Whippet Garbage Collector

This repository is for development of Whippet, a new garbage collector implementation, eventually for use in Guile Scheme.

Whippet is an embed-only C library, designed to be copied into a program's source tree. It exposes an abstract C API for managed memory allocation, and provides a number of implementations of that API.

One of the implementations is also called "whippet", and is the motivation for creating this library. For a detailed introduction, see Whippet: Towards a new local maximum, a talk given at FOSDEM 2023.

Documentation

• Design: What's the general idea?
• Manual: How do you get your program to use Whippet? What is the API?
• Guile: Some notes on a potential rebase of Guile on top of Whippet.

Source repository structure

• api/: The user-facing API. Also, the "embedder API"; see the manual for more.
• doc/: Documentation, such as it is.
• src/: The actual GC implementation. The specific implementations of the Whippet API are semi.c, a semi-space collector; bdw.c, the third-party BDW-GC conservative parallel stop-the-world mark-sweep segregated-fits collector with lazy sweeping; and whippet.c, the whippet collector.
• benchmarks/: Benchmarks. A work in progress.
• test/: A dusty attic of minimal testing.

To do

Missing features before Guile can use Whippet

• Pinning
• Conservative stacks
• Conservative data segments
• Heap growth/shrinking
• Debugging/tracing
• Finalizers
• Weak references / weak maps

Features that would improve Whippet performance

• Immix-style opportunistic evacuation
• [ ] Overflow allocation (should just evacuate instead)
• Generational GC via sticky mark bits
• Generational GC with semi-space nursery
• Concurrent marking with SATB barrier

About the name

It sounds better than WIP (work-in-progress) garbage collector, doesn't it? Also apparently a whippet is a kind of dog that is fast for its size. It would be nice if whippet-gc turns out to have this property.

License

Copyright (c) 2022-2023 Andy Wingo

Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Note that some benchmarks have other licenses; see benchmarks/README.md for more.