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本文主要研究一下elasticsearch的DeadlockAnalyzer

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
    
      threadInfoMap = createThreadInfoMap(deadlockedThreads);        Set
     
      
       > cycles = calculateCycles(threadInfoMap);        Set
       
        
         > chains = calculateCycleDeadlockChains(threadInfoMap, cycles);        cycles.addAll(chains);        return createDeadlockDescriptions(cycles);    }    private Deadlock[] createDeadlockDescriptions(Set
         
          
           > cycles) { Deadlock result[] = new Deadlock[cycles.size()]; int count = 0; for (LinkedHashSet
           
             cycle : cycles) { ThreadInfo asArray[] = cycle.toArray(new ThreadInfo[cycle.size()]); Deadlock d = new Deadlock(asArray); result[count++] = d; } return result; } private Set
            
             
              > calculateCycles(Map
              
                threadInfoMap) { Set
               
                
                 > cycles = new HashSet<>(); for (Map.Entry
                 
                   entry : threadInfoMap.entrySet()) { LinkedHashSet
                  
                    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
                   
                    
                     > calculateCycleDeadlockChains(Map
                     
                       threadInfoMap, Set
                      
                       
                        > cycles) { ThreadInfo allThreads[] = threadBean.getThreadInfo(threadBean.getAllThreadIds()); Set
                        
                         
                          > deadlockChain = new HashSet<>(); Set
                          
                            knownDeadlockedThreads = threadInfoMap.keySet(); for (ThreadInfo threadInfo : allThreads) { Thread.State state = threadInfo.getThreadState(); if (state == Thread.State.BLOCKED && !knownDeadlockedThreads.contains(threadInfo.getThreadId())) { for (LinkedHashSet
                           
                             cycle : cycles) { if (cycle.contains(threadInfoMap.get(Long.valueOf(threadInfo.getLockOwnerId())))) { LinkedHashSet
                            
                              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
                             
                               createThreadInfoMap(long threadIds[]) { ThreadInfo threadInfos[] = threadBean.getThreadInfo(threadIds); Map
                              
                                threadInfoMap = new HashMap<>(); for (ThreadInfo threadInfo : threadInfos) { threadInfoMap.put(threadInfo.getThreadId(), threadInfo); } return unmodifiableMap(threadInfoMap); } //......}
                              
                             
                            
                           
                          
                         
                        
                       
                      
                     
                    
                   
                  
                 
                
               
              
             
            
           
          
         
        
       
      
     
    

• DeadlockAnalyzer提供了findDeadlocks方法用于返回死锁线程的信息，该方法通过ThreadMXBean的findMonitorDeadlockedThreads方法获取deadlockedThreads数组，如果该数组为null或空，则返回NULL_RESULT，否则往下计算
• createThreadInfoMap方法根据threadIds从ThreadMXBean获取对应的threadInfo信息，然后组装成threadId与threadInfo的map；calculateCycles方法则是遍历该map，然后根据threadInfo的getLockOwnerId()构建cycles
• calculateCycleDeadlockChains方法则根据threadInfoMap及cycles构建cycleDeadlockChains，添加到cycles中，最后通过createDeadlockDescriptions方法构建Deadlock数组

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
    
      memberIds;        public Deadlock(ThreadInfo[] members) {            this.members = members;            Set
     
       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包含了members、description、memberIds三个属性，其构造器会根据members来构建description

小结

• DeadlockAnalyzer提供了findDeadlocks方法用于返回死锁线程的信息，该方法通过ThreadMXBean的findMonitorDeadlockedThreads方法获取deadlockedThreads数组，如果该数组为null或空，则返回NULL_RESULT，否则往下计算
• createThreadInfoMap方法根据threadIds从ThreadMXBean获取对应的threadInfo信息，然后组装成threadId与threadInfo的map；calculateCycles方法则是遍历该map，然后根据threadInfo的getLockOwnerId()构建cycles
• calculateCycleDeadlockChains方法则根据threadInfoMap及cycles构建cycleDeadlockChains，添加到cycles中，最后通过createDeadlockDescriptions方法构建Deadlock数组

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