Thread crash

DrCarib has asked for the wisdom of the Perl Monks concerning the following question:

Hi everyone, Calling a subroutine from a regular expression causes a crash when I then try to create/join a thread. Looks like this messes up some internal stuff. Here is the code:

#!/usr/bin/perl
use threads;
use Thread::Semaphore;

sub bad{
    
    sub mysub{
        print "my sub : $1 $2\n";
    }
    $a="Hi there and hi there.\n";
    $a =~ s/(\w+ \w+)(?{mysub();})//gi ;
}


    
sub mythread
{
    print "begin\n";
    print "end\n";
}
                    

bad();

my $thr = threads->new(\&mythread);
@r=$thr ->join();

__END__
[download]

The output is:

  ./testthread.pl 
my sub : Hi there 
my sub : and hi 
begin
end

*** glibc detected *** /usr/bin/perl: double free or corruption (!prev
+): 0x08271ce8 ***
[download]

Does anyone know what's wrong with using a regex this way ? If found it very convenient to process every pattern matching my regex, but I suppose I'll have to do it another way. Thank you.

Comment on Thread crash Select or Download Code

Replies are listed 'Best First'.
Re: Thread crash by gam3 (Curate) on Nov 21, 2007 at 17:16 UTC
I have verified that your code crashed perl v5.8.8. This code does seem to run however. `#!/usr/bin/perl use threads; use Thread::Semaphore; sub bad { sub mysub { print "my sub : $1 $2\n"; } $a = "Hi there and hi there.\n"; $a =~ s/(\w+ \w+)(?{mysub();})//gi ; } sub mythread { print "begin\n"; print "end\n"; } my $thr = threads->new(\&bad); @r=$thr ->join(); my $thr = threads->new(\&mythread); @r=$thr ->join(); __END__` [download] Also `$a =~ s/(\w+ \w+)/&mysub()/ge;` seems to give the same output as your code and also does not seem to cause the crash. You do need to worry about the output of the function though. `#!/usr/bin/perl use threads; use Thread::Semaphore; sub mythread { print "begin\n"; print "end\n"; } sub mysub { print "my sub : $1 $2\n"; ''; } $a = "Hi there and hi there.\n"; $a =~ s/(\w+ \w+)/&mysub()/ge; my $thr = threads->new(\&mythread); @r=$thr ->join(); __END__` [download] -- gam3 A picture is worth a thousand words, but takes 200K.	[reply] [d/l] [select]
Re^2: Thread crash by DrCarib (Initiate) on Nov 21, 2007 at 17:42 UTC
Thank you very much for your fast replies. This is perfect for what I need to do, but I was not aware of this syntax. I'd be interested though in knowing if the crash was caused by my weird code (I'm newbie to Perl) or by an interpreter problem.	[reply]
Re^3: Thread crash by gam3 (Curate) on Nov 21, 2007 at 17:45 UTC
Your weird code found an interpreter problem. -- gam3 A picture is worth a thousand words, but takes 200K.	[reply]
Re: Thread crash by Fletch (Bishop) on Nov 21, 2007 at 17:12 UTC
Threading in perl has been (and still is to some degree, AFAIK) kinda flakey. It'd help if you posted or appended the output from `perl -V` to give people an idea of what version of perl you're experiencing this with. We're looking for a Perl and Database Developer for Corporate Investments Group.	[reply] [d/l]
Re^2: Thread crash by DrCarib (Initiate) on Nov 21, 2007 at 17:24 UTC
Here it is : Summary of my perl5 (revision 5 version 8 subversion 8) configuration: Platform: osname=linux, osvers=2.6.15.7, archname=i486-linux-gnu-thread-mult +i uname='linux palmer 2.6.15.7 #1 smp thu sep 7 19:42:20 utc 2006 i6 +86 gnulinux ' config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dccc +dlflags=-fPIC -Darchname=i486-linux-gnu -Dprefix=/usr -Dprivlib=/usr/ +share/perl/5.8 -Darchlib=/usr/lib/perl/5.8 -Dvendorprefix=/usr -Dvend +orlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/ +local -Dsitelib=/usr/local/share/perl/5.8.8 -Dsitearch=/usr/local/lib +/perl/5.8.8 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/ma +n3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man +3 -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs - +Ud_csh -Uusesfio -Uusenm -Duseshrplib -Dlibperl=libperl.so.5.8.8 -Dd_ +dosuid -des' hint=recommended, useposix=true, d_sigaction=define usethreads=define use5005threads=undef useithreads=define usemulti +plicity=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 -DTHREADS_HAVE_PIDS +-DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE +_SOURCE -D_FILE_OFFSET_BITS=64', optimize='-O2', cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN +-fno-strict-aliasing -pipe -I/usr/local/include' ccversion='', gccversion='4.1.3 20070831 (prerelease) (Ubuntu 4.1. +2-16ubuntu1)', gccosandvers='' intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234 d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=1 +2 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 libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt perllibs=-ldl -lm -lpthread -lc -lcrypt libc=/lib/libc-2.6.1.so, so=so, useshrplib=true, libperl=libperl.s +o.5.8.8 gnulibc_version='2.6.1' Dynamic Linking: dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E' cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib' Characteristics of this binary (from libperl): Compile-time options: MULTIPLICITY PERL_IMPLICIT_CONTEXT PERL_MALLOC_WRAP THREADS_HAVE_PIDS USE_ITHREAD +S USE_LARGE_FILES USE_PERLIO USE_REENTRANT_API Built under linux Compiled at Sep 29 2007 05:57:38 @INC: /etc/perl /usr/local/lib/perl/5.8.8 /usr/local/share/perl/5.8.8 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.8 /usr/share/perl/5.8 /usr/local/lib/site_perl [download]	[reply] [d/l]