Add ParallelAsync for concurrent branch execution (DOTNET-8662) by GarrettBeatty · Pull Request #2375 · aws/aws-lambda-dotnet

GarrettBeatty · 2026-05-14T21:41:49Z

What

Adds parallel branch execution to Amazon.Lambda.DurableExecution. ParallelAsync runs N branches concurrently with configurable concurrency limits and completion policies, returning an IBatchResult<T> with per-branch status and error information. The shared IBatchResult<T> family is reused by MapAsync in Wave 2.

Public API:

Type	Purpose
`IDurableContext.ParallelAsync<T>(Func[], ...)`	Run unnamed branches concurrently.
`IDurableContext.ParallelAsync<T>(DurableBranch<T>[], ...)`	Same, but each branch carries an explicit name for traces / test inspection.
`DurableBranch<T>(Name, Func)`	Named-branch record.
`ParallelConfig`	`MaxConcurrency`, `CompletionConfig`, `NestingType`.
`CompletionConfig`	When the batch is considered complete. Factories: `AllSuccessful()`, `FirstSuccessful()`, `AllCompleted()`. Validated `MinSuccessful` / `ToleratedFailureCount` / `ToleratedFailurePercentage` (0.0–1.0).
`IBatchResult<T>`	Per-branch view: `All` / `Succeeded` / `Failed` / `Started`, `GetResults`, `GetErrors`, `ThrowIfError`, `HasFailure`, `CompletionReason`, count properties.
`IBatchItem<T>`	Single-branch record (`Index`, `Name`, `Status`, `Result`, `Error`).
`BatchItemStatus`	`Succeeded` / `Failed` / `Started`.
`CompletionReason`	`AllCompleted` / `MinSuccessfulReached` / `FailureToleranceExceeded`.
`NestingType`	`Nested` (default); `Flat` reserved for a follow-up PR (throws `NotSupportedException` today).
`ParallelException`	Thrown when `CompletionConfig` signals `FailureToleranceExceeded`; carries the `IBatchResult<T>`.

Per-branch checkpoint payloads are serialized via the ILambdaSerializer registered on ILambdaContext.Serializer — same pattern as StepAsync / RunInChildContextAsync from #2370. There are no separate reflection / AOT-safe overload pairs: the AOT story is determined entirely by which serializer the user registers with the runtime (e.g., SourceGeneratorLambdaJsonSerializer<TContext>).

Testing

31 new unit tests in ParallelOperationTests.cs and supporting fixtures:

CompletionConfig matrix: AllSuccessful, AllCompleted, FirstSuccessful, MinSuccessful, ToleratedFailureCount, ToleratedFailurePercentage — both pass and fail thresholds.
Concurrency: MaxConcurrency enforced via semaphore; unbounded when null; cancel-mid-dispatch leaves no orphan branches.
Concurrent ExecutionState access regression test (parallel writers do not corrupt the visited-set).
Replay determinism: mixed-status replay (SUCCEEDED + FAILED + STARTED), FirstSuccessful with all-fail, named vs. unnamed branches.
IBatchResult<T> accessors and GetResults / GetErrors / ThrowIfError semantics.
NestingType.Flat throws NotSupportedException (placeholder for follow-up).

6 new integration tests build successfully (require AWS credentials to run): happy path, max-concurrency, first-successful, partial-failure, failure-tolerance, and replay-determinism.

+
+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"]


stack-info: PR: #2361, branch: GarrettBeatty/stack/3

Copilot

Pull request overview

Adds a new durable “fan-out” capability to Amazon.Lambda.DurableExecution via IDurableContext.ParallelAsync, enabling concurrent branch execution with configurable completion policies and concurrency limits, while extending replay/state handling to support multi-threaded branch orchestration.

Changes:

Introduces ParallelAsync public API (+ supporting types like ParallelConfig, CompletionConfig, IBatchResult<T>, DurableBranch<T>, and ParallelException).
Implements Internal/ParallelOperation<T> orchestration and makes ExecutionState thread-safe for concurrent branch execution/replay.
Adds extensive unit tests plus multiple end-to-end integration test functions for determinism, throttling, and failure policy behavior.

