child class java.net.InetAddress$NameServiceAddresses for class InetAddress.Addresses should never happens

[Wackerle]

相同的服务运行在多台服务器上，其中有个别服务器偶现报错：

Caused by: java.lang.IllegalStateException: child class java.net.InetAddress$NameServiceAddresses for class InetAddress.Addresses should never happens, report issue for dns-cache-manipulator lib!
	at com.alibaba.dcm.internal.InetAddressCacheUtilForNew.inetAddress$Addresses2DnsCacheEntry(InetAddressCacheUtilForNew.java:243)
	at com.alibaba.dcm.internal.InetAddressCacheUtilForNew.getInetAddressCache(InetAddressCacheUtilForNew.java:203)
	at com.alibaba.dcm.DnsCacheManipulator.getDnsCache(DnsCacheManipulator.java:156)
	... 63 more

版本：1.8.0
环境信息：jdk8，amd

[oldratlee]

@Wackerle 收到。

给一下： ❤️

• 运行的JDK版本
• 所用的java-dns-cache-manipulator库版本

[Wackerle]

jdk 1.8.0_382
java-dns-cache-manipulator 1.8.0

[Wackerle]

复现代码

ExecutorService executorService = Executors.newFixedThreadPool(2);
executorService.execute(() -> {
    try {
        DnsCacheEntry entry = DnsCacheManipulator.getDnsCache("baidu.com");
    } catch (Exception e) {
        e.printStackTrace();
    }
});
executorService.execute(() -> {
    try {
        HttpClient httpClient = HttpClients.custom().build();
        HttpGet httpGet = new HttpGet("http://baidu.com");
        httpClient.execute(httpGet);
    } catch (Exception e) {
        e.printStackTrace();
    }
});
Thread.sleep(100_000);

报错

Caused by: java.lang.IllegalStateException: child class java.net.InetAddress$NameServiceAddresses for class InetAddress.Addresses should never happens, report issue for dns-cache-manipulator lib!
	at com.alibaba.dcm.internal.InetAddressCacheUtilForNew.inetAddress$Addresses2DnsCacheEntry(InetAddressCacheUtilForNew.java:243)
	at com.alibaba.dcm.internal.InetAddressCacheUtilForNew.getInetAddressCache(InetAddressCacheUtilForNew.java:203)
	at com.alibaba.dcm.DnsCacheManipulator.getDnsCache(DnsCacheManipulator.java:156)
	... 4 more

当调用getDnsCache获取域名解析时，同时访问这个域名，会出现这个问题。

原因分析

访问这个域名时，JDK（1.8.0_382）尝试解析这个域名，会先往cache里写入一个NameServiceAddresses，然后委托给NameService解析域名，并将解析结果封装为CachedAddresses替换到cache里。
代码位置：java.net.InetAddress#getAllByName0(java.lang.String, java.net.InetAddress, boolean, boolean)。

在没有替换之前，getDnsCache会从cache里获取到NameServiceAddresses，引发报错。
代码位置：com.alibaba.dcm.internal.InetAddressCacheUtilForNew#getInetAddressCache。

建议

如果从cache里获取到NameServiceAddresses时，不抛出异常，当做没有域名解析处理。

[oldratlee]

@Wackerle COOOL 👍 我看一下。💕

方便可以开个PR？ 😄