Component

Overview

This crate is used for the initialization of the component system, which provides a priority initialization scheme based on the inventory crate.

Usage

Register component

Registering a crate as component by marking a function in the lib.rs with #[init_component] macro. The specific definition of the function can refer to the comments in the macro.

Component initialization

Component system need to be initialized by calling component::init_all function and it needs information about all components. Usually it is used with the component::parse_metadata macro.

Example

// comp1/lib.rs
use std::sync::atomic::AtomicU16;
use std::sync::atomic::Ordering::Relaxed;

use component::init_component;

pub static INIT_COUNT : AtomicU16 = AtomicU16::new(0);

#[init_component]
fn comp1_init() -> Result<(), component::ComponentInitError> {
    assert_eq!(INIT_COUNT.load(Relaxed),0);
    INIT_COUNT.fetch_add(1,Relaxed);
    Ok(())
}

// src/main.rs
use std::sync::atomic::Ordering::Relaxed;

use component::init_component;
use comp1::INIT_COUNT;

#[init_component]
fn init() -> Result<(), component::ComponentInitError> {
    assert_eq!(INIT_COUNT.load(Relaxed),1);
    INIT_COUNT.fetch_add(1,Relaxed);
    Ok(())
}

fn main(){
    component::init_all(component::parse_metadata!()).unwrap();
    assert_eq!(INIT_COUNT.load(Relaxed),2);
}

Notes

Currently, initialization requires the presence of a Components.toml file, which stores some information about components and access control. The tests provides a sample file of it. If the components declared inside Components.toml is inconsistent with the component found by parse_metadata macro (i.e. A crate depends on the component library but is not declared in Components.toml), then a compilation error will occur.
The parse_metadata macro will generate the information of all components. But ultimately which functions are called still depends on which #[init_component] macros are extended. If you want to test a component. Then, other components with a lower priority than it or other unused high-priority components will not be initialized at runtime.

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