[Commit fix] Fix thread pool starvation under multi-concurrency#2395
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Parse AWS_LAMBDA_MAX_CONCURRENCY as integer to use as the default polling task count instead of Math.Max(2, processorCount). This ensures enough polling tasks exist to fill all available concurrency slots. Add AdjustThreadPoolSettings() to pre-size the ThreadPool to mcCount + processorCount at startup, preventing blocking handlers from starving polling task continuations of threads needed to cycle back to RAPID's /next endpoint. Without both changes, blocking handlers (Thread.Sleep, .Result, .Wait()) exhaust the ThreadPool under multi-concurrency, causing Runtime.Unavailable errors because polling tasks cannot resume their await continuations. Changes: - Utils.cs: Add GetMaxConcurrency() method, use parsed MC value in DetermineProcessingTaskCount (fallback to Math.Max(2, processorCount) for non-numeric values) - LambdaBootstrap.cs: Add AdjustThreadPoolSettings() called after AdjustMemorySettings() in RunAsync startup sequence - TestMultiConcurrencyRuntimeApiClient.cs: Make thread-safe for concurrent polling task access (ConcurrentDictionary, lock on Queue) - Add tests demonstrating fix works with MC=10/20 blocking handlers
…ol tuning Add customer-configurable environment variable AWS_LAMBDA_DOTNET_MIN_THREADS to override the ThreadPool minimum worker thread count in multi-concurrency mode. Default remains conservative at 2 * processorCount. This addresses feedback that pre-creating mcCount + processorCount threads is too aggressive. Benchmark data shows 2 * processorCount is sufficient when combined with the polling task count fix (parsing MC value), while the env var gives customers a knob to tune for heavy blocking workloads. Changes: - Constants.cs: Add ENVIRONMENT_VARIABLE_AWS_LAMBDA_DOTNET_MIN_THREADS - LambdaBootstrap.cs: AdjustThreadPoolSettings checks env var override, falls back to 2 * processorCount
normj
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philasmar
approved these changes
May 28, 2026
GarrettBeatty
approved these changes
May 28, 2026
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Issue #, if available:
Recreation of #2387 with cleaned up commits
Description of changes:
Read description here: #2387
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