[jboss-jira] [JBoss JIRA] (JGRP-1877) System.nanoTime() can be negative

[Bela Ban (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-1877?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12998467#comment-12998467 ] 

Bela Ban edited comment on JGRP-1877 at 9/9/14 10:45 AM:
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Thanks David, one of our JGroups users has actually run into problems with {{System.currentTimeMillis()}} when the system time was adjusted via NTP.
I misread the javadoc: {{nanoTime()}} doesn't return negative values, but the origin might be in the future, so I'll use your suggestion.
h5. Correction
{{System.nanoTime()}} can indeed wrap around and become negative when reaching {{Long.MAX_VALUE}}.


was (Author: belaban):
Thanks David, one of our JGroups users has actually run into problems with {{System.currentTimeMillis()}} when the system time was adjusted via NTP.
I misread the javadoc: {{nanoTime()}} doesn't return negative values, but the origin might be in the future, so I'll use your suggestion.

> System.nanoTime() can be negative
> ---------------------------------
>
>                 Key: JGRP-1877
>                 URL: https://issues.jboss.org/browse/JGRP-1877
>             Project: JGroups
>          Issue Type: Bug
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>            Priority: Critical
>             Fix For: 3.5.1, 3.6
>
>
> According to the javadoc, {{System.nanoTime()}} should only be used to measure _elapsed time_, but not compute a _target time in the future_, as {{nanoTime()}} might return a a time in the future. 
> Code like the one below might fail:
> {code:title=Responses.waitFor()|borderStyle=solid}
> public boolean waitFor(long timeout) {
>         long wait_time;
>         final long target_time=System.nanoTime() + TimeUnit.NANOSECONDS.convert(timeout, TimeUnit.MILLISECONDS); // ns
>         lock.lock();
>         try {
>             while(!done && (wait_time=target_time - System.nanoTime()) > 0) {
>                 try {
>                     cond.await(wait_time,TimeUnit.NANOSECONDS);
>                 }
>                 catch(InterruptedException e) {
>                 }
>             }
>             return done;
>         }
>         finally {
>             lock.unlock();
>         }
>     }
> {code}
> When computing {{target_time}}, {{System.nanoTime()}} could return a negative value (numeric overflow) or a value in the future. In the first case, {{target_time}} could be negative, so the method would not block at all. In the latter case, {{target_time}} could be huge, so the method would block for a long time.
> Investigate all occurrences where we use {{nanoTime()}} to compute a time in the future, and see what impact a future value value could have. Possibly replace with {{System.currentTimeMillis()}} or the _time service_.



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