Hmm. I cannot reproduce the delay. How long does it take on your PC? It seems immediate on my PC.

I get strange output from PHP 7. This should be irrelevant.

[yohgaki@dev github-php-src]$ uname -a
Linux dev 4.3.5-300.fc23.x86_64 #1 SMP Mon Feb 1 03:18:41 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux


[yohgaki@dev github-php-src]$ phpenv global 5.5.21
[yohgaki@dev github-php-src]$ php -d open_basedir=`pwd`
<?php
$iv = mcrypt_create_iv(16, MCRYPT_DEV_URANDOM);                                                
var_dump($iv);

string(16) "�K4�w�@�X��K
                          �"

[yohgaki@dev github-php-src]$ php global 5.6.6
Could not open input file: global
[yohgaki@dev github-php-src]$ phpenv global 5.6.5
[yohgaki@dev github-php-src]$ php -d open_basedir=`pwd`
<?php
$iv = mcrypt_create_iv(16, MCRYPT_DEV_URANDOM);                                                
var_dump($iv);

string(16) "���P�)�%
                        �g"
[yohgaki@dev github-php-src]$ phpenv global 7.0.3
[yohgaki@dev github-php-src]$ php -d open_basedir=`pwd`
<?php
$iv = mcrypt_create_iv(16, MCRYPT_DEV_URANDOM);                                                
var_dump($iv);

-:3:
string(16) "��F�9<Y��qÚؓ�G"

[yohgaki@dev github-php-src]$ php -d open_basedir=`pwd` -r 'echo file_get_contents("/dev/urandom", false, null, 0, 100);'
PHP Warning:  file_get_contents(): open_basedir restriction in effect. File(/dev/urandom) is not within the allowed path(s): (/home/yohgaki/git/oss/php.net/github-php-src) in Command line code on line 1
PHP Stack trace:
PHP   1. {main}() Command line code:0
PHP   2. file_get_contents() Command line code:1
PHP Warning:  file_get_contents(/dev/urandom): failed to open stream: Operation not permitted in Command line code on line 1

This appears to be a duplicate of https://bugs.php.net/bug.php?id=69833

Closing.