CC: | bre [...] klaki.net |
Subject: | Closing file handles early breaks IO::Select |
Date: | Tue, 18 May 2010 07:34:02 +0000 |
To: | perlbug [...] perl.org |
From: | bre [...] klaki.net |
This is a bug report for perl from bre@klaki.net,
generated with the help of perlbug 1.39 running under perl 5.10.1.
-----------------------------------------------------------------
[Please describe your issue here]
(re-posting what I sent to perl5-porters: the IO::Select perldoc
should probably recommend perlbug and not perl5-porters as a venue
for bug-reports).
I write to you, because I think I have found and fixed a rather
nasty (and old) bug in IO::Select:
The bug is: IO::Select currently assumes that an IO::Handle will
always have a valid file descriptor, which is not actually the case.
If you add a handle and the handle later loses its file descriptor
(for whatever reason, this appears to be out of the control of the
programmer), then IO::Select will stop working and there is no way
to remove the broken descriptor, because the add/remove code
assumes fileno() will return something useful. The workaround in
my code today is to throw away the IO::Select object and build a
new one.
Attached is a sample program which triggers the bug, and a proposed
modification to IO::Select (NewSelect.pm) which I think should fix
the problem. In case I fail to attach the files correctly, they
can also be found here:
http://bre.klaki.net/programs/Perl-IO-Select-Bug/
Addition:
The real-world impact of this bug, is to cause most servers written
using IO::Select to go into infinite CPU-sucking loops when a
watched file-handle is closed without being removed from IO::Select
first. My fix does not actually prevent that entirely, but it does
give the programmer a mechanism for dealing with the problem and
makes code slightly more resiliant - as long as the file handle
closure is detected *somewhere* and removed from IO::Select
*sometime* the system will recover.
[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
category=library
severity=high
module=IO::Select
---
Site configuration information for perl 5.10.1:
Configured by Debian Project at Fri Apr 23 07:59:14 UTC 2010.
Summary of my perl5 (revision 5 version 10 subversion 1) configuration:
Platform:
osname=linux, osvers=2.6.24-27-server, archname=i486-linux-gnu-thread-multi
uname='linux vernadsky 2.6.24-27-server #1 smp fri mar 12 01:45:06 utc 2010 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/5.10.1 -Dsitearch=/usr/local/lib/perl/5.10.1 -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.5.10.1 -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 -fstack-protector -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 -fstack-protector -I/usr/local/include'
ccversion='', gccversion='4.4.3', 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 =' -fstack-protector -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-2.11.1.so, so=so, useshrplib=true, libperl=libperl.so.5.10.1
gnulibc_version='2.11.1'
Dynamic Linking:
dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib -fstack-protector'
Locally applied patches:
---
@INC for perl 5.10.1:
/etc/perl
/usr/local/lib/perl/5.10.1
/usr/local/share/perl/5.10.1
/usr/lib/perl5
/usr/share/perl5
/usr/lib/perl/5.10
/usr/share/perl/5.10
/usr/local/lib/site_perl
.
---
Environment for perl 5.10.1:
HOME=/home/bre
LANG=en_IE.utf8
LANGUAGE (unset)
LD_LIBRARY_PATH (unset)
LOGDIR (unset)
PATH=/home/bre/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
PERL_BADLANG (unset)
SHELL=/bin/bash