develooper Front page | perl.perl5.porters | Postings from December 2007

[perl #48214] documentation enhancement to perlthrtut

Thread Next
From:
johnh @ isi . edu
Date:
December 5, 2007 18:01
Subject:
[perl #48214] documentation enhancement to perlthrtut
Message ID:
rt-3.6.HEAD-28750-1196876739-1770.48214-75-0@perl.org
# New Ticket Created by  johnh@isi.edu 
# Please include the string:  [perl #48214]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=48214 >



This is a bug report for perl from johnh@isi.edu,
generated with the help of perlbug 1.35 running under perl v5.8.8.


-----------------------------------------------------------------
[Please enter your report here]

A naive user (or at least, I) might assume that perl does an implicit
wait on any running threads when the main line of code exits.

It does not.

This fact is not clear in the documentation,
and the error message "A thread exited while 3 threads were running"
doesn't immidately indicate the problem since there may be no
explicit exit() call.

The attached patch to perlthrtut documents this behavior and shows
how to Do The Right Thing.

   -John Heidemann

----------------------------------------------------------------------
--- /tmp/perlthrtut.pod-        2007-12-05 09:24:45.000000000 -0800
+++ /tmp/perlthrtut.pod 2007-12-05 09:43:40.000000000 -0800
@@ -311,6 +311,36 @@
 that it might have produced (if it was done and waiting for a join) is
 lost.
 
+=head2 Process and Thread Termination
+
+With threads one must be careful to make sure they all have a chance to
+run to completion, assuming that is what you want.
+
+An action that terminates a process will terminate I<all> running
+threads.  die() and exit() have this property,
+and perl does an exit when the main thread exits,
+perhaps implicitly by falling off the end of your code,
+even if that's not what you want.
+
+As an example of this case, this code prints the error message
+"A thread exited while 3 threads were running":
+
+       use threads;
+       my $thr1 = threads->new(\&thrsub, "test1");
+       my $thr2 = threads->new(\&thrsub, "test2");
+       sub thrsub {
+           my($message) = @_;
+           sleep 1;
+           print "thread $message\n";
+       }
+
+But when the following lines are added at the end:
+
+       $thr1->join;
+       $thr2->join;
+
+It prints two lines of output, a perhaps more useful outcome.
+
----------------------------------------------------------------------




[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=docs
    severity=medium
---
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 - Mon Nov 26 14:23:46 EST 2007.

Site configuration information for perl v5.8.8:

Configured by Red Hat, Inc. at Mon Nov 26 14:23:46 EST 2007.

Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=linux, osvers=2.6.20-1.3001.fc6xen, archname=i386-linux-thread-multi
    uname='linux xenbuilder4.fedora.phx.redhat.com 2.6.20-1.3001.fc6xen #1 smp thu aug 9 16:18:42 edt 2007 i686 i686 i386 gnulinux '
    config_args='-des -Doptimize=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables -Dversion=5.8.8 -Dmyhostname=localhost -Dperladmin=root@localhost -Dcc=gcc -Dcf_by=Red Hat, Inc. -Dinstallprefix=/usr -Dprefix=/usr -Darchname=i386-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_proto -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=undef use64bitall=undef 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 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables',
    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 20070925 (Red Hat 4.1.2-27)', 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='gcc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread -lc
    perllibs=-lresolv -lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    libc=/lib/libc-2.6.so, 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/lib/perl5/5.8.8/i386-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 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables -L/usr/local/lib'

Locally applied patches:
    

---
@INC for perl v5.8.8:
    /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.8
    /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.7/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.6/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.5/i386-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/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.7/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.6/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.5/i386-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/lib/perl5/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/5.8.8
    .

---
Environment for perl v5.8.8:
    HOME=/home/johnh
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LD_LIBRARY_PATH=/usr/local/lib
    LOGDIR (unset)
    PATH=/home/johnh/BIN:/home/johnh/BIN/LINUX:/usr/local/bin:/bin:/usr/bin:/home/johnh/BIN/WP:/home/johnh/BIN/HOSTS:/home/johnh/BIN/DB:/usr/X11R6/bin:/usr/local/etc:/usr/local/sbin:/etc:/usr/etc:/sbin:/usr/sbin:/usr/hosts:/usr/local/games:/usr/games:/usr/lib/jre/bin
    PERL5LIB=/usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi:/usr/lib/perl5/site_perl/5.8.8
    PERL_BADLANG (unset)
    SHELL=/bin/bash


Thread Next


nntp.perl.org: Perl Programming lists via nntp and http.
Comments to Ask Bjørn Hansen at ask@perl.org | Group listing | About