RouterNode and FilterNode were the last nodes on a data path still using the
throwing push() and swallowing the result:
try { out_ch_->push(val); } catch (const ChannelOverflowError&) {}
6595e6e made node outputs lossless, 28e0667 stopped them parking a worker,
a8cfe73 did the same for FanoutNode. These two were in none of them.
For ordinary values that is the familiar silent-loss problem: a dropped item
does not degrade a downstream result, it silently changes one, and the
consumer cannot tell it happened.
For a sentinel it is a hang. EOF is what tells every downstream node to shut
down and there is nothing after it to retry, so a filter that passes EOF by
predicate but drops it by backpressure produces a pipeline that never
terminates. scene-actor-extraction's decimator is exactly that shape —
`if (f.eof) return true;` in the predicate, feeding a chain whose slowest
node is an ONNX embedder, so the output is reliably full when EOF arrives.
Everything downstream then waits forever for a token that was discarded, and
the run has to be killed.
Both now route sentinels out-of-band via push_sentinel, which consumes no
ring capacity and cannot overflow, and retry ordinary values until taken.
Like FanoutNode and unlike a pool node, these own a private thread, so
waiting costs no scheduler worker and needs no space-callback park;
stop_flag_ is rechecked every pass so teardown cannot hang on a full output.
Time spent parked is charged to blocked rather than exec, so a held-up node
does not report as busy. An out-of-range router selector still drops by
design — that item was routed nowhere, which is not the same as lost.
is_sentinel_value moves from pool_node.hpp to traits.hpp. Every node type
that forwards a value needs it; these two not having it is the bug.
Verified in both directions. On c73edff the new case delivers 6 of 40 values
and never sets saw_eof; here it delivers 40 and terminates. EOF is emitted
exactly once, as a real source does — a test source that re-offered it would
mask the bug, since a later attempt could find the channel drained.
Note for downstream: the decimator is now a backpressure point rather than a
relief valve, so the source throttles to the face branch instead of quietly
thinning it. That is the intended behaviour, but it changes the shape of a
loaded run and is worth a benchmark comparison on a known clip.
dtourolle
6a4f45f111