C++’s shared pointer has the same problem; Rust avoids it by having two types (Rc and Arc) that the developer can select from (and which the compiler will prevent you from using unsafely).
It doesn't. C++'s shared pointers use atomics, just like Rust's Arc does. There's no good reason (unless you have some very exotic requirements, into which I won't get into here) to implement shared pointers with mutexes. The implementation in the blog post here is just suboptimal.
(But it's true that C++ doesn't have Rust's equivalent of Rc, which means that if you just need a reference counted pointer then using std::shared_ptr is not a zero cost abstraction.)
I'd be interested to know what you are thinking.
The primary exotic thing I can imagine is an architecture lacking the ability to do atomic operations. But even in that case, C11 has atomic operations [1] built in. So worst case, the C library for the target architecture would likely boil down to mutex operations.
I'd much rather it didnt try to be zero-cost and it always used atomics...
(for reference, the person above is referring to what's described here: https://snf.github.io/2019/02/13/shared-ptr-optimization/)
Sure, cross-platform is desirable, if there's no cost involved, and mandatory if you actually need it, but it's a "nice to have" most of the time, not a "needs this".
As for mutex overheads, yep, that's annoying, but really, how annoying ? Modern CPUs are fast. Very very fast. Personally I'm far more likely to use an os_unfair_lock_t than a pthread_mutex_t (see the previous point) which minimizes the locking to a memory barrier, but even if locking were slow, I think I'd prefer safe.
Rust is, I'm sure, great. It's not something I'm personally interested in getting involved with, but it's not necessary for C (or even this extra header) to do everything that Rust can do, for it to be an improvement on what is available.
There's simply too much out there written in C to say "just use Rust, or Swift, or ..." - too many libraries, too many resources, too many tutorials, etc. You pays your money and takes your choice.
> We love its raw speed, its direct connection to the metal
If this is a strong motivating factor (versus, say, refactoring risk), then C’s lack of safe zero-cost abstractions is a valid concern.
For this use-case, you might not notice. ISTR, when examing the pthreads source code for some platform, that mutexes only do a context switch as a fallback, if the lock cannot be acquired.
So, for most use-cases of this header, you should not see any performance impact. You'll see some bloat, to be sure.
There really isn't. Speaking as someone who works in JVM-land, you really can avoid C all the time if you're willing to actually try.
It's an implementation detail. They could have used atomic load/store (since c11) to implement the increment/decrement.
TBH I'm not sure what a mutex buys you in this situation (reference counting)
Do you have a source for this? I couldn't find the implementation in TFA nor a link to safe_c.h
// The old way of manual reference counting
typedef struct {
MatchStore* store;
int ref_count;
pthread_mutex_t mutex;
} SharedStore;In any case, you could use the provided primitives to wrap the C11 mutex, or any other mutex.
With some clever #ifdef, you can probably have a single or multithreaded build switch at compile time which makes all the mutex stuff do nothing.
BTW don’t fight C for portability, it is unlikely you will win.
This is beautiful!
People really need to stop acting like a garbage collector is some sort of cosmic horror that automatically takes you back to 1980s performance or something. The cases where they are unsuitable are a minority, and a rather small one at that. If you happen to live in that minority, great, but it'd be helpful if those of you in that minority would speak as if you are in the small minority and not propagate the crazy idea that garbage collection comes with massive "performance penalties" unconditionally. They come with conditions, and rather tight conditions nowadays.
A CLI tool (which most POSIX tools are) would pick throughput over latency any time.
The real problems start when you need to manage memory lifetimes across the whole program, not locally. Can you return `UniquePtr` from a function? Can you store a copy of `SharedPtr` somewhere without accidentally forgetting to increment the refcount? Who is responsible for managing the lifetimes of elements in intrusive linked lists? How do you know whether a method consumes a pointer argument or stores a copy to it somewhere?
I appreciate trying to write safer software, but we've always told people `#define xfree(p) do { free(p); p = NULL; } while (0)` is a bad pattern, and this post really feels like more of the same thing.
Yes: you can return structures by value in C (and also pass them by value).
> Can you store a copy of `SharedPtr` somewhere without accidentally forgetting to increment the refcount?
No, this you can't do.
Have we? Why?
C23 didn't introduce it, it's still a GCC extension that needs to be spelled as [[gnu::cleanup()]] https://godbolt.org/z/Gsz9hs7TE
https://en.cppreference.com/w/c/language/attributes.html
https://en.cppreference.com/w/cpp/language/attributes.html
https://gcc.gnu.org/onlinedocs/gcc/Attributes.html
https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attribute...
https://thephd.dev/_vendor/future_cxx/technical%20specificat...
Discussion:
https://thephd.dev/_vendor/future_cxx/papers/C%20-%20Improve...
This is cute, but also I'm baffled as to why you would want to use macros to emulate c++. Nothing is stopping you from writing c-like c++ if that's what you like style wise.
Though yes, you should probably just write C-like C++ at that point, and the result sum types used made me chuckle in that regard because they were added with C++17. This person REALLY wants modern CPP features..
