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pd-rs / crankstart

A barely functional, wildly incomplete and basically undocumented Rust crate whose aim is to let you write Games for the Playdate handheld gaming system in Rust.
MIT License
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Which memory allocator is used? #24

Closed laplab closed 2 years ago

laplab commented 2 years ago

Hi!

First of all, thank you for all the effort you put into this crate! It is wonderful to have an option of writing performance-sensitive games for PlayDate in Rust.

I have a question regarding memory allocations. If my understanding is correct, certain PlayDate SDK functions can allocate memory. My guess would be that either standard C allocator is used or some other allocator coming from the SDK.

What allocator is used for the Rust part of the game? Basically, what exactly happens when one writes Box::new in the game's code?

From what I gather, the options are:

  1. The same allocator as PlayDate SDK. There is a global allocator defined somewhere in crankstart, which calls respective malloc/free functions from C
  2. There is a Rust allocator, which has its own separate heap. In this case, the question is how C allocator and Rust allocator share the RAM
  3. Maybe something else I missed!

Would appreciate any pointers/hints to the answer. Thanks!

rtsuk commented 2 years ago

It is a wrapper around the allocator provided by the PlayDate SDK, implemented here: https://github.com/pd-rs/crankstart/blob/main/src/lib.rs#L325.

laplab commented 2 years ago

Makes sense, thank you!