On 25 nov. 2011, at 15:58, Christopher Schultz wrote: > On 11/24/11 4:02 PM, Sylvain Laurent wrote: >> I don't think this ThreadLocal creates a real leak of classloader. >> It would if dayFormat was static. > > IIRC, ThreadLocal essentially puts a key/value pair in a Map in the > Thread. I dunno what kind of reference it is, but I suspect it's a > normal, strong reference. That means that the Thread itself retains a > reference to the instance of the inner class in my servlet. That's > just not going to become available for collection anytime soon.
Actually, in Sun's implementation (1.5 and 1.6 at least), ThreadLocal are implemented with a kind of WeakHashMap in a instance variable of Thread, using your ThreadLocal instance as a weak key and the actual value you stored as value with a strong reference. In your example, the reference to the ThreadLocal instance is stored in an instance variable of your Servlet. So, when your app is stopped, tomcat releases its reference to your Servlet instance so that it can be collected and your ThreadLocal instance too. Since in your case the value that is bound in the ThreadLocal for each thread is a JRE class (SimpleDateFormat), it does not reference the webapp classloader. The latter can then be collected (provided there are no other references pinning it in memory). Note that I was wrong when I wrote that there would be a leak if dayFormat was static : that would only be the case if the value bound in the ThreadLocal was an instance of a class that is loaded by the webapp. It's not the case here (SimpleDateFormat), so that even with a static dayFormat, the classloader would be GCed. Sylvain --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
