rust - 为什么在未标记的枚举中反序列化时 serde_json rust 得这么慢

Question

运行代码时:

#![allow(unused)]
use serde::{Deserialize, Serialize};
use std::collections::HashMap;

use std::time::Instant;

#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
#[serde(untagged)]
enum NumberOrString {
    String(String),
    Int(i64),
    Float(f64),
}

fn main() {
    let json_str = r#"{
        "17594136111": [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268, 269, 270, 271, 272, 273, 274, 275, 276, 277, 278, 279, 280, 281, 282, 283, 284, 285, 286, 287, 288, 289, 290, 291, 292, 293, 294, 295, 296, 297, 298, 299, 300, 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 311, 312, 313, 314, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, 325, 326, 327, 328, 329, 330, 331, 332, 333, 334, 335, 336, 337, 338, 339, 340, 341, 342, 343, 344, 345, 346, 347, 348, 349, 350, 351, 352, 353, 354, 355, 356, 357, 358, 359, 360, 361, 362, 363, 364, 365, 366, 367, 368, 369, 370, 371, 372, 373, 374, 375, 376, 377, 378, 379, 380, 381, 382, 383, 384, 385, 386, 387, 388, 389, 390, 391, 392, 393, 394, 395, 396, 397, 398, 399, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 415, 416, 417, 418, 419, 420, 421, 422, 423, 424, 425, 426, 427, 428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 444, 445, 446, 447, 448, 449, 450, 451, 452, 453, 454, 455, 456, 457, 458, 459, 460, 461, 462, 463, 464, 465, 466, 467, 468, 469, 470, 471, 472, 473, 474, 475, 476, 477, 478, 479, 480, 481, 482, 483, 484, 485, 486, 487, 488, 489, 490, 491, 492, 493, 494, 495, 496, 497, 498, 499],
        "0000000017704043101": ["5", "7"],
        "features": ["a1"]
    }"#;

    let start_time = Instant::now();
    let parsed: HashMap<&str, Vec<serde_json::Value>> = serde_json::from_str(json_str).expect("panicking !!! ");
    println!("Elapsed time: {:.2?}", start_time.elapsed());

    let start_time = Instant::now();
    let parsed2: HashMap<&str, Vec<NumberOrString>> = serde_json::from_str(json_str).expect("panicking !!! ");
    println!("Elapsed time: {:.2?}", start_time.elapsed());
}

输出如下:

$ cargo run 
Compiling rust_tutorial v0.1.0 (/Users/sandeep.yadav/code/codetest/rust/rust_tutorial)
Finished dev [unoptimized + debuginfo] target(s) in 2.26s
Running `target/debug/rust_tutorial`
Elapsed time: 360.78µs
Elapsed time: 2.22ms

$ cargo run --release
Compiling rust_tutorial v0.1.0 (/Users/sandeep.yadav/code/codetest/rust/rust_tutorial)
Finished release [optimized] target(s) in 2.47s
Running `target/release/rust_tutorial`
Elapsed time: 74.82µs
Elapsed time: 439.90µs

$ cargo run --release
Finished release [optimized] target(s) in 0.03s
Running `target/release/rust_tutorial`
Elapsed time: 63.13µs
Elapsed time: 354.89µs

与 serde_json::Value 中定义的另一个枚举相比，为什么 untaggedJson 这么慢？

由于 serde_json::Value 包含的不仅仅是 String int64 和 f64.，它还包含 Null、Bool、List 和 Object。我实际上正在减少可能的可接受值集，但花费的时间仍然至少增加了 5 倍？

我可以使用任何替代方法来获得相同的结果吗？

Answer 1

在为 NumberOrString 枚举实现自定义 Visitor 模式之后——如 @Chayim 正确提到的是 serde-json 如何实现 为 Value here 反序列化——最后，在删除默认的 #derive(Deserialize) 之后，看起来性能时间现在很多 改进，如下所示。

