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Links for 2023-04-11

  • EV Database

    Comparison site for electric cars; actually has a realistic model of genuine range for each EV. Full details on charging connectors, charge curves (for charging speed), etc.

    (tags: ev driving cars vehicles)

  • The Black Magic of (Java) Method Dispatch

    Some fascinating details of low-level Java performance optimization, particularly with JIT applied to OO method dispatch:

    Programming languages like Java provide the facilities for subtyping/polymorphism as one of the ways to construct modular and reusable software. This language choice naturally comes at a price, since there is no hardware support for virtual calls, and therefore runtimes have to emulate this behavior. In many, many cases the performance of method dispatch is not important. Actually, in a vast majority of cases, the low-level performance concerns are not the real concerns. However, there are cases when method dispatch performance is important, and there you need to understand how dispatch works, what runtimes optimize for you, and what you can do to cheat and/or emulate similar behavior in your code. For example, in the course of String Compression work, we were faced with the problem of selecting the coder for a given String. The obvious and highly maintainable approach of creating a Coder interface, a few implementations, and dispatching the virtual calls over it, had met some performance problems on the very tiny benchmarks. Therefore, we needed to contemplate something better. After a few experiments, this post was born as a reference for others who might try to do the same. This post also tangentially touches the inlining of virtual calls, as the natural thing during the optimization.
    Discovered via this amazing commit:

    (tags: optimization performance java oo jit coding polymorphism)

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