#38228 [Fbk->Opn]: Pcntl based parallel threads loose connection to MySQL server

From: Date: Thu, 27 Jul 2006 18:25:31 +0000
Subject: #38228 [Fbk->Opn]: Pcntl based parallel threads loose connection to MySQL server
References: 1  Groups: php.bugs 
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 ID:               38228
 User updated by:  piotr at bulczak dot name
 Reported By:      piotr at bulczak dot name
-Status:           Feedback
+Status:           Open
 Bug Type:         MySQL related
 Operating System: Fedora Core 5 Linux
 PHP Version:      5.1.4
 New Comment:

I compiled php5.2-latest.tar.gz on FC5 with configure options
'--enable-pcntl' '--with-mysql' '--with-mysqli'
'--with-pdo-mysql'.
Undoftunately the bug still exist in this version. My test script
produced again error message "MySQL server has gone away".

Looking for some workaround I noticed that the problem does not occure
if I close all MySQL connections in parrent script before forking
childs. Maybe this info will help to spot problem source.


Previous Comments:
------------------------------------------------------------------------

[2006-07-26 23:23:31] sniper@php.net

Please try using this CVS snapshot:

  http://snaps.php.net/php5.2-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5.2-win32-latest.zip



------------------------------------------------------------------------

[2006-07-26 20:09:18] piotr at bulczak dot name

Description:
------------
For long time I was using multithreaded scripts (pcntl module). Each
script was using their own connection to MySQL server (mysql module).
They are working properly on FC1 - FC4 linuxes (PHP 4.3.11 - 5.0.4). I
tried for the first time to tun them on FC5 which includes standard rpm
packages - PHP 5.1.4 in this case (iptables and selinux turned off).

I noticed that my threads fail with message "server has gone away" when
using "mysql_select_db. The behaviour is the same regardless if it is
connection via unix socket file, tcp/ip connection to localhost or some
remote IP address. It does not matter what MySQL server version I am
connecting to (tried with 3.23.58 - 5.0.22)

I tried also switch to "mysqli" module on FC5 and the script started
working properly again so I assume only "mysql" module is affected.

I do not have major changes to standard php.ini... just
max_execution_time=300 and memory_limit=32M. Test script is just a
minimal version (without any threads synchronization, etc. stuff).

Please help :-)

Reproduce code:
---------------
http://www.buleksoft.pl/mysql_pcntl_test.html

Expected result:
----------------
[root@host ~]# php -q test.php
Forking thread number 0
Thread 0 doing some mysql tasks
Forking thread number 1
Thread 1 doing some mysql tasks
Forking thread number 2
Thread 2 doing some mysql tasks
Forking thread number 3
Thread 3 doing some mysql tasks


Actual result:
--------------
[root@host ~]# php -q test.php
Forking thread number 0
Thread 0 doing some mysql tasks
Forking thread number 1
Thread 1: Could not select DB because MySQL server has gone away
Forking thread number 2
Thread 2: Could not select DB because MySQL server has gone away
Forking thread number 3
Thread 3: Could not select DB because MySQL server has gone away



------------------------------------------------------------------------


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