Small memory improvements to InjectionMetadata and InitDestroyAnnotationBeanPostProcessor.LifecycleMetadata [SPR-9264]

[spring-projects-issues]

Philippe Marschall opened SPR-9264 and commented

We analysed the memory usage of our application and found a lot of empty LinkedHashSet/Collections.synchronizedSet in the following three cases:

org.springframework.beans.factory.annotation.InjectionMetadata.injectedElements

* 

```

org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.LifecycleMetadata.initMethods

* 

```

org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.LifecycleMetadata.destroyMethods

There are two things that can be done to address this:
1. Creating a LinkedHashSet of the "right" size, eg. the default capacity is 16 but the exact capacity is known in advance
1. If the argument is empty then we use Collections.emptySet() which is a constant so no additional memory is used. Since it's immutable there is no need for the Collections.synchronizedSet wrapper.

---

Affects: 3.1 GA

[spring-projects-issues]

Philippe Marschall commented

Here's the pull request #37

[spring-projects-issues]

Chris Beams commented

Thanks, Phillipe. Will take a look.

[spring-projects-issues]

Chris Beams commented

Thanks again, Philippe. This is now merged. See the pull request for comments on the implementation.

commit cdb6d7447eacfd026c7400238493bb3dc9f17e1c
Author: Philippe Marschall <philippe.marschall@gmail.com>
Date:   Sat Feb 11 16:29:35 2012 +0100

    Optimize memory usage in factory *Metadata classes
    
    InjectionMetadata and LifecycleMetadata can end up having mostly empty
    instance variables. In such cases memory usage can be improved a little
    bit.
    
    This patch addresses this in two ways:
    
     - Creating a LinkedHashSet of the "right" size, the default capacity
       is 16 but the exact capacity needed is known in advance.
    
     - If the argument is empty then use Collections#emptySet which is a
       constant so no additional memory is used. Since it's immutable there
       is no need for the Collections#synchronizedSet wrapper.
    
    Issue: SPR-9264