I observed a bottleneck in WebappClassLoaderBase.filter() during a
stress test. The reason is, that the method is synchronized. It looks to
me, that the reason for the synchronization is only the access to the
non-thread safe Matchers packageTriggersPermit and packageTriggersDeny.
Since they are not used anywhere else, IMHO one can get away with using
a separate Lock object for access to the two. E.g.
Index: WebappClassLoaderBase.java
===================================================================
--- WebappClassLoaderBase.java (revision 1726388)
+++ WebappClassLoaderBase.java (working copy)
@@ -191,6 +191,12 @@
// ------------------------------------------------------- Static
Variables
/**
+ * Monitor Object used to synchronize calling
+ * packageTriggersDeny and packageTriggersPermit.
+ */
+ protected final Object packageTriggersLock = new Object();
+
+ /**
* Regular expression of package names which are not allowed to be
loaded
* from a webapp class loader without delegating first.
*/
@@ -2781,7 +2787,7 @@
* @param name class name
* @return <code>true</code> if the class should be filtered
*/
- protected synchronized boolean filter(String name) {
+ protected boolean filter(String name) {
if (name == null)
return false;
@@ -2795,16 +2801,17 @@
else
return false;
- packageTriggersPermit.reset(packageName);
- if (packageTriggersPermit.lookingAt()) {
- return false;
+ synchronized(packageTriggersLock) {
+ packageTriggersPermit.reset(packageName);
+ if (packageTriggersPermit.lookingAt()) {
+ return false;
+ }
+ packageTriggersDeny.reset(packageName);
+ if (packageTriggersDeny.lookingAt()) {
+ return true;
+ }
}
- packageTriggersDeny.reset(packageName);
- if (packageTriggersDeny.lookingAt()) {
- return true;
- }
-
return false;
}
Comments on the patch?
In addition:
Since the calls to filter() are in a hot code path, I wonder whether
using a more complex code instead of a single regexp could be better.
The code should be fast in the common case, which IMHO is the case when
the resource name neither starts with javax nor with org.apache. That
case could be handled by a simple prefix comparison without regexp.
Only when the resource name starts with javax or org.apache (or
org/apache) the various cases to check may make using a regexp be the
better decision. Of course such code is a bit harder to maintain, than a
single regexp.
I think I'll run a simple micro benchmark to get an idea.
Regards,
Rainer
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