Talk about DeadlockAnalyzer of elasticsearch

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This article mainly studies DeadlockAnalyzer of elasticsearch.

DeadlockAnalyzer

elasticsearch-7.0.1/server/src/main/java/org/elasticsearch/monitor/jvm/DeadlockAnalyzer.java

public class DeadlockAnalyzer {

    private static final Deadlock NULL_RESULT[] = new Deadlock[0];
    private final ThreadMXBean threadBean = ManagementFactory.getThreadMXBean();

    private static DeadlockAnalyzer INSTANCE = new DeadlockAnalyzer();

    public static DeadlockAnalyzer deadlockAnalyzer() {
        return INSTANCE;
    }

    private DeadlockAnalyzer() {

    }

    public Deadlock[] findDeadlocks() {
        long deadlockedThreads[] = threadBean.findMonitorDeadlockedThreads();
        if (deadlockedThreads == null || deadlockedThreads.length == 0) {
            return NULL_RESULT;
        }
        Map<Long, ThreadInfo> threadInfoMap = createThreadInfoMap(deadlockedThreads);
        Set<LinkedHashSet<ThreadInfo>> cycles = calculateCycles(threadInfoMap);
        Set<LinkedHashSet<ThreadInfo>> chains = calculateCycleDeadlockChains(threadInfoMap, cycles);
        cycles.addAll(chains);
        return createDeadlockDescriptions(cycles);
    }


    private Deadlock[] createDeadlockDescriptions(Set<LinkedHashSet<ThreadInfo>> cycles) {
        Deadlock result[] = new Deadlock[cycles.size()];
        int count = 0;
        for (LinkedHashSet<ThreadInfo> cycle : cycles) {
            ThreadInfo asArray[] = cycle.toArray(new ThreadInfo[cycle.size()]);
            Deadlock d = new Deadlock(asArray);
            result[count++] = d;
        }
        return result;
    }


    private Set<LinkedHashSet<ThreadInfo>> calculateCycles(Map<Long, ThreadInfo> threadInfoMap) {
        Set<LinkedHashSet<ThreadInfo>> cycles = new HashSet<>();
        for (Map.Entry<Long, ThreadInfo> entry : threadInfoMap.entrySet()) {
            LinkedHashSet<ThreadInfo> cycle = new LinkedHashSet<>();
            for (ThreadInfo t = entry.getValue(); !cycle.contains(t); t = threadInfoMap.get(Long.valueOf(t.getLockOwnerId()))) {
                cycle.add(t);
            }

            if (!cycles.contains(cycle)) {
                cycles.add(cycle);
            }
        }
        return cycles;
    }


    private Set<LinkedHashSet<ThreadInfo>> calculateCycleDeadlockChains(Map<Long, ThreadInfo> threadInfoMap,
            Set<LinkedHashSet<ThreadInfo>> cycles) {
        ThreadInfo allThreads[] = threadBean.getThreadInfo(threadBean.getAllThreadIds());
        Set<LinkedHashSet<ThreadInfo>> deadlockChain = new HashSet<>();
        Set<Long> knownDeadlockedThreads = threadInfoMap.keySet();
        for (ThreadInfo threadInfo : allThreads) {
            Thread.State state = threadInfo.getThreadState();
            if (state == Thread.State.BLOCKED && !knownDeadlockedThreads.contains(threadInfo.getThreadId())) {
                for (LinkedHashSet<ThreadInfo> cycle : cycles) {
                    if (cycle.contains(threadInfoMap.get(Long.valueOf(threadInfo.getLockOwnerId())))) {
                        LinkedHashSet<ThreadInfo> chain = new LinkedHashSet<>();
                        ThreadInfo node = threadInfo;
                        while (!chain.contains(node)) {
                            chain.add(node);
                            node = threadInfoMap.get(Long.valueOf(node.getLockOwnerId()));
                        }
                        deadlockChain.add(chain);
                    }
                }

            }
        }

        return deadlockChain;
    }


    private Map<Long, ThreadInfo> createThreadInfoMap(long threadIds[]) {
        ThreadInfo threadInfos[] = threadBean.getThreadInfo(threadIds);
        Map<Long, ThreadInfo> threadInfoMap = new HashMap<>();
        for (ThreadInfo threadInfo : threadInfos) {
            threadInfoMap.put(threadInfo.getThreadId(), threadInfo);
        }
        return unmodifiableMap(threadInfoMap);
    }

    //......
}
  • DeadlockAnalyzer provides the findDeadlocks method to return the information of the deadlock thread. The method obtains the deadlockedThreads array thr ough the findMonitorDeadlockedThreads method of ThreadMXBean. If the array is null or empty, it returns NULL_RESULT, otherwise it is calculated downwards
  • The createThreadInfoMap method obtains the corresponding threadInfo information from threadadmin according to threadIds, and then assembles the threadId and threadInfo map; ; The calculateCycles method iterates through the map and then builds cycles based on threadInfo’s getLockOwnerId ()
  • The method of calculateCycleDeadlockChains builds cyclededalcockhains according to threadInfoMap and cycles, adds them to cycles, and finally constructs Deadlock array through the method of createDeadlockDescriptions.

Deadlock

elasticsearch-7.0.1/server/src/main/java/org/elasticsearch/monitor/jvm/DeadlockAnalyzer.java

    public static class Deadlock {
        private final ThreadInfo members[];
        private final String description;
        private final Set<Long> memberIds;

        public Deadlock(ThreadInfo[] members) {
            this.members = members;

            Set<Long> builder = new HashSet<>();
            StringBuilder sb = new StringBuilder();
            for (int x = 0; x < members.length; x++) {
                ThreadInfo ti = members[x];
                sb.append(ti.getThreadName());
                sb.append(" > ");
                if (x == members.length - 1) {
                    sb.append(ti.getLockOwnerName());
                }
                builder.add(ti.getThreadId());
            }
            this.description = sb.toString();
            this.memberIds = unmodifiableSet(builder);
        }

        public ThreadInfo[] members() {
            return members;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;

            Deadlock deadlock = (Deadlock) o;

            if (memberIds != null ? !memberIds.equals(deadlock.memberIds) : deadlock.memberIds != null) return false;

            return true;
        }

        @Override
        public int hashCode() {
            int result = members != null ? Arrays.hashCode(members) : 0;
            result = 31 * result + (description != null ? description.hashCode() : 0);
            result = 31 * result + (memberIds != null ? memberIds.hashCode() : 0);
            return result;
        }

        @Override
        public String toString() {
            return description;
        }
    }
  • Deadlock contains three attributes: members, description and memberIds. its constructor builds the description according to members

Summary

  • DeadlockAnalyzer provides the findDeadlocks method to return the information of the deadlock thread. The method obtains the deadlockedThreads array thr ough the findMonitorDeadlockedThreads method of ThreadMXBean. If the array is null or empty, it returns NULL_RESULT, otherwise it is calculated downwards
  • The createThreadInfoMap method obtains the corresponding threadInfo information from threadadmin according to threadIds, and then assembles the threadId and threadInfo map; ; The calculateCycles method iterates through the map and then builds cycles based on threadInfo’s getLockOwnerId ()
  • The method of calculateCycleDeadlockChains builds cyclededalcockhains according to threadInfoMap and cycles, adds them to cycles, and finally constructs Deadlock array through the method of createDeadlockDescriptions.

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