PHP脚本似乎执行了两次

Question

I have a generic PHP maintenance script that sets a database value to prevent running at the same time as another instance. Usually run via cronjob.

I cleared the database value and tried running this script manually with the cronjob turned off. Every time I run it from the browser, it terminates immediately stating it is already running.

The script will run for about 30 seconds as a background process then terminate automatically as if PHP detected the browser was closed (should take about 15 min to complete).

So I added code to echo when the database value is set or read. It never echos when it's set, only when it was read, but I can see the database value is stored each time.

Script always finishes as expected if run from cron.

What could be going on? Could the server be executing scripts twice on each browser based request?

Server runs Hive so different dirs can have different PHP versions. Don't know if this could have something to do with it.

PHP 5.2.17 (default)
PHP 5.3.27 (dir this script is in)
Apache 2.2.25

Code that dictates if it runs is simply this:

$DB = new DbConnector($db_name, $db_user, $db_pass);

if ($DB->queryOne("SELECT COUNT(*) FROM data_vars WHERE name = 'maintenance_running'")) {
    exit('Already running!');
} else {
    $DB->query("INSERT INTO data_vars (name, value) VALUES ('maintenance_running', 1)");
}

At the end of the script, the value is cleared. Again, this problem only happens when run from the browser.

Answer 1

You should set a longer value for execution limit with:

set_time_limit(30*60) // 30 minutes

Also the echo function probably is working, but as the response is sent to the browser until the whole script ends executing that is the cause that you can't see the print, because it´s killed by the execution limit before it ends and prints the response.

You can try echoing partially the response with the help of the

ob_start

and

ob_flush

You can read more about ob_functions here