Reviewed changes

Copilot reviewed 45 out of 45 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
Libraries/test/Amazon.Lambda.DurableExecution.Tests/ParallelOperationTests.cs	New unit tests covering ParallelAsync behavior (completion modes, determinism, cancellation, replay).
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelReplayDeterminismFunction/ParallelReplayDeterminismFunction.csproj	New integration test function project for replay determinism.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelReplayDeterminismFunction/Function.cs	Workflow that validates replay determinism across suspend/resume under parallel branches.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelReplayDeterminismFunction/Dockerfile	Container packaging for the replay determinism test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelPartialFailureFunction/ParallelPartialFailureFunction.csproj	New integration test function project for partial failure behavior.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelPartialFailureFunction/Function.cs	Workflow demonstrating `AllCompleted` with per-branch errors surfaced in the result.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelPartialFailureFunction/Dockerfile	Container packaging for the partial failure test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelMaxConcurrencyFunction/ParallelMaxConcurrencyFunction.csproj	New integration test function project for max concurrency throttling.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelMaxConcurrencyFunction/Function.cs	Workflow that uses durable waits to validate max-concurrency throttling.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelMaxConcurrencyFunction/Dockerfile	Container packaging for the max concurrency test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelHappyPathFunction/ParallelHappyPathFunction.csproj	New integration test function project for the basic happy path.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelHappyPathFunction/Function.cs	Happy-path parallel workflow returning joined results.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelHappyPathFunction/Dockerfile	Container packaging for the happy path test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelFirstSuccessfulFunction/ParallelFirstSuccessfulFunction.csproj	New integration test function project for FirstSuccessful behavior.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelFirstSuccessfulFunction/Function.cs	Workflow exercising `FirstSuccessful` with staggered durable waits.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelFirstSuccessfulFunction/Dockerfile	Container packaging for the FirstSuccessful test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelFailureToleranceFunction/ParallelFailureToleranceFunction.csproj	New integration test function project for failure tolerance exceeded.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelFailureToleranceFunction/Function.cs	Workflow that triggers `ParallelException` via tolerated failure count.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/TestFunctions/ParallelFailureToleranceFunction/Dockerfile	Container packaging for the failure tolerance test function.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/ParallelReplayDeterminismTest.cs	End-to-end test asserting deterministic branch IDs and replayed step outputs.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/ParallelPartialFailureTest.cs	End-to-end test asserting `AllCompleted` surfaces partial failures without failing workflow.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/ParallelMaxConcurrencyTest.cs	End-to-end test asserting max concurrency throttling via timestamp clustering.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/ParallelHappyPathTest.cs	End-to-end happy-path test asserting correct service-side context history.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/ParallelFirstSuccessfulTest.cs	End-to-end test asserting short-circuit semantics and winner reporting.
Libraries/test/Amazon.Lambda.DurableExecution.IntegrationTests/ParallelFailureToleranceTest.cs	End-to-end test asserting workflow fails with ParallelException on exceeded tolerance.
Libraries/src/Amazon.Lambda.DurableExecution/ParallelConfig.cs	New configuration type for parallel execution (concurrency, completion, nesting).
Libraries/src/Amazon.Lambda.DurableExecution/Operation.cs	Adds wire subtypes for Parallel parent and ParallelBranch checkpoints.
Libraries/src/Amazon.Lambda.DurableExecution/NestingType.cs	New enum describing checkpoint graph representation for parallel/map branches.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/ParallelSummary.cs	Internal checkpoint payload schema for parallel parent summary.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/ParallelOperation.cs	Core implementation of durable parallel orchestration + replay reconstruction.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/ParallelJsonContext.cs	Source-generated STJ context for AOT-safe serialization of internal summary payload.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/ExecutionState.cs	Makes execution state thread-safe via a single lock for concurrent branch access.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/BatchResult.cs	Default internal implementation of `IBatchResult<T>` views and helpers.
Libraries/src/Amazon.Lambda.DurableExecution/Internal/BatchItem.cs	Default internal implementation of `IBatchItem<T>`.
Libraries/src/Amazon.Lambda.DurableExecution/IDurableContext.cs	Public interface additions for `ParallelAsync` overloads.
Libraries/src/Amazon.Lambda.DurableExecution/IBatchResult.cs	New public batch result interfaces used by parallel/map.
Libraries/src/Amazon.Lambda.DurableExecution/IBatchItem.cs	New public per-branch/item interface surfaced by batch results.
Libraries/src/Amazon.Lambda.DurableExecution/DurableExecutionException.cs	Adds `ParallelException` carrying completion reason and batch result.
Libraries/src/Amazon.Lambda.DurableExecution/DurableContext.cs	Implements `ParallelAsync` and refactors child-context factory creation.
Libraries/src/Amazon.Lambda.DurableExecution/DurableBranch.cs	New public record representing a named parallel branch.
Libraries/src/Amazon.Lambda.DurableExecution/CompletionReason.cs	New enum describing why a batch resolved.
Libraries/src/Amazon.Lambda.DurableExecution/CompletionConfig.cs	New completion policy type with factories (AllSuccessful/AllCompleted/FirstSuccessful).
Libraries/src/Amazon.Lambda.DurableExecution/BatchItemStatus.cs	New enum describing per-branch outcome status (Succeeded/Failed/Started).
Docs/durable-execution-design.md	Documentation updates reflecting new parallel types and failure-percentage config.

