From user42@zip.com.au

When a PerlIO​::via​::QuotedPrint layer is pushed on an opened file,
autoflush or an explicit ->flush() doesn't send output to the file
immediately.

The program qp.pl below shows the problem. I hoped the OUT->flush would
make the "hello" appear in /tmp/foo immediately, but that doesn't
happen, not until after the program exits after the sleep.

I guess QuotedPrint doesn't supply a FLUSH routine, and the default for
PerlIO​::via in that case is to do nothing, so a top-level flush doesn't
reach the :perlio+​:unix full-buffered output layer below.

Several other PerlIO​::via output modules on cpan behave the same,
I guess having used QuotedPrint as a model. I wonder if either

- The PerlIO​::via docs could advise every output layer to supply a FLUSH
  function calling $fh->flush on the sublayer.

- PerlIO​::via could make such a "propagated" flush the default if you
  don't supply a FLUSH routine.

The latter could make life easier for straightforward non-buffering
transformer layers. The only question would be whether anyone has
omitted a FLUSH func deliberately wanting not to call flush on the
sublayer. That'd seem a bit unlikely to me, or only applicable to
something that was designed to be at the bottom of the stack anyway
(an output capture of some sort say) ...

Flags​:
  category=library
  severity=wishlist

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

qp.pl

From @jkeenan

On Fri Jul 25 17​:52​:12 2008, kryde wrote​:

When a PerlIO​::via​::QuotedPrint layer is pushed on an opened file,
autoflush or an explicit ->flush() doesn't send output to the file
immediately.

The program qp.pl below shows the problem. I hoped the OUT->flush
would
make the "hello" appear in /tmp/foo immediately, but that doesn't
happen, not until after the program exits after the sleep.

I guess QuotedPrint doesn't supply a FLUSH routine, and the default
for
PerlIO​::via in that case is to do nothing, so a top-level flush
doesn't
reach the :perlio+​:unix full-buffered output layer below.

Several other PerlIO​::via output modules on cpan behave the same,
I guess having used QuotedPrint as a model. I wonder if either

- The PerlIO​::via docs could advise every output layer to supply a
FLUSH
function calling $fh->flush on the sublayer.

- PerlIO​::via could make such a "propagated" flush the default if you
don't supply a FLUSH routine.

The latter could make life easier for straightforward non-buffering
transformer layers. The only question would be whether anyone has
omitted a FLUSH func deliberately wanting not to call flush on the
sublayer. That'd seem a bit unlikely to me, or only applicable to
something that was designed to be at the bottom of the stack anyway
(an output capture of some sort say) ...

This is one of three PerlIO-related tickets filed by the same user
several years ago. Is there anyone on list who could take a look at them?

Thank you very much.
Jim Keenan

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