Why does php sleep() return immediately when httpd restarts gracefully.

Issue

• Why does php sleep() return immediately when httpd restarts gracefully.

Sample php script using sleep();

# cat /var/www/html/test1.php 
<?php
  echo "Hello World\n";
  sleep(30);
?>

Run "curl http://webserver/test1.php" on client and run "service httpd graceful" on webserver.

Sample output

# date; curl http://webserver/test1.php; date
Thu Mar 10 10:19:00 JST 2016
Hello World
Thu Mar 10 10:19:03 JST 2016