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https://issues.apache.org/jira/browse/HADOOP-16114?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Steve Loughran reassigned HADOOP-16114:
---------------------------------------
Assignee: Praveen Krishna
> NetUtils#canonicalizeHost gives different value for same host
> -------------------------------------------------------------
>
> Key: HADOOP-16114
> URL: https://issues.apache.org/jira/browse/HADOOP-16114
> Project: Hadoop Common
> Issue Type: Bug
> Components: net
> Affects Versions: 2.7.6, 3.1.2
> Reporter: Praveen Krishna
> Assignee: Praveen Krishna
> Priority: Minor
> Fix For: 3.1.3
>
> Attachments: HADOOP-16114-001.patch
>
>
> In NetUtils#canonicalizeHost uses ConcurrentHashMap#putIfAbsent to add an
> entry to the cache
> {code:java}
> private static String canonicalizeHost(String host) {
> // check if the host has already been canonicalized
> String fqHost = canonicalizedHostCache.get(host);
> if (fqHost == null) {
> try {
> fqHost = SecurityUtil.getByName(host).getHostName();
> // slight race condition, but won't hurt
> canonicalizedHostCache.putIfAbsent(host, fqHost);
> } catch (UnknownHostException e) {
> fqHost = host;
> }
> }
> return fqHost;
> }
> {code}
>
> If two different threads were invoking this method for the first time (so the
> cache is empty) and if SecurityUtil#getByName()#getHostName gives two
> different value for the same host , only one fqHost would be added in the
> cache and an invalid fqHost would be given to one of the thread which might
> cause some APIs to fail for the first time `FileSystem#checkPath` even if the
> path is in the given file system. It might be better if we modify the above
> method to this
>
> {code:java}
> private static String canonicalizeHost(String host) {
> // check if the host has already been canonicalized
> String fqHost = canonicalizedHostCache.get(host);
> if (fqHost == null) {
> try {
> fqHost = SecurityUtil.getByName(host).getHostName();
> // slight race condition, but won't hurt
> canonicalizedHostCache.putIfAbsent(host, fqHost);
> fqHost = canonicalizedHostCache.get(host);
> } catch (UnknownHostException e) {
> fqHost = host;
> }
> }
> return fqHost;
> }
> {code}
>
> So even if other thread get a different host name it will be updated to the
> cached value.
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