Struct PoolInner 

struct PoolInner {
    free: Vec<usize>,
    slot: Option<RawFrame>,
    held: Option<usize>,
    release: bool,
}

Mutex-guarded interior of FramePool: the free-surface index list, the single capture -> encode handoff slot, and the surface the encoder still reads, under one lock so moving a surface between them — acquire, publish, take, recycle, settle — is always a single atomic step.

Fields

free: Vec<usize>

slot: Option<RawFrame>

held: Option<usize>

The surface whose picture the encoder reads through its next encode, out of free until a later encode stops reading it (settle).

release: bool

Whether drain_for_resize asks the encode thread to stop reading held and return it.