[YogurtFiend]

I don't know why you're being downvoted. Memory reclamation is hard in the face of parallelism. It's much easier to design lock-free algorithms in languages with a garbage collector, because memory reclamation issues are taken care of for you (and often times in a batched manner, which won't affect the hot path of your code). There _are_ techniques to avoid using a garbage collector: atomic reference counting, epoch-based reclaimation, hazard points, and more. But they can be quite difficult to implement and difficult to use.

[mcguire]

Rust's Arc is an atomic reference counter. But, as the article describes, those aren't free.

[duped]

One could argue that using a GC for reclamation isn't lock-free if it's not a concurrent GC.

[hayley-patton]

There are very few GCs that are actually lock-free. While uncooperative mutators cannot block other mutators in an on-the-fly collector, for example, the collector is blocked until all mutators cooperate. Nonetheless I'd guess that a sufficiently concurrent collector is good enough.

[quotemstr]

Right. Plus GCs can compact memory, which we can't do with manual memory management. I don't understand why people fetishize manual memory management --- do you want to spend your short time on Earth twiddling references?

[titzer]

After 28 years of programming in C and 25 years programming in C++ (on and off), I am sick to death of managing memory. Programmers can't do it right or well. Let the super-intelligent idiot savant with billions of cycles of computation per second and trillions of bits of storage do the thinking for me.

Personally I glad the world is moving away from unsafe manual memory management in C++, be that with better RAII and managed pointers, Rust's type system, etc. But those things are still breakable and IMHO, ultimately a big waste of people's time. If Rust's lifetime annotations could be inferred by a compiler, then by all means. But if they can't, just GC already. All that extra thinking pushes people to think about the wrong things and designs end up ossified, difficult to refactor because of the extra overhead of radically changing ownership. Forget it already! Let computers figure out the whole memory management problem.

Want your program to go fast? Don't allocate a bunch of garbage. Redesign it to reuse data structures carefully. Don't burden yourself forever twiddling with managing the large and small alike, obsessing over every dang byte.

[rstuart4133]

> Let the super-intelligent idiot savant with billions of cycles of computation per second and trillions of bits of storage do the thinking for me.

Unfortunately, it can't. To be fair, GC does management memory very well, but there is more to memory than handling allocation.

It becomes immediately obvious when you compare Go to Rust. Go strives for simplicity. Compare Go and Rust code, and Rust's overhead for making memory handling safe (type annotations, the type system exploding because it carries information about so many types of ownership) make it horribly complex compared to Go. Go code expresses the same concepts in far fewer tokens, and just as memory safe as the Rust code - provided there is only one thread.

Add a second thread, and the Rust code will continue to work as before. The Go code - well the GC does manages memory allocation only, it does _not_ arbitrate how multiple threads access those objects. Screw up how multiple Go threads access that nice GC managed memory and undefined and non-deterministic behaviour is inevitable result. That IMO is the _worst_ type of bug. Most of the overhead Rust imposes (like ownership) has very little to do with managing memory lifetimes. It is about preventing two threads form stomping on each other. Managing memory lifetimes just comes for free.

I suspect the rise and rise of Rust is mostly due it's concurrency guarantees. Go back a couple of decades and when multiple CPU's were almost non-existent and I suspect the complexity Rust imposes would have been laughed out of the room, given all it really gave you was an very complex alternative to GC - which is what you are effectively saying is all it provides. Nowadays we have $1 computers with multiple ARM cores in a disposable CVOID testing kit. Once you've been hit a couple of times by a currency heisenbug taking out your products in the field, you are screaming out for some tool to save your arse. Rust is one such tool.

[titzer]

Yeah, I recognize that ownership helps with concurrency, and TBH most of the code I write isn't highly concurrent, especially at a fine-grained level. Nevertheless, I think all that ownership is going overboard to solve what is in effect a niche problem. (After all, 30 years ago, engineers at Sun architected the Solaris kernel with very carefully designed fine-grained locking with little more than C. "Solaris Internals" is still highly recommended.).

