JDK1.8 ConcurrentHashMap computeIfAbsent 嵌套的死锁bug

偶然间看到了这个bug,记录一下

Bug信息

• 版本 JDK1.8(目前测试到8u261仍然有这个问题)(是不是有且仅有这个版本还不定),至少可以肯定的是在1.9已经修复
• 场景 ConcurrentHashMap 中computeIfAbsent 的再嵌套computeIfAbsent/putIfAbsent
• 现象 线程死锁

代码

public class CHMTest {
    public static void main(String[] args) {
        normal();
        bug();
    }
    private static void bug(){
        System.out.println("begin bug code ...");
        Map<String, Integer> map = new ConcurrentHashMap<>(16);
        System.out.println(map.size());
        String hash1 = "AaAa";
        String hash2 = "BBBB";
        //hash值,相同产生死锁
        System.out.println("hash1:"+hash1.hashCode()+",hash1:"+hash2.hashCode());
        map.computeIfAbsent(hash1, key -> {
            map.putIfAbsent(hash2,1);
            return 1;
        });
        System.out.println(map.size());
        System.out.println("bug code is exec here?");
    }
    private static  void normal(){

        System.out.println("begin normal code ...");
        Map<String, Integer> map = new ConcurrentHashMap<>(16);
        System.out.println(map.size());
        String hash1 = "AaAa";
        String hash2 = "BBBB2";
        System.out.println("hash1:"+hash1.hashCode()+",hash1:"+hash2.hashCode());
        map.computeIfAbsent(hash1, key -> {
            map.putIfAbsent(hash2,1);
            return 1;
        });
        System.out.println(map.size());
        System.out.println("begin normal code finished");
    }
}

执行上面的代码,bug方法块将死锁.
在computeIfAbsent 中嵌套computeIfAbsent 或者putIfAbsent时,
当两个key对应的hash值相同发生死锁