Use putIfAbsent in CachedIntrospectionResults.addTypeDescriptor [SPR-12102]

[spring-projects-issues]

Craig opened SPR-12102 and commented

In #16486, CachedIntrospectionResults was changed to use a ConcurrentHashMap for typeDescriptorCache. This change is definitely positive and had a significant improvement to performance in my testing.

I think that using putIfAbsent (instead of just put) would be a further improvement in the addTypeDescriptor method. Changing:

void addTypeDescriptor(PropertyDescriptor pd, TypeDescriptor td) {
     this.typeDescriptorCache.put(pd, td);
}

to

void addTypeDescriptor(PropertyDescriptor pd, TypeDescriptor td) {
     this.typeDescriptorCache.putIfAbsent(pd, td);
}

should result in less writes to volatile variables improve performance of getTypeDescriptor.

Changing the other ConcurrentHashMap (strongClassCache and softClassCache) put()'s to putIfAbsent()'s would probably also be beneficial.

---

Affects: 4.1 RC2

Issue Links:

• #16486 Revisit class cache in CachedIntrospectionResults

Referenced from: commits af6ef5f, 781a6d2

[spring-projects-issues]

Juergen Hoeller commented

Good point... Applied to all ConcurrentHashMaps in CachedIntrospectionResults for 4.1 GA!

Juergen

[spring-projects-issues]

Craig commented

Pull request: #629

[spring-projects-issues]

Juergen Hoeller commented

Oops, I just noticed based on your pull request that my commit from a few minutes ago only works on JDK 8... where putIfAbsent has been added as a default method to the Map interface itself. Fixing this now towards ConcurrentMap declarations that work on JDK 6 and 7 as well.

As for using the pre-cached values as returned from putIfAbsent, this doesn't seem to make much difference, since the values are going to be equivalent anyway?

Juergen

[spring-projects-issues]

Craig commented

I figured that using the pre-cached values reduces the total number of objects in memory (by just a tiny amount) so it was worth doing. It doesn't seem like it should really matter, but I figured, why not do it as best as I could think of. :-)

[spring-projects-issues]

Juergen Hoeller commented

Alright, along with fixing the ConcurrentMap declarations, I've changed the code to reuse existing cached values where possible (including TypeDescriptors in BeanWrapperImpl).

Juergen