#![allow(unused)]

use std::collections::HashMap;
use std::fmt;
use std::time::Instant;

use serde::de::{Error, Visitor};
use serde::{Deserialize, Deserializer, Serialize};

#[derive(Serialize, Debug, Clone, PartialEq)]
// note: it appears that an "untagged enum" is not needed anymore
// #[serde(untagged)]
enum NumberOrString {
    String(String),
    Int(i64),
    Float(f64),
}

impl<'de> Deserialize<'de> for NumberOrString {
    #[inline]
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        use crate::NumberOrString::*;

        struct NumberOrStringVisitor;

        impl<'de> Visitor<'de> for NumberOrStringVisitor {
            type Value = NumberOrString;

            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
                formatter.write_str("a number or string")
            }

            #[inline]
            fn visit_i64<E>(self, v: i64) -> Result<Self::Value, E>
            where
                E: Error,
            {
                Ok(Int(v))
            }

            #[inline]
            fn visit_u64<E>(self, v: u64) -> Result<Self::Value, E>
            where
                E: Error,
            {
                Ok(Int(v as i64))
            }

            #[inline]
            fn visit_f64<E>(self, v: f64) -> Result<Self::Value, E>
            where
                E: Error,
            {
                Ok(Float(v))
            }

            #[inline]
            fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
            where
                E: Error,
            {
                Ok(String(v.to_owned()))
            }

            #[inline]
            fn visit_string<E>(self, v: std::string::String) -> Result<Self::Value, E>
            where
                E: Error,
            {
                Ok(String(v))
            }
        }

        deserializer.deserialize_any(NumberOrStringVisitor)
    }
}

fn main() {
    let json_str = r#"{
        "17594136111": [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268, 269, 270, 271, 272, 273, 274, 275, 276, 277, 278, 279, 280, 281, 282, 283, 284, 285, 286, 287, 288, 289, 290, 291, 292, 293, 294, 295, 296, 297, 298, 299, 300, 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 311, 312, 313, 314, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, 325, 326, 327, 328, 329, 330, 331, 332, 333, 334, 335, 336, 337, 338, 339, 340, 341, 342, 343, 344, 345, 346, 347, 348, 349, 350, 351, 352, 353, 354, 355, 356, 357, 358, 359, 360, 361, 362, 363, 364, 365, 366, 367, 368, 369, 370, 371, 372, 373, 374, 375, 376, 377, 378, 379, 380, 381, 382, 383, 384, 385, 386, 387, 388, 389, 390, 391, 392, 393, 394, 395, 396, 397, 398, 399, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 415, 416, 417, 418, 419, 420, 421, 422, 423, 424, 425, 426, 427, 428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 444, 445, 446, 447, 448, 449, 450, 451, 452, 453, 454, 455, 456, 457, 458, 459, 460, 461, 462, 463, 464, 465, 466, 467, 468, 469, 470, 471, 472, 473, 474, 475, 476, 477, 478, 479, 480, 481, 482, 483, 484, 485, 486, 487, 488, 489, 490, 491, 492, 493, 494, 495, 496, 497, 498, 499],
        "0000000017704043101": ["5", "7"],
        "features": ["a1"]
    }"#;

    let start_time = Instant::now();
    let parsed: HashMap<&str, Vec<serde_json::Value>> =
        serde_json::from_str(json_str).expect("panicking !!! ");
    println!("Elapsed time: {:.2?}", start_time.elapsed());

    let start_time = Instant::now();
    let parsed2: HashMap<&str, Vec<NumberOrString>> =
        serde_json::from_str(json_str).expect("panicking !!! ");
    println!("Elapsed time: {:.2?}", start_time.elapsed());
}

我的时间(在我的 Windows 11 PC 上)如下:

$ cargo run --release
Finished release [optimized] target(s) in 0.03s
Running `target/release/rust_tutorial`
Elapsed time: 286.00µs
Elapsed time: 20.50µs

$ cargo run --release
Finished release [optimized] target(s) in 0.03s
Running `target/release/rust_tutorial`
Elapsed time: 303.90µs
Elapsed time: 24.00µs