fix: items propagation, DynamicInvoke wrapping, thread safety

[cloud-hai-vo]

Context

Fixes from 3-round deep code review (Round 1: core mapper, Round 2: expression builder, Round 3: config + DI + tests).

Fixes

1. MapWithItems loses items dictionary on fallback (HIGH)

Before: MapWithItems<S,D>() fell back to Map<S,D>(source) which dropped the items dictionary. Resolvers that depend on ctx.Items would silently receive null.

After: Falls back to MapInternal() which preserves items through base-type walk, interface walk, and collection auto-mapping.

2. PatchSlow DynamicInvoke leaks TargetInvocationException (MEDIUM)

Before: Patch<Derived, Dest>() using base-type fallback threw raw TargetInvocationException — no type context, confusing stack trace.

After: Wraps in MappingException with readable runtime type names.

3. Concurrent open generic compilation waste (MEDIUM)

Before: Multiple threads calling Map<ApiResponse<Order>, ApiResponseDto<OrderDto>>() simultaneously would each independently compile the same delegate. Only one result stored; rest discarded.

After: GetOrAdd with factory delegate ensures only one thread compiles per type pair.

Test plan

• 348 tests pass across net8.0, net9.0, net10.0
• Existing thread safety tests still pass
• Existing open generic tests still pass

🤖 Generated with Claude Code

[github-actions]

📊 Benchmark Results

Generated: 2026-03-26 23:52 UTC  ·  Download full artifacts

Column guide:
Mean = average execution time  ·  Error = half of 99.9 % confidence interval  ·  StdDev = standard deviation  ·  Min / Median / Max = statistical range  ·  Ratio = vs Manual baseline (lower = closer to hand-written speed)  ·  RatioSD = ratio std dev  ·  Rank = 1 is fastest  ·  Gen0/1/2 = GC collections per 1 000 ops  ·  Allocated = managed heap per operation  ·  Alloc Ratio = allocation ratio vs baseline

🔵 Flat Mapping — 10-property object

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	14.26 ns	0.462 ns	0.025 ns	14.24 ns	14.26 ns	14.29 ns	1.00	0.00	1	0.0048	80 B	1.00
EggMapper	24.52 ns	1.248 ns	0.068 ns	24.46 ns	24.51 ns	24.60 ns	1.72	0.00	2	0.0048	80 B	1.00
AutoMapper	82.17 ns	2.144 ns	0.118 ns	82.08 ns	82.12 ns	82.30 ns	5.76	0.01	3	0.0048	80 B	1.00
Mapster	26.84 ns	0.838 ns	0.046 ns	26.79 ns	26.87 ns	26.87 ns	1.88	0.00	2	0.0048	80 B	1.00
MapperlyMap	14.09 ns	0.678 ns	0.037 ns	14.05 ns	14.09 ns	14.13 ns	0.99	0.00	1	0.0048	80 B	1.00
AgileMapper	498.71 ns	27.792 ns	1.523 ns	497.27 ns	498.55 ns	500.30 ns	34.97	0.11	4	0.0200	344 B	4.30
EggMapperGenerator	14.61 ns	0.779 ns	0.043 ns	14.56 ns	14.63 ns	14.63 ns	1.02	0.00	1	0.0048	80 B	1.00
EggMapperClassMapper	14.40 ns	1.324 ns	0.073 ns	14.33 ns	14.39 ns	14.48 ns	1.01	0.00	1	0.0048	80 B	1.00

🟡 Flattening — 2 nested objects → 8 flat properties

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	18.33 ns	6.044 ns	0.331 ns	18.09 ns	18.19 ns	18.71 ns	1.00	0.02	1	0.0048	80 B	1.00
EggMap	28.71 ns	3.175 ns	0.174 ns	28.58 ns	28.64 ns	28.90 ns	1.57	0.03	3	0.0048	80 B	1.00
AutoMapper	87.24 ns	3.666 ns	0.201 ns	87.06 ns	87.20 ns	87.45 ns	4.76	0.07	5	0.0048	80 B	1.00
Mapster	35.19 ns	6.358 ns	0.348 ns	34.90 ns	35.09 ns	35.57 ns	1.92	0.03	4	0.0048	80 B	1.00
MapperlyMap	23.50 ns	2.154 ns	0.118 ns	23.36 ns	23.56 ns	23.57 ns	1.28	0.02	2	0.0062	104 B	1.30
AgileMapper	514.05 ns	47.868 ns	2.624 ns	511.92 ns	513.24 ns	516.98 ns	28.05	0.45	6	0.0200	344 B	4.30

