#42465 [Opn->Bgs]: rand() and mt_rand() return same values from forked processes
ID: 42465
Updated by: jani@php.net
Reported By: bugs at nazarenko dot net
-Status: Open
+Status: Bogus
Bug Type: Math related
Operating System: Linux, Solaris
PHP Version: 5CVS-2007-08-28 (snap)
New Comment:
http://php.net/mt_srand
http://php.net/srand
Previous Comments:
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[2007-08-28 19:31:32] bugs at nazarenko dot net
Description:
------------
Using CLI, if more than 1 process is forked with pcntl_fork() both
functions mt_rand() and rand() return same values in all child
processes.
This only happens when there was a call to mt_rand()/rand() in the
parent process before forking.
Reproduce code:
---------------
Compiled latest available snapshot under Solaris 10 and SuSE Linux 10.1
with the following configure options:
--disable-all --disable-cgi --enable-pcntl --disable-ipv6
The test script is the following:
<?php
echo mt_rand(0,255)."\n"; # comment this line out to see difference
for ($i=0; $i<3; $i++)
{
if (pcntl_fork() == 0)
{
die(mt_rand(0,255)."\n");
}
}
?>
Expected result:
----------------
Expected result is 4 random numbers generated by 4 different Unix
processes (1 parent and 3 children).
Actual result:
--------------
The actual result (both on Solaris and Linux) is that all 3 numbers
generated by the children are the same.
Now comment out the first echo command belonging to the parent process
and the result is 3 random numbers generated by children.
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