Add MapAsync for concurrent collection processing by GarrettBeatty · Pull Request #2408 · aws/aws-lambda-dotnet

GarrettBeatty · 2026-06-05T17:41:02Z

What

Adds IDurableContext.MapAsync to Amazon.Lambda.DurableExecution. MapAsync processes a collection in parallel with one child context per item, mirroring the Python/JS/Java SDKs where Map is a sibling of Parallel sharing one concurrency engine. It reuses the IBatchResult<T> family and concurrency/completion machinery introduced by ParallelAsync in #2375.

Public API:

Type	Purpose
`IDurableContext.MapAsync<TItem, TResult>(IReadOnlyList<TItem> items, Func<IDurableContext, TItem, int, IReadOnlyList<TItem>, CancellationToken, Task<TResult>> func, string? name, MapConfig? config, CancellationToken)`	Process each item concurrently in its own child context, returning `Task<IBatchResult<TResult>>`. The per-item func receives the durable context, the item, its zero-based index, the full source list (matching the Python/JS SDKs), and a `CancellationToken` linking the caller's token with the SDK's workflow-shutdown signal (also tripped cooperatively when a sibling satisfies the `CompletionConfig` and the map short-circuits).
`MapConfig`	`MaxConcurrency` (`int?`, null = unlimited, must be ≥1), `CompletionConfig`, `NestingType`, `ItemNamer`. Defaults `CompletionConfig` to `AllCompleted()` (permissive), matching Python/Java `Map` — intentionally differs from `ParallelConfig`'s `AllSuccessful()`. `NestingType` defaults to `Nested`; `NestingType.Flat` is not yet supported and throws `NotSupportedException` when invoked.
`MapConfig.ItemNamer`	`Func<object, int, string>?` — supplies a per-item branch name (item + zero-based index) surfaced in traces and on `IBatchItem<T>.Name`. When null, branches are named by index (`"0"`, `"1"`, ...). (No `ItemBatcher` — not implemented in any reference SDK.)
`MapException`	Thrown when `CompletionConfig` signals `FailureToleranceExceeded`, so callers can distinguish `Map` failures from `Parallel` failures. Exposes a type-erased `IBatchResult? Result` (cast to `IBatchResult<T>` when the item type is known) and the `CompletionReason`. Base type for map failures; catching it stays forward-compatible.

Behavior: by default (AllCompleted) every item runs regardless of per-item failures, which are captured on the corresponding IBatchItem<T> and surfaced via IBatchResult<T>.Failed rather than thrown. The map throws MapException only when the CompletionConfig criteria are violated. For fail-fast semantics, set CompletionConfig to AllSuccessful() or call IBatchResult<T>.ThrowIfError() on the result.

Implementation notes:

Extracts a ConcurrentOperation<T> base holding all orchestration, completion, checkpoint, and replay logic. ParallelOperation and MapOperation are thin subclasses supplying only the per-unit (name, func), sub-type labels, and failure-exception factory. Adds Map / MapItem to OperationSubTypes.
Generalizes ParallelSummary / ParallelJsonContext into shared BatchSummary / BatchJsonContext.

Per-item checkpoint payloads are serialized via the ILambdaSerializer registered on ILambdaContext.Serializer — the same pattern as ParallelAsync / StepAsync / RunInChildContextAsync. The AOT story is determined entirely by which serializer the user registers with the runtime (e.g., SourceGeneratorLambdaJsonSerializer<TContext>). MapConfig does not expose a serializer slot.

Testing

24 new unit tests in MapOperationTests.cs, mirroring the Parallel set:

CompletionConfig matrix: AllSuccessful, AllCompleted, FirstSuccessful, MinSuccessful, ToleratedFailureCount, ToleratedFailurePercentage — both pass and fail thresholds.
Concurrency: MaxConcurrency enforced; unbounded when null.
Replay determinism: mixed-status replay, named vs. unnamed items via ItemNamer.
IBatchResult<T> accessors and GetResults / GetErrors / ThrowIfError semantics.

6 new integration functions/tests mirroring the Parallel set (require AWS credentials to run): MapHappyPath, MapPartialFailure, MapFailureTolerance, MapFirstSuccessful, MapMaxConcurrency, MapReplayDeterminism.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

+
+COPY bin/publish/ ${LAMBDA_TASK_ROOT}
+
+ENTRYPOINT ["/var/task/bootstrap"]


+
+COPY bin/publish/ ${LAMBDA_TASK_ROOT}
+
+ENTRYPOINT ["/var/task/bootstrap"]


+
+COPY bin/publish/ ${LAMBDA_TASK_ROOT}
+
+ENTRYPOINT ["/var/task/bootstrap"]


+
+COPY bin/publish/ ${LAMBDA_TASK_ROOT}
+
+ENTRYPOINT ["/var/task/bootstrap"]


+
+COPY bin/publish/ ${LAMBDA_TASK_ROOT}
+
+ENTRYPOINT ["/var/task/bootstrap"]


+
+COPY bin/publish/ ${LAMBDA_TASK_ROOT}
+
+ENTRYPOINT ["/var/task/bootstrap"]


Copilot

Pull request overview

This PR adds a new concurrent collection-processing primitive, IDurableContext.MapAsync, to the Amazon.Lambda.DurableExecution SDK. It mirrors the existing ParallelAsync concurrency engine while introducing Map-specific defaults (notably a permissive AllCompleted() completion policy) and Map-specific exception semantics.

