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0 pointsarcticbull3y ago0 comments

> When I hear rhetoric like this, all I think is, "Oh, this person really hates GC, and thinks everyone else should hate GC."

Yeah, I think it's an inelegant, brute-force solution to a language problem - and that we continue to throw good money after bad improving it.

We should be investing in removing the need for GC through smarter compilers and through languages that allow us to better express our intent - and our object graph. Instead, we continue to improve on a giant linked-list traversal through all of live memory to try and infer the object graph at runtime. Without sufficient information to do it efficiently. The fundamental issue is that we don't have languages that express our goals in a way that allows memory management to be elided efficiently.

That doesn't mean I have some particular affinity for reference counting, though. It has its own issues as you rightly point out. I prefer it for its determinism, nothing more.

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klodolph3y ago

> Yeah, I think it's an inelegant, brute-force solution to a language problem - and that we continue to throw good money after bad improving it.

Having studied GC, implemented GC, and used it extensively (either as a dev or someone in operations) I'd say that there's just a lot of people out there who don't understand it. That's why people come to the wrong conclusion that it's somehow "inelegant" or "brute-force", when it is definitely neither of those.

There's also a lot of people who formed their opinions on GC from, say, what the JVM was like in the 1990s.

And there's a lot of people who only have a vague idea of how GC works in theory, but no knowledge of deeper theory and no practical knowledge of how real-world GC algorithms work.

matheusmoreira3y ago

> And there's a lot of people who only have a vague idea of how GC works in theory

I agree. To better understand garbage collection, nothing better than implementation. This article is such a joy to read:

https://journal.stuffwithstuff.com/2013/12/08/babys-first-ga...

ahartmetz3y ago

Even the best "real world" garbage collectors pause the program for order of magnitude a hundred milliseconds, no? I was recently reading some blog posts of the V8 JS engine team.

There is nothing to understand or not understand there, it's hard data.

pjmlp3y ago

And yet GC haters keep ignoring the hard data about languages like D, Oberon family, Modula-3,Nim, .NET, and plenty others where alongside the tracing GC, there are value types, stack, static global memory, manual memory allocation primitives and unsafe code blocks to perform as much C like coding as performance junkies might feel like doing.

Tozen3y ago

Good point. Way too many people act like GC means an unremovable curse, versus it can be another option, among various memory management options of a language.

klodolph3y ago

> Even the best "real world" garbage collectors pause the program for order of magnitude a hundred milliseconds, no?

If you think GC pauses are measured in milliseconds, and not microseconds, then you're reading horribly outdated material. You're off by three orders of magnitude for an off-the-shelf GC with no tuning.

origin_path3y ago

The best real world garbage collectors are like ZGC, Shenandoah or C4 which don't pause your program at all. They are fully concurrent.

Even if you go for a GC that is designed to balance throughput and latency, like G1, you can still configure what pause times it should target and those can easily be ~10-20msec if you want, with the vast majority of pauses being far less than that (less than 3 msec).

"I was recently reading some blog posts of the V8 JS engine team. There is nothing to understand or not understand there"

Look, if your knowledge of GC comes from reading V8 blog posts then you're proving the grandparent's point pretty nicely. You leaped from an extremely basic and remote understanding of GC to "there's nothing to understand or not understand here".

ahartmetz3y ago

Serious questions: if these garbage collectors are so good, why aren't they widely used? My guess is that they have downsides such as low throughput, high CPU usage, high memory usage, etc... You can't import a JVM GC into V8, to stay with my example, but you can reimplement the ideas if you have quasi-infinite money like Google.

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kaba03y ago

But reference counting is a GC-algorithm -- that does exactly the same thing: tries to infer the object graph at runtime.

I really don't think it is a language problem, for several algorithms that one may want to write, GC is a necessity as object lifetime is not decidable at compile time. And it's not just some special parallel algorithm, I believe most business problems fall into this category - that's why we have basically "hacks" like RC, shared ptr, etc in low level languages to let us fake a partial GC (not collecting cycles).

On the plus side of GC, it has been one of the biggest productivity boosters the field has seen since the first non-assembly PL.

eru3y ago

I wouldn't call reference counting a hack.

The paper mention elsewhere in the comments, https://web.eecs.umich.edu/~weimerw/2012-4610/reading/bacon-... "A Unifying Theory of Garbage Collection" put this in context.

For example, a generational garbage collection essentially employs a hybrid approach between tracing and reference counting.

Similarly, depending on your system's trade-offs, reference counting might be better. Eg tracing garbage collection works really great for main memory, but for filesystems we typically use reference counting to decide whether to retire an inode. (The paper explains this in more detail.)

kaba03y ago

I meant hack as in languages meant for primarily for manual memory can still have RC (rust, C++), but that will only be a conservative GC algorithm due to no cycle detection. My use of hack here was only to denote that library-only RC , while possible, may not be the best approach and is used as an escape hatch in rare cases.

eru3y ago

Oh, ok. That makes sense. Though I would count the Boehm Garbage Collector as a hack then, too?

Apropos hacks, have a look at this memory management 'thing' that doesn't move, but manages to compact: https://github.com/plasma-umass/Mesh

j / k navigate · click thread line to collapse

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klodolph3y ago

> Yeah, I think it's an inelegant, brute-force solution to a language problem - and that we continue to throw good money after bad improving it.

There's also a lot of people who formed their opinions on GC from, say, what the JVM was like in the 1990s.

And there's a lot of people who only have a vague idea of how GC works in theory, but no knowledge of deeper theory and no practical knowledge of how real-world GC algorithms work.

matheusmoreira3y ago

> And there's a lot of people who only have a vague idea of how GC works in theory

I agree. To better understand garbage collection, nothing better than implementation. This article is such a joy to read:

https://journal.stuffwithstuff.com/2013/12/08/babys-first-ga...

ahartmetz3y ago

Even the best "real world" garbage collectors pause the program for order of magnitude a hundred milliseconds, no? I was recently reading some blog posts of the V8 JS engine team.

There is nothing to understand or not understand there, it's hard data.

pjmlp3y ago

Tozen3y ago

Good point. Way too many people act like GC means an unremovable curse, versus it can be another option, among various memory management options of a language.

klodolph3y ago

> Even the best "real world" garbage collectors pause the program for order of magnitude a hundred milliseconds, no?

origin_path3y ago

The best real world garbage collectors are like ZGC, Shenandoah or C4 which don't pause your program at all. They are fully concurrent.

"I was recently reading some blog posts of the V8 JS engine team. There is nothing to understand or not understand there"

ahartmetz3y ago

1 more reply

kaba03y ago

But reference counting is a GC-algorithm -- that does exactly the same thing: tries to infer the object graph at runtime.

On the plus side of GC, it has been one of the biggest productivity boosters the field has seen since the first non-assembly PL.

eru3y ago

I wouldn't call reference counting a hack.

The paper mention elsewhere in the comments, https://web.eecs.umich.edu/~weimerw/2012-4610/reading/bacon-... "A Unifying Theory of Garbage Collection" put this in context.

For example, a generational garbage collection essentially employs a hybrid approach between tracing and reference counting.

kaba03y ago

eru3y ago

Oh, ok. That makes sense. Though I would count the Boehm Garbage Collector as a hack then, too?

Apropos hacks, have a look at this memory management 'thing' that doesn't move, but manages to compact: https://github.com/plasma-umass/Mesh

j / k navigate · click thread line to collapse