[4.2][Debug] Do not overwrite startTime.

[sfadschm]

This PR gives a little change to the execution time collection, by only overwriting the startTime property of the CodeIgniter4 object, if it is not yet set.

This property gets first set here in the constructor:

CodeIgniter4/system/CodeIgniter.php

Line 160 in 9ceb5e3

$this->startTime = microtime(true);

After that, it gets overwritten from bootstrap.php during $app->run() via:

CodeIgniter4/system/CodeIgniter.php

Line 514 in 9ceb5e3

$this->startTime = microtime(true);

I am not sure what was the goal here. In the current state, we basically restart the "total execution" timer and possibly miss some ms (i.e., the time that $app->initialize(); takes). This is not really helpful I think.

As far as I can tell, the part now included in the if could be removed completely, as startTime will likely never be null at this point.

Checklist:

• Securely signed commits
• Conforms to style guide

[sfadschm]

Judging from @lonnieezell's (very old) commits, this has been some debate in the past:

https://github.com/codeigniter4/CodeIgniter4/commits/9521545bdce6a33f56e0f48767f4bf9855110e7d

However, in the current state, startTime will always be overwritten before it is used unless someone edits index.php and puts some content between the CodeIgniter4 app construction and $app->run().

[MGatner]

I think this is fine. We can see if Lonnie weighs in but we have come a long ways and I don't think comparing internal benchmarking between CI3 and CI4 does anything useful.

FWIW I have plans for a benchmarking workflow. I will probably dig into this a bit more when I get to that.

[sfadschm]

Should I change to just remove the line?
I do not think the conditional will ever be true as the method cannot be run without the constructor being run beforehand.
Only way would be if someone intentionally resets startTime to null after the constructor.

[sfadschm]

FWIW I have plans for a benchmarking workflow. I will probably dig into this a bit more when I get to that.

Sounds great 😄