[fpc-pascal] POpen en PClose

[Adriaan van Os]

On 20/07/2026 19:56, Adriaan van Os via fpc-pascal wrote:
>
>
> On 20/07/2026 16:19, Marco van de Voort via fpc-pascal wrote:
>>
>> Op 20-7-2026 om 15:13 schreef Adriaan van Os via fpc-pascal:
>>>>
>>>> So popen/pclose are a more high level (FILE * using) part of libc, 
>>>> while we tend to only use the basis.
>>>
>>> Ah, so that means that I couldn't just call naively into libc popen 
>>> with FileRec.Handle ?
>>>
>> Indeed.   And FILE* is opague and thus target specific,  it would 
>> mean another structure to maintain, and to somehow to determine for a 
>> new *nix target. STAT and STATFS already give us grief enough.
>
> Right. So now I am calling PClose and it will hang. Why ? Well, PClose 
> calls WaitProcess in unx.pp, which in turn calls fpWaitPid in a loop, 
> which returns (on Darwin) 0 for a process that has died ....
>
>   repeat
>     r:=fpWaitPid(Pid, at s,0);
>     if (r=-1) and (fpgeterrno=ESysEIntr) Then
>       r:=0;
>   until (r<>0);
>
> In general, I find such a loop, that depends on result codes, quite 
> risky. The POSIX standard says here 
> <https://pubs.opengroup.org/onlinepubs/9699919799/functions/wait.html>
>
>     "If/wait/() or/waitpid/() return because the status of a child 
> process is available, these functions shall return a value equal to 
> the process ID of the child process. In this case, if the value of the 
> argument/stat_loc/is not a null pointer, information shall be stored 
> in the location pointed to by/stat_loc/. The value stored at the 
> location pointed to by/stat_loc/shall be 0 if and only if the status 
> returned is from a terminated child process that terminated by one of 
> the following means:"

This is nonsense. I apologize for the noise. The reason for the hang is 
not the loop but the child process that has not terminated.

By the way, how do I flush the output to the POpen child process ? I 
tried SysUtils.FileFlush with FileRec( File).Handle. but it failed.

Regards,

Adriaan van Os

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