Cwd::cwd() use in File::Spec::Unix use causes unnecessary fork()

[p5pRT]

Migrated from rt.perl.org#43633 (status was 'resolved')

Searchable as RT43633$

[p5pRT]

From steve@silug.org

This is a bug report for perl from steve@​silug.org,
generated with the help of perlbug 1.35 running under perl v5.8.8.

---

File​::Spec​::Unix contains the following code​:

sub _cwd {
  require Cwd;
  Cwd​::cwd();
}

I think we can safely say that getcwd() will exist on anything Unix-y
enough to run File​::Spec​::Unix, so changing the cwd() to getcwd()
would avoid a fork() to run /bin/pwd. This code can apparently end up
in a hot code path by using IO​::File, which uses File​::Spec.

In light testing, the following patch seems to work fine​:

Inline Patch

--- perl-5.8.8/lib/File/Spec/Unix.pm.orig	2005-08-27 12:14:38.000000000 -0500
+++ perl-5.8.8/lib/File/Spec/Unix.pm	2007-07-07 22:13:51.000000000 -0500
@@ -470,7 +470,7 @@
 # File::Spec subclasses use this.
 sub _cwd {
     require Cwd;
-    Cwd::cwd();
+    Cwd::getcwd();
 }
 
 

I've also verified that the above patch applies cleanly to 5.9.5.

---

---

Flags​:
  category=core
  severity=high

---

This perlbug was built using Perl v5.8.8 in the Red Hat build system.
It is being executed now by Perl v5.8.8 - Wed May 16 22​:56​:53 EDT 2007.

Site configuration information for perl v5.8.8​:

Configured by Red Hat, Inc. at Wed May 16 22​:56​:53 EDT 2007.

Summary of my perl5 (revision 5 version 8 subversion 8) configuration​:
  Platform​:
  osname=linux, osvers=2.6.20-1.2933.fc6xen, archname=x86_64-linux-thread-multi
  uname='linux xenbuilder3.fedora.phx.redhat.com 2.6.20-1.2933.fc6xen #1 smp mon mar 19 11​:17​:46 edt 2007 x86_64 x86_64 x86_64 gnulinux '
  config_args='-des -Doptimize=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -Dversion=5.8.8 -Dmyhostname=localhost -Dperladmin=root@​localhost -Dcc=gcc -Dcf_by=Red Hat, Inc. -Dinstallprefix=/usr -Dprefix=/usr -Dlibpth=/usr/local/lib64 /lib64 /usr/lib64 -Dprivlib=/usr/lib/perl5/5.8.8 -Dsitelib=/usr/lib/perl5/site_perl/5.8.8 -Dvendorlib=/usr/lib/perl5/vendor_perl/5.8.8 -Darchlib=/usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi -Dsitearch=/usr/lib64/perl5/site_perl/5.8.8/x86_64-linux-thread-multi -Dvendorarch=/usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi -Darchname=x86_64-linux -Dvendorprefix=/usr -Dsiteprefix=/usr -Duseshrplib -Dusethreads -Duseithreads -Duselargefiles -Dd_dosuid -Dd_semctl_semun -Di_db -Ui_ndbm -Di_gdbm -Di_shadow -Di_syslog -Dman3ext=3pm -Duseperlio -Dinstallusrbinperl=n -Ubincompat5005 -Uversiononly -Dpager=/usr/bin/less -isr -Dd_gethostent_r_proto -Ud_endhostent_r_pro
to -Ud_sethostent_r_proto -Ud_endprotoent_r_proto -Ud_setprotoent_r_proto -Ud_endservent_r_proto -Ud_setservent_r_proto -Dinc_version_list=5.8.7 5.8.6 5.8.5 -Dscriptdir=/usr/bin'
  hint=recommended, useposix=true, d_sigaction=define
  usethreads=define use5005threads=undef useithreads=define usemultiplicity=define
  useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
  use64bitint=define use64bitall=define uselongdouble=undef
  usemymalloc=n, bincompat5005=undef
  Compiler​:
  cc='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -I/usr/include/gdbm',
  optimize='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic',
  cppflags='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include -I/usr/include/gdbm'
  ccversion='', gccversion='4.1.2 20070502 (Red Hat 4.1.2-12)', gccosandvers=''
  intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
  ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
  alignbytes=8, prototype=define
  Linker and Libraries​:
  ld='gcc', ldflags =''
  libpth=/usr/local/lib64 /lib64 /usr/lib64
  libs=-lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread -lc
  perllibs=-lresolv -lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
  libc=, so=so, useshrplib=true, libperl=libperl.so
  gnulibc_version='2.6'
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E -Wl,-rpath,/usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/CORE'
  cccdlflags='-fPIC', lddlflags='-shared -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic'

Locally applied patches​:
 

---

@​INC for perl v5.8.8​:
  /usr/lib64/perl5/site_perl/5.8.8/x86_64-linux-thread-multi
  /usr/lib64/perl5/site_perl/5.8.7/x86_64-linux-thread-multi
  /usr/lib64/perl5/site_perl/5.8.6/x86_64-linux-thread-multi
  /usr/lib64/perl5/site_perl/5.8.5/x86_64-linux-thread-multi
  /usr/lib/perl5/site_perl/5.8.8
  /usr/lib/perl5/site_perl/5.8.7
  /usr/lib/perl5/site_perl/5.8.6
  /usr/lib/perl5/site_perl/5.8.5
  /usr/lib/perl5/site_perl
  /usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi
  /usr/lib64/perl5/vendor_perl/5.8.7/x86_64-linux-thread-multi
  /usr/lib64/perl5/vendor_perl/5.8.6/x86_64-linux-thread-multi
  /usr/lib64/perl5/vendor_perl/5.8.5/x86_64-linux-thread-multi
  /usr/lib/perl5/vendor_perl/5.8.8
  /usr/lib/perl5/vendor_perl/5.8.7
  /usr/lib/perl5/vendor_perl/5.8.6
  /usr/lib/perl5/vendor_perl/5.8.5
  /usr/lib/perl5/vendor_perl
  /usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi
  /usr/lib/perl5/5.8.8
  .

---

Environment for perl v5.8.8​:
  HOME=/home/steve
  LANG=en_US.UTF-8
  LANGUAGE (unset)
  LC_COLLATE=C
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)
  PATH=/usr/lib64/ccache​:/usr/lib64/qt-3.3/bin​:/usr/bin​:/bin​:/usr/X11R6/bin​:/usr/local/bin​:/usr/games​:/home/steve/bin
  PERL_BADLANG (unset)
  SHELL=/bin/bash

[p5pRT]

From @rgs

Thanks, applied as #31686 to bleadperl.

[p5pRT]

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

[p5pRT]

@rgs - Status changed from 'open' to 'resolved'

[p5pRT]

From @schwern

Turns out this caused a bug on OS X and broke the documented interface
of File​::Spec->rel2abs() which is supposed to use cwd().

See https://rt.cpan.org/Ticket/Display.html?id=47637