Rust Memory Management: Ownership vs. Reference Counting
18 hours ago
- #Ownership
- #Memory Safety
- #Rust
- Rust ensures memory safety without a garbage collector through a strict ownership system, where each value has a single owner, and memory is deterministically freed when the owner goes out of scope.
- Reference counting (via Rc<T> and Arc<T>) serves as an escape hatch for shared ownership, moving ownership logic to runtime with counters, useful for scenarios like graph nodes or shared configuration.
- Ownership and borrowing are enforced at compile time with zero runtime overhead, using rules like aliasing XOR mutability to prevent bugs like data races and iterator invalidation.
- Rc<T> provides non-atomic reference counting for single-threaded use, while Arc<T> offers atomic reference counting for thread safety, both requiring additional mechanisms like RefCell or Mutex for interior mutability.
- Performance trade-offs include overhead from heap allocation, pointer indirection, and counter operations for Rc/Arc, with Arc adding atomic operation costs, but these are often negligible in application code.
- Reference cycles can cause memory leaks with Rc/Arc, which can be mitigated using Weak<T> for non-owning references, such as in parent pointers in trees.