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GarrettBeatty · 2026-06-05T19:25:21Z

+    /// </summary>
+    /// <remarks>
+    /// Not yet implemented in the .NET SDK; passing this value throws
+    /// <see cref="System.NotSupportedException"/>.


will do in another pr

philasmar · 2026-06-09T13:54:50Z

Important

ExecutionState single-lock may bottleneck for high branch counts

The switch from ConcurrentDictionary to a single lock is well-reasoned (compound operations in LoadFromCheckpoint need atomicity). Each critical section is O(1). For the branch
counts in this PR's tests (3-10), contention is negligible. However, the lock is on the read path (GetOperation, IsReplaying) that every branch hits during replay. If MapAsync
(mentioned as a follow-up) dispatches hundreds of items, this could become measurable. No action needed now — just flag for the MapAsync PR to benchmark.

Dispatched branches are never cancelled on short-circuit

The design explicitly states: once dispatched, branches are never cancelled — even after a MinSuccessful or FailureToleranceExceeded short-circuit fires. This guarantees replay
determinism (all dispatched branches end in a terminal state), but it means with MaxConcurrency=null and FirstSuccessful, all branches execute to completion even though only
the first one's result matters. The parallel.md doc doesn't mention this tradeoff. Consider adding a note like: "Dispatched branches always run to completion for replay
determinism — use MaxConcurrency to limit wasted compute under FirstSuccessful."

ParallelException.Result is type-erased (IBatchResult not IBatchResult)

public IBatchResult? Result { get; init; }

Since ParallelException isn't generic, the result is boxed behind the non-generic IBatchResult marker. Callers who catch ParallelException need to cast:
(IBatchResult)ex.Result. This is fine, but worth noting in the exception's XML doc that the cast is expected (it's mentioned on ParallelException but a snippet would
help users).

GarrettBeatty · 2026-06-09T14:42:45Z

Important
1. ExecutionState single-lock may bottleneck for high branch counts
The switch from ConcurrentDictionary to a single lock is well-reasoned (compound operations in LoadFromCheckpoint need atomicity). Each critical section is O(1). For the branch counts in this PR's tests (3-10), contention is negligible. However, the lock is on the read path (GetOperation, IsReplaying) that every branch hits during replay. If MapAsync (mentioned as a follow-up) dispatches hundreds of items, this could become measurable. No action needed now — just flag for the MapAsync PR to benchmark.
2. Dispatched branches are never cancelled on short-circuit
The design explicitly states: once dispatched, branches are never cancelled — even after a MinSuccessful or FailureToleranceExceeded short-circuit fires. This guarantees replay determinism (all dispatched branches end in a terminal state), but it means with MaxConcurrency=null and FirstSuccessful, all branches execute to completion even though only the first one's result matters. The parallel.md doc doesn't mention this tradeoff. Consider adding a note like: "Dispatched branches always run to completion for replay determinism — use MaxConcurrency to limit wasted compute under FirstSuccessful."
3. ParallelException.Result is type-erased (IBatchResult not IBatchResult)
public IBatchResult? Result { get; init; }

Since ParallelException isn't generic, the result is boxed behind the non-generic IBatchResult marker. Callers who catch ParallelException need to cast: (IBatchResult)ex.Result. This is fine, but worth noting in the exception's XML doc that the cast is expected (it's mentioned on ParallelException but a snippet would help users).

