[solved] macOS Process and Pipes

[Espectr0]

Hola,

I want to run an app and receive the output texts, in windows it works correctly but in macOS I do not receive anything when executing the app.
What can be?

Code: Pascal  [Select][+][-]

1. TUWProcessCB = procedure(const TimeElapsed: Double; var Cancel: Boolean);
2.  
3. procedure ExecuteAppEx(const AAppFileName: String; const AParams: TStringArray; var Output: TStringList; const ACB: TUWProcessCB = NIL);
4. const
5.   READ_BYTES = 2048;
6.  
7. var
8.   AProcess: TProcess;
9.   ACancel: Boolean;
10.   ATimeElapsed: Double;
11.   i: Integer;
12.   MemStream: TMemoryStream;
13.   NumBytes: LongInt;
14.   BytesRead: LongInt;
15. begin
16.   AProcess := TProcess.Create(NIL);
17.   try
18.     AProcess.ShowWindow := swoHide;
19.     AProcess.Executable := AAppFileName;
20.     AProcess.Options    := AProcess.Options + [poUsePipes, poStderrToOutPut];
21.  
22.     for i := 0 to High(AParams) do
23.       AProcess.Parameters.Add(AParams[i]);
24.  
25.     AProcess.Execute;
26.  
27.     ACancel      := False;
28.     ATimeElapsed := 0;
29.     BytesRead := 0;
30.     MemStream := TMemoryStream.Create;
31.     try
32.       while AProcess.Running do
33.       begin
34.         MemStream.SetSize(BytesRead + READ_BYTES);
35.  
36.         NumBytes := AProcess.Output.Read((MemStream.Memory + BytesRead)^, READ_BYTES);
37.         if NumBytes > 0 then
38.           Inc(BytesRead, NumBytes)
39.         else
40.           Break;
41.  
42.         Application.ProcessMessages;
43.         Sleep(100);
44.         ATimeElapsed += 0.1;
45.         if Assigned(ACB) then
46.         begin
47.           ACB(ATimeElapsed, ACancel);
48.           Application.ProcessMessages;
49.           if ACancel then AProcess.Terminate(-1);
50.         end;
51.       end;
52.       MemStream.SetSize(BytesRead);
53.       if not Assigned(Output) then  Output := TStringList.Create;
54.       Output.LoadFromStream(MemStream);
55.     finally
56.       MemStream.Free;
57.     end;
58.   finally
59.     AProcess.Free;
60.   end;
61. end;
62.  

Thanks!

[marcov]

How do you check that you don't receive anything? Does it hang or finish?

OS behaviour can vary depending on the size of buffers and blocking behaviour of pipes.  A good guard against that is the way that runcommandloop does it by always first checking how many bytes are available and then read those.

[Espectr0]

well the stringlist is empty.

I tried running the app, let's say "ffmpeg" in the terminal and there are texts but nothing when running in lazarus process.

Can you tell me that it is better to remove my Loop and use RunCommandLoop and possibly work?

[Jonas Maebe]

I think ffmpeg writes its output to stderr instead of stdout

[Espectr0]

I'm not sure, but I use the "poStderrToOutPut" flag anyway.

[JdeHaan]

This works for me under MacOs:

Code: Pascal  [Select][+][-]

1. procedure TForm1.ProjectRunExecute(Sender: TObject);
2. const
3.   BUF_SIZE = 2048;
4. var
5.   aProcess: TProcess;
6.   aMessages, aErrors: TStringList;
7.   OutputStream : TStream;
8.   BytesRead    : longint;
9.   Buffer       : array[1..BUF_SIZE] of byte;
10. begin
11.   try
12.     aProcess := TProcess.Create(nil);
13.     aMessages := TStringList.Create;
14.     aErrors := TStringList.Create;
15.     aProcess.Executable := your app;
16.     aProcess.Parameters.Add(parameter);
17.  
18.     aProcess.Options := [poUsePipes, poStderrToOutPut];
19.     try
20.       aProcess.Execute;
21.       OutputStream := TMemoryStream.Create;
22.       repeat
23.         BytesRead := AProcess.Output.Read(Buffer, BUF_SIZE);
24.         OutputStream.Write(Buffer, BytesRead)
25.       until BytesRead = 0;
26.  
27.       with aMessages do
28.       begin
29.         OutputStream.Position := 0; // Required to make sure all data is copied from the start
30.         LoadFromStream(OutputStream);
31.       end;
32.  
33.       // Clean up
34.       OutputStream.Free;
35.  
36.     except
37.       aErrors.LoadFromStream(aProcess.Stderr);
38.       //MemoOutput.Text := aErrors.Text; // copy errors to a memo
39.       ShowMessage('ExitStatus : ' + IntToStr(aProcess.ExitStatus));
40.     end;
41.   finally
42.     aMessages.Free;
43.     aProcess.Free;
44.     aErrors.Free;
45.   end;
46.  
47. end;
48.