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I had the 2012 print edition. One of the best books available - the best book that I knew - about GC at that time.
Anti-pattern: Regarding the 2023 e-book edition, I do not see a way to buy it from the site, or even a link to buy.
I thought I was missing something but figured they just didn't have a link to purchase it. I ended up going to the publisher's site to track it down:
https://www.routledge.com/The-Garbage-Collection-Handbook-Th...
How on earth is the ebook more expensive than the physical copy!
And it's not an actual ebook. You have to create an account on the "ebook" provider's site and read it through their website or app.
I hate when they do this. I'd rather just buy the physical book, donate it to a library and then obtain the liberated version of the ebook "elsewhere".
Worthless.
Yuck. I'd never buy that, no matter how much I wanted to read the content.
The physical copy will only get used by one reader (at a time). The ebook is going to be, err, "liberated" more often than not around a dorm?
In all seriousness, this is likely a nudge to a preference they have for how they want to sell this and how you should want to buy it.
They advertise the ebook as having interactive features and more compared to the print version. Shouldn't it be the preferred one?
I have the 2012 print edition too and fully concur with the assessment. The best book about garbage collection at the time (and maybe still?)
I have this book and like it.
I also wish there was a book that guided you through the process of implementing a language with accurate garbage collection, similar to how Crafting Interpreters teaches you to implement a language. Perhaps it could start with a shadow stack + simple mark-and-sweep and then move on to stack maps + generational GC.
Previously:
I remember reading it before. My son threw it away when we moved houses, not knowing how important it was. I'd recommend it.
Ironic that this of all books got garbage collected prematurely.
Q: what kind of collection is this real world example illustrating?
A: Copying Garbage Collector (semi space). Chapter 4!
Great book. I was always fascinated by bakers treadmill. Always wanted a real world case where I could implement one with Fibonacci sized mills.
How good are AIs at coding manual memory management? Is this a sea change in automatic memory management?
In my opinion, the "manual" memory management, introduced by the IBM PL/I programming language by the end of 1964, and inherited by C and other languages, i.e. where the programmer is responsible for invoking "free", was a serious mistake and it was an obsolete technique already at the date of its introduction.
When the explicit "free" was invented, automatic memory reclamation while avoiding the non-determinism of garbage collectors had already been known for 4 years, since 1960, when another IBM employee had invented reference counting (as a reaction to the garbage collector of LISP I).
When implemented naively, reference counting has some disadvantages, but those can be circumvented relatively easily in an optimized implementation. The book discussed in the parent article also has a chapter about reference counting.
I have written C programs for many decades, but I have never invoked "free" directly, because I have always used reference counts. I have never encountered a circumstance when I would have wanted to invoke "free" directly.
C has the disadvantage that the compiler will not do implicitly things like virtual function invocation, reference counts handling etc. but any such techniques that are provided by higher-level languages can still be used in a language like C, even if they require more boilerplate code.
I do not like the "shared_ptr" implementation of reference counting in C++, because that data type is not directly usable in places where a plain reference or pointer is expected. Implementations that do not have this problem exist.
> where the programmer is responsible for invoking "free", was a serious mistake and it was an obsolete technique already at the date of its introduction.
It wasn’t obsolete then nor now. Garbage collected languages, to this day, still use on average about 2x-5x the working memory of carefully written manual memory programs. A significant amount of devices then and even today cannot support such sloppy use of resources.
I think they mean something more akin to RAII in C++/rust. Manually writing a free statement is very error-prone and there are better language-level features to avoid that.
RAII has nothing to do with garbage collection. It only provides a way to get a resource somewhat atomically. If the creator doesn’t delete the object, or if the object has a malformed destructor, it fails. If the creator calls delete twice, it fails. There’s really no garbage collection at all here.
Is there a scheme where memory is auto-freed if it goes out of scope?
If so, are there benefits/drawbacks to that?
If it's on the stack, it's almost free to do.
If it's held by a unique_ptr, then it auto frees, but there is a lot of programmer work to ensure things behave well, and there are nuances to allocating something into the unique_ptr.
If it's a std::shared_ptr, which is the closest to what people think of, it's then a reference counted object, which requires a little more storage, and also has the ability to be mishandled as a pointer, screwing it up, or making the wrong type of copy of the shared_ptr, so two there are two things, and also fails to release object in the case of circluar references.
Then there's a lot of other subtle things you can do, and none of this is as lightweight as a pointer, and none is as automatic as what most people think of as garbage collection.
And each has costs and tradeoffs, which is why C++ added them: making certain tradeoffs easier to use, but it requires solid understanding of how such things work.
