Errors from background jobs

Hi TIM.
Here is a part of my log.

[18-Oct-2017 13:06:54 Europe/Paris] Warning: set_time_limit(): Cannot set max execution time limit due to system policy in ~/admin/modules.app/run_job.inc.php (Line 2)
 ← ~/admin/index.php (Line 121) in include()
Request: GET /admin/?app=modules&doc=run_job&module_id=job_mysql_optimizer HTTP/1.1
Client: 195.220.159.34 (jonathan.enac.fr)
User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.62 Safari/537.36

[18-Oct-2017 13:10:44 Europe/Paris] Warning: set_time_limit(): Cannot set max execution time limit due to system policy in ~/admin/modules.app/run_job.inc.php (Line 2)
 ← ~/admin/index.php (Line 124) in include()
Request: GET /admin/?app=modules&doc=run_job&module_id=job_error_reporter HTTP/1.1
Client: 195.220.159.34 (jonathan.enac.fr)
User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.62 Safari/537.36

[18-Oct-2017 13:10:44 Europe/Paris] Fatal error: Invalid email address () in ~/includes/classes/email.inc.php (Line 21)
 ← ~/includes/functions/func_email.inc.php (Line 10) in set_sender()
 ← ~/includes/library/lib_functions.inc.php (Line 13) in email_send()
 ← ~/includes/modules/jobs/job_error_reporter.inc.php (Line 56) in __callstatic()
 ← ~/includes/modules/mod_jobs.inc.php (Line 30) in process()
 ← ~/admin/modules.app/run_job.inc.php (Line 9) in process()
 ← ~/admin/index.php (Line 124) in include()
Request: GET /admin/?app=modules&doc=run_job&module_id=job_error_reporter HTTP/1.1
Client: 195.220.159.34 (****)
User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.62 Safari/537.36

~/admin/modules.app/run_job.inc.php  => set_time_limit(60*5); is not supported
When I remove this line, the job module  can be configured, instead of an error in the browser too (Fatal error: Invalid email address () in ~/includes/classes/email.inc.php (Line 21)).
For the admin email, ouch, I didn't touch anything about that, and it's well configured !
I'm recieving sometimes a mail with the job result.

Are you on PHP safe mode? Its a bit unconventional to forbid use of set_time_limit()? What is the code your host uses to forbid it? That way I could add a condition before.

When it comes to the email address, there might be a bug inte current dev. But did you check the email address in the error reporter module settings?

No, of course not, I'm not in PHP safe mod.
I remember I've already seen this problem before but I just removed the line and error_job_reporter was working as it was intended to.
After the latest commits, as this mod was not included in my core vqmod, the error reappeared.
It's not a conventional error, but I can't modify php settings on my web host, except very few parameters via a .user.ini.

Could you ask your web host with which setting they enable this protection? So I can detect it from a condition.

Generally, set_time_limit() is disabled by web hosts for security reasons

Yes you mentioned that. How can I detect that before attempting to call the command?

I'm googling about that. Lots of people have this problem, with other CMS like wordpress for example.
When you put a @ before the line, it' just not executed.
I'm trying parameters via php.ini, but no way yet.

I've just tried this function in a new php file:

And, safe_mod is disabled on my web host.

A track start :
in php.ini (or .user.ini, depends on web host)
max_execution_time must be set to 0 to use set_time_limit().
In my case I used a value of 300.
It seems it causes problems with the php function set_time_limit().
With max_execution_time = 0, there is no more problems with litecart. BUT it could be a problem for other scripts, as everything is shared...

max_execution_time must be set to 0 to use set_time_limit().

• Really?

And it's not in ini_get('disable_functions') ?

The default limit is 30 seconds or, if it exists, the max_execution_time value defined in the php.ini

When called, set_time_limit() restarts the timeout counter from zero.

http://php.net/manual/en/function.set-time-limit.php

I agree but, as usual, it's only a theory ! Web hosts do what they want !
With a value of max_execution_time defined in the php.ini (or .user.ini), in fact, you can't use set_time_limit() without a php error, like my logs for litecart.  On my web host in fact (the others, I  don't know). Trust me, my web site is well configured and optimized for best performance, I can mistake but I'm not a beginner.
So I disable the line cause I prefer having max_execution_time set. I've already seen that, as I said, with wordpress plugins or so on.
More over, max_execution_time = 300 is fully compliant with your line (60*5) : it's the same interval !
It's not a new error, I saw it before and just forgot to tell about that (all my hands and fingers are used !), and in the previous files, I removed the line too. 
Recently I crushed my litecart with the latest commit of 2.0.3, and this problem appeared again.

"max_execution_time must be set to 0 to use set_time_limit().

• Really?"
  It seems so. I've tried that successfully, it's well documented on the web and it's a recurrent clue.

"And it's not in ini_get('disable_functions') ?" Where is that ?

For a detection before using the function, wow it's not easy I guess.

What is returned by this code?

Could you link me up to a reference saying max_execution_time must be set to 0 to use set_time_limit()?

What did your web host say about this setting? How did they set it? How do we identify it?

gives
string(100) "disk_total_space, diskfreespace, exec, system, popen, proc_open, proc_nice, shell_exec, passthru, dl"

For example a google search on "Warning: set_time_limit(): Cannot set max execution time limit due to system policy"

First result and links inside (and lots of other links in google results with the same complaint ...)
https://www.silverstripe.org/community/forums/general-questions/show/10952
exact case of mine
By my own experience, I know that Drupal, Prestashop and Wordpress are affected by this problem. 
Safe mod off.
Web host doesn't want to modify its configuration (I can understand that)

Scenario: 
php.ini with max_execution-time = 300 (good practice)
I must remove via a vqmod the line set_time_limit in run_job_inc.php, cause there's the warning in litecart or php logs
php.ini with max_execution-time = 0 or line emptied
No more error on set_time_limit in logs but I'm not able to know if it works

php setting is prior to any script. I'd rather keep max_execution-time = 300

Notice : most of users won't even see this problem, because you only see it when analysing logs !

That link was regarding safe_mode and mentions nothing about max_execution_time must set to 0 to enable usage of set_time_limit().

Can you email me the results of the following code: