Tryst::SDL::AudioCapture::RingState

Shared state between the audio-thread callback (the producer, #push) and the drain fiber (the consumer, #pop). A struct, not a Crystal object, reached through a raw pointer - same reasoning as ever: the audio thread must never touch a Crystal object or dispatch a method on one.

Every mutable field here is an Atomic, and every mutation goes through a method call on pointer.value (@produced.add(...) and friends) rather than a field assignment. That distinction matters and is not obvious: pointer.value.field = x and pointer.value.field += x both silently write to a throwaway copy and never reach the pointee - Crystal's op-assign desugars to evaluating pointer.value once into a local temporary and never writing it back. A plain method call on that same receiver does not have this problem - Crystal passes self for a struct method by the address the receiver dereferenced from, so pointer.value.push(...) mutates the real memory in place, including under genuine concurrent multi-thread stress. Every mutator on this struct is therefore a method, never a bare field write, and that rule must not be broken by future edits here.

produced is written only by the audio thread, consumed only by the drain fiber - the single-writer-per-counter property that makes this lock-free. Both are monotonic counts of samples ever produced/consumed, not ring positions - % capacity turns one into the other where needed.