I like the power of destructors (auto cleanup) and templates (generic containers). But I also want a language that I can parse. Like, at all.
C is pretty easy to parse. Quite a few annoying corner cases, some context sensitive stuff, but still pretty workable. C++ on the other hand? It’s mostly pick a frontend or the highway.
C’s simplicity can be frustrating, but it’s an extremely hackable language thanks to that simplicity. Once you opt in to C++, even nominally, you lose that.
(Agree on your other points for what it's worth.)
It's choosing which features are allowed in.
[1] https://doc.rust-lang.org/beta/rustc/platform-support.html
Quite frankly I'm not sure why you wouldn't given that most are using GCC on common architectures. The chip vendor doesn't have to do any work unless they are working on an obscure architecture.
You'll just have to get used to the C++ community screaming at you that it's the wrong way to write C++ and that you should just use Go or Zig instead
A global constraint handler is still by far better than dynamic env handlers, and most of the existing libc/POSIX design failures.
You can disable this global constraint handler btw.
Macros are simply a fact of life in any decent-sized C codebase. The Linux kernel has some good guidance to try to keep it from getting out of hand but it is just something you have to learn to deal with.
Discussed here https://news.ycombinator.com/item?id=22191790
Nim is a language that compiles to C. So it is similar in principle to the "safe_c.h". We get power and speed of C, but in a safe and convenient language.
> It's finally, but for C
Nim has `finally` and `defer` statement that runs code at the end of scope, even if you raise.
> memory that automatically cleans itself up
Nim has ARC[1]:
"ARC is fully deterministic - the compiler automatically injects destructors when it deems that some variable is no longer needed. In this sense, it’s similar to C++ with its destructors (RAII)"
> automated reference counting
See above
> a type-safe, auto-growing vector.
Nim has sequences that are dynamically sized, type and bounds safe
> zero-cost, non-owning views
Nim has openarray, that is also "just a pointer and a length", unfortunately it's usage is limited to parameters. But there is also an experimental view types feature[2]
> explicit, type-safe result
Nim has `Option[T]`[3] in standard library
> self-documenting contracts (requires and ensures)
Nim's assert returns message on raise: `assert(foo > 0, "Foo must be positive")`
> safe, bounds-checked operations
Nim has bounds-checking enabled by default (can be disabled)
> The UNLIKELY() macro tells the compiler which branches are cold, adding zero overhead in hot paths.
Nim has likely / unlikely template[4]
------------------------------------------------------------
[1] https://nim-lang.org/blog/2020/10/15/introduction-to-arc-orc...
[2] https://nim-lang.org/docs/manual_experimental.html#view-type...
You can do cleanup handling that integrates with your exception handling library by using pairs of macros inspired by the POSIX pthread_cleanup_push stuff.
#define cleanup_push(fn, type, ptr, init) { \
cleanup_node_t node; \
type ptr = init; do cleanup_push_api(&node, fn, ptr) while (0)
#define cleanup_pop(ptr) cleanup_pop_api(ptr) \
}
The cleanup_pop_api call removes the top node, doing a sanity check that the ptr in the node is the same as ptr. It calls fn(ptr).
The fact that cleanup_push leaves an open curly brace closed by cleanup_pop catches some balancing errors at compile time.
The POSIX pthread_cleanup_pop has an extra boolean parameter indicating whether to do the cleanup call or not. That's sometimes useful when the cleanup is only something done in the case of an abort. E.g. suppose tha the "cleanup" routine is rollback_database_transaction. We don't want that in the happy case; in the happy case we call commit_database_transaction.
But if you can stay out of MSVC world, awesome! You can do so much with a few preprocessor blocks in a header
Github has several repositories named cgrep, but the first results are written in other languages than C (Haskell, Python, Typescript, Java, etc).
For the first item on reference counting, batched memory management is a possible alternative that still fits the C style. The use of something like an arena allocator approximates a memory lifetime, which can be a powerful safety tool. When you free the allocator, all pages are freed at once. Not only is this less error prone, but it can decrease performance. There’s no need to allocate and free each reference counted pointer, nor store reference counts, when one can free the entire allocator after argument parsing is done.
This also decreases fallible error handling: The callee doesn’t need to free anything because the allocator is owned by the caller.
Of course, the use of allocators does not make sense in every setting, but for common lifetimes such as: once per frame, the length of a specific algorithm, or even application scope, it’s an awesome tool!
I don't see it that way, mostly because ADTs don't require automatic destructors or GC, etc, but also because I never considered a unique/shared pointer type to be an abstract data type
> When you free the allocator, all pages are freed at once. Not only is this less error prone, but it can decrease performance.
How does it decrease performance? My experience with arenas is that they increase performance at the cost of a little extra memory usage.
ack, thanks! You’re exactly right, I got my words mixed up.
https://herbsutter.com/2012/05/03/reader-qa-what-about-vc-an...
https://devblogs.microsoft.com/cppblog/c11-atomics-in-visual...
https://learn.microsoft.com/en-us/cpp/c-runtime-library/comp...
