Regarding race conditions, note that the MDC manages contextual information on a per thread basis [1].

[1] http://logback.qos.ch/manual/mdc.html

On 09.11.2012 01:42, Adam Gordon wrote:

I was able to get this working using the SiftingAppender.  Thanks!  My
request filter pulls the child app name from the URI and sets the MDC
variable which yields the appropriate behavior of Spring logging to the
correct log files.

One final question:  is this going to be subject to race conditions?  If
user A is using child app A at the same time as user B is using child
app B, they're going to go through the same request filter so it's
feasible that A's value gets set and that thread goes to do some
intensive business logic (which let's say has a bunch of logging), B's
thread comes in and changes the value, will A's thread suddenly switch
log files?

I guess the real question is when does the SiftingAppender query MDC for
the value and when does it update it for the nested <appender>?

--adam

http://gordonizer.com

On Thu, Nov 8, 2012 at 2:27 PM, ceki <ceki@qos.ch <mailto:ceki@qos.ch>>

wrote:


    Have you looked at SiftingAppender [1]? If you can set an MDC
    variable at the beginning of a request served by each child app, the
    results should be rather close to what you are aiming. Give it a try.

    [1] http://logback.qos.ch/manual/__appenders.html#SiftingAppender

    <http://logback.qos.ch/manual/appenders.html#SiftingAppender>


    On 08.11.2012 19:54, Adam Gordon wrote:

        Ok, I really should have thought about what I really needed
        before posting.

        We have a "parent" GWT web application and we have children
        applications
        that are plugged into it.  The children can run as standalone web
        applications but this is really only for development.  Since
        each child
        can run independently, each has its own logback.xml file.

        Unfortunately, when the parent is built, the children are just
        JAR file
        dependencies and the parent also has it's own logback.xml file.

        Using only the parent's logback.xml file, we can configure different
        appenders (and thus different log files) for each of the
        children, but
        this only works because of the child namespacing (the Java package
        name).  The parent's logback.xml defines the root logger to use the
        parent's appender.  What this means is that if the children are
        using a
        common framework, say Spring, all the Spring logging doesn't go
        into the
        correct child's logfile, but rather the parent's.

        What we need is a way to either allow each child it's own,
        completely
        separate logging configuration or we need to "tag" the logging
        statement
        in the parent's log file with some name that indicates which
        child the
        message came from.

        I was looking at the concept of a context selector, but it
        wasn't clear
        how I'd be able to configure this to return the correct
        LoggingContext
        depending on which child issued the logging statement.

        Alternatively, I suppose I could add a filter which "sets" the
        current
        logging context based on the request URI - the children's
        request URIs
        are also namespaced so that each child's request URI always
        starts with
        /child_name/...

        Was this clear?  Do anyone have any thoughts on how best to approach
        this problem?

        Thanks,

        --adam

        http://gordonizer.com



        On Thu, Nov 8, 2012 at 11:01 AM, ceki <ceki@qos.ch

        <mailto:ceki@qos.ch> <mailto:ceki@qos.ch <mailto:ceki@qos.ch>>>

        wrote:


             Please see [1] in the docs. For your use case, you need to
        define
             the property in the context scope [2].

             [1]

        http://logback.qos.ch/manual/____configuration.html#____variableSubstitution
        <http://logback.qos.ch/manual/__configuration.html#__variableSubstitution>

        <http://logback.qos.ch/manual/__configuration.html#__variableSubstitution
        <http://logback.qos.ch/manual/configuration.html#variableSubstitution>>
             [2]

        http://logback.qos.ch/manual/____configuration.html#scopes
        <http://logback.qos.ch/manual/__configuration.html#scopes>

             <http://logback.qos.ch/manual/__configuration.html#scopes
        <http://logback.qos.ch/manual/configuration.html#scopes>>


             On 08.11.2012 18:54, Adam Gordon wrote:

                 The Layout chapter indicates it supports property value
                 retrieval via
                 %property{key} and states that the logging context is
        where one
                 might
                 put a property (along w/ System properties).  I believe
        log4j
                 did this
                 w/ the <param name="key_name" value="some_value">
        element in the
                 <appender> and referenced it via %properties{key_name}.

                 I'm not seeing how to do this in Logback in XML. Would
        it go in the
                 <logger> element?  What's the syntax?  Could someone please
                 point me to
                 the relevant section in the appropriate chapter of the
        manual?

                 Thanks,

                 --adam



    --
    Ceki
    65% of statistics are made up on the spot

--
Ceki
65% of statistics are made up on the spot
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