I've always thought that one of the biggest tiny mistakes in the history of this industry. It means, more or less, that you're forcing the memory allocator to keep track of these sizes when it shouldn't have to. There's virtually no sensible case where the person calling free() doesn't know the size of the allocation, so now we're keeping that book-keeping twice, in "user-space" and inside the memory allocator. Like, think about the cases when you'd call malloc:
* For allocating a single object of type T, the size is just `sizeof(T)`, so you can just pass that to free()
* For allocating an array of objects, the size is `count
* sizeof(T)`, and I can't think of a single time where you DON'T know what `count` is. It's either statically sized (in which case it's just a constant), or if you have a dynamically growing array, you need to keep track of the reserved space to know when you reallocate. If nothing else, you need it for bounds-checking.
* For chunks of raw memory, you also presumably know when deallocating what the size of the raw memory you allocated is, for the same reasons as the previous point. Like, just having a raw char* pointer lying around with no size information is just terrible C practice.
If you truly don't know the size of your allocation (very hard to imagine when this would ever happen), you should be forced on the user-side to keep track of it somehow, not delegate that to the allocator.
It's a tiny amount of overhead, but it's for EVERY SINGLE MEMORY ALLOCATION since like 1975. Imagine how many times malloc() and free() has called since then! How much electricity, CPU usage, and memory has been wasted! It boggles the mind!
I tried using TCMalloc with rustc, and it segfaulted. Rust knows the sizes of its allocations, but things can still go wrong at the allocator boundary.
Size should be an optimization hint, not a correctness requirement. Otherwise, it's just another security pitfall
Also 'arena allocators' (this meant something different like 20 years ago so I think the name just got rebranded) are not that good, they make some things easier and improve performance sometimes, they also are liable to use more memory and cause more fragmentation if not used with care. That is one of the many reasons why we slowly evolved away from the old linear allocators, but also because we just wanted a simple and flexible interface to hide complexity.
It's amazing that a method like the Bump Allocator was already tried.
How were the senior programmers able to do all of this? I'm just amazed.
> How were the senior programmers able to do all of this? I'm just amazed.
Secondly the systems in that time where less complex meaning it was easier to understand and experiment with fundamental parts of the computer.
Lastly at that time "programming" was closer to the metal so a average computer scientist at that time would likely have more knowledge of the deep internals compared to an average programmer today.
> C seems like a language that is simple but can really do a lot
most people open an ide and start coding, or write some basic diagrams to get an overview/mental model. Back in the day any bitnlarge program would take hours to compile so really u did not want to have any bug or typo just to sit for hours until a compile error or logic mistake. Take it even further back to days before C and that is even more needed.
a lot of high level modern languages seem to alleviate that need, likely so that enterprise software can be written a bit faster because the features need to arrive faster.
still in more modern languages i'd recommend starting with pencil and paper, write most of it if not the whole thing out. u'll find much nicer patterns and will save yourself a bunch of refactoring. even for small programs.
The old saying "Necessity is the mother of invention" applies. Smart people + system constraints => ingenuity.