Channel Synchronization in Pascal

Our example demonstrates how to synchronize execution across threads using a simple channel-like mechanism. In Pascal, we’ll use a boolean variable and a semaphore to achieve similar functionality.

program ChannelSynchronization;

uses
  SysUtils, SyncObjs;

var
  Done: Boolean;
  Semaphore: TSemaphore;

procedure Worker;
begin
  Write('working...');
  Sleep(1000);  // Simulate work by sleeping for 1 second
  WriteLn('done');
  
  // Signal that we're done
  Done := True;
  Semaphore.Release;
end;

begin
  Done := False;
  Semaphore := TSemaphore.Create(nil, 0, 1, '');
  try
    // Start a worker thread
    TThread.CreateAnonymousThread(Worker).Start;
    
    // Wait for the worker to finish
    Semaphore.Acquire;
    
    // At this point, we know the worker has finished
  finally
    Semaphore.Free;
  end;
end.

In this Pascal version:

1. We define a global Done boolean variable and a Semaphore to synchronize between threads.

2. The Worker procedure simulates work by printing a message, sleeping for a second, and then signaling completion by setting Done to True and releasing the semaphore.

3. In the main program, we create the semaphore and start an anonymous thread that runs the Worker procedure.

4. We then wait for the worker to finish by acquiring the semaphore. This blocks until the worker releases it.

5. After the semaphore is acquired, we know the worker has finished its task.

To run this program:

$ fpc channel_synchronization.pas
$ ./channel_synchronization
working...done

If you removed the Semaphore.Acquire line from this program, it would exit before the worker thread even started its work.

This example demonstrates a basic form of thread synchronization in Pascal. For more complex scenarios involving multiple threads, you might want to explore other synchronization primitives provided by the SyncObjs unit or consider using a thread pool.