gc.md

Golang Realtime GC

• Guide to the Go Garbage Collector
• A walk through the tricolor mark-and-sweep algorithm

Other GC Algorithms `⸜( ◜࿁◝ )⸝︎︎

Concurrent Mark and Sweep (CMS):

• Performs most marking concurrently with the application
• Uses incremental updates to track new references
• Reduces pause times but has higher overhead
• More complex than the current implementation

Garbage First (G1) Collector:

• Divides heap into equal-sized regions
• Collects regions with most garbage first
• Provides more predictable pause times
• Would require significant restructuring of heap layout

ZGC (by Oracle):

• Uses colored pointers
• Performs concurrent operations without stop-the-world pauses
• Scales well to large heaps
• Very complex to implement in assembly

૮₍ • ᴥ • ₎ა gARM彡 WIP coming soon

Generational Garbage Collection

Call init_gen_gc at program start This sets up three generation spaces:

1. Eden (4MB) new allocations
2. Survivor space (16MB) for young surviving objects
3. Tenured space (44MB) for long-lived objects

Allocation:

Objects are initially allocated in eden space

ALLOC_STRING 32    // Allocate 32-byte string
ALLOC_ARRAY 100, 4 // Allocate array of 100 integers

• UseGEN_ALLOC macro for basic allocation
• Helper macros like ALLOC_STRING and ALLOC_ARRAY for specific types.

Root registration:

bl register_thread_roots  // Register current thread roots

• Registers thread roots (stack, registers)
• Registers global roots
• GC tracks them to find live objects

Collection Triggers:

• Minor GC happens automatically when eden fills
• Objects surviving multiple minor GCs promote to tenured space
• Full GC triggers when tenured space fills

Advantages

• Fast allocation in eden space
• Much faster minor collections since most objects die young
• Age-based promotion policy (eden -> survivor -> tenured)
• Better cache locality in the nursery
• Reduced pause times as full collections are less frequent
• Reduced write barrier overhead

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