fixed number 2 only, the rest are already documented 3179531

philasmar · 2026-06-09T14:46:47Z

@@ -0,0 +1,15 @@
+namespace Amazon.Lambda.DurableExecution.Internal;


add license header

philasmar · 2026-06-09T14:46:52Z

@@ -0,0 +1,80 @@
+namespace Amazon.Lambda.DurableExecution.Internal;


add license header

philasmar · 2026-06-09T14:47:07Z

@@ -0,0 +1,15 @@
+using System.Text.Json.Serialization;


add license header

philasmar · 2026-06-09T14:47:13Z

@@ -0,0 +1,654 @@
+using System.IO;


add license header

philasmar · 2026-06-09T14:47:17Z

@@ -0,0 +1,31 @@
+using System.Text.Json.Serialization;


add license header

philasmar · 2026-06-09T14:48:57Z

@@ -0,0 +1,72 @@
+using System.Linq;


add license header

philasmar · 2026-06-09T14:49:00Z

@@ -0,0 +1,76 @@
+using System.Linq;


add license header

philasmar · 2026-06-09T14:49:04Z

@@ -0,0 +1,74 @@
+using System.Linq;


add license header

philasmar · 2026-06-09T14:49:09Z

@@ -0,0 +1,122 @@
+using System.Linq;


add license header

philasmar · 2026-06-09T14:49:14Z

@@ -0,0 +1,1163 @@
+using Amazon.Lambda.DurableExecution;


add license header

GarrettBeatty · 2026-06-09T16:38:07Z

+    /// <remarks>
+    /// <see cref="NestingType.Flat"/> is not yet supported in the .NET SDK and
+    /// will throw <see cref="System.NotSupportedException"/> when the parallel
+    /// operation is invoked.


will be implemented in #2409

GarrettBeatty · 2026-06-09T16:46:06Z

+/// <see cref="CompletionReason.FailureToleranceExceeded"/> does the parallel
+/// throw.
+/// </remarks>
+internal sealed class ParallelOperation<T> : DurableOperation<IBatchResult<T>>


this whole class is going to get refactored later on in #2408 to support mapasync as well

normj · 2026-06-09T16:38:15Z

+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>


All test projects should target .NET 10

normj · 2026-06-09T18:08:42Z

+                {
+                    try
+                    {
+                        await Task.WhenAll(inFlight).ConfigureAwait(false);


As we discussed on the side. We need a mechanism to communicate to the inflight branches that they should cleanly shut down. For example provide them their own cancellation token that we cancel from here.

GarrettBeatty · 2026-06-09T18:09:18Z

+                {
+                    try
+                    {
+                        await Task.WhenAll(inFlight).ConfigureAwait(false);


@normj i think in your example on the call, you were thinking something like

new ParallelConfig { MaxConcurrency = 10, CompletionConfig = new CompletionConfig { MinSuccessful = 2 } }

in this case the short circuit would not fire and we would await all 10 tasks.

but in the case like

new ParallelConfig { MaxConcurrency = 3, CompletionConfig = new CompletionConfig { MinSuccessful = 2 } }

When does MinSuccessful actually save work?

Lower the concurrency window. Same 10 branches, MaxConcurrency = 3, MinSuccessful = 2:

Time In flight Done succeeded Action

t0 branches 0,1,2 – 0 semaphore full; dispatch loop blocked on WaitAsync

t1 branches 1,2,3 0 1 branch 0 finishes → releases slot → loop wakes, dispatches branch 3

t2 branches 2,3 0,1 2 branch 1 finishes → ShouldStopDispatching is true → release slot, break out of dispatch loop

t3 – 0,1,2,3 2+ Task.WhenAll settles the two in-flight branches (2 and 3)

end – 0,1,2,3 – branches 4–9 were never dispatched; they surface as Started

Result: 4 Succeeded, 6 Started, CompletionReason = MinSuccessfulReached — six branches' worth of compute saved.

and as far as cancellation token goes - i think you were saying we can still cancel the inflight ones. but my only thing i would need to think about is if cancellation -> FAILED status. i think in other places (i would need to double check), we decided cancellation is different than having it failed.

i think theres some edge cases where if we just cancel the task, and some checkpoints are written already (and we just cancel it without it letting write the final checkpoints) then the replay will be corrupted

But given the default of MaxConcurrency is the number of branches I suspect we will get more task running at a time then MinSuccessful.

You also have the problem which is probably more common that if you have an exception in one of the branches and the configuration is to break if any exceptions have occurred we still wait for all inflight branches even though they won't matter because we are going to return a failure back.

github-advanced-security AI found potential problems May 14, 2026

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GarrettBeatty force-pushed the gcbeatty/durable-parallel branch from 19c0128 to fa13eef Compare May 14, 2026 21:49

GarrettBeatty force-pushed the gcbeatty/durable-wave0 branch from 464c591 to d308c3b Compare May 14, 2026 21:49

GarrettBeatty force-pushed the gcbeatty/durable-parallel branch from fa13eef to b7a06b4 Compare May 14, 2026 22:19

GarrettBeatty added 2 commits May 15, 2026 18:13

add design doc (#2361)

