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Date: Tue, 20 Sep 2011 19:55:02 +0100
From: Mark Thomas <markt@apache.org>
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To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: Executor thread lifecycle
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On 20/09/2011 19:29, Dan Checkoway wrote:
> I'm curious how long Executor threads live prior to being
> recycled/replaced/what have you.  Is there a way to control this lifecycle?

No.

> I'm using ThreadLocal to allocate some resources per thread...

That is asking for a memory leak. There is a simple rule for correctly
using a ThreadLocal in a web application.

The ThreadLocal must be removed from the thread before the
request/response in which it was created completes processing.

> and the
> behavior I'm seeing is that after some period of time, my ThreadLocal<Thing>
> goes away and needs to be reinitialized.  It's implying to me that the
> thread itself has been recycled.

More recent versions of Tomcat will re-cycle threads and/or remove
ThreadLocals detected when an application is reloaded as part of the
memory leak prevention code.

> What's making this more confusing is that the thread IDs appear to be
> getting reused, so logging the thread ID isn't helping (it's probably
> confusing me more than anything).
> 
> Anyway, can somebody confirm if Tomcat has explicit deliberate control over
> the Executor thread lifecycle, and if so, how I might be able to control
> it?  And if not, is there a way to control it?

ThreadLocals are likely to be the wrong solution to the problem. If you
need a resource across multiple, unrelated requests, the ServletContext
is probably the way to go.

Mark

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