How to re use a process

[nikel]

Hello, I'm trying to use a process multiple times in my console program. The second time I run it doesn't work. I don't remember whether it gave me error. I had to create a new process add

Code: Pascal  [Select][+][-]

1. poStderrToOutPut

in options. Here's my first process.

Code: Pascal  [Select][+][-]

1. // Find the key and set var
2. AProcess:=TProcess.Create(nil);
3. with AProcess do
4. begin
5.   Executable:='keyfinder-cli';
6.   with Parameters do
7.   begin
8.     Add('-n');
9.     Add('standard');
10.     Add(Song.GetPath());
11.   end;
12.   CurrentDirectory:='/usr/local/bin/';
13.   Options:=AProcess.Options + [poUsePipes, poWaitOnExit];
14.   Execute;
15. end;
16. ListOfOutput.LoadFromStream(AProcess.Output);
17. AProcess:=nil;
18. AProcess.Free;
19. if (Length(ListOfOutput.CommaText) <= 5) then
20. begin
21.   Song.SetKey(ListOfOutput.CommaText);
22. end;
23. ListOfOutput.Clear;

How can I use the process multiple times correctly?

[Remy Lebeau]

Hello, I'm trying to use a process multiple times in my console program. The second time I run it doesn't work.

Can you be more specific? WHAT doesn't work, exactly?

I don't remember whether it gave me error.

Can you run it again and find out?


On a side note:

Code: Pascal  [Select][+][-]

1. AProcess:=nil;
2. AProcess.Free;

This causes a memory leak.  You need to reverse the order of these lines.

[nikel]

Thank you for your reply. I notice it doesn't give me error anymore after poStderrToOutPut.

[Remy Lebeau]

Thank you for your reply. I notice it doesn't give me error anymore after poStderrToOutPut.

Are you sure the process actually attempts to write anything to stderr in the first place?

[Thaddy]

I think he means that stderr should not write to stdout,
He needs to configure stderr to redirect to file or a stream that can be used with a error reporting component. AFAIK there are several examples on the form. It is a recurring issue.
The Lazarus IDE uses this redirection itself.
If there is no redirection then the only way is to redirect stderr to stdout.
Here's a utility unit I wrote that extends CreatePipeStream with a third writestream for stdErr:

Code: Pascal  [Select][+][-]

1. unit ExtendedPipes;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   {$ifdef unix}baseunix,unix,{$endif}{$ifdef mswindows}jwaWindows,{$endif}Classes, SysUtils, Pipes,streamio;
9.  
10. procedure CreateExtPipeStreams(out ReadPipe: TInputPipeStream;
11.                              out WritePipe: TOutputPipeStream;
12.                              out ErrWritePipe: TOutputPipeStream);
13. implementation
14.  
15. procedure CreateExtPipeStreams(out ReadPipe: TInputPipeStream;
16.                              out WritePipe: TOutputPipeStream;
17.                              out ErrWritePipe: TOutputPipeStream);
18. var
19.   Pipe1Read, Pipe1Write: THandle;
20.   Pipe2Read, Pipe2Write: THandle;
21. begin
22.   // Create first pipe (normal input/output)
23.   if not CreatePipeHandles(Pipe1Read, Pipe1Write) then
24.     raise EPipeError.Create('Failed to create primary pipe');
25.    
26.   // Create second pipe (for stderr)
27.   if not CreatePipeHandles(Pipe2Read, Pipe2Write) then
28.   begin
29.     CloseHandle(Pipe1Read);
30.     CloseHandle(Pipe1Write);
31.     raise EPipeError.Create('Failed to create stderr pipe');
32.   end;
33.  
34.   try
35.     // Create the pipe stream objects
36.     ReadPipe := TInputPipeStream.Create(Pipe1Read);
37.     WritePipe := TOutputPipeStream.Create(Pipe1Write);
38.     ErrWritePipe := TOutputPipeStream.Create(Pipe2Write);
39.  
40.     // Redirect stderr to our error pipe
41.     AssignStream(ErrOutput, ErrWritePipe);
42.     Rewrite(ErrOutput);
43.   except
44.     // Cleanup if something goes wrong
45.     CloseHandle(Pipe1Read);
46.     CloseHandle(Pipe1Write);
47.     CloseHandle(Pipe2Read);
48.     CloseHandle(Pipe2Write);
49.     raise;
50.   end;
51. end;
52.  
53. end.

(I always had the plan to write that, this looked like a good opportunity to finally do it. I had a little help from deepseek, but quite a few manual changes necessary)

Use is the same as for CreatePipeStream, except stderr now has its own stream.