I too have written C programs for decades. I encountered reference counting when I learned how to write Windows kernel drivers. It was very liberating to see that there were so fewer opportunities for memory leaks when reference counts were applied liberally.
I have never seen Codex or Claude get manual memory management wrong. I used to be pretty fastidious about using leak sanitizer or other such tools to catch my own memory management issues, and while not quite useless, that sort of testing has dropped way down my list of worries the more I lean on LLMs. I am constantly surprised by how many formerly tedious or error prone tasks stopped being either of those, and I expect to see practice shift away from middle-safe languages like C++ to not just much more safe languages like Rust but surprisingly also to much less safe ones like C and platform specific assembly.
The hard part was never getting it correct on a local scope, that's mostly solved by a linter, or even C++'s RAII will get it right.
The hard part is doing it correctly on a global scope with non-trivial lifetimes, possibly influenced by multiple threads.
And in my experience LLMs are still hit or miss on these kind of problems, they can find problems from time to time, but they can't really reason well about more complex global state reliably. They will come up with "hypotheses" that 'oh sure this is the root cause of the issue' only to say something completely wrong (which you may notice or not, only to fail later)
GC's strength is not only in the ease of writing but at also reading, since you don't need to interleave allocation and business logic everywhere (be it through types or imperative code).
GC simply is the only way to approach the clarity of pseudo-code in real code. That's one of my later realizations concerning the subject (https://world-playground-deceit.net/blog/2024/11/how-i-learn...)
You mean "interleave deallocation and business logic everywhere".
For allocation there is no difference between automatic memory management with garbage collectors or reference counts and manual memory management, where the programmer is responsible for invoking "free".
These alternative memory management methods differ only in how deallocation is handled.
Allocation must always be done by defining a new object, regardless of how memory is managed. Moreover, allocation also does not depend on whether an object is allocated in static storage, in a stack or in a heap. You always must define the object, so that memory should be allocated for it at compile-time if in static storage, or at run-time if in a stack or in a heap.
Well, it's true that most of the noise comes from deallocation but I did mention types for good reasons: having your code littered with std::shared_ptr (or worse for Rust where encoding lifetime goes much further than Rc/Arc) is a direct consequence of wanting GC without a global one.
The source of my second revelation: GC should be opt-out (e.g. SBCL's arena system) instead of opt-in via refcounted types.
While C and C++ have ugly syntaxes for "malloc", "std::shared_ptr" and the like, it is quite easy to mask that ugliness by using macros and writing thus only cleanly-looking programs, without any noise words and symbols around dynamic allocations.
In general, by using macros it is possible to transform so much a C or C++ program, that it becomes unrecognizable as C/C++ and it can mimic reasonably well any other programming language that you might fancy.
The problem is when you work in a team, because even if everyone will agree that such programming languages have great deficiencies, it would be impossible to reach a consensus about how the ideal programming language should look like, so eventually the team remains stuck with writing programs in the ugly standard manner.
In Zig, pretty good, but not perfect yet
What I didn’t like about this series of books was choosing “garbage collection” as umbrella term for both tracing GC and reference counting, without verifying if programming community would agree with that, which turned out they didn’t.
I’ve seen a lot of threads here and on reddit where people were arguing about terminology purely because of this book alone.
By that definition, C++ code has garbage collection if it uses std::shared_ptr, going against widespread common usage of the term “garbage collected programming language” which specifically contrasts manual languages like C++ or Rust against garbage collected ones.
“Automatic Memory Management” is a lot more suitable description to what programmers have to do to manage memory; it is now in the title but still hasn’t become the primary term.
> What I didn’t like about this series of books was choosing “garbage collection” as umbrella term for both tracing GC and reference counting, without verifying if programming community would agree with that, which turned out they didn’t.
This has been the standard terminology in memory management research for many decades. The only programmers who don't like it are those who don't understand the principles of memory management.
> By that definition, C++ code has garbage collection if it uses std::shared_ptr
That's right.
> going against widespread common usage of the term “garbage collected programming language” which specifically contrasts manual languages like C++ or Rust against garbage collected ones.
Since this contrast mostly exists in the minds of people who don't understand memory management, going against this common misconception is good. That's not to say that there aren't some interesting tradeoffs that often align with the colloquial perception, "garbage collection" isn't the interesting part. As you said, both C++ and Rust use GC; in fact, they use a GC somewhat similar to the one used by CPython.
