[jira] [Work logged] (LOG4J2-3040) ShutdownCallbackRegistry should be part of log4j-api, not log4j-core

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ASF GitHub Bot logged work on LOG4J2-3040:
------------------------------------------

                Author: ASF GitHub Bot
            Created on: 28/Feb/23 15:02
            Start Date: 28/Feb/23 15:02
    Worklog Time Spent: 10m 
      Work Description: vy closed pull request #790: [LOG4J2-3040][3.x] Avoid ClassCastException in JeroMqManager with custom LoggerContextFactory
URL: https://github.com/apache/logging-log4j2/pull/790




Issue Time Tracking
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            Worklog Id:     (was: 848093)
    Remaining Estimate: 0h
            Time Spent: 10m

> ShutdownCallbackRegistry should be part of log4j-api, not log4j-core
> --------------------------------------------------------------------
>
>                 Key: LOG4J2-3040
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-3040
>             Project: Log4j 2
>          Issue Type: Bug
>            Reporter: Grzegorz Grzybek
>            Priority: Major
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> I'm working on https://github.com/ops4j/org.ops4j.pax.logging/issues/395 related to Pax Logging project, which implements OSGi Log specification based on 3 _backends_:
> * Log4j1
> * Logback
> * Log4j2
> and several _frontends_:
> * Commons Logging
> * JULI Logging
> * javax.logging
> * SLF4J
> * Avalong
> * Log4j1 (API)
> * Log4j2 (API)
> * JBoss Logging
> Pax Logging implements own {{org.apache.logging.log4j.spi.LoggerContextFactory}}, where the {{org.apache.logging.log4j.spi.LoggerContext}} returned is managed by OSGi runtime (without using {{org.apache.logging.log4j.core.selector.ContextSelector}}).
> The problem is that several libraries assume that some casts are possible. There was an elasticsearch problem described [here|https://groups.google.com/g/ops4j/c/yjqOzvrKRkc/m/DZeUSdZeCAAJ], where level was set through configuration and {{org.apache.logging.log4j.core.LoggerContext#getContext(boolean)}} explicitly calls (in {{org.apache.logging.log4j.core.config.Configurator#setLevel()}}):
> {code:java}
> public static LoggerContext getContext(final boolean currentContext) {
>     return (org.apache.logging.log4j.core.LoggerContext) LogManager.getContext(currentContext);
> }
> {code}
> assuming that {{org.apache.logging.log4j.LogManager#getContext(boolean)}} returns log4j-core specific implementation of the context.
> With https://github.com/ops4j/org.ops4j.pax.logging/issues/395 there's different problem.
> {{org.apache.logging.log4j.core.appender.mom.jeromq.JeroMqAppender}} (part of log4j-core library) [long time ago|https://github.com/apache/logging-log4j2/commit/a6af67c5d6faee5b4d422add674e4c518c33d528] started to use {{org.apache.logging.log4j.core.util.ShutdownCallbackRegistry}} for cleanup. Now this is moved to {{org.apache.logging.log4j.core.appender.mom.jeromq.JeroMqManager}}, but still there's this explicit code:
> {code:xml}
> if (enableShutdownHook) {
>     SHUTDOWN_HOOK = ((ShutdownCallbackRegistry) LogManager.getFactory()).addShutdownCallback(CONTEXT::close);
> {code}
> While normally, LogManager.getFactor() returns an instance of {{org.apache.logging.log4j.core.impl.Log4jContextFactory}}, it's *not* guaranteed by {{org.apache.logging.log4j.LogManager#getFactory}} API and indeed - pax-logging-api's implementation returns a factory that doesn't implement {{ShutdownCallbackRegistry}}.
> I tried two approaches:
> # _move_ (in OSGi terms) some packages from log4j-core to pax-logging-api (for now, pax-logging-api only operates on log4j-api), howver, transitively I ended up with almost entire log4j-core inside pax-logging-api
> # refactor log4j2 itself (locally) so {{ShutdownCallbackRegistry}} (and {{Cancellable}}) are part of {{org.apache.logging.log4j.spi}} package, but I ended with quite long list of errors from org.revapi:revapi-maven-plugin:0.11.1:check
> Mind that even {{org.apache.logging.log4j.core.LoggerContext#setUpShutdownHook()}} correctly checks for the interface to be implemented:
> {code:java}
> final LoggerContextFactory factory = LogManager.getFactory();
> if (factory instanceof ShutdownCallbackRegistry) {
> {code}
> It's *only* org.apache.logging.log4j.core.appender.mom.jeromq.JeroMqManager that blindly calls:
> {code:java}
> SHUTDOWN_HOOK = ((ShutdownCallbackRegistry) LogManager.getFactory()).addShutdownCallback(CONTEXT::close);
> {code}
> Summarizing - ideally (IMO) {{ShutdownCallbackRegistry}} should be part of the API, but if it's not possible, please fix {{JeroMqManager}} to check for the implementation.



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