From user42@zip.com.au

On the debian i386 packaged perl 5.10.0 the foo.pl program below run
just as "perl foo.pl" doesn't print "hello" until after 10 seconds,
whereas I hoped setting $|=1 would force immediate output.

Using IO​::Handle->flush seems to have the same non-effect, ie. doesn't
flush the hello.

But it's possible I'm labouring under some misunderstanding of what
flush/autoflush should do. I thought it meant "make the output go to
the system", but some experimenting with how a pushed :encoding layer or
a :perlio buffer layer call their sub-layer "Write" and "Flush" funcs
made me wonder if it's not. (I saw Flush after every 4096 or 1024 byte
block, not only in response to a top-level autoflush or flush method
call.) At any rate if non-output in foo.pl below is what's expected
then a little further explanation in perliol or perlvar $| would be
good.

Flags​:
  category=
  severity=normal

Site configuration information for perl 5.10.0​:

Configured by Debian Project at Thu May 8 13​:32​:42 UTC 2008.

Summary of my perl5 (revision 5 version 10 subversion 0) configuration​:
  Platform​:
  osname=linux, osvers=2.6.24.4, archname=i486-linux-gnu-thread-multi
  uname='linux ninsei 2.6.24.4 #1 smp preempt fri apr 18 15​:36​:09 pdt 2008 i686 gnulinux '
  config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=i486-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.10 -Darchlib=/usr/lib/perl/5.10 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.10.0 -Dsitearch=/usr/local/lib/perl/5.10.0 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -DDEBUGGING=-g -Doptimize=-O2 -Duseshrplib -Dlibperl=libperl.so.5.10.0 -Dd_dosuid -des'
  hint=recommended, useposix=true, d_sigaction=define
  useithreads=define, usemultiplicity=define
  useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
  use64bitint=undef, use64bitall=undef, uselongdouble=undef
  usemymalloc=n, bincompat5005=undef
  Compiler​:
  cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
  optimize='-O2 -g',
  cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include'
  ccversion='', gccversion='4.2.3 (Debian 4.2.3-5)', gccosandvers=''
  intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
  ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
  alignbytes=4, prototype=define
  Linker and Libraries​:
  ld='cc', ldflags =' -L/usr/local/lib'
  libpth=/usr/local/lib /lib /usr/lib /usr/lib64
  libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
  perllibs=-ldl -lm -lpthread -lc -lcrypt
  libc=/lib/libc-2.7.so, so=so, useshrplib=true, libperl=libperl.so.5.10.0
  gnulibc_version='2.7'
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
  cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib'

From user42@zip.com.au

foo.pl

From p5p@perl.wizbit.be

Citeren Kevin Ryde <perlbug-followup@​perl.org>​:

# New Ticket Created by Kevin Ryde
# Please include the string​: [perl #55172]
# in the subject line of all future correspondence about this issue.
# <URL​: http​://rt.perl.org/rt3/Ticket/Display.html?id=55172 >

On the debian i386 packaged perl 5.10.0 the foo.pl program below run
just as "perl foo.pl" doesn't print "hello" until after 10 seconds,
whereas I hoped setting $|=1 would force immediate output.

Using IO​::Handle->flush seems to have the same non-effect, ie. doesn't
flush the hello.

But it's possible I'm labouring under some misunderstanding of what
flush/autoflush should do. I thought it meant "make the output go to
the system", but some experimenting with how a pushed :encoding layer or
a :perlio buffer layer call their sub-layer "Write" and "Flush" funcs
made me wonder if it's not. (I saw Flush after every 4096 or 1024 byte
block, not only in response to a top-level autoflush or flush method
call.) At any rate if non-output in foo.pl below is what's expected
then a little further explanation in perliol or perlvar $| would be
good.

You need to turn autoflush on beforing the print statement.
Or add print "" after turning autoflush on.

Kind regards,

Bram

The RT System itself - Status changed from 'new' to 'open'

From user42@zip.com.au

"Bram via RT" <perlbug-followup@​perl.org> writes​:

You need to turn autoflush on beforing the print statement.

Umm, that's not what I was trying to get at. It's that unflushed output
sitting there when a :encoding is pushed can't then be flushed with $|
or ->flush().

Or add print "" after turning autoflush on.

I tried that, it has no effect. Printing a non-empty string does make
it go.

My gues is that :encoding will pass on a flush call to its sublayer only
when it's seen output pass through itself. I guess not flushing the
sublayer when you know there's nothing to go out is a nice optimization,
but when first pushed it can't know what might or might not be sitting
beneath it. (As before, assuming "make the output go" is what flush
really means.)