Who Owns the Memory? Part 1: What Is an Object?
4 months ago
- #low-level
- #memory-management
- #performance
- Memory in C, C++, and Rust is managed at a low level starting with bytes, building up to objects, storage duration, lifetime, and aliasing.
- A 64-bit processor sees memory as a flat array of addressable bytes, unaware of types like structs or ints.
- Modern operating systems use virtual address spaces for process isolation and portability, managed by the MMU.
- Alignment is crucial for performance; accessing misaligned data can cause penalties or hardware traps.
- Cache lines and memory bandwidth optimization are influenced by data structure layout and padding.
- Memory allocators like malloc manage metadata and impose overhead, with alignment guarantees.
- Objects in memory can be viewed as arrays of bytes, with semantic meaning imposed by the type system.
- C uses effective type rules to determine how memory can be accessed, enabling optimizations.
- C++ introduces object lifetime, distinguishing between storage duration and when objects can be accessed.
- Rust enforces validity invariants, where producing an invalid value is immediate undefined behavior.
- Storage duration categories include static, thread, automatic, and allocated (dynamic) storage.
- Stack allocation is efficient but limited by size; heap allocation involves more overhead and complexity.
- Ownership in Rust ensures memory safety by tracking lifetimes and enforcing compile-time checks.
- Aliasing rules in C, C++, and Rust optimize performance by restricting how pointers can overlap.
- Rust's borrow checker enforces shared XOR mutable references, preventing data races and enabling optimizations.