初始化函数在"lazy_static"块中被调用两次

Question

我有一个大项目，我用lazy_static创建一个singleton。我认为lazy_static机箱中有一个错误(只出现在大型项目中(，或者我做错了什么，因为必须调用一次才能创建singleton的初始化函数被调用了两次。

项目结构如下

---

Foo
|__foo-core
|  |__src
|  |  |__lib.rs
|  |__Cargo.toml
|
|__foo-high
|  |__src
|  |  |__lib.rs
|  |__Cargo.toml
|
|__src
|  |__lib.rs
|__Cargo.toml

---

Foo/Foo-core/src/lib.rs

pub mod my_file {
pub struct MyFile {
file: std::fs::File,
}
impl MyFile {
pub fn open(
path: &'static str,
) -> Result<MyFile, Box<dyn std::error::Error + Send + Sync>> {
let file_ = std::fs::File::create(path)?;
Ok(MyFile { file: file_ })
}
}
}

Foo/Foo high/src/lib.rs

mod high {
mod high_child {
#[cfg(test)]
mod high_child_unit_tests {
use crate::high::my_file::*;
#[test]
fn some_fun_test_runner() {
MyFile::get();
auto_fun();
MyFile::get();
}
fn auto_fun() {
// super::super::layer ::some_fun();
foo::high::some_fun();
}
}
}
pub mod layer {
use crate::high::my_file::*;
pub fn some_fun() {
MyFile::get();
}
}
mod my_file {
pub use foo_core::my_file as core_my_file;
use std::sync::{Mutex, MutexGuard};
lazy_static::lazy_static! {static ref INSTANCE: Mutex<core_my_file::MyFile> = init_fun();}
fn init_fun() -> Mutex<core_my_file::MyFile> {
println!("INIT");
let location = "location.txt";
Mutex::new(core_my_file::MyFile::open(location).expect("nSome Error has occurred."))
}
pub struct MyFile {}
impl MyFile {
pub fn get() -> MutexGuard<'static, core_my_file::MyFile> {
println!("GET");
INSTANCE.lock().expect("The mutex has been poisoned")
}
}
}
}
pub mod layer {
pub use crate::high::layer::*;
}

Foo/Foo-core/Cocargo.toml

[package]
name = "foo-core"
version = "0.1.0"
edition = "2018"

Foo/Foo-high/Cargo.toml

[package]
name = "foo-high"
version = "0.1.0"
edition = "2018"
[dependencies]
foo-core = { version = "0.1.0", path = "../foo-core" }
lazy_static = "1.4.0"
[dev-dependencies]
foo = { version = "0.1.0", path = "../" }

食品/货物.toml

[package]
name = "foo"
version = "0.1.0"
edition = "2018"
[dependencies]
foo-high = { version = "0.1.0", path = "foo-high" }
[workspace]
members = ["foo-high", "foo-core"]

当我用-- --no-capture运行some_fun_test_runner测试时，我看到3个GETs和2个INITs，而INIT必须只打印一次。当我更改体系结构时，函数被调用过一次，但我需要这个体系结构。当我将foo::high::some_fun();(在auto_fun中(更改为super::super::layer::some_fun();时，函数也被调用了一次。我不能理解这种行为。我也用了once_cell，但我得到了相同的结果

Answer 1

您与foo-high->有一个间接循环依赖关系；foo工作区->CCD_ 14。Rust和Cargo在设计时并没有考虑到依赖循环；您的体系结构应该避免它们。确切地说，问题的出现是因为foo-high的两个实例都有自己的statics集。

在单元测试中，super::super::layer::some_fun表示fn机箱内变体"fn"；A"；，而CCD_ 18表示fn在板条箱中的变体"fn"；B"；。前者在您的上下文中运行良好，而后者通过单独的statics揭示了问题。这种重复在这里发生，但当不同的机箱版本被拉入依赖图的某个位置时也会发生。

我不确定您的机箱体系结构背后的动机，但一个潜在的解决方案是消除对foo的开发依赖。然后，为了伪造您想要的模块结构，您可能会有以下内容：您在foo-high的根处添加

mod foo {
mod high {
pub use crate::*;
}
pub use foo_core as core;
}

---

此外，单元测试通过项目的全局路径引用项目是不常见的。最好保持当地特色。否则，最好编写一个集成测试。