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Posted to log4j-dev@logging.apache.org by "Nick Williams (JIRA)" <ji...@apache.org> on 2014/01/03 18:41:59 UTC
[jira] [Comment Edited] (LOG4J2-479) Use of InheritableThreadLocal
in Map ThreadContext is dangerous and unhelpful
[ https://issues.apache.org/jira/browse/LOG4J2-479?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13861703#comment-13861703 ]
Nick Williams edited comment on LOG4J2-479 at 1/3/14 5:40 PM:
--------------------------------------------------------------
In my opinion, we need to take one of two paths:
# Remove uses of {{InheritableThreadLocal}} completely.
# Make a system option to enable use of {{InheritableThreadLocal}}, but *disable it by default* so that values are not inherited unless specifically enabled.
In applications that use thread pools to spin off long-running processes (and this is a lot of applications), an {{InheritableThreadLocal}} is *dangerous*. Before the thread pool is used for the first time, it is initially empty. It hasn't yet created any threads. If a thread sets the value in an {{InheritableThreadLocal}} and then borrows a thread from that pool, the pool will create a thread with the same {{InheritableThreadLocal}} values. That thread will then always have that value, even after the application returns it to the pool. Even worse, in a web application multiple applications could share a single thread pool, resulting in information leaking from one application to another.
was (Author: beamerblvd):
In my opinion, we need to take one of two paths:
#Remove uses of {{InheritableThreadLocal}} completely.
#Make a system option to enable use of {{InheritableThreadLocal}}, but *disable it by default* so that values are not inherited unless specifically enabled.
In applications that use thread pools to spin off long-running processes (and this is a lot of applications), an {{InheritableThreadLocal}} is *dangerous*. Before the thread pool is used for the first time, it is initially empty. It hasn't yet created any threads. If a thread sets the value in an {{InheritableThreadLocal}} and then borrows a thread from that pool, the pool will create a thread with the same {{InheritableThreadLocal}} values. That thread will then always have that value, even after the application returns it to the pool. Even worse, in a web application multiple applications could share a single thread pool, resulting in information leaking from one application to another.
> Use of InheritableThreadLocal in Map ThreadContext is dangerous and unhelpful
> -----------------------------------------------------------------------------
>
> Key: LOG4J2-479
> URL: https://issues.apache.org/jira/browse/LOG4J2-479
> Project: Log4j 2
> Issue Type: Bug
> Reporter: MK
>
> Described here http://logging.apache.org/log4j/2.x/manual/thread-context.html
> The use of InheritableThreadLocal creates subtle and hard to track bugs while not really adding much useful. It is counterintuitive -- I don't see why would anyone expect logging context to be inherited. But it breaks down completely when used with Thread Executors.
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