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From Remko Popma <remko.po...@gmail.com>
Subject Re: [jira] [Created] (LOG4J2-1375) Update SLF4J from 1.7.13 to 1.7.21
Date Sun, 24 Apr 2016 01:16:45 GMT
I agree with Ralph that implementing the new SLF4J method and Log4j startup
are separate topics.

So let's focus on SLF4J. What are our options? These are the ones I see:
1. We compile our log4j-slf4j-impl and log4j-to-slf4j modules with 1.7.13
2. We compile our log4j-slf4j-impl and log4j-to-slf4j modules with 1.7.21
but DON'T implement the log(org.slf4j.event.LoggingEvent) method
3. We compile our log4j-slf4j-impl and log4j-to-slf4j modules with 1.7.21
and DO implement the log(org.slf4j.event.LoggingEvent) method

If doing 3 means we break some applications I would favour 2.




On Sun, Apr 24, 2016 at 6:33 AM, Ralph Goers <ralph.goers@dslextreme.com>
wrote:

> I would suggest others review the code in question, but here is what I see.
>
> LoggerFactory initializes dynamically. The first caller binds to the
> implementation of the LoggerFactory by calling
> StaticLoggerBinder.getSingleton(), but only if it is the first caller.
> Other callers are given a substitute logger factory until the binding is
> complete. Log4j’s implementation creates a Log4jLoggerFactory instance but
> performs no initialization at this time, so the amount of time that SLF4J
> would be in this state should be very small. Regardless, events could still
> be routed to the substitute logger. If we want to ensure that these events
> are not discarded then we have to implement the new method.
>
> Note that due to the way Log4j initializes we don’t have this kind of race
> going on anywhere. Ceki seems to imply that the race is in the underlying
> logging framework, but it is not. Or perhaps he is just assuming that all
> log events are coming through SLF4J, which may or may not actually be the
> case.  The race is entirely within SLF4J’s initialization logic. Anyone
> using just the Log4j API will not have this problem.
>
> As I said previously, A Log4j LoggerContext always has a configuration, at
> least until it is shut down, and logging an event requires a constructed
> LoggerContext. A LoggerContext has a default configuration until the actual
> configuration file is processed and the full configuration constructed. The
> default configuration logs errors to the console. So any log events that
> actually make it to Log4j will have something done with them, but maybe not
> what the user wants.  If we wanted to have any events that occur before
> configuration is completed subject to that configuration the default
> configuration would have to capture them and then republish the events when
> the configuration is stopped, which is similar in concept to what SLF4J is
> doing. But we can’t rely on SLF4J’s substitute loggers for this as SLF4J
> may not even be in the picture.
>
> So as I see it, the discussion on whether to implement the support for the
> new SLF4J method is completely separate from enhancing support of Log4j
> logging during startup.
>
> Ralph
>
>
>
>
> On Apr 23, 2016, at 11:16 AM, Ceki Gulcu <ceki@qos.ch> wrote:
>
>
> 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 <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 <remko.popma@gmail.com>>
> <mailto:remko.popma@gmail.com <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 <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 <jira@apache.org>><javascript:;>
>   <mailto:jira@apache.org <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 <log4j-dev@logging.apache.org>
> ><javascript:;>
>   <mailto:log4j-dev@logging.apache.org <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 <log4j-dev@logging.apache.org>
> ><javascript:;>
>    >>> <mailto:log4j-dev@logging.apache.org <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
>    >>>
>    >>>
>    >>>
>    >>> --
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>    >>> (v6.3.4#6332)
>    >>>
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