Reduce async overhead by pentp · Pull Request #2664 · App-vNext/Polly

pentp · 2025-07-04T10:23:53Z

Remove many unnecessary async awaits from the pipeline hot path.
Also cleaned up some excessive use of lambdas.

martincostello · 2025-07-04T10:34:36Z

Thanks for your PR.

I'm not against any improvements that don't impact the public API surface, but ValueTask was specifically adopted during the development of Polly v8 to reduce memory allocations so those parts of the changes raise some questions.

Have you run the latest benchmarks before and after these changes? We'd want to see some concrete numbers on any improvements and trade-offs that these changes might make.

Some parts could potentially be moved out into separate smaller PRs as they're pretty uncontroversial (e.g. using ArgumentNullException.ThrowIfNull(), the unused Stopwatch) so would get merged sooner.

- Avoid LINQ to create components. - Do not recreate `Outcome<T>` for chaos. - Avoid predicate allocation. - Use `ArgumentNullException.ThrowIfNull()` where possible. - Add throw helper for `ObjectDisposedException`. - Remove unused `Stopwatch`. - Use `Volatile.Read` instead of `Interlocked.CompareExchange()`. Cherry-picked from #2664. Co-Authored-By: Pent Ploompuu <kaalikas@gmail.com>

martincostello · 2025-07-08T14:27:04Z

I've cherry-picked some of the changes here into #2667, which has now been merged.

codecov · 2025-07-08T23:19:24Z

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✅ All modified and coverable lines are covered by tests.
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pentp · 2025-07-08T23:27:35Z

The changes from ValueTask to Task are improvements - removing an async ValueTask wrapping method around a Task.
The other changes are just reducing async overhead - ValueTask is allocation free only for synchronously completed methods (or if using pooling) and even then the async machinery has overhead.

martincostello · 2025-07-09T06:17:47Z

Have you run the latest benchmarks before and after these changes? We'd want to see some concrete numbers on any improvements and trade-offs that these changes might make.

pentp · 2025-08-19T12:29:28Z

Some benchmark numbers:

Baseline	Mean	Error	StdDev	Ratio	Gen0	Allocated
Hedging_Primary	483.1 ns	10.93 ns	16.36 ns	1.00	-	-
Hedging_Secondary	850.4 ns	46.46 ns	69.54 ns	1.76	0.0143	240 B
Hedging_Primary_AsyncWork	2,165.3 ns	43.49 ns	62.38 ns	4.49	0.1335	2287 B
Hedging_Secondary_AsyncWork	2,666.8 ns	47.49 ns	69.61 ns	5.53	0.1488	2514 B

PR	Mean	Error	StdDev	Ratio	Gen0	Allocated
Hedging_Primary	308.9 ns	2.98 ns	4.46 ns	1.00	-	-
Hedging_Secondary	553.4 ns	5.53 ns	8.28 ns	1.79	0.0143	240 B
Hedging_Primary_AsyncWork	1,356.6 ns	84.79 ns	126.91 ns	4.39	0.0763	1279 B
Hedging_Secondary_AsyncWork	1,658.0 ns	39.59 ns	59.26 ns	5.37	0.0877	1489 B

Baseline	Mean	Error	StdDev	Ratio	Gen0	Allocated
ExecuteStrategyPipeline_Generic_V7	833.3 ns	5.22 ns	7.65 ns	1.00	0.1640	2744 B
ExecuteStrategyPipeline_Generic_V8	831.1 ns	2.77 ns	4.06 ns	1.00	0.0019	40 B
ExecuteStrategyPipeline_GenericTelemetry_V8	1,139.6 ns	8.02 ns	12.00 ns	1.37	0.0019	40 B
ExecuteStrategyPipeline_NonGeneric_V8	884.4 ns	5.82 ns	8.71 ns	1.06	0.0019	40 B
ExecuteStrategyPipeline_NonGenericTelemetry_V8	1,204.2 ns	6.91 ns	10.35 ns	1.45	0.0019	40 B

PR	Mean	Error	StdDev	Ratio	Gen0	Allocated
ExecuteStrategyPipeline_Generic_V7	800.7 ns	4.52 ns	6.76 ns	1.00	0.1640	2744 B
ExecuteStrategyPipeline_Generic_V8	719.3 ns	2.86 ns	4.29 ns	0.90	0.0019	40 B
ExecuteStrategyPipeline_GenericTelemetry_V8	983.1 ns	3.09 ns	4.62 ns	1.23	0.0019	40 B
ExecuteStrategyPipeline_NonGeneric_V8	821.5 ns	3.29 ns	4.93 ns	1.03	0.0019	40 B
ExecuteStrategyPipeline_NonGenericTelemetry_V8	1,073.5 ns	2.95 ns	4.42 ns	1.34	0.0019	40 B

For actually async flows the improvements are significant, but even just sync flows benefit from the reduced overhead. Unfortunately almost all existing benchmarks are synchronous so the async overhead of many layers of (Value)Tasks isn't very visible.

martincostello · 2025-08-20T10:12:11Z

Thanks for taking the time to run the benchmarks - it looks like all the numbers have improved for both duration and memory consumption.

src/Polly.Core/CircuitBreaker/Controller/CircuitStateController.cs

src/Polly.Core/Hedging/Controller/TaskExecution.cs

src/Polly.Core/Registry/ResiliencePipelineRegistry.TResult.cs

src/Polly.Core/Timeout/TimeoutResilienceStrategy.cs

src/Polly.Core/Utils/Pipeline/PipelineComponent.cs

src/Polly.Core/Utils/Pipeline/ReloadableComponent.cs

test/Polly.Core.Tests/CircuitBreaker/Controller/ScheduledTaskExecutorTests.cs

test/Polly.Core.Tests/Utils/Pipeline/PipelineComponentFactoryTests.cs

martincostello · 2025-08-21T15:29:32Z

Just one last comment and fixing the mutation tests and this looks good to merge.

Update benchmark results ahead of merging #2664.

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martincostello mentioned this pull request Jul 8, 2025

Performance tweaks #2667

Merged

Reduce async overhead

cd7a6bf

pentp force-pushed the async-opts branch from 8a59eaf to cd7a6bf Compare July 8, 2025 23:15

Fix

e14f82b

pentp added 2 commits August 12, 2025 12:20

Merge branch 'main' into async-opts

a346758

Cleanup. Improve test coverage.

67150d2

pentp force-pushed the async-opts branch from 32e80e8 to 67150d2 Compare August 13, 2025 20:44

pentp added 3 commits August 18, 2025 14:50

Merge branch 'main' into async-opts

5779cd0

More cleanup and test coverage.

ff0cf20

More cleanup and test coverage.

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martincostello added the performance label Aug 20, 2025

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pentp added 3 commits August 21, 2025 15:37

Address PR feedback

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Fix formatting

6631630

Try to fix mutation score

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pentp added 2 commits August 21, 2025 19:29

Try to fix mutation score. Cleanup.

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Address PR feedback

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martincostello added a commit that referenced this pull request Aug 22, 2025

Update benchmarks

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Update benchmark results ahead of merging #2664.

martincostello mentioned this pull request Aug 22, 2025

Update benchmarks #2712

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Update benchmarks

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Update benchmark results ahead of merging #2664.

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