AbCip whole-UDT read optimization (#194) #158

dohertj2 · 2026-04-20T04:19:42-04:00

dohertj2 commented

2026-04-20 04:19:42 -04:00

Closes #194. Declaration-driven UDT read grouping collapses N per-member libplctag reads into one parent read + client-side decode at computed member offsets. Conservative BOOL/String/Structure opt-out � Template-Object-backed richer path is a follow-up. AbCip.Tests 227/227 (was 211, +16).

dohertj2 added 1 commit 2026-04-20 04:19:43 -04:00

AbCip whole-UDT read optimization (#194 ) — declaration-driven member grouping collapses N per-member reads into one parent-UDT read + client-side decode. Closes task #194 . On a batch that includes multiple members of the same hand-declared UDT tag, ReadAsync now issues one libplctag read on the parent + decodes each member from the runtime's buffer at its computed byte offset. A 6-member Motor UDT read goes from 6 libplctag round-trips to 1 — the Rockwell-suggested pattern for minimizing CIP request overhead on batch reads of UDT state (decision #11 's follow-through on what the template decoder from task #179 was meant to enable). AbCipUdtMemberLayout is a pure-function helper that computes declared-member byte offsets under Logix natural-alignment rules (SInt 1-byte / Int 2-byte / DInt + Real + Dt 4-byte / LInt + ULInt + LReal 8-byte; alignment pad inserted before each member as needed). Opts out for BOOL / String / Structure members — BOOL storage in Logix UDTs packs into a hidden host byte whose position can't be computed from declaration-only info, and String members need length-prefix + STRING[82] fan-out which libplctag already handles via a per-tag DecodeValue path. The CIP Template Object shape from task #179 (when populated via FetchUdtShapeAsync) carries real offsets for those members — layering that richer path on top of the planner is a separate follow-up and does not change this PR's conservative behaviour. AbCipUdtReadPlanner is the scheduling function ReadAsync consults each batch — pure over (requests, tagsByName), emits Groups + Fallbacks. A group is formed when (a) the reference resolves to "parent.member"; (b) parent is a Structure tag with declared Members; (c) the layout helper succeeds on those members; (d) the specific member appears in the computed offset map; (e) at least two members of the same parent appear in the batch — single-member groups demote to the fallback path because one whole-UDT read vs one per-member read is equivalent cost but more client-side work. Original batch indices are preserved through the plan so out-of-order batches write decoded values back at the right output slot; the caller's result array order is invariant. IAbCipTagRuntime.DecodeValueAt(AbCipDataType, int offset, int? bitIndex) is the new hot-path method — LibplctagTagRuntime delegates to libplctag's offset-aware Get*(offset) calls (GetInt32, GetFloat32, etc.) that were always there; previously every call passed offset 0. DecodeValue(type, bitIndex) stays as the shorthand + forwards to DecodeValueAt with offset 0, preserving the existing single-tag read path + every test that exercises it. FakeAbCipTag gains a ValuesByOffset dictionary so tests can drive multi-member decoding by setting offset→value before the read fires; unmapped offsets fall back to the existing Value field so the 200+ existing tests that never set ValuesByOffset keep working unchanged. AbCipDriver.ReadAsync refactored: planner splits the batch, ReadGroupAsync handles each UDT group (one EnsureTagRuntimeAsync on the parent + one ReadAsync + N DecodeValueAt calls), ReadSingleAsync handles each fallback (the pre-#194 per-tag path, now extracted + threaded through). A per-group failure stamps the mapped libplctag status across every grouped member only — sibling groups + fallback refs are unaffected. Health-surface updates happen once per successful group rather than once per member to avoid ping-ponging the DriverState bookkeeping. Five AbCipUdtMemberLayoutTests: packed atomics get natural-alignment offsets including 8-byte pad before LInt; SInts pack without padding; BOOL/String/Structure opt out + return null; empty member list returns null. Six AbCipUdtReadPlannerTests: two members group; single-member demotes to fallback; unknown references fall back without poisoning groups; atomic top-level tags fall back untouched; UDTs containing BOOL don't group; original indices survive out-of-order batches. Five AbCipDriverWholeUdtReadTests (real driver + fake runtime): two grouped members trigger exactly one parent read + one fake runtime (proving the optimization engages); each member decodes at its own offset via ValuesByOffset; parent-read non-zero status stamps Bad across the group; mixed UDT-member + atomic top-level batch produces 2 runtimes + 2 reads (not 3); single-member-of-UDT still uses the member-level runtime (proving demotion works). Driver builds 0 errors; AbCip.Tests 227/227 (was 211, +16 new). 780358c790

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

dohertj2 merged commit f6d5763448 into v2

2026-04-20 04:19:52 -04:00

dohertj2 referenced this issue from a commit

2026-04-20 04:19:54 -04:00

Merge pull request 'AbCip whole-UDT read optimization (#194)' (#158) from abcip-whole-udt-read into v2

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Reference: dohertj2/lmxopcua#158