Flush all opened STDIO streams

dmitnin has asked for the wisdom of the Perl Monks concerning the following question:

Hello, guys!

I use some XS library, that writes to stderr itself log by the libc fprintf() function. In perl script I wanna catch all stderr, produced by this library, but I couldn't, due to stdio makes output buffered.

Code like:

  select(STDERR);
  $| = 1;
[download]

did not help, because XS and perl code have the same file descriptor (2), but the different bound stdio buffers.

The only thing, that helped me, is flushing of all open output streams:

use Inline C => <<'END_C';
void make_flush() {
    fflush(NULL);
}
END_C
[download]

Please, can anyone help me to make this flush without using of C inlined code?

Comment on Flush all opened STDIO streams Select or Download Code

Replies are listed 'Best First'.
Re: Flush all opened STDIO streams by Anonymous Monk on Feb 03, 2014 at 12:57 UTC
Try Capture::Tiny	[reply]
Re^2: Flush all opened STDIO streams by dmitnin (Initiate) on Feb 03, 2014 at 14:20 UTC
List, what I tried to use: 1. Reopen STDERR to variable; 2. Reopen STDERR to file; 3. Capture::Tiny and some others (sorry do not understand already); 4. Make hook on $SIG{__WARN__} 5. Use eval {} I figured out slowest and ugly solution: write my perl code to an individual script, and system() or `backtick` it with grabbing stderr.	[reply]
Re: Flush all opened STDIO streams by Anonymous Monk on Feb 03, 2014 at 13:01 UTC
Try `use IO::Handle; STDERR->flush;` [download]	[reply] [d/l]
Re^2: Flush all opened STDIO streams by dmitnin (Initiate) on Feb 03, 2014 at 14:10 UTC
Sorry, but it did not work. Also, I tried: `STDERR->autoflush(1)` [download] Another thing, that works is to recompile XS with fflush after logging: `fprintf(stderr, "..."); fflush(stderr);` [download] but I can't install/update XS package on the production servers. May be anyone knows some perl module, that can do fflush(NULL)?	[reply] [d/l] [select]
Re^3: Flush all opened STDIO streams by Anonymous Monk on Feb 03, 2014 at 15:30 UTC
What is the fileno of that c/xs stderr versus perl's STDERR? Maybe you can fake it `sub flushall { for my $fileno (0..1024){ ## blah blah constants open my($fake), "<&=$fileno"; ## UGLY $fake->flush; } }` [download] Maybe you can fake it `sub flushall { use POSIX(); for my $fileno (0.. POSIX::dup( fileno( STDERR) ) ){ open my($fake), ">&=$fileno"; ## UGLY $fake->flush; } }` [download]	[reply] [d/l] [select]
Re: Flush all opened STDIO streams by oiskuu (Hermit) on Feb 03, 2014 at 16:57 UTC
Take a look at perlapio.	[reply]
Re^2: Flush all opened STDIO streams by Anonymous Monk on Feb 03, 2014 at 20:36 UTC
Take a look at perlapio. Why?	[reply]
Re: Flush all opened STDIO streams by dmitnin (Initiate) on Feb 04, 2014 at 12:12 UTC
The code: `use Inline C => <<'END_C'; void print_2() { fprintf(stdout, "2\n"); } END_C print STDOUT "1"; print_2(); print STDOUT "\n";` [download] prints: `2 1` [download] It says, that perl has its own system of stream buffering.	[reply] [d/l] [select]