Rust 异步并发安全与内存管理实战指南

*注：原示例未加锁导致竞争，此处修正为使用 Arc<Mutex> 展示正确用法，若不加锁则结果不确定。

死锁

两个任务互相等待对方持有的锁，导致程序卡死。

use std::sync::Mutex;
use tokio::spawn;

#[tokio::main]
async fn main() {
    let mutex1 = Mutex::new(1);
    let mutex2 = Mutex::new(2);
    
    let handle1 = spawn(async move {
        let lock1 = mutex1.lock().unwrap();
        println!("Handle1 got lock1");
        tokio::time::sleep(std::time::Duration::from_millis(100)).await;
        let lock2 = mutex2.lock().unwrap();
        println!("Handle1 got lock2");
    });
    
    let handle2 = spawn(async move {
        let lock2 = mutex2.lock().unwrap();
        println!("Handle2 got lock2");
        tokio::time::sleep(std::time::Duration::from_millis(100)).await;
        let lock1 = mutex1.lock().unwrap();
        println!("Handle2 got lock1");
    });
    
    handle1.await.unwrap();
    handle2.await.unwrap();
}

*注意：这种嵌套获取锁的方式极易引发死锁，生产环境中需严格规定锁的获取顺序。

活锁

任务不断改变状态但无法推进，通常发生在重试逻辑中。

use std::sync::Mutex;
use tokio::spawn;

#[tokio::main]
async fn main() {
    let data = Mutex::new(0);
    
    let handle1 = spawn(async move {
        loop {
            let mut lock = data.lock().unwrap();
            if *lock < 1000 {
                *lock += 1;
                println!("Handle1: {}", *lock);
            } else {
                break;
            }
            drop(lock);
            tokio::time::sleep(std::time::Duration::from_millis(1)).await;
        }
    });
    
    let handle2 = spawn(async move {
        loop {
            let mut lock = data.lock().unwrap();
            if *lock > 0 {
                *lock -= 1;
                println!("Handle2: {}", *lock);
            } else {
                break;
            }
            drop(lock);
            tokio::time::sleep(std::time::Duration::from_millis(1)).await;
        }
    });
    
    handle1.await.unwrap();
    handle2.await.unwrap();
}

资源泄漏

任务被取消但未清理资源，或句柄未关闭。

use tokio::spawn;
use std::sync::Arc;

struct MyData { value: i32 }
impl Drop for MyData {
    fn drop(&mut self) {
        println!("MyData dropped");
    }
}

#[tokio::main]
async fn main() {
    let data = Arc::new(MyData { value: 42 });
    let handle = spawn(async move {
        println!("Task running");
        tokio::time::sleep(std::time::Duration::from_secs(5)).await;
        println!("Task finished");
    });
    
    handle.abort(); // 撤销任务
    if let Err(e) = handle.await {
        println!("Task aborted: {:?}", e);
    }
    println!("Main task finished");
}

解决方案与最佳实践

1. 共享状态：Arc + Mutex/RwLock

对于写多读少的场景，Arc<Mutex<T>> 是标准解法；读多写少则可用 RwLock。

use std::sync::Arc;
use tokio::sync::Mutex;
use tokio::spawn;

#[tokio::main]
async fn main() {
    let data = Arc::new(Mutex::new(0));
    let mut handles = Vec::new();
    
    for _ in 0..10 {
        let data_clone = Arc::clone(&data);
        handles.push(spawn(async move {
            for _ in 0..1000 {
                let mut lock = data_clone.lock().await;
                *lock += 1;
            }
        }));
    }
    
    for handle in handles {
        handle.await.unwrap();
    }
    println!("Data: {}", data.lock().await);
}

2. 原子操作：AtomicI32

简单计数无需锁开销，直接使用 std::sync::atomic。

use std::sync::Arc;
use std::sync::atomic::{AtomicI32, Ordering};
use tokio::spawn;

#[tokio::main]
async fn main() {
    let data = Arc::new(AtomicI32::new(0));
    let mut handles = Vec::new();
    
    for _ in 0..10 {
        let data_clone = Arc::clone(&data);
        handles.push(spawn(async move {
            for _ in 0..1000 {
                data_clone.fetch_add(1, Ordering::Relaxed);
            }
        }));
    }
    
    for handle in handles {
        handle.await.unwrap();
    }
    println!("Data: {}", data.load(Ordering::Relaxed));
}

3. 消息传递：Channel

避免共享状态最彻底的方式是'不要共享'，改用通道通信。

use tokio::sync::mpsc;
use tokio::spawn;

#[tokio::main]
async fn main() {
    let (sender, mut receiver) = mpsc::channel(10);
    let mut handles = Vec::new();
    
    for _ in 0..10 {
        let sender_clone = sender.clone();
        handles.push(spawn(async move {
            for i in 0..1000 {
                sender_clone.send(i).await.unwrap();
            }
        }));
    }
    
    handles.push(spawn(async move {
        let mut sum = 0;
        while let Some(msg) = receiver.recv().await {
            sum += msg;
        }
        println!("Sum: {}", sum);
    }));
    
    drop(sender); // 关闭发送端
    for handle in handles {
        handle.await.unwrap();
    }
}

