Overview

Relevant source files

• Cargo.toml
• README.md

Purpose and Scope

This document provides an overview of the lazyinit crate, a Rust library that enables thread-safe lazy initialization of static values. The material covers the crate's core purpose, key features, architecture, and usage patterns. For detailed implementation specifics of the LazyInit<T> struct, see LazyInit Implementation. For API documentation and method details, see API Reference. For project configuration and dependencies, see Project Configuration.

What is LazyInit

The lazyinit crate provides the LazyInit<T> type for initializing static values lazily in a thread-safe manner. Unlike compile-time initialization or macro-based solutions like lazy_static, LazyInit<T> allows runtime initialization with arbitrary logic while guaranteeing that initialization occurs exactly once across all threads.

The core abstraction is the LazyInit<T> struct, which wraps a value of type T and manages its initialization state through atomic operations. The value remains uninitialized until the first call to init_once or call_once, at which point it becomes permanently initialized and accessible.

Sources: README.md(L7 - L11)  Cargo.toml(L6) 

Key Features and Capabilities

Sources: README.md(L15 - L57)  Cargo.toml(L12) 

Core Architecture

The following diagram illustrates the relationship between the main components and their roles in the codebase:

LazyInit Core Components and Relationships

flowchart TD
subgraph subGraph2["Memory Safety Guarantees"]
    single_init["Single Initialization Guarantee"]
    thread_safety["Thread Safety"]
    memory_ordering["Memory Ordering (Acquire/Relaxed)"]
end
subgraph subGraph1["Internal State Management"]
    AtomicBool["AtomicBool (initialization flag)"]
    UnsafeCell["UnsafeCell<MaybeUninit<T>> (data storage)"]
    compare_exchange["compare_exchange_weak operations"]
end
subgraph subGraph0["Public API Layer"]
    LazyInit["LazyInit<T>"]
    new["LazyInit::new()"]
    init_once["init_once(value: T)"]
    call_once["call_once(f: FnOnce() -> T)"]
    get["get() -> Option<&T>"]
    get_mut["get_mut() -> Option<&mut T>"]
    is_inited["is_inited() -> bool"]
    get_unchecked["get_unchecked() -> &T"]
end

AtomicBool --> compare_exchange
LazyInit --> call_once
LazyInit --> get
LazyInit --> get_mut
LazyInit --> get_unchecked
LazyInit --> init_once
LazyInit --> is_inited
LazyInit --> new
call_once --> AtomicBool
call_once --> UnsafeCell
compare_exchange --> memory_ordering
compare_exchange --> single_init
compare_exchange --> thread_safety
get --> AtomicBool
get --> UnsafeCell
get_mut --> UnsafeCell
get_unchecked --> UnsafeCell
init_once --> AtomicBool
init_once --> UnsafeCell
is_inited --> AtomicBool

Sources: README.md(L16 - L28)  README.md(L32 - L57) 

API Surface Overview

The following diagram shows the complete API surface and usage patterns supported by LazyInit<T>:

LazyInit API Methods and Usage Patterns

flowchart TD
subgraph subGraph4["Return Types"]
    option_some["Some(&T) / Some(&mut T)"]
    option_none["None"]
    panic_behavior["Panic on double init"]
    direct_ref["&T / &mut T"]
end
subgraph subGraph3["Status Methods"]
    is_inited_method["is_inited() -> bool"]
end
subgraph subGraph2["Access Methods"]
    get_method["get() -> Option<&T>"]
    get_mut_method["get_mut() -> Option<&mut T>"]
    deref_impl["Deref/DerefMut traits"]
    get_unchecked_method["get_unchecked() -> &T (unsafe)"]
end
subgraph subGraph1["Initialization Methods"]
    init_once_method["init_once(value: T)"]
    call_once_method["call_once(f: FnOnce() -> T)"]
end
subgraph Creation["Creation"]
    LazyInit_new["LazyInit::new()"]
end
true_false["true / false"]

LazyInit_new --> call_once_method
LazyInit_new --> init_once_method
call_once_method --> option_none
call_once_method --> option_some
deref_impl --> direct_ref
deref_impl --> panic_behavior
get_method --> option_none
get_method --> option_some
get_mut_method --> option_none
get_mut_method --> option_some
get_unchecked_method --> direct_ref
init_once_method --> option_some
init_once_method --> panic_behavior
is_inited_method --> true_false

Sources: README.md(L18 - L27)  README.md(L39 - L56) 

Use Cases and When to Use LazyInit

LazyInit<T> is designed for scenarios where you need lazy initialization with these characteristics:

Primary Use Cases

1. Static Variables with Runtime Initialization: When you need a static variable that requires runtime computation or I/O to initialize
2. Expensive Computations: When initialization is costly and should only occur if the value is actually needed
3. Resource Initialization: When initializing system resources, file handles, or network connections that should be shared globally
4. Multi-threaded Environments: When multiple threads might attempt to initialize the same static value concurrently

Advantages Over Alternatives

• vs. lazy_static!: Provides more flexible initialization patterns and doesn't require macro-based declaration
• vs. std::sync::Once: Combines synchronization with storage, providing a more ergonomic API
• vs. std::cell::OnceCell: Offers thread-safe initialization for static contexts

Sources: README.md(L9 - L11)  Cargo.toml(L11) 

Project Characteristics

No-std Compatibility

The crate is designed for no-std environments, making it suitable for:

• Embedded systems
• Kernel-level code
• WebAssembly targets
• Bare metal programming

Licensing and Distribution

Supported Targets

The crate supports multiple target architectures through CI validation, including both hosted and bare-metal targets.

Sources: Cargo.toml(L1 - L15)