I have tested this item ✅ successfully on 6fdb602

I have tested this item ✅ successfully on 6fdb602

RTC after two successful tests.

This works. Why do we need to create an empty file though. I'm worried about forcing sites with inode restrictions that people accessing pages that don't exist can just try and access 100 404 id'd and suddenly you've managed to destroy their site.

I agree with @wilsonge, it would be better, if we don't create empty files

I have the same feelings but lock() method is not very flexible.

Do you know a way to lock file without creating it?

Currently we have steps if page exists:

1. Check if file exists, answer no
2. Lock file - create empty file.
3. Call view->display()
4. Save data to file.
5. Unlock file.
6. Display data.

If error 404:

1. Check if file exists, answer no
2. Lock file - create empty file.
3. Call view->display()
   a. Error 404
   b. Now joomla creates a new view with 404 or other error.
   c. Joomla call exit()

4. Save data to file.
5. Unlock file.
6. Display data.

This PR can wait, maybe we will find a better way.

Maybe try looking at Symfony's LockHandler for inspiration?

With 4.0 their new Lock component may also be helpful?

I think about add register_shutdown_function to cache file constructor.
The function will do:

foreach ($this->_locked_files as $path => $handle)
{
	if ($handle && filesize($path) === 0)
	{
		@flock($this->_locked_files[$path], LOCK_UN);
		@fclose($this->_locked_files[$path]);
		@unlink($path);
	}
}

I have created a better solution at PR #15592 which does not leave empty cache file.

So we can close here? If #15592 is the better fix?

Yes

Could you consider #15875 instead?