState.LOOKING.equals(getPeerState())) {
                                        roZk.startup();
                                    }
                                } catch (InterruptedException e) {
                                    LOG.info("Interrupted while attempting to start ReadOnlyZooKeeperServer, not started");
                                } catch (Exception e) {
                                    LOG.error("FAILED to start ReadOnlyZooKeeperServer", e);
                                }
                            }
                        };
                        try {
                            roZkMgr.start();
                            reconfigFlagClear();
                            if (shuttingDownLE) {
                                shuttingDownLE = false;
                                startLeaderElection();
                            }
                            setCurrentVote(makeLEStrategy().lookForLeader());
                            checkSuspended();
                        } catch (Exception e) {
                            LOG.warn("Unexpected exception", e);
                            setPeerState(ServerState.LOOKING);
                        } finally {
                            // If the thread is in the grace period, interrupt
                            // to come out of waiting.
                            roZkMgr.interrupt();
                            roZk.shutdown();
                        }
                    } else {
                        try {
                            reconfigFlagClear();
                            checkSuspended();
                            if (shuttingDownLE) {
                                shuttingDownLE = false;
                                startLeaderElection();
                            }
                            setCurrentVote(makeLEStrategy().lookForLeader());
                        } catch (Exception e) {
                            LOG.warn("Unexpected exception", e);
                            setPeerState(ServerState.LOOKING);
                        }
                    }
                    break;
                case OBSERVING:
                    try {
                        LOG.info("OBSERVING");
                        setObserver(makeObserver(logFactory));
                        observer.observeLeader();
                    } catch (Exception e) {
                        LOG.warn("Unexpected exception", e);
                    } finally {
                        observer.shutdown();
                        setObserver(null);
                        updateServerState();

                        // Add delay jitter before we switch to LOOKING
                        // state to reduce the load of ObserverMaster
                        if (isRunning()) {
                            Observer.waitForObserverElectionDelay();
                        }
                    }
                    break;
                case FOLLOWING:
                    try {
                        LOG.info("FOLLOWING");
                        setFollower(makeFollower(logFactory));
                        follower.followLeader();
                    } catch (Exception e) {
                        LOG.warn("Unexpected exception", e);
                    } finally {
                        follower.shutdown();
                        setFollower(null);
                        updateServerState();
                    }
                    break;
                case LEADING:
                    LOG.info("LEADING");
                    try {
                        setLeader(makeLeader(logFactory));
                        leader.lead();
                        setLeader(null);
                    } catch (Exception e) {
                        LOG.warn("Unexpected exception", e);
                    } finally {
                        if (leader != null) {
                            leader.shutdown("Forcing shutdown");
                            setLeader(null);
                        }
                        updateServerState();
                    }
                    break;
                }
            }
        } finally {
            LOG.warn("QuorumPeer main thread exited");
            MBeanRegistry instance = MBeanRegistry.getInstance();
            instance.unregister(jmxQuorumBean);
            instance.unregister(jmxLocalPeerBean);

            for (RemotePeerBean remotePeerBean : jmxRemotePeerBean.values()) {
                instance.unregister(remotePeerBean);
            }

            jmxQuorumBean = null;
            jmxLocalPeerBean = null;
            jmxRemotePeerBean = null;
        }
    }