develooper Front page | perl.perl5.porters | Postings from February 2011

[perl #84496] Race condition with close() in multiple threads

Father Chrysostomos
February 20, 2011 13:09
[perl #84496] Race condition with close() in multiple threads
Message ID:
# New Ticket Created by  Father Chrysostomos 
# Please include the string:  [perl #84496]
# in the subject line of all future correspondence about this issue. 
# <URL: >

Commit 2e0c6a16 (the fix for 78494) causes a new race condition.

Up till now, there has already been a race condition when two threads close() the same handle. Either one thread or the other would get the exit status, but not both. It was never predictable which thread would get it.

Now, there is the slight possibility that *neither* thread will receive the exit status.

I believe any code that runs into this is already buggy, as, in 5.13.9 and earlier, close() in one thread blocks until close is called in every other thread (provided the pipe was open when the threads were created, and got cloned as a result).

So I think this bug is acceptable for 5.14, as fixing it would require no small amount of code restructuring.

Site configuration information for perl 5.13.9:

Configured by sprout at Sat Feb 12 14:34:11 PST 2011.

Summary of my perl5 (revision 5 version 13 subversion 9) configuration:
  Snapshot of: a5547419d5b6611afb483a3a32dc19fa18b2f172
    osname=darwin, osvers=10.5.0, archname=darwin-thread-multi-2level
    uname='darwin pint.local 10.5.0 darwin kernel version 10.5.0: fri nov 5 23:20:39 pdt 2010; root:xnu-1504.9.17~1release_i386 i386 '
    config_args='-de -Dusedevel'
    hint=previous, 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
    cc='cc', ccflags ='-fno-common -DPERL_DARWIN -no-cpp-precomp -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include',
    cppflags='-no-cpp-precomp -fno-common -DPERL_DARWIN -no-cpp-precomp -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -fno-common -DPERL_DARWIN -no-cpp-precomp -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.2.1 (Apple Inc. build 5664)', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='env MACOSX_DEPLOYMENT_TARGET=10.3 cc', ldflags =' -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib
    libs=-ldbm -ldl -lm -lutil -lc
    perllibs=-ldl -lm -lutil -lc
    libc=/usr/lib/libc.dylib, so=dylib, useshrplib=false, libperl=libperl.a
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=bundle, d_dlsymun=undef, ccdlflags=' '
    cccdlflags=' ', lddlflags=' -bundle -undefined dynamic_lookup -L/usr/local/lib -fstack-protector'

Locally applied patches:

@INC for perl 5.13.9:

Environment for perl 5.13.9:
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PERL_BADLANG (unset)
    SHELL=/bin/bash Perl Programming lists via nntp and http.
Comments to Ask Bjørn Hansen at | Group listing | About