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Bug #61369 shm_put_var problem
Submitted: 2012-03-13 08:56 UTC Modified: 2012-03-13 09:03 UTC
Votes:3
Avg. Score:4.3 ± 0.9
Reproduced:2 of 2 (100.0%)
Same Version:1 (50.0%)
Same OS:2 (100.0%)
From: llongo at sata-hts dot com Assigned:
Status: Open Package: Semaphore related
PHP Version: Irrelevant OS: CentOS release 6.2 (Final)
Private report: No CVE-ID: None
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From: llongo at sata-hts dot com
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 [2012-03-13 08:56 UTC] llongo at sata-hts dot com
Description:
------------
There is a problem with shm_put_var: when you call shm_put_var with a "long" 
string as value (100 chars at least) in a shared memory area with some variables 
already created, after updating the other variables with successive calls to 
shm_put_var, this variables become non-existent and you cannot get their values 
with shm_get_var.

Test script:
---------------
<?php
$key = 1000;
$test1 = "short string";
$test2 = "long string with at least 100 characters abcdefghilmnopqrstuvzabcdefghilmnopqrstuvzabcdefghilmnopqrstuvzabcdefghilmnopqrstuvz";
$test3 = "different short string";
$res = shm_attach($key);	// attach to shared memory
if (false === shm_put_var ($res,1,$test1)) {		// write var 1
	echo "unable to put var 1 with ".$test1."\n";
}
if (false === shm_put_var ($res,2,$test1)) {		// write var 2
	echo "unable to put var 2 with ".$test1."\n";
}
if (false === shm_put_var ($res,3,$test2)) {		// write var 3
	echo "unable to put var 3 with ".$test2."\n";
}
if (false === shm_put_var ($res,2,$test3)) {		// write again var 2 => after this put var, var 2 and 3 disappear... bug?
	echo "unable to put var 2 with ".$test1."\n";
}
if (false === ($var = shm_get_var ($res,2))) {		// get var 2
	echo "Error reading variable 2, bug!\n";
	var_dump($var);
} else {
	echo "variable 2: ".$var."\n";
}
shm_remove($res);		// remove shared memory
shm_detach($res);
exit;
?>

Expected result:
----------------
variable 2: different short string

Actual result:
--------------
Error reading variable 2, bug!
bool(false)

And php warning:
PHP Warning:  shm_get_var(): variable key 2 doesn't exist in 
/root/test_bug_shm.php on line 19

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 [2012-03-13 09:03 UTC] llongo at sata-hts dot com
I've seen the bug with php version 5.3.3 that comes with Centos 6.2 (php-5.3.3-
3.el6_2.6.x86_64). With the same version of php in Centos 5.7 (php53-5.3.3-
1.el5_7.6) the test script works in the right way.
 [2013-08-13 18:40 UTC] igor at scalr dot com
I have the same issue on CentOS 6.X. I found that with the same version of php and 
all extensions, problem exists on CentOS 6, but everything works on CentOS 5. The 
only difference is kernel version, on CentOS 6 it's 2.6.32. 

Any help on this issue would be appreciated, because shm functionality is critical 
for our application.
 
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