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multithreading-如何在Rust中为不同的线程克隆随机数生成器?

(multithreading - How can I clone a Random Number Generator for different threads in Rust?)

发布于 2020-11-28 18:20:40

我正在研究基于C ++代码库(如果有人熟悉的话,请使用PBRT)的Ray Tracer的Rust实现。C ++版本定义的类之一是一系列采样器,以减少渲染图像中的噪声。在渲染过程中,每当需要随机数时,都会将此采样器克隆到每个渲染线程中。这就是我选择在Rust中进行操作的方式,我承认这有点令人费解:

#[derive(Clone)]
pub struct PixelSampler {
    samples_1d: Vec<Vec<f64>>,
    samples_2d: Vec<Vec<Point2<f64>>>,
    current_1d_dimension: i32,
    current_2d_dimension: i32,
    rng: rngs::ThreadRng
}
pub enum Samplers {
    StratifiedSampler {x_samples: i64, y_samples: i64, jitter_samples: bool, pixel: PixelSampler },
    ZeroTwoSequenceSampler { pixel: PixelSampler }
}

impl Clone for Samplers {
    fn clone(&self) -> Self {
        match self {
            Samplers::StratifiedSampler { x_samples, y_samples, jitter_samples, pixel } => { 
                Samplers::StratifiedSampler {x_samples: *x_samples,
                                             y_samples: *y_samples,
                                             jitter_samples: *jitter_samples,
                                             pixel: pixel.clone() }
             }
            Samplers::ZeroTwoSequenceSampler { pixel } => { Samplers::ZeroTwoSequenceSampler{ pixel: pixel.clone() } }
        }
    }
}

然后我也有一个Integrator具有Samplers变体字段的。在主渲染循环中,我为每个线程运行以下循环:

for _ in 0..NUM_THREADS {
    let int_clone = integrator.clone(); // integrator just contains a Samplers
    thread_vec.push(thread::spawn(move || {
        loop {
            // do main rendering loop
        }
    }));
}

但是当我用这个编译时,我得到了错误:

“该特性std::marker::Send未实现std::ptr::NonNull<rand::rngs::adapter::reseeding::ReseedingRng<rand_chacha::chacha::ChaCha20Core, rand_core::os::OsRng>>”。

我的理解是,因为我只将克隆的版本移到线程中,Send所以不需要实现我究竟做错了什么?

Questioner
Calvin Godfrey
Viewed
11
user4815162342 2020-11-29 03:40:22

thread_rng()文档所述,它是:

基本上只是对线程本地内存中的PRNG的引用。

因此,通过克隆“ rng”,你不会复制带有状态的生成器(我认为这是你的意图),但是创建了线程本地RNG的新句柄。此句柄不是故意的,Send因为它无需锁定即可访问线程本地RNG,以提高效率。

如果要让结构包含实际的RNG,并克隆该结构以复制它,则可以使用该StdRng类型,这是当前推荐的高效RNG。要实例化它,请使用特征中的方法SeedableRng例如:

#[derive(Clone)]
pub struct PixelSampler {
    samples_1d: Vec<Vec<f64>>,
    samples_2d: Vec<Vec<Point2<f64>>>,
    current_1d_dimension: i32,
    current_2d_dimension: i32,
    rng: StdRng,
}
// ...

let sampler = Samplers::ZeroTwoSequenceSampler {
    pixel: PixelSampler {
        samples_1d: vec![],
        samples_2d: vec![],
        current_1d_dimension: 0,
        current_2d_dimension: 0,
        rng: SeedableRng::from_entropy(),
    },
};
// compiles because SeedableRng is Send
std::thread::spawn(move || sampler).join().unwrap();

操场上的完整例子