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CHANGELOG.md

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Changelog

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog.

[0.5.0] - 2026-04-13

Added

  • examples/Starter/Starter.lpr — a heavily-commented "Hello, ThreadPool" entry point for new users; includes compile instructions and expected output in the file header
  • README: decision flowchart for choosing ThreadPool.Simple vs ThreadPool.ProducerConsumer
  • README: Queue overload reference table documenting all 4 Queue signatures side-by-side with use-cases and examples
  • README: Common Mistakes section covering the four most frequent pitfalls (free-before-WaitForAll, missing WaitForAll, LastError overwrites, manual free of GlobalThreadPool)
  • README: compilation sanity-check section with fpc and lazbuild one-liners, expected output, and {$mode objfpc}{$H+} reminder
  • README: LastError overwrite warning — clarifies only the last exception per pool cycle is stored
  • {$REGION} / {$ENDREGION} grouping in ThreadPool.Simple.pas (Public API, Internal Worker Thread, Internal Work Item, Global instance)
  • {$REGION} / {$ENDREGION} grouping in ThreadPool.ProducerConsumer.pas (Public API, Internal Worker Thread, Internal Work Item, Internal Queue, DebugLog)
  • Object lifetime WARNING comments in SimpleDemo.lpr and ProdConSimpleDemo.lpr explaining why objects must not be freed before WaitForAll

Fixed

  • Test07_ParallelExecution: removed LogTest calls from IncrementCounter — 2 000 serialised WriteLn calls across 1 000 tasks were the bottleneck, consistently exceeding the timing assertion; these calls were present since the test was first written
  • Test08_QueueFullBehavior: replaced SlowTask (250 ms) with LongTask (5 000 ms) so the single worker cannot drain the 2-slot queue before the third enqueue — the race condition was present since the test was first written
  • Test12_LoadFactorCalculation: increased queued task count from 2 to 50 — LoadFactor drops to 0 the moment TryDequeue succeeds (not when execution finishes), so 4+ workers racing to dequeue 2 tasks left the queue empty before the assertion ran; the flaw was present since the test was first written

[0.4.0] - 2024-xx-xx

Added

  • ThreadPool.ProducerConsumer — second thread pool implementation with fixed-size circular queue (default 1 024 items) and built-in backpressure
  • Configurable TBackpressureConfig record (load thresholds, adaptive delays, max retry attempts)
  • EQueueFullException raised when queue remains full after all retry attempts
  • TThreadSafeQueue with LoadFactor, TryEnqueue, TryDequeue
  • WorkQueue property on TProducerConsumerThreadPool for monitoring and configuration
  • 3 new Producer-Consumer examples: ProdConSimpleDemo, ProdConSquareNumbers, ProdConMessageProcessor
  • API and technical documentation for ThreadPool.ProducerConsumer
  • Documentation: Interface Reference Counting and Object Lifetime Management in FPC
  • Lazarus package (package/lazarus/threadpool_fp.lpk)

Fixed

  • Incorrect freeing of work items in ThreadPool.ProducerConsumer
  • Double decrement of work item counter
  • Race condition in exception propagation from worker threads

[0.3.0] - 2024-xx-xx

Added

  • ThreadPool.Types unit — shared interfaces (IThreadPool, IWorkItem, IWorkerThread) and base class TThreadPoolBase
  • Thread count safety limits: minimum 4 threads, maximum 2× ProcessorCount
  • ClearLastError method on all pool implementations
  • Comprehensive unit tests for ThreadPool.Simple

Changed

  • Refactored ThreadPool.Simple onto the new TThreadPoolBase class
  • Improved method names in unit tests

Fixed

  • Race condition in error handling in ThreadPool.Simple

[0.2.0] - 2024-xx-xx

Added

  • Thread count safety: enforced minimum and maximum bounds
  • Technical documentation and sequence diagrams
  • SimpleWordCounter and SimpleSquareNumbers examples

Changed

  • Improved comments in the interface section of the unit

[0.1.0] - 2024-xx-xx

Added

  • Initial implementation of ThreadPool.Simple with global GlobalThreadPool singleton
  • 4 Queue overloads: plain procedure, object method, indexed procedure, indexed method
  • WaitForAll and LastError / ClearLastError
  • SimpleDemo and SimpleThreadpoolDemo examples
  • MIT licence