On Fri, Nov 3, 2023 at 5:02 PM Nisha Moond <nisha.moond412@gmail.com> wrote:
>
> On Thu, Nov 2, 2023 at 11:52 AM Kyotaro Horiguchi
> <horikyota.ntt@gmail.com> wrote:
> >
> > At Tue, 31 Oct 2023 18:11:48 +0530, vignesh C <vignesh21@gmail.com> wrote in
> > > Few others are also facing this problem with similar code like in:
> > > https://stackoverflow.com/questions/15882799/fgets-returning-error-for-file-returned-by-popen
> >
> > I'm inclined to believe that the pipe won't enter the EOF state until
> > the target command terminates (then the top-level cmd.exe). The target
> > command likely terminated prematurely due to an error before priting
> > any output.
> >
> > If we append "2>&1" to the command line, we can capture the error
> > message through the returned pipe if any. Such error messages will
> > cause the subsequent code to fail with an error such as "unexpected
> > string: 'the output'". I'm not sure, but if this is permissive, the
> > returned error messages could potentially provide insight into the
> > underlying issue, paving the way for a potential solution.
> >
>
> Appending '2>&1 test:
> The command still results in NULL and ends up failing as no data is
> returned. Which means even no error message is returned. The error log
> with appended '2>$1' is -
>
> no data was returned by command
> ""D:/Project/pg1/postgres/tmp_install/bin/pg_resetwal" -V 2>&1"
>
> check for "D:/Project/pg1/postgres/tmp_install/bin/pg_resetwal"
> failed: cannot execute
> Failure, exiting
>
> Further observations:
> 1. To make sure the forked process completes before fgets(), I tested
> with Sleep(100) before fgets() call.
> ...
> ...
> if ((pgver = popen(cmd, "r")) == NULL)
> {
> perror("popen failure");
> return NULL;
> }
>
> errno = 0;
> Sleep(100);
> if (fgets(line, maxsize, pgver) == NULL)
> {
> if (feof(pgver))
> fprintf(stderr, "no data was returned by command \"%s\"\n", cmd);
> ...
> ...
>
> This also doesn't resolve the issue, the error is still seen intermittently.
>
> 2. Even though fgets() fails, the output is still getting captured in
> 'line' string.
> Tested with printing the 'line' in case of failure:
> ...
> ...
> if ((pgver = popen(cmd, "r")) == NULL)
> {
> perror("popen failure");
> return NULL;
> }
>
> errno = 0;
> if (fgets(line, maxsize, pgver) == NULL)
> {
> if (line)
> fprintf(stderr, "cmd output - %s\n", line);
>
> if (feof(pgver))
> fprintf(stderr, "no data was returned by command \"%s\"\n", cmd);
> …
> …
> And the log looks like -
> cmd output - postgres (PostgreSQL) 17devel
> no data was returned by command
> ""D:/Project/pg1/postgres/tmp_install/bin/pg_controldata" -V"
>
> check for "D:/Project/pg1/postgres/tmp_install/bin/pg_controldata"
> failed: cannot execute
> Failure, exiting
>
> Attached test result log for the same - "regress_log_003_logical_slots".
The same failure is observed with test 't\002_pg_upgrade.pl' too
(intermittently). So, it is not limited to "t/003_logical_slots.pl"
test alone. It is more closely associated with the pg_upgrade command
run.
--
Thanks,
Nisha Moond
