Try to get the value first to avoid creating a lambda

[guidomedina]

Try to get the value first which is most likely to be cached to avoid creating a lambda.

Similar to:
https://github.com/quickfix-j/quickfixj/blob/master/quickfixj-core/src/main/java/org/quickfixj/SimpleCache.java

I was going to submit this PR yesterday but I was so busy that got distracted and forgot.

[coveralls]

Coverage remained the same at 82.412% when pulling bcdc6d4 on guidomedina:master into 249bf33 on svendiedrichsen:master.

[svendiedrichsen]

@guidomedina I mad some comments in the code.

[guidomedina]

@svendiedrichsen I can't see your comments, I don't know what to do, I even tried from an incognito session and your comments are not there.

[svendiedrichsen]

@guidomedina If you are logged in you can see them right in this conversation or when you are looking at the 'Files changed' tab.

[guidomedina]

@svendiedrichsen can you see this comment? I know where comments are made in the code, but trust me when I tell you that I cannot see your comments.

[svendiedrichsen]

Comments:

1. What is the reason for calling getDeclaredConstructor Method?
2. Why check cache first? Isn't this the exact purpose of the computIfAbsent Method?

[guidomedina]

• In Java 9+ newInstance() is deprecated, newInstance() will get the declared constructor without parameters and create a new instance anyway (I can undo this part if you want, I'm running IntelliJ with Java 9 and it is shown as deprecated when I analysed the code)
• computeIfAbsent will lock the bucket corresponding to that hash internally and create a new lambda because the ValueHandler function is not static but dynamic, even though Java is very effective at caching lambdas it is also a mechanism that it is easily exploited, for our case it is most likely that the value was computed before and hence avoid a lambda creation.

If the function were static and not a lambda dynamically created the difference would be very minimal; for caches with high reading pattern vs write calling first get is more effective.

For example, in SimpleCache there is a pre-defined loading function for the whole cache and not one created per key.

[svendiedrichsen]

Ok, sounds good to me then. Thanks for the work.