使用 Box 分配大型数组时，线程“<main>”堆栈溢出

Question

我正在实施 combsort. I'd like to create fixed-size array on the stack, but it shows stack overflow. When I change it to be on the heap (Rust by Example says to allocate in the heap we must use Box)，它仍然显示 stack overflow。

fn new_gap(gap: usize) -> usize {
    let ngap = ((gap as f64) / 1.3) as usize;
    if ngap == 9 || ngap == 10 {
        return 11;
    }
    if ngap < 1 {
        return 1;
    }
    return ngap;
}

fn comb_sort(a: &mut Box<[f64]>) {
    // previously: [f64]
    let xlen = a.len();
    let mut gap = xlen;
    let mut swapped: bool;
    let mut temp: f64;
    loop {
        swapped = false;
        gap = new_gap(gap);
        for i in 0..(xlen - gap) {
            if a[i] > a[i + gap] {
                swapped = true;
                temp = a[i];
                a[i] = a[i + gap];
                a[i + gap] = temp;
            }
        }
        if !(gap > 1 || swapped) {
            break;
        }
    }
}

const N: usize = 10000000;

fn main() {
    let mut arr: Box<[f64]> = Box::new([0.0; N]); // previously: [f64; N] = [0.0; N];
    for z in 0..(N) {
        arr[z] = (N - z) as f64;
    }
    comb_sort(&mut arr);
    for z in 1..(N) {
        if arr[z] < arr[z - 1] {
            print!("!")
        }
    }
}

输出：

thread '<main>' has overflowed its stack
Illegal instruction (core dumped)

或

thread 'main' has overflowed its stack
fatal runtime error: stack overflow

我知道我的stack size不够，和C++在函数内部创建一个非堆数组时太大，但是这段代码是用了heap但还是显示stack overflow。这段代码到底有什么问题？

Answer 1

据我所知，代码似乎仍在尝试先在堆栈上分配数组，然后再将其移入框中。

如果我像这样切换到 Vec<f64> 代替 Box<[f64]>，它对我有用：

fn new_gap(gap: usize) -> usize {
    let ngap = ((gap as f64) / 1.3) as usize;
    if ngap == 9 || ngap == 10 {
        return 11;
    }
    if ngap < 1 {
        return 1;
    }
    return ngap;
}

fn comb_sort(a: &mut [f64]) {
    // previously: [f64]
    let xlen = a.len();
    let mut gap = xlen;
    let mut swapped: bool;
    let mut temp: f64;
    loop {
        swapped = false;
        gap = new_gap(gap);
        for i in 0..(xlen - gap) {
            if a[i] > a[i + gap] {
                swapped = true;
                temp = a[i];
                a[i] = a[i + gap];
                a[i + gap] = temp;
            }
        }
        if !(gap > 1 || swapped) {
            break;
        }
    }
}

const N: usize = 10000000;

fn main() {
    let mut arr: Vec<f64> = std::iter::repeat(0.0).take(N).collect();
    //let mut arr: Box<[f64]> = Box::new([0.0; N]); // previously: [f64; N] = [0.0; N];
    for z in 0..(N) {
        arr[z] = (N - z) as f64;
    }
    comb_sort(arr.as_mut_slice());
    for z in 1..(N) {
        if arr[z] < arr[z - 1] {
            print!("!")
        }
    }
}

Answer 2

将来，box 语法将得到稳定。如果是，它将支持这种大分配，因为不需要对 Box::new 的函数调用，因此数组永远不会被放置在堆栈上。例如：

#![feature(box_syntax)]

fn main() {
    let v = box [0i32; 5_000_000];
    println!("{}", v[1_000_000])
}

使用 Box 分配大型数组时，线程“<main>”堆栈溢出

Thread '<main>' has overflowed its stack when allocating a large array using Box

heap-memory

dynamic-memory-allocation

rust