FW: process output pipe autoflush
Many thanks to $Bill, Carl and Michael,
The cause was the buffering in the executable involved,
I had the coder insert fflush(stdout) after each printf statement.
Also my understanding on buffering has somewhat improved.
Thanks again.
|__
| Mark Zvolanek
| +612 9227 0479
-Original Message-
From: $Bill Luebkert [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, 5 December 2000 15:08
To: Mark Zvolanek
Cc: '[EMAIL PROTECTED]'
Subject: Re: process output pipe autoflush
Mark Zvolanek wrote:
Hello,
I have a problem with autoflush. Platform is Windows NT 4 / sp6.
I use the following code:
$command = 'executable.exe param1 ';#option 1
# $command = 'DIR C:\ /S'; #option 2
open (PIPE, "$command |");
$| = 1;
while (PIPE){
print;
}
If I use line with (option 2) the output does not get buffered as
expected.
If I use line with (option 1) the output of the executable is buffered.
If I execute the line "executable.exe param1" on the DOS prompt
the oputput is produced immediately.
I tried both autoflush PIPE and select((select(PIPE), $| = 1)[0])
commands,
I even print out the value of $| during execution, it is set to 1.
What am I doing wrong?
How do you know the data is being buffered or not?
Are you doing this under CGI conditions?
Do you understand what buffering does?
It basically forces each line out individually (when $| is set) rather
then waiting for an internal buffer (maybe 512/1024 bytes??) to fill before
outputting. Leaving STDOUT buffered ($| not set) is more efficient.
If you were to slip a sleep 1 into your loop, you would see the result
since one would print one line every second and the other would wait several
seconds and then print several lines.
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RE: process output pipe autoflush
Everybody, all of the issues being discussed here are fully explained in the attatched link. I repeat myself... You should read M-J. Dominus's excellent Perl Journal article, "Suffering from Buffering?". This will give you all the answers you need. http://perl.plover.com/FAQs/Buffering.html Michael Erskine (MSEmtd) mailto:[EMAIL PROTECTED] JAPH ___ Perl-Win32-Users mailing list [EMAIL PROTECTED] http://listserv.ActiveState.com/mailman/listinfo/perl-win32-users
RE: process output pipe autoflush
-Original Message- From: Mark Zvolanek [mailto:[EMAIL PROTECTED]] Sent: 05 December 2000 03:48 To: '[EMAIL PROTECTED]' Cc: Mark Zvolanek Subject: process output pipe autoflush I have a problem with autoflush. Platform is Windows NT 4 / sp6. Mark, (in fact everyone!) You should read M-J. Dominus's excellent Perl Journal article, "Suffering from Buffering?". This will give you all the answers you need. http://perl.plover.com/FAQs/Buffering.html In fact everyone who hasn't already should read *ALL* of M-J's articles - it almost makes newsgroup support obsolete (except for all the Win32 caveats of course!)... http://perl.plover.com/ Michael Erskine (MSEmtd) mailto:[EMAIL PROTECTED] JAPH ___ Perl-Win32-Users mailing list [EMAIL PROTECTED] http://listserv.ActiveState.com/mailman/listinfo/perl-win32-users
Re: process output pipe autoflush
"$Bill Luebkert" wrote:
Mark Zvolanek wrote:
Hi Carl,
I am sorry I don't understand.
I was talking about $| variable and not $!.
I am trying to figure out why my perl code
is buffering the (STDOUT) output of the executable
even though I have set the variable $| to 1.
Whereas when I execute the executable at
the command prompt its output is not buffered.
You also said: The PIPE handle is an input handle.
Why is it then my perl code below produces output
as passed to it by the executable.
...
while (PIPE){
print;
}
...
A new little test shows some insight. Maybe buffering isn't used when
writing to the console (vs a file/pipe):
Driver:
snip to last test block
# this should print 1 line per second
Whoops, this last one should wait 10 seconds and then print all 10 lines
if buffering is on, but doesn't when going direct to console.
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Re: process output pipe autoflush
Mark Zvolanek wrote:
Hi Carl,
I am sorry I don't understand.
I was talking about $| variable and not $!.
I am trying to figure out why my perl code
is buffering the (STDOUT) output of the executable
even though I have set the variable $| to 1.
Whereas when I execute the executable at
the command prompt its output is not buffered.
You also said: The PIPE handle is an input handle.
Why is it then my perl code below produces output
as passed to it by the executable.
...
while (PIPE){
print;
}
...
A new little test shows some insight. Maybe buffering isn't used when
writing to the console (vs a file/pipe):
Driver:
use strict;
$| = 1; # buffering off
# ARGV[0] = $|, ARGV[1] = sleep, ARGV[2] = count
# this should wait 10 seconds and then print all 10 lines
open PIPE, "c:\\perl\\bin\\perl pipe.pl 0 1 10 |" or
die "Error starting pipe: $!\n";
while (PIPE) {
print;
}
close PIPE;
# this should print 1 line per second
open PIPE, "c:\\perl\\bin\\perl pipe.pl 1 1 10 |" or
die "Error starting pipe: $!\n";
while (PIPE) {
print;
}
close PIPE;
$| = 0; # buffering on
# this should wait 10 seconds and then print all 10 lines
open PIPE, "c:\\perl\\bin\\perl pipe.pl 0 1 10 |" or
die "Error starting pipe: $!\n";
while (PIPE) {
print;
}
close PIPE;
# this should print 1 line per second
open PIPE, "c:\\perl\\bin\\perl pipe.pl 1 1 10 |" or
die "Error starting pipe: $!\n";
while (PIPE) {
print;
}
close PIPE;
__END__
Test exe (pipe.pl):
use strict;
print STDERR "buffer=$ARGV[0]; " if defined $ARGV[0];
print STDERR "sleep=$ARGV[1]; " if defined $ARGV[1];
print STDERR "count=$ARGV[2]\n" if defined $ARGV[2];
$| = $ARGV[0] if defined $ARGV[0];
my $count = 1000;
$count = $ARGV[2] if defined $ARGV[2];
for (my $ii = 0; $ii $count; $ii++) {
print
"$ii: Testing 1234567890 The quick brown fox jumped over the lazy dog's back\n";
sleep $ARGV[1] if defined $ARGV[1] and $ARGV[1] 0;
}
__END__
If you pipe the output to less, you get different results than if
you let it go to console. 1-4 are the four exe executions.
1) wait 10; print 10
2) wait 1; print 1 - ten times
3) wait 10; print 10
4a) wait 10; print 10 (when going to pipe)
4b) wait 1; print 1 - ten times (when going to console)
--
,-/- __ _ _ $Bill Luebkert ICQ=14439852
(_/ / )// // DBE Collectibles http://www.wgn.net/~dbe/
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process output pipe autoflush
Hello,
I have a problem with autoflush. Platform is Windows NT 4 / sp6.
I use the following code:
$command = 'executable.exe param1 ';#option 1
# $command = 'DIR C:\ /S'; #option 2
open (PIPE, "$command |");
$| = 1;
while (PIPE){
print;
}
If I use line with (option 2) the output does not get buffered as expected.
If I use line with (option 1) the output of the executable is buffered.
If I execute the line "executable.exe param1" on the DOS prompt
the oputput is produced immediately.
I tried both autoflush PIPE and select((select(PIPE), $| = 1)[0]) commands,
I even print out the value of $| during execution, it is set to 1.
What am I doing wrong?
Thanks,
|__
| Mark Zvolanek
| +612 9227 0479
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