Bug #51382 [Com]: session_start() blocks execution

Edit report at http://bugs.php.net/bug.php?id=51382&edit=1

 ID:               51382
 Comment by:       abca_b_cabcom at hotmail dot com
 Reported by:      info at lategoodbye dot de
 Summary:          session_start() blocks execution
 Status:           Open
 Type:             Bug
 Package:          Session related
 Operating System: Linux 2.4.35.4 mips
 PHP Version:      5.3.2

 New Comment:

Maybe you can post your backtrace result here first, i just guess it is
a compiler error, cause php_combined_lcg function should have no error.


Previous Comments:
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[2010-03-25 15:11:53] info at lategoodbye dot de

May be i expressed myself bad about the option session.gc_divisor.
Setting the option to 100000 is nearly like disabling garbage
collection. The chance to reproduce the problem is very, very low but
possible.

How can i findout that it's a compile error?

Nevertheless i will make the backtrace.

------------------------------------------------------------------------
[2010-03-25 08:47:54] abca_b_cabcom at hotmail dot com

From you description I traced back to the line 1475 in
./etc/session/session.c,
it is the only line which will be affect by the php.ini variable
session.gc_divisor you describe.

The line is show below:
nrand = (int) ((float) PS(gc_divisor) * php_combined_lcg(TSRMLS_C));

So, I think it may be a compiling error.

------------------------------------------------------------------------
[2010-03-24 19:04:24] [email protected]

One way to figure that out is to attach gdb to a hanging fcgi process
and get a 
backtrace (bt) from gdb which should show where it is stuck.

------------------------------------------------------------------------
[2010-03-24 18:44:22] info at lategoodbye dot de

Description:
------------
Hi, i'm running PHP 5.3.2 via FastCGI with lighttpd 1.4.25 and uclibc
0.9.29. I experienced that after a period of time, all session driven
pages hang and deliver no content to the client. But all static content
like images are accessible. Below i appended a little script, how the
problem can be reproduced.

Here are the options from the php.ini:

session.save_handler = files
session.save_path = "/tmp"
session.gc_probability = 1
session.gc_divisor     = 100
session.gc_maxlifetime = 1440

Here is the configure line:

'./configure' '--target=mipsel-linux' '--host=mipsel-linux'
'--build=i486-linux-gnu' '--program-prefix=' '--program-suffix='
'--prefix=/usr' '--exec-prefix=/usr' '--bindir=/usr/bin'
'--sbindir=/usr/sbin' '--libexecdir=/usr/lib' '--sysconfdir=/etc'
'--datadir=/usr/share' '--localstatedir=/var' '--mandir=/usr/man'
'--infodir=/usr/info' '--disable-nls' '--enable-shared'
'--disable-static' '--disable-rpath' '--disable-debug' '--without-pear'
'--with-config-file-path=/etc' '--enable-magic-quotes'
'--disable-short-tags' '--without-gettext' '--disable-simplexml'
'--with-zlib=/home/10_openwrt/staging_dir/mipsel/usr'
'--with-zlib-dir=/home/10_openwrt/staging_dir/mipsel/usr'
'--with-pcre-regex=/home/10_openwrt/staging_dir/mipsel/usr'
'--disable-phar' '--enable-ctype=shared' '--without-curl'
'--disable-fileinfo' '--disable-dom' '--disable-exif' '--disable-ftp'
'--without-gd' '--without-gmp' '--disable-hash' '--without-iconv'
'--enable-json=shared' '--without-ldap' '--disable-mbstring'
'--without-mcrypt' '--without-mysql' '--without-openssl'
'--enable-pdo=shared' '--without-pdo-mysql' '--without-pdo-pgsql'
'--with-pdo-sqlite=shared,/home/10_openwrt/staging_dir/mipsel/usr'
'--without-pgsql' '--enable-session=shared' '--disable-soap'
'--enable-sockets=shared' '--without-sqlite'
'--with-sqlite3=shared,/home/10_openwrt/staging_dir/mipsel/usr'
'--disable-tokenizer'
'--enable-xml=shared,/home/10_openwrt/staging_dir/mipsel/usr'
'--with-libexpat-dir=/home/10_openwrt/staging_dir/mipsel/usr'
'--disable-xmlreader' '--disable-xmlwriter' '--disable-apc'
'--disable-filter' '--disable-libxml' '--enable-sysvsem'
'--enable-sysvshm' '--enable-sysvmsg' '--enable-pcntl' '--disable-cli'
'--enable-cgi'

The filesystem behind /tmp is tmpfs.

After that i played a little bit with option session.gc_divisor. If i
set the option to 2, then the problem happend immediately. But if i set
the option to 100000, the problem is not reproducable.

Is this a dead lock caused by the session garbage collector?

Test script:
---------------
<?php
session_start();
session_write_close();  
?>
<html><body>Content</body></html>

Expected result:
----------------
PHP delivers "Content" to the browser.

Actual result:
--------------
The browser didn't get "Content" and wait for a response.


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Edit this bug report at http://bugs.php.net/bug.php?id=51382&edit=1