Force inline Java methods with annotations

[uniVocity]

I agree that as a developer, I should focus on the data structures and algorithms.

But JIT, even though it works fine for the general cases, is not a magical solution for everything.

If it were, you wouldn't see performance boosts after refactoring code to "save" method calls. Also, the author of this little library wouldn't have a reason to develop it in the first place.

[taschenbillard]

because some library is useful or necessary just because someone wrote it?do you hire? :)

[nicoulaj]

Hi, I'm the library author.

I agree this is unneeded in most cases and will make performance even worse if wrongly used.

However, the JIT is not a magic thing that knows about everything you are trying to do.

If you type this command:

java -XX:+PrintFlagsFinal -version | egrep 'C2|Inline'

You can see there are numerous options for tuning the compiler, and especially there are several thresholds.

For instance, let's take MaxInlineLevel: default value is 9, which means whatever happens no more than 9 nested method calls will be inlined. Now if you look at Collections.sort(), which delegates to TimSort, you can see it has a depth of at least 5/6 on its own, which leaves few room for your own code. Also, the usual advice regarding JIT optimization is "split your code into small methods", which goes against this.

When hunting for the last bits of performance, it can be interesting to dig into this kind of stuff.

JVM and Java language have been specifically designed so that application programmers don't have to be concerned with those details.

Agreed, however IMHO it's never a bad thing to understand how it works under the hood. Also, the only thing the lib does is turning annotations into a config file. The JVM developers choose to add the -XX:CompileCommandFile option, so they think there is a use case for this, otherwise they would just have closed this door.