[infinispan-dev] JGRP-1877

[Romain Pelisse]

Given the pattern of it, I might be able to produce a PMD checks for this.
This way, you could run it across the code base and check for all
occurences of it.

On 10 September 2014 13:58, Alan Field <afield at redhat.com> wrote:

> Hey Bela,
>
> > Just a quick heads up. I'm currently working on
> > https://issues.jboss.org/browse/JGRP-1877, which it critical as it may:
> > - cause RPCs to return prematurely (possibly with a TimeoutException), or
> > - cause RPCs to blocks for a long time (pick which one is worse :-))
>
> How frequently can these errors occur? Is this something that is not very
> likely to happen or something that requires an external action to trigger
> it? (i.e. changing the time via NTP) Just trying to determine the priority
> of this issue.
>
> Thanks,
> Alan
>
> ----- Original Message -----
> > From: "Bela Ban" <bban at redhat.com>
> > To: infinispan-dev at lists.jboss.org
> > Sent: Wednesday, September 10, 2014 12:05:11 PM
> > Subject: [infinispan-dev] JGRP-1877
> >
> > Just a quick heads up. I'm currently working on
> > https://issues.jboss.org/browse/JGRP-1877, which it critical as it may:
> > - cause RPCs to return prematurely (possibly with a TimeoutException), or
> > - cause RPCs to blocks for a long time (pick which one is worse :-))
> >
> > This is due to my misunderstanding of the semantics of
> > System.nanoTime(), I frequently have code like this, which computes a
> > future deadline for a timeout:
> >
> >              long wait_time=TimeUnit.NANOSECONDS.convert(timeout,
> > TimeUnit.MILLISECONDS);
> >              final long target_time=System.nanoTime() + wait_time;
> >              while(wait_time > 0 && !hasResult) { /* Wait for responses:
> */
> >                  wait_time=target_time - System.nanoTime();
> >                  if(wait_time > 0) {
> >                      try {cond.await(wait_time, TimeUnit.NANOSECONDS);}
> > catch(Exception e) {}
> >                  }
> >              }
> >              if(!hasResult && wait_time <= 0)
> >                  throw new TimeoutException();
> >
> > Variable target_time can possibly become *negative* if nanoTime()
> > returns a negative value. If so, hasResult is false and wait_time
> > negative, and therefore a TimeoutException would be thrown !
> >
> > While I'm at it, I'll also fix my uses of System.currentTimeMillis(),
> > and replace it with nanoTime(). Our good friend Erik has run into issues
> > with RPCs (using currentTimeMillis()) hanging forever when their
> > NTP-based servers adjusted the time .... backwards !
> >
> > Please be aware of nanoTime() in your own code, e.g.
> > long t0=nanoTime();
> > ...
> > long t1=nanoTime();
> >
> > It is *not* guaranteed that t1 > t0 because of numeric overflow (t0
> > might be Long.MAX_VALUE-1 and t1 Long.MAX_VALUE +2 !). The only way to
> > compare them is t1 - t0 > 0 (t1 is more recent) or < 0 t0 is more recent.
> >
> > Just thought I wanted to pass this on, in case somebody made the same
> > stupid mistake...
> >
> > Thanks to David Lloyd for pointing this out !
> >
> > --
> > Bela Ban, JGroups lead (http://www.jgroups.org)
> > _______________________________________________
> > infinispan-dev mailing list
> > infinispan-dev at lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/infinispan-dev
> >
> _______________________________________________
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> infinispan-dev at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>



-- 
Romain PELISSE,
*"The trouble with having an open mind, of course, is that people will
insist on coming along and trying to put things in it" -- Terry Pratchett*
Belaran ins Prussia (blog) <http://blog.wordpress.belaran.eu/>     (...
finally up and running !)
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