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Bradlee Speice 2019-01-01 14:31:15 -05:00
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_drafts/understanding-allocations-in-rust.md
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@ -16,11 +16,11 @@ type all the time, but there's a rich history of the Rust language itself wrappe
In a similar vein, I want you to look at code and understand memory; In a similar vein, I want you to look at code and understand memory;
the complex choreography of processor, operating system, and program that frees you the complex choreography of processor, operating system, and program that frees you
to focus on functionality far beyond frivolous book-keeping. The Rust compiler relieves to focus on functionality far-flung from frivolous book-keeping. The Rust compiler relieves
a great deal of the cognitive burden associated with memory management, but let's make time a great deal of the cognitive burden associated with memory management, but let's make time
to explore what's going on under the hood. to explore what's going on under the hood.
Let's learn a bit about allocating memory in Rust. Let's learn a bit about memory in Rust.
# Table of Contents # Table of Contents
@ -30,11 +30,11 @@ section for easy citation in the future. To that end, a table of contents is pro
to assist in easy navigation: to assist in easy navigation:
- [Foreword](#foreword) - [Foreword](#foreword)
- Non-Heap Memory Types - [Non-Heap Memory Types](#non-heap-memory-types)
- Piling On - the Heap in Rust - [Piling On - Rust and the Heap](#piling-on-rust-and-the-heap)
- Compiler Optimizations Make Everything Complicated - [Compiler Optimizations Make Everything Complicated](#compiler-optimizations-make-everything-complicated)
- Summary: When Does Rust Allocate? - Summary: When Does Rust Allocate?
- Appendix and Further Reading - [Appendix and Further Reading](#appendix-and-further-reading)
# Foreword # Foreword
@ -75,9 +75,7 @@ include a warning worth repeating here:
> Rust does not currently have a rigorously and formally defined memory model. > Rust does not currently have a rigorously and formally defined memory model.
> - the [Rust docs](https://doc.rust-lang.org/std/ptr/fn.read_volatile.html) > - the [Rust docs](https://doc.rust-lang.org/std/ptr/fn.read_volatile.html)
# Distinguishing regions of memory # Non-Heap Memory Types
# Rust and the Stack
Example: Why doesn't `Vec::new()` go to the allocator? Example: Why doesn't `Vec::new()` go to the allocator?
@ -91,7 +89,7 @@ Questions:
6. How are arrays allocated? 6. How are arrays allocated?
7. Legal to pass an array as an argument? 7. Legal to pass an array as an argument?
# Rust and the Heap # Piling On - Rust and the Heap
Example: How to trigger a heap allocation Example: How to trigger a heap allocation
@ -99,13 +97,20 @@ Questions:
1. Where do collection types allocate memory? 1. Where do collection types allocate memory?
2. Does a Box<> always allocate heap? 2. Does a Box<> always allocate heap?
- Yes, with exception of compiler optimizations
3. Passing Box<Trait> vs. genericizing/monomorphization 3. Passing Box<Trait> vs. genericizing/monomorphization
- If it uses `dyn Trait`, it's on the heap.
4. Other pointer types? Do Rc<>/Arc<> force heap allocation? 4. Other pointer types? Do Rc<>/Arc<> force heap allocation?
- Maybe? Part of the alloc crate, but should use qadapt to check
# Understanding compiler optimizations # Compiler Optimizations Make Everything Complicated
Example: Compiler stripping out allocations of Box<>, Vec::push() Example: Compiler stripping out allocations of Box<>, Vec::push()
# Appendix and Further Reading
[Embedonomicon]:
[embedonomicon]: https://docs.rust-embedded.org/embedonomicon/ [embedonomicon]: https://docs.rust-embedded.org/embedonomicon/
[libc]: CRATES.IO LINK [libc]: CRATES.IO LINK
[winapi]: CRATES.IO LINK [winapi]: CRATES.IO LINK