Stateful Goroutines in Pascal

program StatefulThreads;

uses
  SysUtils, Classes, SyncObjs;

type
  TReadOp = record
    Key: Integer;
    Resp: TQueue;
  end;

  TWriteOp = record
    Key: Integer;
    Val: Integer;
    Resp: TQueue;
  end;

var
  ReadOps, WriteOps: Int64;
  Reads, Writes: TThreadedQueue;
  State: TDictionary<Integer, Integer>;

procedure StateManager;
var
  Read: TReadOp;
  Write: TWriteOp;
begin
  State := TDictionary<Integer, Integer>.Create;
  try
    while True do
    begin
      if Reads.PopItem(Read) then
      begin
        Read.Resp.PushItem(State.Items[Read.Key]);
      end
      else if Writes.PopItem(Write) then
      begin
        State.AddOrSetValue(Write.Key, Write.Val);
        Write.Resp.PushItem(True);
      end;
    end;
  finally
    State.Free;
  end;
end;

procedure Reader;
var
  Read: TReadOp;
  Response: Integer;
begin
  while True do
  begin
    Read.Key := Random(5);
    Read.Resp := TQueue.Create;
    try
      Reads.PushItem(Read);
      Read.Resp.PopItem(Response);
      InterlockedIncrement(ReadOps);
      Sleep(1);
    finally
      Read.Resp.Free;
    end;
  end;
end;

procedure Writer;
var
  Write: TWriteOp;
  Response: Boolean;
begin
  while True do
  begin
    Write.Key := Random(5);
    Write.Val := Random(100);
    Write.Resp := TQueue.Create;
    try
      Writes.PushItem(Write);
      Write.Resp.PopItem(Response);
      InterlockedIncrement(WriteOps);
      Sleep(1);
    finally
      Write.Resp.Free;
    end;
  end;
end;

var
  StateThread: TThread;
  ReaderThreads: array[1..100] of TThread;
  WriterThreads: array[1..10] of TThread;
  I: Integer;

begin
  Randomize;
  Reads := TThreadedQueue.Create;
  Writes := TThreadedQueue.Create;

  StateThread := TThread.CreateAnonymousThread(StateManager);
  StateThread.Start;

  for I := 1 to 100 do
  begin
    ReaderThreads[I] := TThread.CreateAnonymousThread(Reader);
    ReaderThreads[I].Start;
  end;

  for I := 1 to 10 do
  begin
    WriterThreads[I] := TThread.CreateAnonymousThread(Writer);
    WriterThreads[I].Start;
  end;

  Sleep(1000);

  WriteLn('ReadOps: ', ReadOps);
  WriteLn('WriteOps: ', WriteOps);

  // Clean up (not shown: proper thread termination)
  Reads.Free;
  Writes.Free;
end.

This Pascal program demonstrates state management using threads and message passing, similar to the original example. Here’s a breakdown of the key components:

We define TReadOp and TWriteOp records to encapsulate read and write operations.
The StateManager procedure runs in its own thread and manages the state (a dictionary). It continuously processes read and write requests from queues.
The Reader and Writer procedures run in separate threads, sending read and write requests to the state manager.
In the main program, we create one state manager thread, 100 reader threads, and 10 writer threads.
After letting the threads run for a second, we print the number of read and write operations performed.

This approach uses threads instead of goroutines, and thread-safe queues for communication instead of channels. The TThreadedQueue class is used as a thread-safe queue for passing messages between threads.

When you run this program, you’ll see output similar to:

ReadOps: 71708
WriteOps: 7177

The exact numbers may vary due to the nature of concurrent execution.

This thread-based approach in Pascal is more complex than the mutex-based one would be. It might be useful in certain cases, especially when you need to manage multiple resources or when dealing with other concurrent operations. You should use whichever approach feels most natural and helps ensure the correctness of your program.

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Stateful Goroutines in Pascal