Why the extra stack frames with Clojure 1.8.0-RC2 vs 1.7.0?

[Andy Fingerhut]

See the README for this example repository:

    https://github.com/jafingerhut/st

and the example output files:

    https://github.com/jafingerhut/st/blob/master/out-clj17.txt
    https://github.com/jafingerhut/st/blob/master/out-clj18-rc2.txt

This might all be perfectly normal, but I couldn't easily see the cause of the change.  Just noticed it when diff'ing some stack traces thrown by Eastwood that are otherwise similar between Clojure 1.7.0 and 1.8.0-RC2.

Andy

[Andy Fingerhut]

I've determined that the extra stack frames were definitely introduced between Clojure 1.8.0-alpha2 and 1.8.0-alpha3, when direct linking was introduced.

Does anyone know if the extra stack frames in the stack traces represent additional method calls being made at run time?

If so, does that hurt or offset the speed gains desired from direct linking?

Andy

[Nicola Mometto]

Andy, with 1.8, whenever a function can be direct linked, it's class representation will be something like this:

public class .. implements IFn {
..
public static Object invokeStatic() {
<CODE HERE>
}
public Object invoke() {
return invokeStatic();
}
..
}

while in 1.7, without invokeStatic, the bytecode would be directly in invoke().

I don't think this will have any impact since this 1 method indirection has been there for invokePrim aswell

Nicola

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