2c228b6

stack-info: PR: #2361, branch: GarrettBeatty/stack/3

Add Amazon.Lambda.DurableExecution project scaffolding (#2359)

6306d2f

GarrettBeatty force-pushed the gcbeatty/durable-wave0 branch from d308c3b to be4c3ad Compare May 18, 2026 15:23

GarrettBeatty force-pushed the gcbeatty/durable-parallel branch from b7a06b4 to 08b2095 Compare May 18, 2026 15:44

GarrettBeatty added 2 commits May 19, 2026 18:58

Add durable execution Step + Wait end-to-end (#2360)

a8b59d9

Mark Amazon.Lambda.DurableExecution as preview (0.0.1-preview) (#2386)

6708a79

GarrettBeatty force-pushed the gcbeatty/durable-wave0 branch 3 times, most recently from ad4d208 to 3acbed5 Compare May 20, 2026 17:46

Base automatically changed from gcbeatty/durable-wave0 to gcbeatty/durable-child-context May 20, 2026 17:46

GarrettBeatty force-pushed the gcbeatty/durable-child-context branch from 646b841 to 4d97473 Compare May 21, 2026 15:22

Adds retry support to the Amazon.Lambda.DurableExecution (#2363)

8371959

GarrettBeatty force-pushed the gcbeatty/durable-child-context branch from 4d97473 to 8a6c41c Compare May 21, 2026 18:56

Add RunInChildContextAsync (#2370)

b414d04

Base automatically changed from gcbeatty/durable-child-context to feature/durablefunction May 23, 2026 15:58

Add CreateCallbackAsync and WaitForCallbackAsync (DOTNET-8660) (#2373)

edd1cc0

GarrettBeatty force-pushed the gcbeatty/durable-parallel branch 2 times, most recently from 8664e8c to e4da00c Compare May 28, 2026 18:47

GarrettBeatty added 2 commits June 1, 2026 12:10

Add InvokeAsync for chained durable function calls (DOTNET-8661) (#2374)

43d617b

license (#2398)

3c42dd9

GarrettBeatty force-pushed the gcbeatty/durable-parallel branch from e4da00c to 9485866 Compare June 1, 2026 16:40

GarrettBeatty added 3 commits June 2, 2026 12:41

Durable functions doc updates and first changefile for preview (#2392)

110135d

Update README.md

ca3e151

Cherry-pick replay-aware logger into feature branch (#2405)

72049dd

GarrettBeatty force-pushed the gcbeatty/durable-parallel branch from 9485866 to cff0b86 Compare June 5, 2026 15:59

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GarrettBeatty mentioned this pull request Jun 5, 2026

Add MapAsync for concurrent collection processing #2408

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GarrettBeatty commented Jun 5, 2026

View reviewed changes

Add WaitForConditionAsync polling primitive (DOTNET-8665) (#2376)

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

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normj mentioned this pull request Jun 10, 2026

cancellation token #2414

Merged

cancellation token (#2414)

92c89d4

GarrettBeatty force-pushed the gcbeatty/durable-parallel branch from 628ebff to c3162e0 Compare June 11, 2026 17:53

parallel

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GarrettBeatty force-pushed the gcbeatty/durable-parallel branch from c3162e0 to c88ad8a Compare June 11, 2026 17:54

Base automatically changed from feature/durablefunction to dev June 11, 2026 17:56


		COPY bin/publish/ ${LAMBDA_TASK_ROOT}

		ENTRYPOINT ["/var/task/bootstrap"]

		@@ -0,0 +1,15 @@
		namespace Amazon.Lambda.DurableExecution.Internal;

		@@ -0,0 +1,80 @@
		namespace Amazon.Lambda.DurableExecution.Internal;

Time	In flight	Done	`succeeded`	Action
t0	branches 0,1,2	–	0	semaphore full; dispatch loop blocked on `WaitAsync`
t1	branches 1,2,3	0	1	branch 0 finishes → releases slot → loop wakes, dispatches branch 3
t2	branches 2,3	0,1	2	branch 1 finishes → `ShouldStopDispatching` is true → release slot, `break` out of dispatch loop
t3	–	0,1,2,3	2+	`Task.WhenAll` settles the two in-flight branches (2 and 3)
end	–	0,1,2,3	–	branches 4–9 were never dispatched; they surface as `Started`

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When does MinSuccessful actually save work?

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GarrettBeatty commented May 14, 2026 •

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When does `MinSuccessful` actually save work?

GarrettBeatty Jun 9, 2026 •

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