SessionMap is not thread-safe
-----------------------------
Key: WW-3576
URL: https://issues.apache.org/jira/browse/WW-3576
Project: Struts 2
Issue Type: Bug
Components: Other
Affects Versions: 2.2.1
Reporter: S. Veyrié
Searching for a bug after some stress test (Exception on "getAttribute":
already invalidated session), I reviewed SessionMap.java.
Following WW-239, SessionMap has been made thread-safe.
All methods are like this :
public void doSomething() {
if (session == null) {
return;
}
synchronized (session) {
session.doSometing();
}
}
For example:
public void invalidate() {
if (session == null) {
return;
}
synchronized (session) {
session.invalidate();
session = null;
entries = null;
}
}
IMHO this is not thread-safe. With the example of invalidate(), if there is a
context switch just before the synchronized, the nullity is no more checked. If
another invalidate() is called at least a NPE can be thrown. There are probably
other side-effects like my exception problem).
As now Struts 2 only support Java 5+, there is two ways to fix it :
* use a double-check-locking (DCL) and set session "volatile" (easy way)
* use java.util.concurrent instead of synchronized keyword
If you agree and choose one of those fixes, I can provide a patch.
For the moment, I don't know if my bug is resolved if we directly use javax
session, without this wrapper.
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