See below for comments:
On May 1, 2013, at 4:13 PM, Pedro Ruivo <pedro(a)infinispan.org> wrote:
Hi Galder,
On 05/01/2013 08:43 AM, Galder Zamarreño wrote:
> Hi Pedro,
>
> On Apr 29, 2013, at 6:34 PM, Pedro Ruivo <pedro(a)infinispan.org> wrote:
>
>> Hi,
>>
>> The TimeService interface is going to replace all the System.nanoTime()
>> and System.currentTimeMillis() in the code and it will allow to replace
>> in the test suite in order to provide a better control over the time
>> dependent code (if needed).
>
> Great idea, hopefully it will make time related tests more reliable :).
>
> However, is the testsuite the only use case?
>
> There's already been calls for a TimeService or ClockService as indicated by
Sanne, here's one of the discussion threads:
>
http://lists.jboss.org/pipermail/infinispan-dev/2013-January/011933.html
thanks for the link :)
>
> I like the ClockService name better :)
>
>>
>> The objective of this email is to discuss possible implementation and
>> interface that will cover the needs of everybody (or at least try it).
>> Later I'll create a JIRA and start the implementation (except if someone
>> really wants to implement it :P)
>>
>> * Interface:
>>
>> //return the current time in nanoseconds and milliseconds respectively
>> long nowNanos()
>> long nowMillis()
>>
>> //return the duration between now() and the startNanos/Millis
>> long durationNanos(long startNanos)
>> long durationMillis(long startMillis)
>>
>> //return the duration between start+ and end+
>> long durationNanos(long startNanos, long endNanos)
>> long durationMillis(long startMillis, long endMillis)
>>
>> Any other method? Maybe adding a TimeUnit parameter instead of duplicate
>> methods (e.g. now(TimeUnit))? Maybe some convert() with double
>> precision, since the TimeUnit.convert(...) usually loses precision?
>>
>> (I need double precision for the Extended Statistics, but I can put this
>> converters in my classes)
>
> ^ Can you explain the use cases for each of these methods?
>
> Why do you need double precision for extended statistics? And what are these extended
statistics? Have they been discussed in the dev list?
I haven't discussed the Extended Statistic in the mailling list because
it was discussed between Mircea, Manik, Paolo and me (it will be ported
from the Cloud-TM project). However, a JIRA already exists for it:
https://issues.jboss.org/browse/ISPN-2861
The double precision is needed, for example, for the transaction arrival
rate (total number of transactions committed divide by the duration
since last statistic reset). The arrival rate is calculated in tx/sec
and if I'm going to convert nanoseconds to seconds, in the first second
the arrival rate is NaN. The same for throughput.
I took a look in the mails from the mailling list and I think the
caching the value will be prejudicial for the Extended Statistics.
However, I think it can work to expire the cache entries.
^ Indeed, that's why I wanted to open up the discussion to the topic in that thread,
because it'd be good to come up with a timer/clock service that works for both use
cases, or have different APIs, interfaces, or implementations based on the precision
required, the need for multiple time unit supports (or not)…etc.
Also, I think a method like boolean isExpired(long timestamp) is
useful
to add to the interface.
>
>>
>> * Scope:
>>
>> Should the TimeService be in a cache or global scope? My vote is per
>> cache…
>
> ^ My feeling is that it should be global. Why per cache?
When recovery is enabled, the recovery manager creates a second cache.
Someone may want to replace the Clock/TimeService for the "normal" cache
and left the default implementation in the "recovery" cache.
^ Why would an end-user want to replace the Clock/TimeService?
Remember what I said in my previous email: I can see someone changing the service
implementation for testing reasons, and in that case, a global clock/timer service
that's swapable via system property would work just fine IMO.
>
>>
>> * Configuration
>>
>> Should we provide a configuration to pass an implementation of the
>> TimeService interface? if yes, we may need to change the methods above
>> to return some interface (e.g. TimeStamp) in order to support almost
>> anything.
>
> Hmmm, -1. As Manik said in another paralell discussion, we should separate between
what really makes sense to be configured from a user perspective, and what we might wanna
swap for testing.
>
My 2cents, we only allow to be configured if we use some caching
approach to configure the update interval, or to disable it.
The two use cases I see for the clock/time service are:
- statistics
- expiration calculation
The former is already controlled by configuration, and the latter depends on whether
expiration is enabled globally (i.e. global lifespan or maxIdle) or by having the user
call a put call with lifespan/maxIdle.
If no stats are enabled, no global expiration is configured, and there's no user calls
to cache with lifespan/maxIdle, inherently, the clock service won't be used. So, I
don't see disabling the clock service something the user should have to worry about.
Not sure what the update interval. Also, what is the reason why a end-user might want to
change it?
Finally, remember that keeping the service global has the benefit of consuming less
resources, particularly in environments with a lot of caches.
Cheers,
>>
>> Any other subject? Thoughts?
>>
>> If I was not clear let me know...
>>
>> Cheers,
>> Pedro Ruivo
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>>
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>
>
> --
> Galder Zamarreño
> galder(a)redhat.com
>
twitter.com/galderz
>
> Project Lead, Escalante
>
http://escalante.io
>
> Engineer, Infinispan
>
http://infinispan.org
>
>
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--
Galder Zamarreño
galder(a)redhat.com
twitter.com/galderz
Project Lead, Escalante
http://escalante.io
Engineer, Infinispan
http://infinispan.org