threading

Threading & Multi-Threading — Skill

Use this skill when working with threads, asynchronous tasks and parallelism in Delphi projects.

When to Use

• When performing time-consuming operations without blocking the UI (VCL/FMX)
• When implementing parallel data processing
• When creating servers/workers that process concurrent requests
• When synchronizing access to shared resources
• When managing thread pools and work queues
• By implementing graceful thread cancellation

Golden Rule of Threading in Delphi

NEVER access visual components (VCL/FMX) directly from a secondary thread. Use TThread.Synchronize or TThread.Queue to update the UI.

Quick Reference

Simplest way to run something in the background and touch the UI when done:

TTask.Run(
  procedure
  begin
    PerformHeavyCalculation;
    TThread.Queue(nil,
      procedure
      begin
        lblResult.Caption := 'Cálculo concluído';
      end);
  end);

Golden rules: never touch VCL/FMX from a secondary thread (Synchronize/Queue only), never Sleep() on the main thread, protect every shared variable (TCriticalSection/TMonitor/TInterlocked), never call WaitFor on a thread with FreeOnTerminate := True. Full details and code for each are in the reference files below — read the one that matches the task at hand rather than guessing.

references/

Read only the file(s) relevant to the current task — this skill file is intentionally short; the depth lives in these files.

• basics-and-ppl.md — approach comparison table, TThread (inheritance and CreateAnonymousThread), Synchronize vs Queue, and the PPL (TTask, TTask.Run, TParallel.For, TFuture<T>).
• thread-safety.md — TCriticalSection, TMonitor, TInterlocked, TThreadList<T>, TMultiReadExclusiveWriteSynchronizer, plus TEvent/TSemaphore signaling.
• patterns.md — Producer-Consumer with TThreadedQueue, a custom thread pool, cancellation tokens, the generic background-worker-with-result pattern, and a periodic timer thread.
• debugging-and-checklist.md — anti-patterns to avoid, naming threads for the IDE debugger, and the pre-flight checklist.