🟣 Deep Mapping — 2 nested address objects

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	51.38 ns	0.789 ns	0.043 ns	51.34 ns	51.39 ns	51.42 ns	1.00	0.00	1	0.0162	272 B	1.00
EggMapper	68.33 ns	7.621 ns	0.418 ns	68.07 ns	68.11 ns	68.82 ns	1.33	0.01	2	0.0162	272 B	1.00
AutoMapper	117.68 ns	5.301 ns	0.291 ns	117.39 ns	117.68 ns	117.97 ns	2.29	0.01	3	0.0162	272 B	1.00
Mapster	65.09 ns	3.467 ns	0.190 ns	64.92 ns	65.05 ns	65.29 ns	1.27	0.00	2	0.0162	272 B	1.00
MapperlyMap	47.14 ns	2.076 ns	0.114 ns	47.02 ns	47.15 ns	47.25 ns	0.92	0.00	1	0.0162	272 B	1.00
AgileMapper	499.92 ns	25.457 ns	1.395 ns	498.89 ns	499.38 ns	501.51 ns	9.73	0.02	4	0.0248	424 B	1.56

🟢 Complex Mapping — nested object + collection

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	66.69 ns	6.415 ns	0.352 ns	66.47 ns	66.50 ns	67.09 ns	1.00	0.01	1	0.0191	320 B	1.00
EggMapper	86.74 ns	0.776 ns	0.043 ns	86.69 ns	86.74 ns	86.78 ns	1.30	0.01	2	0.0191	320 B	1.00
AutoMapper	150.44 ns	7.631 ns	0.418 ns	150.10 ns	150.32 ns	150.91 ns	2.26	0.01	3	0.0196	328 B	1.02
Mapster	85.78 ns	2.001 ns	0.110 ns	85.66 ns	85.80 ns	85.87 ns	1.29	0.01	2	0.0191	320 B	1.00
MapperlyMap	68.40 ns	3.233 ns	0.177 ns	68.25 ns	68.35 ns	68.59 ns	1.03	0.01	1	0.0191	320 B	1.00
AgileMapper	573.91 ns	7.609 ns	0.417 ns	573.44 ns	574.04 ns	574.24 ns	8.61	0.04	4	0.0315	528 B	1.65

🟠 Collection — 100-item List<T>

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	1.644 μs	0.0214 μs	0.0012 μs	1.643 μs	1.645 μs	1.645 μs	1.00	1	0.5283	0.0172	8.65 KB	1.00
EggMapper	1.682 μs	0.0687 μs	0.0038 μs	1.678 μs	1.683 μs	1.686 μs	1.02	1	0.5283	0.0172	8.65 KB	1.00
AutoMapper	2.249 μs	0.0717 μs	0.0039 μs	2.245 μs	2.250 μs	2.253 μs	1.37	2	0.6065	0.0191	9.95 KB	1.15
Mapster	1.677 μs	0.1059 μs	0.0058 μs	1.671 μs	1.677 μs	1.683 μs	1.02	1	0.5283	0.0172	8.65 KB	1.00
MapperlyMap	1.719 μs	0.4494 μs	0.0246 μs	1.704 μs	1.705 μs	1.747 μs	1.05	1	0.5283	0.0172	8.65 KB	1.00
AgileMapper	2.430 μs	0.1199 μs	0.0066 μs	2.423 μs	2.433 μs	2.435 μs	1.48	2	0.5417	0.0153	8.91 KB	1.03