This reminds me a bit of the way academics in programming language theory internalized the type-theoretic definition of the word “type” over and against the traditional programming definition. You sometimes see people who try to correct the term “dynamically typed language,” which makes perfect sense when types are data types, to “untyped” or “unityped,” which makes sense when types are mathematical constructs equivalent to proofs.
The colloquial term is clear in context, and it draws its boundaries in useful places. If academia prefers other boundaries to simplify its formal definitions, that’s understandable. But the rest of us shouldn’t restrict our language in that way.
It's not about restricting the language. It's that practising programmers often don't know a subject well enough, so they use different words to make distinctions that don't matter as much as they think (see "transpile"). "Dynamically typed" is actually not that big of an offence (because the distinction is real, it's just that the terminology is a bit muddled), and the people in PL theory who are bothered by this (most notably one person) are considered pedants even among their colleagues.
E.g. many practising programmers don't know that tracing moving collectors are used to avoid some of the high overheads associated with memory allocators (malloc/free), which are themselves big and complex beasts that make up substantial "runtimes" (another misused and misleading word).
I think GC's definition is pretty clear cut. How is counting references to determine when a lifetime ends materially different from another way of doing the same thing? Like there is even a paper that shows that one is tracking liveness, while the other tracks "deadness" and they are literally going at the same thing from different ends.
If anything, I often see a bias against tracing GCs from the people misusing the term, to "hype up" their choice of language that it must be better for not having (tracing) GC, when it usually just has ref counting which in many metrics is actually worse, given equal usage -- rust/cpp gets away from that because they only use it on a handful of objects, other lifetimes being driven by RAII, which is pretty much just compile-time decidable ref counting?
Right, and there are differences within tracing GCs that are just as big as between refcounting (and even manual malloc/free) and tracing. For example, Go uses tracing to determine when an object lifetime ends. But the moving collectors in Java, .NET, and V8 don't know and don't care when objects die, and they have no "free" operation at all. In many ways, the performance profile (of favouring smaller footprint or higher throughput) of memory management in C++, Rust, Python, and Go share more similarities among themselves than Java, .NET, V8, and Zig, which also share a more similar profile (arenas, like moving collectors, don't need or want to know when an object's lifetime ends).
Another distinction without a difference that is really just giving a name to a misconception is the notion of "a runtime". When I learnt C in the late 80s or early 90s, the book said something like, "C is not just the language, but a rich runtime". Indeed, modern malloc/free implementations mean that a C program ends up needing a larger and more elaborate runtime than a program in some educational language that uses a trivial implementation of a mark-and-sweep collector. Modern malloc/free allocators also sometimes come with an impressive set of tuning knobs. It's just that people who haven't had a lot of experience writing large programs in low-level languages don't know about them (or they just work to avoid allocations as much as possible, because that's what they've been told to do).
> Like there is even a paper that shows that one is tracking liveness, while the other tracks "deadness" and they are literally going at the same thing from different ends.
I think a lot of people just want to be able to discuss different areas of the automatic memory management design space separately, and maintaining the distinction between reference counting and garbage collection (meaning tracing GCs) lets them do that.
As for me personally, I consider refcounting and GC overlapping categories. I am perfectly willing to call CPython’s reference counting plus cycle collector a form of garbage collection, because it is transparent to the programmer. Every memory management technique has tradeoffs and pathological edge cases, but since you don’t have to consider them in the ordinary course of programming I’d say it counts. If you had to break cycles manually, or to annotate which references should be counted, I’d call that refcounting but not GC – as in the C++ stdlib.
By that definition even C has garbage collection. Automatic storage duration types have compiler-determined lifetime and automatic deallocation.
If the definition of a word/concept does not match how the word is used in real life, the definition is wrong. After all, semantics is about common understanding of concepts. If your definition of a word doesn't match how it's used, using that definition is not beneficial to use.
The Linux kernel has garbage collection, and not just the controversial refcount kind.
I'll go further. Linux heavily uses a form of garbage collection that cannot be implemented in typical userspace (without awkward & slower additions to the consistency algorithm).
Instead of "garbage collection", you can say "dynamic lifetime determination". If code does work at runtime to answer the question "is it safe to free this piece of memory?", that's dynamic lifetime determination, and is a property shared by both reference-counting and more sophisticated GC schemes.
I've always considered shared_ptr to be semi-garbage collection. Allows me to code C++ almost as if it were Java so long as circular references are avoided. I'm perfectly fine with it being considered a type of garbage collection.
> so long as circular references are avoided
And there's always weak_ptr if a cycle makes sense for some reason but you still want it to clean up correctly. Like having a child node point up to a parent or the root in a tree structure.