There are a lot of other strategies for writing concurrent systems, like, for example, making most data immutable, coarse-grained sharing, shared-nothing multi-process architectures like actors, using race detectors and/or thread sanitizers, using good concurrent libraries (with lock-free hashtables and other datastructures).

The difference between the number of concurrency bugs causing catastrophic failure and all other kinds of bugs causing catastrophic failure has gotta be at least 100 or maybe 1000 to 1. So forcing everyone to think about ownership because maybe they are writing concurrent code (then again maybe they aren't) so that "congrats your memory management problems are solved" seems like a Pyrrhic victory--you've already blown their brain cells on the wrong problem. Worse, you've forced them to bake ownership into the seams in every part of the system, making it more difficult to refactor and evolve that system in the future. [1]

> Screw up how multiple Go threads access that nice GC managed memory and undefined and non-deterministic behaviour is inevitable result.

You get race conditions, you don't get undefined behavior (nasal daemons). Go and Java have memory models that at least your program doesn't violate the source type system and you don't get out-of-thin air results. You get tearing and deadlocks and race conditions, not undefined behavior. At Google we used TSAN extensively in Chrome and V8 and similar tools exist for Java, and I assume so as well for Go.

It's a broader conversation, but I don't think advocating that everyone write highly concurrent programs with shared mutable state, no matter what tools they have at their disposal, is pushing in the right direction. Erlang, Actors, sharing less, immutable data, and finding better higher level parallel programming constructs should be what we focus our and other's precious brain cycles on, not getting slapped around by a borrower checker or thread sanitizer. We gotta climb out of this muck one of these decades.

[1] If you are instead saying that people should think about the design of their system from the beginning so that they don't have to refactor as much, then I agree; but just don't waste time thinking about ownership, or worse, architecting ownership into the system; it will alter the design.

[nyanpasu64]

> So forcing everyone to think about ownership because maybe they are writing concurrent code (then again maybe they aren't) so that "congrats your memory management problems are solved" seems like a Pyrrhic victory--you've already blown their brain cells on the wrong problem.

https://manishearth.github.io/blog/2015/05/17/the-problem-wi... argues that "[a]liasing with mutability in a sufficiently complex, single-threaded program is effectively the same thing as accessing data shared across multiple threads without a lock". This is especially true in Qt apps which launch nested event loops, which can do anything and mutate data behind your back, and C++ turns it into use-after-free UB and crashing (https://github.com/Nheko-Reborn/nheko/issues/656, https://github.com/Nheko-Reborn/nheko/commit/570d00b000bd558...). I find Rust code easier to reason about than C++, since I know that unrelated function calls will never modify the target of a &mut T, and can only change the target of a &T if T has interior mutability.

Nonetheless the increased complexity of Rust is a definite downside for simple/CRUD application code.

On the other hand, when a programmer does write concurrent code with shared mutability (in any language), in my experience, the only way they'll write correct and understandable code is if they've either learned Rust, or were tutored by someone at the skill level of a Solaris kernel architect. And learning Rust is infinitely more scalable.

Rust taught me to make concurrency tractable in C++. In Rust, it's standard practice to designate each piece of data as single-threaded, shared but immutable, atomic, or protected by a mutex, and separate single-threaded data and shared data into separate structs. The average C++ programmer who hasn't studied Rust (eg. the developers behind FamiTracker, BambooTracker, RtAudio, and RSS Guard) will write wrong and incomprehensible threading code which mixes atomic fields, data-raced fields, and accessing fields while holding a mutex, sometimes only holding a mutex on the writer but not reader, sometimes switching back and forth between these modes ad-hoc. Sometimes it only races on integer/flag fields and works most of the time on x86 (FamiTracker, BambooTracker, RtAudio), and sometimes it crashes due to a data race on collections (https://github.com/martinrotter/rssguard/issues/362).

[ghusbands]

Though I can't find it right now, there was a recent paper that did do some effective copying/compaction under a normal malloc/free regime. It did so by noting that once two pages were getting somewhat empty, and the allocations within them wouldn't then overlap, it could use virtual memory to put them in the same physical page. I believe it claimed effective results, though I cannot recall the scale.