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From Ceki Gulcu <c...@qos.ch>
Subject Re: [jira] [Created] (LOG4J2-1375) Update SLF4J from 1.7.13 to 1.7.21
Date Sat, 23 Apr 2016 18:16:19 GMT

SLF4J will replay the events it captured during the initialization of 
the underlying logging framework, log4j2 in this case, assuming log4j2 
supports SLF4J replay via the Logger.log(o.s.event.LoggingEvent) method.

What Raplh seems to suggest is to duplicate the SLF4J replay 
functionality within log4j2. However, given that SLF4J captures events 
generated during initialization, log4j2 cannot see them unless it 
supports SLF4J replay. For logging frameworks without replay support, 
i.e. those which lack the Logger.log(o.s.event.LoggingEvent) method, 
slf4j will simply drop the events it captured. Note that log4j1, logback 
prior to 1.1.4, and slf4j-jul and slf4j-simple prior to version 1.7.15 
all lacked replay support but continue to work just fine under slf4j-api 
1.7.15+.

Also note that if N is the version of slf4j-api and M is the slf4j-api 
version with which a binding is compiled, then slf4j ensures binary 
compatibility for all N and M in the 1.6.x and the 1.7.x series. For 
example, the slf4j-api-1.6.0.jar/slf4j-simple-1.7.21.jar combination 
will work just fine, same goes for the 
slf4j-simple-1.7.21.jar/slf4j-api-1.6.0.jar combination.

Compatibility is broken when the binding voluntarily supports event 
replay, as was the case with logback versions 1.1.4+ which require SLF4J 
version 1.7.15+. The question is whether log4j2 wants to support event 
replay at the cost of dropping compatibility with earlier versions of 
slf4j-api.

