[SOLR-14586] replace the second function parameter in Map#computeIfAbsent with static vars

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Won't Fix
• Assignee: Unassigned
• Reporter: Noble Paul
• Created: 22/Jun/20 13:35
• Updated: 16/Feb/22 00:24
• Resolved: 16/Feb/22 00:24

Description

continuing discussion from  SOLR-14579

consider the following

mapObject.computeIfAbsent(key, o -> new HashMap<>());

vs.

mapObject.computeIfAbsent(key, Utils.NEW_HASHMAP_FUN)

 
The first code fragment is executed as following

s.computeIfAbsent(key, new Function() {
 @Override
 public Object apply(String key) {

 return new HashMap<>();
 }
}

So, there are two problems with this

• A new anonymous inner class is created for that lambda. This one extra class becomes a part of your binary
• a new instance of that class is created everytime the computeIfAbsent() method is invoked, irrespective of whether the value is absent for that key or not. Now imagine that method getting called millions of times and creating millions of such objects for no reason

OTOH

when I use Utils.NEW_HASHMAP_FUN

• Only a single anonymous class is created for the entire codebase
• Only single instance of that object is created in the VM

Ideally, we should go all over the codebase and remove such lambdas

Issue Links

• relates to: SOLR-14579 Comment SolrJ 'Utils' generic map functions
• links to: GitHub Pull Request #1599