内存管理实战

优化分配与池化

频繁分配小对象会增加 GC 压力（虽然 Rust 无 GC，但有堆分配开销）。复用缓冲区是个好主意。

use tokio::spawn;
use bytes::BytesMut;

#[tokio::main]
async fn main() {
    let mut handles = Vec::new();
    let pool = BytesMut::with_capacity(1024);
    
    for _ in 0..10 {
        let mut pool_clone = pool.clone();
        handles.push(spawn(async move {
            for _ in 0..1000 {
                pool_clone.clear();
                pool_clone.extend_from_slice(b"hello world");
            }
        }));
    }
    
    for handle in handles {
        handle.await.unwrap();
    }
    println!("Memory usage: {}", pool.capacity());
}

任务配置

使用 Builder 调整线程栈大小，防止栈溢出。

use tokio::runtime::Builder;
use tokio::time::sleep;
use std::time::Duration;

fn main() {
    let runtime = Builder::new_multi_thread()
        .worker_threads(4)
        .thread_stack_size(2 * 1024 * 1024)
        .build()
        .unwrap();
    
    runtime.block_on(async {
        let mut handles = Vec::new();
        for _ in 0..10 {
            handles.push(tokio::spawn(async move {
                println!("Task running");
                sleep(Duration::from_millis(100)).await;
                println!("Task finished");
            }));
        }
        for handle in handles {
            handle.await.unwrap();
        }
    });
}

项目中的落地

HTTP 客户端缓存

在公共模块中，使用 Arc<Mutex<HashMap>> 实现线程安全的请求缓存。

// common/src/http.rs
use reqwest::{Client, Response};
use tokio::sync::Mutex;
use std::sync::Arc;
use std::collections::HashMap;

pub struct HttpClient {
    client: Client,
    cache: Arc<Mutex<HashMap<String, String>>>,
}

impl HttpClient {
    pub fn new() -> Self {
        HttpClient {
            client: Client::new(),
            cache: Arc::new(Mutex::new(HashMap::new())),
        }
    }
    
    pub async fn get<T: serde::de::DeserializeOwned>(&self, url: &str) -> Result<T, AppError> {
        let mut cache = self.cache.lock().await;
        if let Some(cached) = cache.get(url) {
            return Ok(serde_json::from_str(cached)?);
        }
        let response = self.client.get(url).send().await?;
        let body = response.text().await?;
        cache.insert(url.to_string(), body.clone());
        Ok(serde_json::from_str(&body)?)
    }
}

数据库连接池

使用 sqlx 管理连接，避免重复创建。

// common/src/db.rs
use sqlx::PgPool;

pub async fn create_pool(config: DbConfig) -> Result<PgPool, AppError> {
    let pool = PgPool::connect_with(
        config.url.parse().unwrap().max_connections(10).min_connections(2),
    ).await?;
    Ok(pool)
}

Redis 连接共享

Redis 客户端本身支持克隆，配合 Arc 即可安全共享。

// common/src/redis.rs
use redis::Client;
use std::sync::Arc;

pub struct RedisClient {
    client: Arc<Client>,
}

impl RedisClient {
    pub async fn new(url: &str) -> Result<Self, AppError> {
        let client = Arc::new(Client::open(url.parse().unwrap())?);
        Ok(RedisClient { client })
    }
    
    pub async fn get_connection(&self) -> Result<redis::Connection, AppError> {
        Ok(self.client.get_connection()?)
    }
}

任务限流

使用信号量限制并发度，保护下游服务。

// user-sync-service/src/sync.rs
use tokio::sync::Semaphore;
use std::sync::Arc;

async fn sync_users(config: &AppConfig) -> Result<(), AppError> {
    let pool = create_pool(config.db.clone()).await?;
    let redis_client = create_client(config.redis.clone()).await?;
    let semaphore = Arc::new(Semaphore::new(10));
    
    let mut handles = Vec::new();
    for third_party_user in users {
        let permit = semaphore.clone().acquire_owned().await.unwrap();
        let pool_clone = pool.clone();
        let redis_client_clone = redis_client.clone();
        
        handles.push(tokio::spawn(async move {
            let result = process_user(third_party_user, &pool_clone, &redis_client_clone).await;
            drop(permit);
            result
        }));
    }
    
    for handle in handles {
        handle.await.unwrap()?;
    }
    Ok(())
}

总结

Rust 异步开发的核心在于平衡性能与安全。理解所有权机制能帮你避开大部分陷阱，而合理选择 Arc、Mutex、原子变量或通道，则取决于具体的读写模式。在实战中，结合连接池、任务限流和内存复用策略，能让你的系统在保持高可靠性的同时，发挥出极致的性能。掌握这些技巧，你的 Rust 代码会更稳健。