@fbourigault impressive work you did here! The Blackfire comparisons are incredible (the second one removes hundreds of thousands of function calls!!).

In order to help the Symfony Docs team, we'd need a few more things here:

• The examples you showed, it's all you need to use this in the stand-alone component?
• When using this inside the Symfony Framework, do you need to enable/change something? Some config option? Some code?

Thanks!

@stof here are the benchmark

• master vs master+PhpArrayAdapter, 100 iterations with complexity of 1
• master vs master+PhpArrayAdapter, 3 iterations with complexity of 60
• master vs this PR, 100 iterations with complexity of 1
• master vs this PR, 3 iterations with complexity of 60

I used the following code to use the PhpArrayAdapter:

$adapter = new ApcuAdapter('SymfonyMetadata');

$adapter = new PhpArrayAdapter(__DIR__.'/../metadata.cache', $adapter);

$classMetadataFactory = new CacheClassMetadataFactory(
    new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader())),
    $adapter
);

And here is the code for the warmup:

$classMetadataFactory = new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader()));

$classMetadatas = [];

foreach([Category::class, Comment::class, Forum::class, Thread::class, User::class] as $class) {
    $classMetadatas[strtr($class, '\\', '_')] = $classMetadataFactory->getMetadataFor($class);
}

$adapter = new PhpArrayAdapter(__DIR__.'/../../metadata.cache', new NullAdapter());
$adapter->warmUp($classMetadatas);

I also switched from backfire run to blackfire/php-sdk to exclude the warmup from the profile.

The examples you showed, it's all you need to use this in the stand-alone component?

Yes :)

When using this inside the Symfony Framework, do you need to enable/change something? Some config option? Some code?

This is not yet defined, but it's maybe something to enable. Scanning the whole src/Entity directory could be part of the recipe.

I fixed all comments.

Now I want to write the CacheWarmer and the FrameworkBundle integration.

What about having something like:

framework:
    serializer:
        metadata:
            warmup:
                - directory: '%kernel.project_dir%/src/Entity'
                - class: App\Model\MyModelToWarmup
                - directory: '@SomeBundle/Model'

Third party bundles would be able to add entries to this list by prepending configuration.
Then the DI extension will build a Finder and find classes for directory entries.
Then a class list will be built and used as CacheWarmer argument.

I also have a few questions:

• Where should this CacheWarmer live? The Serializer component or the FrameworkBundle?
• Do we have some reusable code for scanning directories and finding classes?

Should I add the symfony/var-exporter as a requirement or a suggestion?

EDIT: I added it as suggestion.

I rebased and fixed CS. I think this PR is ready now!

Is this still relevant now that many things moved on the topic?
If yes, can you please rebase?

Thank you @fbourigault.

@fbourigault Can you have a look at CompiledClassMetadataCacheWarmer::warmUp()? In 5.2, it should return an array of classes to preload in 7.4. I've returned an empty array for now, but we might do something better. Thank you.