And the new guidelines regarding the use of unsafe languages at Microsoft, I wouldn't bet waiting that it will ever happen, even after 2040.
https://azure.microsoft.com/en-us/blog/microsoft-azure-secur...
https://blogs.windows.com/windowsexperience/2024/11/19/windo...
The benefit of these types is that they're a pair of pointer+size, instead of just a bare pointer without a known size.
In fact I don't see anything here from Rust that isn't also in C++. They talk about Result and say "Inspired by Rust, Result forces you to handle errors explicitly by returning a type that is either a success value or an error value", but actually, unlike Rust, nothing enforces that you don't just incorrectly use value without checking status first.
It's just some macros the author likes. And strangely presented—why are the LIKELY/UNLIKELY macros thrown in with the CLEANUP one in that first code snippet? That non sequitur is part of what gives me an LLM-written vibe.
> In cgrep, parsing command-line options the old way is a breeding ground for CVEs and its bestiary. You have to remember to free the memory on every single exit path, difficult for the undisciplined.
No, no, no. Command line options that will exist the entire lifetime of the program are the quintessential case for not ever calling free() on them because it's a waste of time. There is absolutely no reason to spend processor cycles to carefully call free() on a bunch of individual resources when the program is about to exit and the OS will reclaim the entire process memory in one go much faster than your program can. You're creating complexity and making your program slower and there is literally no upside: this isn't a tradeoff, it's a bad practice.
Pros: preallocating one arena is likely faster than many smaller allocations.
Cons: preallocation is most effective if you can accurately predict usage for the arena; if you can't, then you either overshoot and allocate more memory than you need, or undershoot and have to reallocate which might be less performant than just allocating as-needed.
In short, if you're preallocating, I think decisions need to be made based on performance testing and the requirements of your program (is memory usage more important than speed?). If you aren't preallocating and just using arenas for to free in a group, then I'm going to say using an arena for stuff that is going to be freed by the OS at program exit is adding complexity for no benefit--it depends on your arena implementation (arenas aren't in the C standard to my knowledge).
In general, I'd be erring on the side of simplicity here and not using arenas for this by default--I'd only consider adding arenas if performance testing shows the program spending a lot of time in individual allocations. So I don't think a blanket recommendation for arenas is a good idea here.
EDIT: In case it's not obvious: note that I'm assuming that the reason you want to use an arena is to preallocate. If you're thinking that you're going to call free on the arena on program exit, that's just as pointless as calling free on a bunch of individual allocations on program exit. It MIGHT be faster, but doing pointless things faster is still not as good as not doing pointless things.
(These features are still essentially unsafe: the unique pointer implementation still permits UAF, for example, because nothing prevents another thread from holding the pointer and failing to observe that it has been freed.)
Like, if I was stuck in a C codebase today, [[cleanup]] is great -- I've used this in the past in a C-only shop. But vectors, unique_ptrs, and (awful) shared_ptrs? Just use C++.
// The Old Way (don't do this)
char* include_pattern = NULL;
if (optarg) {
include_pattern = strdup(optarg);
}
// ...200 lines later...
if (some_error) {
if (include_pattern) free(include_pattern); // Did I free it? Did I??
return 1;
// ...200 lines later...
// common return block
out:
free(include_pattern); // free(NULL) allowed since before 1989 ANSI C
return result;Given how simple examples in this blog post are, I ask myself, why don't we already have something like that as a part of the standard instead of a bunch of one-off personal, bug-ridden implementations?
It's just, I'd rather play with my own toys instead of using someone else's toy. Especially since I don't think it would ever grow up to be something more than a toy.
For serious work, I'd use some widely used, well-maintained, and battle-tested library instead of my or someone else's toy.
If you need to cleanup stuff on early return paths, use goto.. Its nothing wrong with it, jump to end when you do all the cleanup and return. Temporary buffers? if they arent big, dont be afraid to use static char buf[64]; No need to waste time for malloc() and free. They are big? preallocate early and reallocate or work on chunk sizes. Simple and effective.
My thoughts as well. The only thing I would be willing to use is the macro definition for __attribute__, but that is trivial. I use C, because I want manual memory handling, if I wouldn't want that I would use another language. And now I don't make copies when I want to have read access to some things, that is simply not at a problem. You simply pass non-owning pointers around.
In a function? That makes the function not-threadsafe and the function itself stateful. There are places, where you want this, but I would refrain from doing that in the general case.
Just don't use C for sending astronauts in space. Simple.
C wasn't designed to be safe, it was designed so you don't have to write in assembly.
Just a quick look through this and it just shows one thing: someone else's walled garden of hell.
But do use C to control nuclear reactors https://list.cea.fr/en/page/frama-c/
It's a lot easier to catch errors of omission in C than it is to catch unintended implicit behavior in C++.
Last time I checked, even SpaceX uses C to send astronauts to space...