Changes:

Introduces MapAsync + MapConfig + MapException, and a new MapOperation built on shared concurrency orchestration.
Refactors the ParallelAsync implementation by extracting shared logic into ConcurrentOperation<T> and generalizing parent checkpoint summaries to BatchSummary.
Adds unit and integration tests plus integration test Lambda function projects for Map scenarios (happy path, partial failure, max concurrency, first-successful, failure tolerance, replay determinism).

Reviewed changes

Copilot reviewed 41 out of 41 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
MAP-IMPLEMENTATION-PLAN.md	Design/implementation plan for MapAsync and related refactors.
Libraries/test/Amazon.Lambda.DurableExecution.Tests/ParallelOperationTests.cs	Updates replay JSON payload shape from `Branches` to `Units` for parallel tests.
Libraries/test/Amazon.Lambda.DurableExecution.Tests/MapOperationTests.cs	Adds comprehensive unit tests for MapAsync behavior, replay, naming, and completion policies.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapReplayDeterminismFunction/MapReplayDeterminismFunction.csproj	New integration test function project for map replay determinism.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapReplayDeterminismFunction/Function.cs	Workflow that forces suspend/resume to validate per-item replay determinism.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapReplayDeterminismFunction/Dockerfile	Container packaging for the replay determinism test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapPartialFailureFunction/MapPartialFailureFunction.csproj	New integration test function project for permissive-default partial failure.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapPartialFailureFunction/Function.cs	Workflow validating Map default `AllCompleted()` preserves partial failures without failing workflow.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapPartialFailureFunction/Dockerfile	Container packaging for the partial failure test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapMaxConcurrencyFunction/MapMaxConcurrencyFunction.csproj	New integration test function project for `MaxConcurrency`.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapMaxConcurrencyFunction/Function.cs	Workflow validating dispatch throttling via durable waits + timestamps.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapMaxConcurrencyFunction/Dockerfile	Container packaging for the max concurrency test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapHappyPathFunction/MapHappyPathFunction.csproj	New integration test function project for map happy path.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapHappyPathFunction/Function.cs	Workflow validating step-per-item processing and ItemNamer visibility.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapHappyPathFunction/Dockerfile	Container packaging for the happy path test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapFirstSuccessfulFunction/MapFirstSuccessfulFunction.csproj	New integration test function project for first-successful short-circuit.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapFirstSuccessfulFunction/Function.cs	Workflow validating `FirstSuccessful()` and started/unfinished item reporting.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapFirstSuccessfulFunction/Dockerfile	Container packaging for the first-successful test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapFailureToleranceFunction/MapFailureToleranceFunction.csproj	New integration test function project for failure tolerance exceeded.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapFailureToleranceFunction/Function.cs	Workflow validating failure tolerance triggers `MapException` and fails workflow.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/MapFailureToleranceFunction/Dockerfile	Container packaging for the failure tolerance test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/MapReplayDeterminismTest.cs	Integration test asserting deterministic item operation IDs and replayed step results.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/MapPartialFailureTest.cs	Integration test asserting permissive default allows partial failure with SUCCEEDED workflow.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/MapMaxConcurrencyTest.cs	Integration test asserting `MaxConcurrency` throttles dispatch waves.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/MapHappyPathTest.cs	Integration test validating end-to-end happy path and history events/names.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/MapFirstSuccessfulTest.cs	Integration test validating first-successful short-circuit behavior.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/MapFailureToleranceTest.cs	Integration test validating failure tolerance triggers FAILED workflow + MapException indication.
Libraries/src/Amazon.Lambda.DurableExecution/Operation.cs	Adds `OperationSubTypes.Map` and `OperationSubTypes.MapItem`.
Libraries/src/Amazon.Lambda.DurableExecution/MapConfig.cs	Adds Map configuration object with permissive default completion config and ItemNamer.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/ParallelSummary.cs	Removes the Parallel-specific summary type (replaced by shared BatchSummary).
Libraries/src/Amazon.Lambda.DurableExecution/Internal/ParallelOperation.cs	Refactors ParallelOperation to a thin subclass of ConcurrentOperation.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/ParallelJsonContext.cs	Removes Parallel-specific JSON context (replaced by BatchJsonContext).
Libraries/src/Amazon.Lambda.DurableExecution/Internal/MapOperation.cs	Adds MapOperation as a thin subclass of ConcurrentOperation.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/ConcurrentOperation.cs	Adds extracted shared orchestration/replay/checkpoint engine for Parallel + Map.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/BatchSummary.cs	Adds shared parent checkpoint payload type for concurrent ops.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/BatchJsonContext.cs	Adds shared source-gen JSON context for BatchSummary payloads.
Libraries/src/Amazon.Lambda.DurableExecution/IDurableContext.cs	Adds public `MapAsync<TItem, TResult>` API with XML docs.
Libraries/src/Amazon.Lambda.DurableExecution/DurableExecutionException.cs	Adds `MapException` type parallel to `ParallelException`.
Libraries/src/Amazon.Lambda.DurableExecution/DurableContext.cs	Wires MapAsync into the durable context runtime implementation.
Docs/durable-execution-design.md	Updates design docs: Map default completion behavior and removes ItemBatcher references.

