Re: POpen en PClose
Adriaan van Os via fpc-pascal <[email protected]> Mon, 20 Jul 2026 17:56:16 +0000 (UTC)
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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,@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:"
Regards,
Adriaan van Os
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<div class="moz-cite-prefix">On 20/07/2026 16:19, Marco van de Voort
via fpc-pascal wrote:<br>
</div>
<blockquote type="cite"
cite="mid:1e42618f-b947-4f98-83ae-ed562439302d-wEdTOCGUvwedTX5a5knrmyH1kwoRJHTR@public.gmane.org">
<br>
Op 20-7-2026 om 15:13 schreef Adriaan van Os via fpc-pascal:
<br>
<blockquote type="cite">
<blockquote type="cite">
<br>
So popen/pclose are a more high level (FILE * using) part of
libc, while we tend to only use the basis.
<br>
</blockquote>
<br>
Ah, so that means that I couldn't just call naively into libc
popen with FileRec.Handle ?
<br>
<br>
</blockquote>
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.
<br>
</blockquote>
<br>
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 ....<br>
<br>
repeat<br>
r:=fpWaitPid(Pid,@s,0);<br>
if (r=-1) and (fpgeterrno=ESysEIntr) Then<br>
r:=0;<br>
until (r<>0);<br>
<br>
In general, I find such a loop, that depends on result codes, quite
risky. The POSIX standard says here
<a class="moz-txt-link-rfc2396E" href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/wait.html"><https://pubs.opengroup.org/onlinepubs/9699919799/functions/wait.html></a><br>
<br>
<span
style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13.333333px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration: none; display: inline !important; float: none;">
"If<span class="Apple-converted-space"> </span></span><i
style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13.333333px; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">wait</i><span
style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13.333333px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration: none; display: inline !important; float: none;">()
or<span class="Apple-converted-space"> </span></span><i
style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13.333333px; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">waitpid</i><span
style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13.333333px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration: none; display: inline !important; float: none;">()
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<span
class="Apple-converted-space"> </span></span><i
style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13.333333px; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">stat_loc</i><span
style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13.333333px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration: none; display: inline !important; float: none;">is
not a null pointer, information shall be stored in the location
pointed to by<span class="Apple-converted-space"> </span></span><i
style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13.333333px; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">stat_loc</i><span
style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13.333333px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration: none; display: inline !important; float: none;">.
The value stored at the location pointed to by<span
class="Apple-converted-space"> </span></span><i
style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13.333333px; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">stat_loc</i><span
style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 13.333333px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration: none; display: inline !important; float: none;"><span
class="Apple-converted-space"> </span>shall be 0 if and only if
the status returned is from a terminated child process that
terminated by one of the following means:"<br>
<br>
Regards,<br>
<br>
Adriaan van Os<br>
<br>
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