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).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Joseph Doherty
@@ -287,56 +287,127 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
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var now = DateTime.UtcNow;
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var results = new DataValueSnapshot[fullReferences.Count];
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for (var i = 0; i < fullReferences.Count; i++)
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{
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var reference = fullReferences[i];
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if (!_tagsByName.TryGetValue(reference, out var def))
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{
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results[i] = new DataValueSnapshot(null, AbCipStatusMapper.BadNodeIdUnknown, null, now);
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continue;
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}
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if (!_devices.TryGetValue(def.DeviceHostAddress, out var device))
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{
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results[i] = new DataValueSnapshot(null, AbCipStatusMapper.BadNodeIdUnknown, null, now);
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continue;
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}
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// Task #194 — plan the batch: members of the same parent UDT get collapsed into one
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// whole-UDT read + in-memory member decode; every other reference falls back to the
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// per-tag path that's been here since PR 3. Planner is a pure function over the
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// current tag map; BOOL/String/Structure members stay on the fallback path because
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// declaration-only offsets can't place them under Logix alignment rules.
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var plan = AbCipUdtReadPlanner.Build(fullReferences, _tagsByName);
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try
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{
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var runtime = await EnsureTagRuntimeAsync(device, def, cancellationToken).ConfigureAwait(false);
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await runtime.ReadAsync(cancellationToken).ConfigureAwait(false);
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foreach (var group in plan.Groups)
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await ReadGroupAsync(group, results, now, cancellationToken).ConfigureAwait(false);
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var status = runtime.GetStatus();
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if (status != 0)
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{
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results[i] = new DataValueSnapshot(null,
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AbCipStatusMapper.MapLibplctagStatus(status), null, now);
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_health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
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$"libplctag status {status} reading {reference}");
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continue;
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}
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var tagPath = AbCipTagPath.TryParse(def.TagPath);
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var bitIndex = tagPath?.BitIndex;
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var value = runtime.DecodeValue(def.DataType, bitIndex);
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results[i] = new DataValueSnapshot(value, AbCipStatusMapper.Good, now, now);
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_health = new DriverHealth(DriverState.Healthy, now, null);
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}
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catch (OperationCanceledException)
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{
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throw;
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}
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catch (Exception ex)
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{
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results[i] = new DataValueSnapshot(null,
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AbCipStatusMapper.BadCommunicationError, null, now);
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_health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
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}
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}
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foreach (var fb in plan.Fallbacks)
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await ReadSingleAsync(fb, fullReferences[fb.OriginalIndex], results, now, cancellationToken).ConfigureAwait(false);
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return results;
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}
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private async Task ReadSingleAsync(
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AbCipUdtReadFallback fb, string reference, DataValueSnapshot[] results, DateTime now, CancellationToken ct)
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{
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if (!_tagsByName.TryGetValue(reference, out var def))
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{
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results[fb.OriginalIndex] = new DataValueSnapshot(null, AbCipStatusMapper.BadNodeIdUnknown, null, now);
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return;
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}
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if (!_devices.TryGetValue(def.DeviceHostAddress, out var device))
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{
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results[fb.OriginalIndex] = new DataValueSnapshot(null, AbCipStatusMapper.BadNodeIdUnknown, null, now);
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return;
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}
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try
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{
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var runtime = await EnsureTagRuntimeAsync(device, def, ct).ConfigureAwait(false);
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await runtime.ReadAsync(ct).ConfigureAwait(false);
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var status = runtime.GetStatus();
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if (status != 0)
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{
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results[fb.OriginalIndex] = new DataValueSnapshot(null,
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AbCipStatusMapper.MapLibplctagStatus(status), null, now);
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_health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
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$"libplctag status {status} reading {reference}");
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return;
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}
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var tagPath = AbCipTagPath.TryParse(def.TagPath);
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var bitIndex = tagPath?.BitIndex;
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var value = runtime.DecodeValue(def.DataType, bitIndex);
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results[fb.OriginalIndex] = new DataValueSnapshot(value, AbCipStatusMapper.Good, now, now);
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_health = new DriverHealth(DriverState.Healthy, now, null);
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}
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catch (OperationCanceledException)
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{
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throw;
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}
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catch (Exception ex)
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{
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results[fb.OriginalIndex] = new DataValueSnapshot(null,
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AbCipStatusMapper.BadCommunicationError, null, now);
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_health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
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}
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}
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/// <summary>
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/// Task #194 — perform one whole-UDT read on the parent tag, then decode each
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/// grouped member from the runtime's buffer at its computed byte offset. A per-group
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/// failure (parent read raised, non-zero libplctag status, or missing device) stamps
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/// the mapped fault across every grouped member only — sibling groups + the
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/// per-tag fallback list are unaffected.
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/// </summary>
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private async Task ReadGroupAsync(
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AbCipUdtReadGroup group, DataValueSnapshot[] results, DateTime now, CancellationToken ct)
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{
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var parent = group.ParentDefinition;
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if (!_devices.TryGetValue(parent.DeviceHostAddress, out var device))
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{
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StampGroupStatus(group, results, now, AbCipStatusMapper.BadNodeIdUnknown);
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return;
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}
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try
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{
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var runtime = await EnsureTagRuntimeAsync(device, parent, ct).ConfigureAwait(false);
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await runtime.ReadAsync(ct).ConfigureAwait(false);
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var status = runtime.GetStatus();
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if (status != 0)
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{
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var mapped = AbCipStatusMapper.MapLibplctagStatus(status);
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StampGroupStatus(group, results, now, mapped);
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_health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
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$"libplctag status {status} reading UDT {group.ParentName}");
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return;
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}
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foreach (var member in group.Members)
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{
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var value = runtime.DecodeValueAt(member.Definition.DataType, member.Offset, bitIndex: null);
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results[member.OriginalIndex] = new DataValueSnapshot(value, AbCipStatusMapper.Good, now, now);
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}
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_health = new DriverHealth(DriverState.Healthy, now, null);
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}
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catch (OperationCanceledException)
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{
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throw;
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}
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catch (Exception ex)
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{
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StampGroupStatus(group, results, now, AbCipStatusMapper.BadCommunicationError);
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_health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
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}
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}
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private static void StampGroupStatus(
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AbCipUdtReadGroup group, DataValueSnapshot[] results, DateTime now, uint statusCode)
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{
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foreach (var member in group.Members)
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results[member.OriginalIndex] = new DataValueSnapshot(null, statusCode, null, now);
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}
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// ---- IWritable ----
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/// <summary>
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