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GarrettBeatty · 2026-06-05T23:00:29Z

+internal sealed class BatchSummary
+{
+    [JsonPropertyName("CompletionReason")]
+    public string? CompletionReason { get; set; }
+
+    [JsonPropertyName("Units")]
+    public IList<BatchUnitSummary> Units { get; set; } = new List<BatchUnitSummary>();
+}


this is fine - since we are in preview

Copilot

Pull request overview

Copilot reviewed 41 out of 41 changed files in this pull request and generated 3 comments.

GarrettBeatty · 2026-06-16T15:48:43Z

-using SdkErrorObject = Amazon.Lambda.Model.ErrorObject;
-using SdkOperationUpdate = Amazon.Lambda.Model.OperationUpdate;

 namespace Amazon.Lambda.DurableExecution.Internal;


all the common logic (mostly everything) shared between map and parallel was moved to ConcurrentOperation

…CCEED The parent context for both ParallelAsync and MapAsync now always checkpoints as Action=SUCCEED with the summary (including CompletionReason) in the Payload field, matching the wire format used by the Python, JS, and Java SDKs. Previously the C# SDK emitted Action=FAIL for FailureToleranceExceeded, which left ContextDetails.Result empty (Payload is forbidden on FAIL updates) and made it impossible for replay to reconstruct a caught ParallelException/MapException deterministically. The exception is now thrown SDK-side after the checkpoint based on the CompletionReason in the reconstructed BatchResult.

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GarrettBeatty force-pushed the gcbeatty/durable-parallel branch from 1a1d5bc to 69364a0 Compare June 8, 2026 15:44

GarrettBeatty force-pushed the gcbeatty/durable-map branch from 97d51e0 to e0b6f5f Compare June 8, 2026 18:36

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Comment thread Libraries/src/Amazon.Lambda.DurableExecution/Internal/ConcurrentOperation.cs

Comment thread Libraries/test/Amazon.Lambda.DurableExecution.Tests/ParallelOperationTests.cs

Comment thread Libraries/test/Amazon.Lambda.DurableExecution.Tests/MapOperationTests.cs

GarrettBeatty mentioned this pull request Jun 9, 2026

Add ParallelAsync for concurrent branch execution (DOTNET-8662) #2375

Merged

GarrettBeatty force-pushed the gcbeatty/durable-parallel branch 3 times, most recently from c88ad8a to d347067 Compare June 12, 2026 15:24

GarrettBeatty force-pushed the gcbeatty/durable-map branch from e0b6f5f to dcda8da Compare June 12, 2026 18:54

Base automatically changed from gcbeatty/durable-parallel to dev June 15, 2026 17:47

GarrettBeatty force-pushed the gcbeatty/durable-map branch from dcda8da to fb4572a Compare June 16, 2026 15:32

GarrettBeatty commented Jun 16, 2026

View reviewed changes

mapasync

02c23f5

GarrettBeatty force-pushed the gcbeatty/durable-map branch from fb4572a to 02c23f5 Compare June 16, 2026 16:26

GarrettBeatty added 3 commits June 16, 2026 12:27

Update durable-mapasync.json

f3ea95f

update changefile

9ac6ab9

GarrettBeatty marked this pull request as ready for review June 16, 2026 17:46

GarrettBeatty requested review from a team as code owners June 16, 2026 17:46

GarrettBeatty requested review from normj and philasmar June 16, 2026 17:46

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Add MapAsync for concurrent collection processing#2408

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		COPY bin/publish/ ${LAMBDA_TASK_ROOT}

		ENTRYPOINT ["/var/task/bootstrap"]

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GarrettBeatty commented Jun 5, 2026 •

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