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Single write barrier section

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Justin Ethier 2022-11-30 14:28:52 -08:00
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docs/Garbage-Collector-Revised-2022.md
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@ -11,8 +11,7 @@
- [Minor Collection](#minor-collection) - [Minor Collection](#minor-collection)
- [Cheney on the MTA](#cheney-on-the-mta) - [Cheney on the MTA](#cheney-on-the-mta)
- [Our Implementation](#our-implementation) - [Our Implementation](#our-implementation)
- [Write Barrier for Heap Object References](#write-barrier-for-heap-object-references) - [Write Barriers](#write-barriers)
- [Write Barrier to Relocate Shared Objects](#write-barrier-to-relocate-shared-objects)
- [Major Collection](#major-collection) - [Major Collection](#major-collection)
- [Lazy Sweeping](#lazy-sweeping) - [Lazy Sweeping](#lazy-sweeping)
- [Object Marking](#object-marking) - [Object Marking](#object-marking)
@ -147,7 +146,9 @@ The collection algorithm itself operates as follows:
Any objects left on the stack after `longjmp` are considered garbage. There is no need to clean them up because the stack will just re-use the memory as it grows. Any objects left on the stack after `longjmp` are considered garbage. There is no need to clean them up because the stack will just re-use the memory as it grows.
## Write Barrier for Heap Object References ## Write Barriers
### Heap Object References
Baker's paper does not mention one important detail. A heap object can be modified to contain a reference to a stack object. For example, by using a `set-car!` to change the head of a list: Baker's paper does not mention one important detail. A heap object can be modified to contain a reference to a stack object. For example, by using a `set-car!` to change the head of a list:
@ -157,7 +158,7 @@ This is problematic since stack references are no longer valid after a minor GC
The write barrier must be called by each primitive in the runtime that modifies object pointers - `set-car!`, `set-cdr!`, `vector-set!`, etc. Fortunately there are only a handful of these functions. The write barrier must be called by each primitive in the runtime that modifies object pointers - `set-car!`, `set-cdr!`, `vector-set!`, etc. Fortunately there are only a handful of these functions.
## Write Barrier to Relocate Shared Objects ### Relocating Shared Objects
Cyclone must guarantee the objects located on each mutator thread's stack are only used by that thread. Cyclone must guarantee the objects located on each mutator thread's stack are only used by that thread.