Timeouts in Pascal

program Timeouts;

uses
  SysUtils, DateUtils;

var
  startTime: TDateTime;

function WaitForResult(delay: Integer): string;
begin
  Sleep(delay * 1000);
  Result := 'result ' + IntToStr(delay);
end;

function TimedOperation(timeout: Integer): string;
var
  endTime: TDateTime;
begin
  startTime := Now;
  endTime := IncSecond(startTime, timeout);
  
  while Now < endTime do
  begin
    if WaitForResult(2) <> '' then
    begin
      Result := WaitForResult(2);
      Exit;
    end;
  end;
  
  Result := 'timeout';
end;

begin
  WriteLn(TimedOperation(1));
  WriteLn(TimedOperation(3));
end.

In Pascal, we don’t have built-in concurrency primitives like channels or goroutines. Instead, we simulate the timeout behavior using a combination of the Sleep function and time comparisons.

The WaitForResult function simulates an operation that takes a certain amount of time to complete. It uses the Sleep function to pause execution for the specified number of seconds.

The TimedOperation function implements the timeout logic. It sets a start time and an end time based on the specified timeout. It then enters a loop that continues until the current time exceeds the end time. Within this loop, it checks if the WaitForResult function has completed. If it has, it returns the result. If the loop completes without getting a result, it returns ’timeout'.

In the main program, we call TimedOperation twice with different timeout values:

1. With a 1-second timeout, which should result in a timeout because WaitForResult takes 2 seconds.
2. With a 3-second timeout, which should succeed because it’s longer than the 2-second delay in WaitForResult.

To run this program:

1. Save it as timeouts.pas
2. Compile it using a Pascal compiler (e.g., Free Pascal):

$ fpc timeouts.pas

3. Run the compiled program:

$ ./timeouts
timeout
result 2

This output shows that the first operation timed out (as expected with a 1-second timeout for a 2-second operation), while the second operation succeeded (as the 3-second timeout was sufficient for the 2-second operation to complete).

Note that this Pascal implementation is a simplified simulation of the timeout behavior. In a real-world scenario, you might want to use more sophisticated concurrency techniques, possibly involving separate threads or processes, depending on your specific requirements and the capabilities of your Pascal environment.