I hope this further clarifies the matter,

--
Ceki



On 4/23/2016 19:00, Ralph Goers wrote:
> I suppose that depends on the definition of “event loss”.  You can’t log
> without a LoggerContext and the LoggerContext is initialized with a
> default configuration, which means errors will be logged to the console.
> We could create a default configuration that buffers the events and logs
> then again when stop is called.
>
> Ralph
>
>> On Apr 23, 2016, at 7:18 AM, Ceki Gulcu <ceki@qos.ch
>> <mailto:ceki@qos.ch>> wrote:
>>
>> You are welcome.
>>
>> In the principle, the  event loss issue (fixed by event replay
>> post-initialization) depends on the time it takes for the underlying
>> implementation to initialize. Unless you can guarantee that log4j2
>> initializes instantly**, during SLF4J initialization event loss will
>> occur with log4j2 as well. Note the event loss issue is limited to
>> applications using slf4j which are multi-threaded early on.
>>
>> > Would you mind sharing which applications perform reflection on
>> > the org.slf4j.Logger implementation (and why)?
>>
>> The typical example is Spring which may do reflection on logger
>> instances. If the org.slg4j.Logger implementation offers the
>> log(org.slf4j.event.LoggingEvent) method, then the
>> org.slf4j.event.LoggingEvent interface must exist on the class path.
>> Otherwise, the Spring initialization will fail. The
>> org.slf4j.event.LoggingEvent interface was introduced in slf4j-api
>> version 1.7.15. It follows that if you decide to make use of the slf4j
>> replay feature, then log42 will de facto depend on slf4j version
>> 1.7.15 both at compile and runtime.
>>
>> --
>> Ceki
>>
>> **I am presuming here that log4j2 initializes when it creates and
>> returns its first Logger.
>>
>> On 4/23/2016 15:54, Remko Popma wrote:
>>> ...and thank you for the info, Ceki, that is certainly helpful!
>>>
>>> Remko
>>>
>>> On Saturday, 23 April 2016, Remko Popma <remko.popma@gmail.com
>>> <mailto:remko.popma@gmail.com>
>>> <mailto:remko.popma@gmail.com>> wrote:
>>>
>>>    Question: does the replay support solve a problem in SLF4J or in
>>>    Logback initialization?
>>>
>>>    If the latter, then perhaps there's no need to implement the new
>>>    method since log4j-slf4j-impl binds to log4j2 anyway, no?
>>>
>>>    Remko
>>>
>>>    Sent from my iPhone
>>>
>>>     > On 2016/04/23, at 22:12, Ceki Gulcu <ceki@qos.ch
>>> <mailto:ceki@qos.ch> <javascript:;>>
>>>    wrote:
>>>     >
>>>     > Hello,
>>>     >
>>>     > For your information, slf4j-api version 1.7.21 will work with
>>>    current versions of log4j2 just fine albeit without replay support.
>>>    For replay support, log4j2's implementation of org.slf4j.Logger
>>>    interface needs to have a method with the signature
>>>    log(org.slf4j.event.LoggingEvent) in which case events generated
>>>    during SLF4J initialization will be replayed. Note that if log4j2's
>>>    Logger implementation chooses to implement the aforementioned log
>>>    method, log42 will de facto depend on SLF4J version 1.7.15 and later
>>>    both at compile and *runtime*.
>>>     >
>>>     > The runtime dependency might seem surprising but some
>>>    applications perform reflection on the org.slf4j.Logger
>>>    implementation which will fail without slf4j-api 1.7.15 or later
>>>    being present on the classpath.
>>>     >
>>>     > I hope this helps,
>>>     >
>>>     > --
>>>     > Ceki
>>>     >
>>>     >> On 4/23/2016 14:47, Ralph Goers wrote:
>>>     >> We are not fully compatible with this version of SLF4J.  It
>>> had some
>>>     >> initialization race conditions so Substitute Loggers were
>>> invented.
>>>     >> Anyway, there is a new interface we need to implement.
>>>     >>
>>>     >> Ralph
>>>     >>
>>>     >> Begin forwarded message:
>>>     >>
>>>     >>> *From:* "Remko Popma (JIRA)" <jira@apache.org
>>> <mailto:jira@apache.org><javascript:;>
>>>    <mailto:jira@apache.org<javascript:;>>>
>>>     >>> *Date:* April 23, 2016 at 4:13:12 AM MST
>>>     >>> *To:*log4j-dev@logging.apache.org
>>> <mailto:log4j-dev@logging.apache.org><javascript:;>
>>>    <mailto:log4j-dev@logging.apache.org<javascript:;>>
>>>     >>> *Subject:* *[jira] [Closed] (LOG4J2-1375) Update SLF4J from
>>>    1.7.13 to
>>>     >>> 1.7.21*
>>>     >>> *Reply-To:* "Log4J Developers List"
>>>    <log4j-dev@logging.apache.org
>>> <mailto:log4j-dev@logging.apache.org><javascript:;>
>>>     >>> <mailto:log4j-dev@logging.apache.org<javascript:;>>>
>>>     >>>
>>>     >>>
>>>     >>>    [
>>>     >>>
>>> https://issues.apache.org/jira/browse/LOG4J2-1375?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
>>>     >>> ]
>>>     >>>
>>>     >>> Remko Popma closed LOG4J2-1375.
>>>     >>> -------------------------------
>>>     >>>   Resolution: Fixed
>>>     >>>
>>>     >>>> Update SLF4J from 1.7.13 to 1.7.21
>>>     >>>> ----------------------------------
>>>     >>>>
>>>     >>>>               Key: LOG4J2-1375
>>>     >>>>               URL:
>>> https://issues.apache.org/jira/browse/LOG4J2-1375
>>>     >>>>           Project: Log4j 2
>>>     >>>>        Issue Type: Improvement
>>>     >>>>        Components: SLF4J Bridge
>>>     >>>>  Affects Versions: 2.5
>>>     >>>>          Reporter: Remko Popma
>>>     >>>>          Assignee: Remko Popma
>>>     >>>>           Fix For: 2.6
>>>     >>>>
>>>     >>>>
>>>     >>>> Update SLF4J from 1.7.13 to 1.7.21
>>>     >>>
>>>     >>>
>>>     >>>
>>>     >>> --
>>>     >>> This message was sent by Atlassian JIRA
>>>     >>> (v6.3.4#6332)
>>>     >>>
>>>     >>>
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