[tptacek]

Did you read the deck? The GC isn't the problem; it's layout and management of allocations that's the problem, whether you use a garbage collector or explicit deallocation to clean up the resulting mess.

I think the idea that GC is what slows down dynamic languages has to be the most prevalent misconception about language performance.

[jholman]

Yeah. I dunno about "most prevalent", though. TFA contained two "lame excuses", both of which are things I believed to be causes of slowness in dynamic languages, and now I have to reconsider.

    dynamic typing prevents type-based optimization
    monkey patching prevents optimization

I think the most common complaint I hear about GC is not that it affects computational throughput, but that it affects _predictability_ of computational throughput. One maybe doesn't care in scientific computing, but game developers are always going on about how they can't use a GC language because a stall mid-frame will knock them over 16ms/frame or 33ms/frame, which for console certification is a project-killer.

[cheald]

It's worth noting that WoW uses Lua; at some point Blizzard switched from Lua 5.0 (with used a stop-the-world GC) to 5.1 (which introduced an incremental GC) specifically because of this problem. Before, UI code could generate excess tables, kick in the GC, and dramatically impact your framerate. The incremental GC significantly helped this, since it permits the GC to be run over multiple frames, reducing or even eliminating the perceptible impact on the user experience.

[cheald]

I did, and I think I might have mis-stated my point. GC thrash is a symptom of the problem, not the core problem itself. Manually managing allocations avoids the "resulting mess" that must be cleaned up from, which is where your big speed boost comes from. In general, the higher up you go, the further abstracted away from memory management you become. It's not that GC is inherently slow or anything, but simply that giving up control of where and how memory is allocated (in exchange for a more flexible language) is the reason for the speed difference.