Rewrite benchmarks

mix run bench/rewrite.exs compares declarative, streamed, and legacy-callback rewrites of one larger document. mix run bench/load.exs exercises concurrency and native lifecycle behavior. Neither is a statistical performance suite.

Load benchmark

JOBS=2000 ROUNDS=3 ELEMENTS=100 CHUNK_BYTES=4096 CONCURRENCY=1,8,32 \
  mix run bench/load.exs

These are the defaults. Each case processes JOBS independent documents with at most CONCURRENCY tasks. Each dynamic document starts a fresh session/native worker. All modes set the same attribute on each p; output size and CRC32 are checked against a whole-document rewrite. Dynamic mode replies once per element; dynamic_no_matches uses native rules with an unmatched dynamic selector to isolate the opt-in session overhead. Warmup exercises all four modes.

CSV reports:

• End-to-end documents/second, including task/session startup and shutdown.
• Per-document p95 latency (including dynamic session startup, excluding task startup).
• Number of samples and maximum sampler timer lateness on the BEAM.
• Maximum observed mailbox length of an owner task or session, not a VM-wide sum.
• Observed peak native worker count and reserved bounded-output-buffer capacity.
• Sampled BEAM memory growth and post-quiescence process RSS/change, in MiB.

Sampling runs every 10ms, adds overhead, and can miss short-lived allocations or mailbox bursts. n/a means no samples were collected; even a sampled zero is not proof that a transient allocation never occurred. Timer lateness includes sampler work and host scheduling noise. RSS uses ps where available; it is not peak RSS, and includes allocator caches, thread stacks, code, and BEAM memory. Native counters exclude legacy callback workers, LOL HTML allocations, input, BEAM binaries, and whole-document output vectors. All cases wait for tracked workers/buffers/capacity to reach {0, 0, 0} before continuing. This final native quiescence wait and the subsequent RSS measurement are outside throughput timing.

For multi-chunk documents, increase ELEMENTS or decrease CHUNK_BYTES. Increase JOBS for meaningful sampling of short native-only cases. Repeated rounds in the same VM help distinguish allocator warmup from continuing memory growth.

Local baseline

Apple M5, Darwin arm64, OTP 27, Elixir 1.19.5, 10 BEAM schedulers; Rust 1.95.0, release native build. Default workload above: 3,692 input bytes and 100 elements per document. Median throughput across three rounds:

Observed over this run:

• All 36 cases returned tracked native resources to zero.
• Maximum sampled mailbox length: 5 messages; sampler timer lateness: 18ms.
• At concurrency 32, dynamic mode reached 32 tracked workers and 32 MiB reserved output-buffer capacity (the default is 1 MiB/session, not all resident).
• Post-quiescence RSS at the end of each round: 122.80, 124.70, 124.67 MiB. This short run is consistent with warmup/retention, not proof that all memory is leak-free.
• Dynamic p95 document latency at concurrency 32 varied from 14.39 to 33.22ms, illustrating host/load variability. Native high-concurrency cases had only 1–4 samples per case, so their sampled peaks are especially weak evidence.

An additional 200-document run with 1,000 elements/document (37,893 bytes, multiple 4,096-byte chunks) at concurrency 32 also returned all tracked resources to zero. It measured 13,572 native, 12,071 streamed, 3,583 unmatched-dynamic, and 250 fully dynamic documents/second; sampled timer lateness stayed at or below 5ms. This is a single additional run, not a stable throughput estimate.

The existing 71,000-byte / 3,000-match comparison measured medians of 0.89ms native, 0.95ms streaming, and 13.26ms legacy callbacks (five runs each).

Implication: keep declarative transformations on the native fast path. Per-element messaging is expensive, while an unmatched dynamic session is still substantially more expensive than a native rewrite. This does not establish that worker pooling is the right optimization: profile startup versus message costs on a representative workload before changing worker ownership or semantics.

Hardening tests

mix test test/laughter/rewriter/lifecycle_test.exs test/laughter/rewriter/equivalence_test.exs

Lifecycle tests serialize around VM-global counters and cover forced process termination, owner death, both cancel/reply and delivered-timeout/reply orderings, stale timer delivery during a later request, real native watchdog races, repeated EOF/startup-error/overflow cleanup, and resource destruction without explicit close. Delivered-timer orderings use a suspended session and queued owner calls rather than relying on sleep timing. Real watchdog tests accept either legitimate race winner but require one terminal event and prompt cleanup.

Equivalence tests use 120 fixed random seeds to vary mutations and byte-level chunk boundaries (including split UTF-8, entities, empty chunks, and incomplete EOF tokens). Whole-document, streaming, and dynamic results must match exactly. They use sibling p elements and a stable tag selector so the compared modes have equivalent matching semantics; they are not exhaustive HTML fuzzing.