M02 Resource

by actionbook5c40d3ad7851No license1.5K starsListed Oct 8, 2026Updated Oct 8, 2026Repository updated 6 weeks ago

CRITICAL: Use for smart pointers and resource management. Triggers: Box, Rc, Arc, Weak, RefCell, Cell, smart pointer, heap allocation, reference counting, RAII, Drop, should I use Box or Rc, when to use Arc vs Rc, 智能指针, 引用计数, 堆分配

Instructions onlySoftware Development

AI-generated overview

Guides Rust developers in choosing smart pointers and ownership patterns such as Box, Rc, Arc, Weak, Cell and RefCell.

What it does: This skill is a decision guide for Rust resource management. It walks through ownership models, thread context and reference cycles, then maps situations to types like Box, Rc, Arc, Weak, Cell and RefCell. It also lists common errors, anti-patterns and related topics to consult when a pointer choice is unclear.
When to use it: Use it when deciding between smart pointers, such as Box versus Rc or Arc versus Rc, or when diagnosing issues like Rc memory leaks, RefCell panics or unnecessary Arc overhead. It is also useful when reasoning about heap allocation, reference counting, RAII or Drop behavior.
Requirements: No tools, packages or credentials are required; it is an instructions-only skill with no scripts.

Resource Management

Layer 1: Language Mechanics

Core Question

What ownership pattern does this resource need?

Before choosing a smart pointer, understand:

Is ownership single or shared?
Is access single-threaded or multi-threaded?
Are there potential cycles?

Error → Design Question

Error	Don't Just Say	Ask Instead
"Need heap allocation"	"Use Box"	Why can't this be on stack?
Rc memory leak	"Use Weak"	Is the cycle necessary in design?
RefCell panic	"Use try_borrow"	Is runtime check the right approach?
Arc overhead complaint	"Accept it"	Is multi-thread access actually needed?

Thinking Prompt

Before choosing a smart pointer:

What's the ownership model?
- Single owner → Box or owned value
- Shared ownership → Rc/Arc
- Weak reference → Weak
What's the thread context?
- Single-thread → Rc, Cell, RefCell
- Multi-thread → Arc, Mutex, RwLock
Are there cycles?
- Yes → One direction must be Weak
- No → Regular Rc/Arc is fine

Trace Up ↑

When pointer choice is unclear, trace to design:

"Should I use Arc or Rc?"    ↑ Ask: Is this data shared across threads?    ↑ Check: m07-concurrency (thread model)    ↑ Check: domain-* (performance constraints)

"Should I use Arc or Rc?"    ↑ Ask: Is this data shared across threads?    ↑ Check: m07-concurrency (thread model)    ↑ Check: domain-* (performance constraints)

Situation	Trace To	Question
Rc vs Arc confusion	m07-concurrency	What's the concurrency model?
RefCell panics	m03-mutability	Is interior mutability right here?
Memory leaks	m12-lifecycle	Where should cleanup happen?

Trace Down ↓

From design to implementation:

"Need single-owner heap data"    ↓ Use: Box<T>
"Need shared immutable data (single-thread)"    ↓ Use: Rc<T>
"Need shared immutable data (multi-thread)"    ↓ Use: Arc<T>
"Need to break reference cycle"    ↓ Use: Weak<T>
"Need shared mutable data"    ↓ Single-thread: Rc<RefCell<T>>    ↓ Multi-thread: Arc<Mutex<T>> or Arc<RwLock<T>>

"Need single-owner heap data"    ↓ Use: Box<T>
"Need shared immutable data (single-thread)"    ↓ Use: Rc<T>
"Need shared immutable data (multi-thread)"    ↓ Use: Arc<T>
"Need to break reference cycle"    ↓ Use: Weak<T>
"Need shared mutable data"    ↓ Single-thread: Rc<RefCell<T>>    ↓ Multi-thread: Arc<Mutex<T>> or Arc<RwLock<T>>

Quick Reference

Type	Ownership	Thread-Safe	Use When
`Box<T>`	Single	Yes	Heap allocation, recursive types
`Rc<T>`	Shared	No	Single-thread shared ownership
`Arc<T>`	Shared	Yes	Multi-thread shared ownership
`Weak<T>`	Weak ref	Same as Rc/Arc	Break reference cycles
`Cell<T>`	Single	No	Interior mutability (Copy types)
`RefCell<T>`	Single	No	Interior mutability (runtime check)

Decision Flowchart

Need heap allocation?├─ Yes → Single owner?│        ├─ Yes → Box<T>│        └─ No → Multi-thread?│                ├─ Yes → Arc<T>│                └─ No → Rc<T>└─ No → Stack allocation (default)
Have reference cycles?├─ Yes → Use Weak for one direction└─ No → Regular Rc/Arc
Need interior mutability?├─ Yes → Thread-safe needed?│        ├─ Yes → Mutex<T> or RwLock<T>│        └─ No → T: Copy? → Cell<T> : RefCell<T>└─ No → Use &mut T

Need heap allocation?├─ Yes → Single owner?│        ├─ Yes → Box<T>│        └─ No → Multi-thread?│                ├─ Yes → Arc<T>│                └─ No → Rc<T>└─ No → Stack allocation (default)
Have reference cycles?├─ Yes → Use Weak for one direction└─ No → Regular Rc/Arc
Need interior mutability?├─ Yes → Thread-safe needed?│        ├─ Yes → Mutex<T> or RwLock<T>│        └─ No → T: Copy? → Cell<T> : RefCell<T>└─ No → Use &mut T

Common Errors

Problem	Cause	Fix
Rc cycle leak	Mutual strong refs	Use Weak for one direction
RefCell panic	Borrow conflict at runtime	Use try_borrow or restructure
Arc overhead	Atomic ops in hot path	Consider Rc if single-threaded
Box unnecessary	Data fits on stack	Remove Box

Anti-Patterns

Anti-Pattern	Why Bad	Better
Arc everywhere	Unnecessary atomic overhead	Use Rc for single-thread
RefCell everywhere	Runtime panics	Design clear ownership
Box for small types	Unnecessary allocation	Stack allocation
Ignore Weak for cycles	Memory leaks	Design parent-child with Weak

Related Skills

Source and attribution

Source:actionbook/rust-skillsinskills/m02-resourceat commit5c40d3a

License: No license

Content belongs to its original authors. SourceWeft indexes it from a public repository.

Report or request removal

When	See
Ownership errors	m01-ownership
Interior mutability details	m03-mutability
Multi-thread context	m07-concurrency
Resource lifecycle	m12-lifecycle

M02 Resource

Resource Management

Core Question

Error → Design Question

Thinking Prompt

Trace Up ↑

Trace Down ↓

Quick Reference

Decision Flowchart

Common Errors

Anti-Patterns

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Source and attribution

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