[fpc-pascal] Re: Linux program sometimes crashes with "EProcess : Failed to create pipes"

[Funky Beast]

Burkhard Carstens wrote:
> Am Donnerstag, 10. September 2009 11:01 schrieb T. Guilleminot:
>> Hi,
>>
>> Have a Linux program that recently started to crash several times
>> with such message :
>> An unhandled exception occurred at $080A4CB9 :
>> EProcess : Failed to create pipes
>>   $080A4CB9
>>   $080A4D3D
>>   $080526E0
>>   $08057C11
>>   $08058809
>>   $B7B082B6
>>   $B7B07B88
>>   $B7B0B0EB
>>   $B7B0B5BA
>>   $B7CF57D9
>>   $0805AABD
>>
>> This seems only occurs after a long running period of time.
>> Considering error message and as it runs very often some OS processes
>> I suspect TProcess. I use such procedure :
>>
>>   Procedure Run_Command(Wait : boolean; TheCommand : ansistring);
>> cdecl; export;
>>   var
>>     AProcess: TProcess;
>>   Begin
>>     AProcess := TProcess.Create(nil);
>>     AProcess.CommandLine := TheCommand;
>>     if Wait = true then AProcess.Options := AProcess.Options +
>> [poWaitOnExit];
>>     AProcess.Execute;
>>     AProcess.Free;
>>   end;
>>
>> I think I may hit some OS limits or I overload system.
>> Does anyone know how to diagnose this further (why it fails...)
>> and/or to fix this ?
> Using this procedure with wait=false leaves you a zombie process. I.e. 
> even, if "TehCommand" finished, the process isn't closed unless you 
> call fpWaitPID (or better WaitOnExit) on it's pid.
> Not sure, but probably the zombie still holds the pipes and therefore 
> you run out of handles and some point.
> 
> see also: http://mantis.freepascal.org/view.php?id=11797 
> 
> regards
>  Burkhard
> 
> _______________________________________________
> fpc-pascal maillist  -  fpc-pascal-PD4FTy7X32k2wBtHl531yWD2FQJk+8+b at public.gmane.org
> http://lists.freepascal.org/mailman/listinfo/fpc-pascal
> 

Hi,

If you don't need to wait for the program, I have a work around that prevents zombies with
the simple class I wrote below. Note that it works only on Linux. I wrote it in a class because
I might add other signals to ignore later on as I travel on further on the multi-process route.

Usage: Create an instance of TIgnoreSignal on your process calling program, and call its
       DoIgnoreChildProc procedure at anywhere before you execute your external processes or
       when your program starts. Once executed, any external process/es signals are ignored
       from then on.

**********************************************************************************************
unit IgnoreSignal;

//This is a class to allow a main application who executes external child processes(programs)
//to ignore / let go of them after executing them. This is to prevent zombies, if the child
//misbehaves.

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, BaseUnix, Unix;

type

  { TIgnoreSignal }

  TIgnoreSignal = class
  public
   procedure DoIgnoreChildProc;
  end;

implementation

{ TIgnoreSignal }

procedure TIgnoreSignal.DoIgnoreChildProc;
var sigact: sigactionrec;
begin
 sigact.sa_flags := SA_NOCLDWAIT;
 FPSigaction(SIGCHLD, @sigact, nil);
end;

end.
**********************************************************************************************

HTH,
Funky Beast