Using named pipes
lazarus / 32-Linux

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JPT · 2014-11-26 13:13

Hi,

I try to exchange messages between two programs via named pipes.
Doesn't work, because they wait forever on opening the pipes even if
there is no other program active.
Or crash when another app tries to access the pipes (e.g. cat)

Code: [Select]program testserver;

{$MODE Delphi}

uses
        Classes,SysUtils,Crt;

var
  output: TFileStream;
  input: TFileStream;
  buffer: String[255];
  size: integer;
  ctr: integer;

begin
  output := TFileStream.Create('input.pipe',  fmOpenWrite or
fmShareDenyWrite);
  input  := TFileStream.Create('output.pipe', fmOpenRead or 
fmShareDenyRead);
 
  try
    buffer:='';
    ctr:=0;
    while not keypressed do begin
      size:= input.read(buffer[1], 1);
      if (size > 0) then begin
        writeln('Request: ', buffer, InttoHex(byte(buffer[1]),2));   
        if buffer[1] = '#128' then begin // data requested
          inc(ctr);
          buffer:= IntToStr(ctr) + '.0'#13#10;
        end;
        writeln('Answer: ', buffer);     
        output.write(buffer[1], length(buffer));
      end;
      sleep(200);
    end;
  finally
    output.free;
    input.free;
  end;
end.

Background:
I have to port an old DOS based app that reads measurements from
serial port.
The hardware is still in production, so I don't have access to it.
As you can see, this program is emulating the hardware. the other
program looks quite the same, except the file names are opposite and
it is requesting data.
I added the fmShareDeny... constants but this did not help.

any idea?

thanks,

Jan

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JPT · 2014-11-26 13:18

Changed to mode OBJFPC this changed the behavior:
Start A, opens input, waits on output.
Start B, opens input, waits on output, crashs A
Start A, opens input, waits on output, crashs B

An unhandled exception occurred at $08065ECF :
EFOpenError : Unable to open file "output.pipe"
$08065ECF
$08048166

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marcov · 2014-11-26 13:51

I don't see any pipes in your examples. You try to open two different
normal files "input.pipe" and "output.pipe", and do something with
totally unrelated function crt.keypressed!?!?!?

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JPT · 2014-11-26 14:00

I created the files using mkfifo.
I can remove the keypressed and use while true...
I don't think this will change anything.

I already tried AssignPipe and FOpen but it seems they both do
something completely different.