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https://issues.apache.org/jira/browse/HDFS-17309?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17801113#comment-17801113
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ASF GitHub Bot commented on HDFS-17309:
---------------------------------------
LiuGuH opened a new pull request, #6390:
URL: https://github.com/apache/hadoop/pull/6390
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### Description of PR
With [HDFS-17116](https://issues.apache.org/jira/browse/HDFS-17116), Router
safemode check contidition use monotonicNow().
For code in RouterSafemodeService.periodicInvoke()
```
long now = monotonicNow();
long cacheUpdateTime = stateStore.getCacheUpdateTime();
boolean isCacheStale = (now - cacheUpdateTime) > this.staleInterval;
```
Function monotonicNow() is implemented with System.nanoTime().
System.nanoTime() in javadoc description:
```
This method can only be used to measure elapsed time and is not related to
any other notion of system or wall-clock time. The value returned represents
nanoseconds since some fixed but arbitrary origin time (perhaps in the future,
so values may be negative).
```
The following situation maybe exists ：
If refreshCaches is not success in the beginning, cacheUpdateTime will be 0
, and now - cacheUpdateTime is arbitrary origin time，so isCacheStale maybe be
true or false.
> Fix Router Safemode check contidition error
> -------------------------------------------
>
> Key: HDFS-17309
> URL: https://issues.apache.org/jira/browse/HDFS-17309
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: liuguanghua
> Priority: Major
>
> With HDFS-17116, Router safemode check contidition use monotonicNow().
> For code in RouterSafemodeService.periodicInvoke()
> long now = monotonicNow();
> long cacheUpdateTime = stateStore.getCacheUpdateTime();
> boolean isCacheStale = (now - cacheUpdateTime) > this.staleInterval;
>
> Function monotonicNow() is implemented with System.nanoTime().
> System.nanoTime() in javadoc description:
> This method can only be used to measure elapsed time and is not related to
> any other notion of system or wall-clock time. The value returned represents
> nanoseconds since some fixed but arbitrary origin time (perhaps in the
> future, so values may be negative).
>
> The following situation maybe exists ：
> If refreshCaches not success in the beginning, cacheUpdateTime will be 0 ,
> and now - cacheUpdateTime is arbitrary origin time，so isCacheStale maybe be
> true or false.
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