🟠 Collection — 100-item List<T>

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	5.074 μs	0.3246 μs	0.0178 μs	5.056 μs	5.075 μs	5.092 μs	1.00	1	1.6708	0.0916	27.4 KB	1.00
EggMapper	5.571 μs	0.4137 μs	0.0227 μs	5.556 μs	5.559 μs	5.597 μs	1.10	1	1.6708	0.0916	27.4 KB	1.00
AutoMapper	6.285 μs	0.0963 μs	0.0053 μs	6.280 μs	6.286 μs	6.291 μs	1.24	1	1.7548	0.1068	28.7 KB	1.05
Mapster	5.588 μs	0.1242 μs	0.0068 μs	5.582 μs	5.585 μs	5.595 μs	1.10	1	1.6708	0.0916	27.4 KB	1.00
MapperlyMap	5.115 μs	0.1515 μs	0.0083 μs	5.107 μs	5.115 μs	5.123 μs	1.01	1	1.6785	0.0992	27.42 KB	1.00
AgileMapper	5.017 μs	0.3602 μs	0.0197 μs	4.995 μs	5.023 μs	5.032 μs	0.99	1	1.0223	0.0610	16.72 KB	0.61

🟠 Collection — 100-item List<T>

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	16.27 μs	2.867 μs	0.157 μs	16.09 μs	16.33 μs	16.39 μs	1.00	1	5.2490	1.3123	85.99 KB	1.00
EggMapper	16.42 μs	2.854 μs	0.156 μs	16.24 μs	16.50 μs	16.52 μs	1.01	1	5.2490	1.3123	85.99 KB	1.00
AutoMapper	20.87 μs	1.616 μs	0.089 μs	20.77 μs	20.89 μs	20.94 μs	1.28	1	5.7678	1.4343	94.34 KB	1.10
Mapster	16.78 μs	0.212 μs	0.012 μs	16.77 μs	16.78 μs	16.79 μs	1.03	1	5.2490	1.3123	85.99 KB	1.00
MapperlyMap	17.97 μs	0.623 μs	0.034 μs	17.94 μs	17.95 μs	18.01 μs	1.10	1	5.2490	1.2817	86.02 KB	1.00
AgileMapper	19.73 μs	1.308 μs	0.072 μs	19.65 μs	19.76 μs	19.78 μs	1.21	1	5.2795	1.3123	86.25 KB	1.00

⚪ Startup / Configuration time

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
EggMapperStartup	1,307.479 μs	1,671.8997 μs	91.6425 μs	1,210.844 μs	1,318.452 μs	1,393.141 μs	1.003	0.09	3	3.9063	1.9531	95.29 KB	1.00
AutoMapperStartup	439.799 μs	658.3421 μs	36.0860 μs	410.643 μs	428.597 μs	480.158 μs	0.337	0.03	2	5.8594	-	104.16 KB	1.09
MapsterStartup	2.388 μs	0.2922 μs	0.0160 μs	2.377 μs	2.379 μs	2.406 μs	0.002	0.00	1	0.7019	0.0267	11.51 KB	0.12

EggMapper.Benchmarks.ColdStartBenchmark-report-github

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
EggMapper	1.286 ms	1.744 ms	0.0956 ms	1.225 ms	1.237 ms	1.396 ms	1.00	0.09	1	5.8594	3.9063	95.43 KB	1.00
AutoMapper	4.366 ms	11.433 ms	0.6267 ms	3.738 ms	4.368 ms	4.992 ms	3.41	0.47	2	15.6250	7.8125	310.51 KB	3.25
Mapster	4.081 ms	6.573 ms	0.3603 ms	3.670 ms	4.231 ms	4.342 ms	3.19	0.31	2	39.0625	15.6250	756.28 KB	7.92

---

📝 Notes

• Each benchmark class is decorated with [MemoryDiagnoser] and [RankColumn].
• The global config (see src/EggMapper.Benchmarks/Program.cs) adds Min, Median, and Max columns.
• Manual is the hand-written baseline (ratio = 1.00). A ratio < 1 means faster than manual.
• Benchmarks run on GitHub-hosted runners — absolute times may vary between runs; focus on Ratio for comparisons.
• To reproduce locally:

  cd src/EggMapper.Benchmarks
  dotnet run --configuration Release -- --filter '*'