docs/zh/plans/render-pipeline-threads.md M4: the thread pipeline now
keeps its decode thread ahead of the render thread and the app's
playback window consumes in-process frames.
- Render queue: priority-ordered by JobSchedule.priority (Seek >
Playback > Background, FIFO within a class), so interactive frames
jump playback exports/autocache. Seek posts may over-admit the bound:
priority only reorders queued jobs, so a full queue of background work
must not park the UI thread until an export frame finishes.
- Decode queue: rendezvous Requests are served ahead of queued
Prefetches (a frame the renderer needs never waits behind speculative
decodes); Sync barriers stay FIFO. The queue is a bounded
Mutex+Condvar structure, preserving the request backpressure and the
wait_idle contract.
- Playback read-ahead: a Playback job's footage decode requests are
derived from its montage/footage spec on post (same media time, size
and force_format.unwrap_or(F32) as the eval) and queued immediately,
so frame N+1 decodes while frame N runs its GPU passes.
- App window: PreviewWindow slots are generalized to
PreviewSlot::{Shm, Video}; the pipeline's in-process TicketPayload is
cached and consumed by cpu_frame exactly like a worker slot.
PipelineBackend::preview_window_capacity reports the render-queue
headroom, so playback posts are capped to what the queue can take;
cancel_preview_frame drops queued frames the playhead has passed,
matched on the full (sequence, frame, version) key so one monitor's
window never drops the other sequence's same-numbered frame.
- Tests: decode-queue preemption/FIFO, render-queue ordering, request
derivation, and deterministic end-to-end M4 tests: a prefetch that
must be reused by the render request (LRU hit, single decode — the
read-ahead claim is falsifiable), a parked-render-thread priority test
where a full queue of background work still lets a Seek over-admit and
run first, and a sequence-aware cancel test. The playback prefetch
smoke asserts prefetches == distinct decodes == frames; it does not
claim zero heap copies (Frame.data is deep-copied at the eval-cache
and service-LRU boundaries today).
- bench_playback gains a pipeline mode with CPU (self+children) and
first-frame latency; both backends now produce F32 frames so the
comparison is like-for-like. The §3.4 backfill records the numbers:
at the proxy size the pipeline is faster with a lower first frame; at
1080p peak throughput is below the multi-worker pool, but that is an
artifact of the decode still being CPU software (M5), not a case for
pooling decode threads — GPU decode is a single device/queue and the
zero-copy import shares one GPU memory pool, so the single decode
thread stays the target shape.
Mike-Solar
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