如何更好地存储字符串以避免出现多次克隆? [英] How can I better store a string to avoid many clones?

问题描述

我正在使用 tokio 的 UdpCodec 特性:

I am using tokio's UdpCodec trait:

pub trait UdpCodec {
    type In;
    type Out;
    fn decode(&mut self, src: &SocketAddr, buf: &[u8]) -> Result<Self::In>;
    fn encode(&mut self, msg: Self::Out, buf: &mut Vec<u8>) -> SocketAddr;
}

我的 In 关联类型是 (SocketAddr, Vec).Metric 定义为:

My associated type for In is a (SocketAddr, Vec<Metric>). Metric is defined as:

#[derive(Debug, PartialEq)]
pub struct Metric {
    pub name: String,
    pub value: f64,
    pub metric_type: MetricType,
    pub sample_rate: Option<f64>,
}

我使用了拥有的字符串来避免关联类型的生命周期限制.但是，我也使用这些指标名称进行 HashMap 查找和插入，这涉及大量克隆，因为我在其他函数中借用了指标.

I have used owned strings to avoid lifetime constraints with the associated types. However I also do HashMap lookups and inserts with these metric names which involves a lot of cloning since I borrow metrics in other functions.

如何更好地在此 Metric 类型中存储字符串以避免许多低效克隆?使用 Cow 类型已经让我想到了，但它显然也有终身关联.

How can I better store a string within this Metric type to avoid many inefficient clones? Using the Cow type has crossed my mind but it also obviously has a lifetime association.

推荐答案

扩展@Jos​​h 的建议，我建议使用实习.

Expanding on @Josh's suggestion, I would suggest using interning.

根据您的任务的内存或 CPU 密集程度，在以下选项之间进行选择:

Depending on how memory or CPU intensive your task is, make your pick between:

• 双哈希映射:ID <-> String，在组件之间共享
• 单个哈希映射:String -> Rc

• A double hash-map: ID <-> String, shared between components
• A single hash-map: String -> Rc<str>

如果你能负担得起后者，我绝对建议.另请注意，您可能会在 Rc 中折叠 MetricType:Rc<(MetricType, str)>.

If you can afford the latter, I definitely advise it. Also note that you can likely fold MetricType within the Rc: Rc<(MetricType, str)>.

那么你仍然需要向左和向右调用clone，但每个都只是一个廉价的非原子增量操作......而移动到多线程就像交换Arc一样简单Rc 的代码>.

Then you still need to call clone left and right, but each is just a cheap non-atomic increment operation... and moving to multithread is as simple as swapping Arc for Rc.

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