ContextClassLoader problems for the Evictor thread
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Key: POOL-161
URL: https://issues.apache.org/jira/browse/POOL-161
Project: Commons Pool
Issue Type: Bug
Affects Versions: 1.5.4
Reporter: Sylvain Laurent
Fix For: 2.0
Since a single Timer is used for several GenericObjectPool instances, this may
create classloader issues and a memory leak of one classloader :
Let's imagine the following scenario :
- commons-pool.jar is in the classpath of a webapp container (e.g. tomcat).
- 2 webapps A and B are deployed, each creating an instance of
GenericObjectPool for its own usage.
- each webapp makes use of the idle object evictor and sets a positive number
for minIdle
- first, webapp A instantiates its GenericObjectPool. Since this is the first
TimerTask to be created, the Timer instance is created, thus creating a Thread
whose ContextClassLoader is the current one, that is webapp A's
ContextClassLoader.
The TimerTask properly creates instances of idle objects in the pool, making
use of the ObjectFactory provided by A.
- then B instantiates its GenericObjectPool. A new TimerTask is created, and it
tries to invoke the ObjectFactory provided by B. But when it needs a class that
only exists in B webapp, it cannot find it because the ContextClassLoader of
the Timer Thread is A's classloader.
Other side effect : if webapp A is undeployed, but B is still running, then A's
webappClassLoader cannot be GCed because the Timer Thread keeps a strong
reference to A's classloader (as its context classloader).
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