About this Session
Green Tea's insight is elegant: scan spans, not objects. But how do you actually implement that? What data structures track which objects are marked vs. scanned? Why does the ownership protocol use three states? And how did span-based scanning unlock SIMD optimizations that were impossible before? This talk dissects Green Tea's implementation: the inline mark bits structure, the FIFO span queues, the ownership protocol that prevents duplicate work, and the AVX-512 SIMD kernels in Go 1.26 that use a cryptographic instruction (VGF2P8AFFINEQB) for bitmap expansion. I've read the actual runtime code and understand why each design decision was made.
