并行更改二维向量

如何解决并行更改二维向量

我正在尝试使用crossbeam_utils版本0.8.0在二维矢量（图形）的每个位置设置值1。每个线程接收的子矩阵是不相交的。我在Windows上使用cargo run运行代码。我的代码基于这些question1和question2。但是，出现以下错误：

thread '<unnamed>' panicked at 'index out of bounds: the len is 3 but the index is 3'

但是，如果我在产生的线程中注释命令(*slice)[row][col] = 1，则可以看到线程在控制台中打印时工作正常。

什么原因导致此错误？

use crossbeam_utils::thread;
use std::slice;

const NTHREADS: usize = 2;

fn build_graph() -> Vec<Vec<usize>> {

    let dictionary: Vec<String> = vec!["monk".to_string(),"mock".to_string(),"pock".to_string(),"pork".to_string(),"perk".to_string(),"perl".to_string()];
    let s_graph = dictionary.len();
    let mut graph: Vec<Vec<usize>> = vec![vec![0; s_graph]; s_graph];
    
    let chunk = f32::ceil(s_graph as f32 / NTHREADS as f32) as usize;
    let mut sliced_graph: Vec<&mut [Vec<usize>]> = Vec::with_capacity(NTHREADS);
    let ptr_graph = graph.as_mut_ptr();

    let mut offset;
    let mut count_of_items;
    
    // Creating mutable references for slices of the matrix
    for n_th in 0..NTHREADS {
        offset = n_th * chunk;
        count_of_items = if offset + chunk > s_graph { s_graph - offset } else { chunk };
        unsafe {
            sliced_graph.push(slice::from_raw_parts_mut(ptr_graph.offset((offset) as isize),count_of_items));
        }
    }

    thread::scope(|scope| {

        let mut n_th: usize = 0;
        let mut min_bound;
        let mut max_bound;

        for slice in &mut sliced_graph {
            
            min_bound = n_th * chunk;
            max_bound = if min_bound + chunk > s_graph { s_graph } else { min_bound + chunk};

            scope.spawn(move |_| {

                println!("thread number: {} - ini: {} - end: {}",n_th,min_bound,max_bound);

                for row in min_bound..max_bound {

                    for col in 0..s_graph {

                        println!("th:{} -->> set row:{} col:{}",row,col);
                        (*slice)[row][col] = 1;
                    }
                }

                println!("thread number: {} - Finished!",n_th);
            });

            n_th += 1;
        }
    }).unwrap();

    graph
} 

fn main() {
    build_graph();
}

解决方法

@Masklinn提出的解决方案：

use crossbeam_utils::thread;
use std::slice;

const NTHREADS: usize = 2;

fn build_graph() -> Vec<Vec<usize>> {

    let dictionary: Vec<String> = vec!["monk".to_string(),"mock".to_string(),"pock".to_string(),"pork".to_string(),"perk".to_string(),"perl".to_string()];
    let s_graph = dictionary.len();
    let mut graph: Vec<Vec<usize>> = vec![vec![0; s_graph]; s_graph];
    
    let chunk = f32::ceil(s_graph as f32 / NTHREADS as f32) as usize;
    let mut sliced_graph: Vec<&mut [Vec<usize>]> = Vec::with_capacity(NTHREADS);
    let ptr_graph = graph.as_mut_ptr();

    // Creating mutable references for slices of the matrix
    for n_th in 0..NTHREADS {
        let offset = n_th * chunk;
        let count_of_items = if offset + chunk > s_graph { s_graph - offset } else { chunk };
        unsafe {
            sliced_graph.push(slice::from_raw_parts_mut(ptr_graph.offset((offset) as isize),count_of_items));
        }
    }

    thread::scope(|scope| {
        for (n_th,slice) in sliced_graph.iter_mut().enumerate() {
            scope.spawn(move |_| {
                println!("thread number: {} - {:?}",n_th,slice);
                for (row,r) in slice.into_iter().enumerate() {
                    for (col,cell) in r.into_iter().enumerate() {
                        println!("th:{} -->> set row:{} col:{}",row,col);
                        *cell = 1;
                    }
                }

                println!("thread number: {} - Finished!",n_th);
            });
        }
    }).unwrap();
    graph
} 

fn main() {
    build_graph();
}