TThreadCustom for Free Pascal / Lazarus

An elegant and robust anonymous thread implementation for Free Pascal/Lazarus, inspired by Delphi's TThread.CreateAnonymousThread. Make multi-threaded development easier and safer!

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🚀 Features

• Compatible: Free Pascal 3.2.3+
• Delphi-like interface: Easy code migration
• Structured callbacks: OnShow, OnProcess, OnComplete, OnFinally, OnError
• Automatic Synchronize: UI callbacks run in the main thread
• Cancellation control: Supports Terminate and CheckTerminated
• Robust exception handling: OnError receives exception message
• Auto-destruction: FreeOnTerminate := True automatically
• No external dependencies: Only Classes and SysUtils

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📦 Installation

1. Copy the uThread.pas file to your project
2. Add uThread to your uses clause
3. Ready to go!

uses
  uThread;

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💡 Basic Usage Example

procedure TForm1.Button1Click(Sender: TObject);
begin
  TThreadCustom.Start(
    @ShowProgress,    // OnShow (UI thread)
    @DoHeavyWork,     // OnProcess (background)
    @WorkComplete,    // OnComplete (UI thread)
    @WorkFinally,     // OnFinally (UI thread)
    @HandleError,     // OnError (UI thread)
    True              // Execute OnComplete even on error
  );
end;

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🔄 Cancellation Control

private
  FCurrentThread: TThreadCustom;

procedure TForm1.StartLongTask;
begin
  FCurrentThread := TThreadCustom.Start(
    @ShowTaskStart,
    @DoLongTask,
    @TaskComplete,
    @TaskFinally,
    @TaskError,
    True
  );
end;

procedure TForm1.CancelTask;
begin
  if Assigned(FCurrentThread) and not FCurrentThread.IsTerminated then
  begin
    FCurrentThread.Terminate;
    ShowMessage('Cancelling...');
  end;
end;

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🔧 API Reference

class function Start(
  AOnShow, AOnProcess, AOnComplete: TProc;
  AOnFinally: TProcBoolean; 
  AOnError: TProcString = nil;
  const ADoCompleteWithError: Boolean = True
): TThreadCustom;

Callback Types:

• TProc = procedure of object;
• TProcBoolean = procedure(AIsTerminated: Boolean) of object;
• TProcString = procedure(const AExceptionMessage: string) of object;

Properties:

• IsTerminated: Boolean

Methods:

• Terminate

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🎯 Usage Examples

• File processing
• Data download
• Database operations

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⚠️ Important Notes

✅ Do's

• Declare callbacks as class methods (procedure of object)
• Use @MethodName to reference callbacks
• Access UI only in OnShow, OnComplete, OnFinally, and OnError
• Use TThread.CheckTerminated in long loops
• Handle exceptions properly

❌ Don'ts

• Do not access visual components in OnProcess
• Do not use inline anonymous procedures (not supported in FPC 3.2.3)
• Do not use WaitFor or FreeAndNil (destruction is automatic)

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🔄 Delphi → FPC/Lazarus Migration

Delphi:

TThread.CreateAnonymousThread(
  procedure
  begin
    // work here
    TThread.Synchronize(nil, 
      procedure
      begin
        // update UI
      end);
  end
).Start;

FPC/Lazarus:

TThreadCustom.Start(
  nil,           // OnShow
  @DoWork,       // OnProcess
  @UpdateUI,     // OnComplete  
  nil,           // OnFinally
  @HandleError,  // OnError
  True
);

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📋 Requirements

• Free Pascal 3.2.0 or higher
• Lazarus (any recent version)
• Platforms: Windows, Linux, macOS

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🤝 Contributing

Contributions are welcome!

1. Fork the project
2. Create a feature branch: git checkout -b feature/YourFeature
3. Commit your changes: git commit -m 'Add YourFeature'
4. Push to the branch: git push origin feature/YourFeature
5. Open a Pull Request

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📄 License

This project is licensed under the MIT License. See the LICENSE file for details.