Back when I was a wee bit Java noob, I was trying to write a RuneScape bot to play Soul Wars. I had a basic recursive pathfinding algo for figuring out how to walk around the map, but it blew out of memory very quickly (each tile has 4 options, do that recursively, etc). So I added caching. Anyways, I never cleared the caching. So after 20 minutes of running the script, you had like 2GB of allocated RAM calculating the best path from any 2 tiles in the minigame.
Great times. No amount of language safety features would have saved me from that stupidity.
You don’t need unsafe. Just keep pushing to a vec and never remove anything. Memory leaks are more than lost memory allocations. You can even have them with rc/arc cycles
Yeah. Lot of people also use Ai generated code… so…
I have tested if clippy would warn me with a simple example (generates 6.7gb memory usage, be careful not to crash your computer if you add another 0…), while I watch with a system monitor (in KDE):
use std::thread;
use std::time;
fnmain() {
letmut vec = Vec::new(); // Create an empty Vector.fornumberin0..900000000 {
letbign: i64 = number * number;
vec.push(bign);
}
thread::sleep(time::Duration::from_secs(10));
}
I used the pedantic option of clippy and the only thing it complained was about the notation of the number…:
$ cargo clippy -- -W clippy::pedantic
warning: long literal lacking separators
--> src/main.rs:7:22
|
7 | for number in0..900000000 {
| ^^^^^^^^^ help: consider: `900_000_000`
|
= help:for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unreadable_literal
= note:`-W clippy::unreadable-literal` implied by `-W clippy::pedantic`
= help: to override `-W clippy::pedantic` add `#[allow(clippy::unreadable_literal)]`warning:`notright` (bin "notright") generated 1 warning
Finished`dev` profile [unoptimized + debuginfo] target(s) in0.00s
You can have a memory leak when items are still in scope in some loop or when you have a reference count cycle. The latter happens with the Rc/Arc types in rust.
An example for the former can be a web server that keeps track of every request it’s ever received in memory. You will eventually run out of memory. But you did not violate any memory rules (dangling pointer, etc.). Memory leaks can be caused by design issues.
That doesn’t fit the definition of memory leak in my mind, had thought a memory leak was specifically when the program completely loses track of memory
That’s one kind, and Rust’s “ownership” concept does mean there’s built-in compile time checks to prevent dangling pointers or unreachable memory. But there’s also just never de-allocating stuff you allocated even though it’s still reachable. Like you could just make a loop that allocates memory and never stops and that’s a memory leak, or more generally a “resource leak”, if you prefer.
Rust is really good at keeping you from having a reference to something that you think is valid but it turns out it got mutated way down in some class hierarchy and now it’s dead, so you have a null pointer or you double free, or whatever. But it can’t stop the case where your code is technically valid but the resource leak is caused by bad “logic” in your design, if that makes sense.
But muh Rust??
Rust doesn’t prevent memory leaks. You can do that in every language
Back when I was a wee bit Java noob, I was trying to write a RuneScape bot to play Soul Wars. I had a basic recursive pathfinding algo for figuring out how to walk around the map, but it blew out of memory very quickly (each tile has 4 options, do that recursively, etc). So I added caching. Anyways, I never cleared the caching. So after 20 minutes of running the script, you had like 2GB of allocated RAM calculating the best path from any 2 tiles in the minigame.
Great times. No amount of language safety features would have saved me from that stupidity.
Oops, banned for botting
Especially if you have to use unsafe libraries from C, or use any unsafe block at all to do low level programming or for performance.
You don’t need unsafe. Just keep pushing to a vec and never remove anything. Memory leaks are more than lost memory allocations. You can even have them with rc/arc cycles
Yeah. Lot of people also use Ai generated code… so…
I have tested if clippy would warn me with a simple example (generates 6.7gb memory usage, be careful not to crash your computer if you add another 0…), while I watch with a system monitor (in KDE):
use std::thread; use std::time; fn main() { let mut vec = Vec::new(); // Create an empty Vector. for number in 0..900000000 { let bign: i64 = number * number; vec.push(bign); } thread::sleep(time::Duration::from_secs(10)); }I used the pedantic option of clippy and the only thing it complained was about the notation of the number…:
$ cargo clippy -- -W clippy::pedantic warning: long literal lacking separators --> src/main.rs:7:22 | 7 | for number in 0..900000000 { | ^^^^^^^^^ help: consider: `900_000_000` | = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unreadable_literal = note: `-W clippy::unreadable-literal` implied by `-W clippy::pedantic` = help: to override `-W clippy::pedantic` add `#[allow(clippy::unreadable_literal)]` warning: `notright` (bin "notright") generated 1 warning Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00sSurely that’s not a memory leak, that’s just the program using a lot of memory intentionally
Thought the whole point was that it forced you to handle memory properly and automatically released things when they go out of scope
What kind of situation can cause a memory leak in rust
You can have a memory leak when items are still in scope in some loop or when you have a reference count cycle. The latter happens with the Rc/Arc types in rust.
An example for the former can be a web server that keeps track of every request it’s ever received in memory. You will eventually run out of memory. But you did not violate any memory rules (dangling pointer, etc.). Memory leaks can be caused by design issues.
That doesn’t fit the definition of memory leak in my mind, had thought a memory leak was specifically when the program completely loses track of memory
That’s one kind, and Rust’s “ownership” concept does mean there’s built-in compile time checks to prevent dangling pointers or unreachable memory. But there’s also just never de-allocating stuff you allocated even though it’s still reachable. Like you could just make a loop that allocates memory and never stops and that’s a memory leak, or more generally a “resource leak”, if you prefer.
Rust is really good at keeping you from having a reference to something that you think is valid but it turns out it got mutated way down in some class hierarchy and now it’s dead, so you have a null pointer or you double free, or whatever. But it can’t stop the case where your code is technically valid but the resource leak is caused by bad “logic” in your design, if that makes sense.