[gatherknwldg]

"write a memory recycler"

sigh This is by far go's biggest wart IMO, and one that frequently sends me back to a pauseless (hah! at least less pausy:) systems language. I sure do like it in almost every other meaningful regard. But I wish latency wasn't something the designers punted on.

[saidajigumi]

I occasionally hear this kind of complaint, but I've yet to see any silver-bullet memory management system. AFAICT, the best we've been able to accomplish is to provide a easier path to correctness with decent overall performance. Also, GC latency isn't the only concern. As soon as the magic incantation "high performance" is uttered, all bets are off.

There's been decades of work on real-time garbage collection yet all of those approaches still have tradeoffs. Consider that object recycling is a ubiquitous iOS memory management pattern. This reduces both memory allocation latencies and object recreation overhead. Ever flick-scroll a long list view on an iPhone? Those list elements that fly off the top are virtually immediately recycled back to the bottom -- it's like a carousel with only about as many items as you can see on screen. The view objects are continually reused, just with new backing data. This approach to performance is more holistic than simply pushing responsibility onto the memory allocator.

Memory recycling here also reminds me of frame-based memory allocator techniques written up in the old Graphics Gems books, a technique likewise covered in real-time systems resources. Allocating memory from the operating system can be relatively expensive and inefficient, even using good ol' malloc. A frame-based allocator grabs a baseline number of pages and provides allocation for one or more common memory object sizes (aka "frames"). Pools for a given frame size are kept separate, which prevents memory fragmentation. Allocation performance is much faster than straight malloc, while increasing memory efficiency for small object allocation and eliminating fragmentation. Again, this is a problem-specific approach that considers needs beyond latency.

[pcwalton]

"AFAICT, the best we've been able to accomplish is to provide a easier path to correctness with decent overall performance."

Precisely. Which is why for performance-critical systems code it's important to give the programmer the choice of memory allocation techniques, but to add features to the language to make memory use safer.

Garbage collection is great, but occasionally it falls down and programmers have to resort to manual memory pooling. Then it becomes error-prone (use after free, leaks) without type system help such as regions and RAII.

[haberman]

I can't speak for the grandparent, but for my part I agree with your point that allocation patterns matter and that there is no silver bullet to memory management, which is exactly the reason that GC'd languages like Go are uninteresting as systems languages. Why use a language where you have to work around one of its main features when you care about performance?

I find Rust's approach much more interesting, because GC is entirely optional, but it provides abstractions that make it easier to write clear and correct manual memory management schemes.

[saidajigumi]

Hm, Rust keeps hitting my radar with interesting attributes like this. Time to go have a look see. Thanks!

[zurn]

> I wish latency wasn't something the designers punted on.

The simplistic GC isn't part of the language design, it's a stopgap in the first version.

[cwzwarich]

Do they have a standard ABI or FFI for interaction with C? If so, they probably designed the assumption of a conservative GC into it. You can always make an incompatible change, but it's a pain.