Lazy services - service proxies #7527

Ocramius · 2013-03-30T02:16:02Z

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets	#6140 (supersedes) #5012 #6102 (maybe)
License	MIT (attached code) - BSD-3-Clause (transitive optional dependency)
Doc PR	Please pester me to death so I do it

This PR introduces lazy services along the lines of zendframework/zendframework#4146

It introduces an OPTIONAL dependency to ProxyManager and transitively to "zendframework/zend-code": "2.*".

Lazy services: why? A comprehensive example

For those who don't know what this is about, here's an example.

Assuming you have a service class like following:

class MySuperSlowClass
{
    public function __construct()
    {
        // inject large object graph or do heavy computation
        sleep(10);
    }

    public function doFoo()
    {
        echo 'Foo!';
    }
}

The DIC will hang for 10 seconds when calling:

$container->get('my_super_slow_class');

With this PR, this can be avoided, and the following call will return a proxy immediately.

$container->getDefinitions('my_super_slow_class')->setLazy(true);
$service = $container->get('my_super_slow_class');

The 10 seconds wait time will be delayed until the object is actually used:

$service->doFoo(); // wait 10 seconds, then 'Foo!'

A more extensive description of the functionality can be found here.

When do we need it?

Lazy services can be used to optimize the dependency graph in cases like:

Webservice endpoints
Db connections
Objects that cause I/O in general
Large dependency graphs that are not always used

This could also help in reducing excessive service location usage as I've explained here.

Implementation quirks of this PR

There's a couple of quirks in the implementation:

Symfony\Component\DependencyInjection\CompilerBuilder#createService is now public because of the limitations of PHP 5.3
Symfony\Component\DependencyInjection\Dumper\PhpDumper now with extra mess!
The proxies are dumped at the end of compiled containers, therefore the container class is not PSR compliant anymore

Todos

Fix license compatibility
Fix: real instantiation of the service swaps the registered instance in the DIC
Generate runtime proxies via eval
Generate proxies in the compiled DIC
5.3 compatibility
Check all links to ProxyManager to ensure the dependency is completely optional
Handle disabled eval case
Add class resources to handle changes in definitions

Crell · 2013-03-30T03:50:56Z

@jrobeson pointed me here.

The functionality definitely sounds valuable. I know Lukas has been talking about this for a long time. However, the dependency chain here is not fun.

I cannot speak for Fabien, but I'd be wary of adding a dependency on 2 additional libraries to DependencyInjection just for this functionality. Even that aside, the cg-library package is licensed under Apache 2. That's a problem. Specifically, it means that the DI Component cannot run without Apache 2 code, which in turn means that it has the same impact license-wise as being Apache 2. That is, it becomes incompatible with GPLv2 and GPLv2+ code.

While Symfony itself is not GPL licensed, many of the systems that are now depending on it are. In particular, Drupal and phpBB are both GPLv2+ licensed. GPLv2 is incompatible with Apache 2. That would make the DI component, and by extension Symfony fullstack, unusable for both Drupal and phpBB, as well as likely others. (I don't know the license of any of the other Symfony-based systems off hand.) It also makes it unsuable for bespoke systems by shops that use GPLv2 (and there are a lot of them) that want to build off of Symfony2.

So, yeah. Introducing an Apache2 dependency would be a massive license-breaking and ecosystem-crippling change. :-/ jrobeson indicated that there was an alternative library, or that the cg-library could be relicensed if we convince the maintainer to do so. Either way the licensing issue would go away. The question of introducing additional dependencies I leave to fabpot.

Disclaimer: I'm the former Director of Legal Affairs for the Drupal Association, so I've spent a fair bit of time looking into this subject. I'm not just making it up. :-)

Ocramius · 2013-03-30T04:20:53Z

@Crell I've been told that today, and didn't reallly expect it (I have no idea whatsoever this involves, I write code :( ). If BSD-3-Clause is compliant, I can convert my library to use Zend\Code instead. That would take me a couple of days, but is no problem at all.

Ocramius · 2013-03-30T11:00:44Z

@Crell I removed usage of cg-lib in ProxyManager as of Ocramius/ProxyManager#18 - should be ok now

lyrixx · 2013-03-30T12:02:54Z

Do you have any benchmark on a "classic" Symfony2 application ? (without sleep ;) ).

Ocramius · 2013-03-30T12:18:08Z

@lyrixx no, I actually don't use Symfony SE. You can actually benchmark it yourself by insulating a portion of your object graph that is not used and marking the root node of that portion as lazy. From what I know, the security component should be quite large.

Another thing this tries to remove is excessive usage of service location for performance optimizations, as I've explained here.

You can also read a detailed description of how lazy loading proxies (as implemented here) work here

OOTB, as it is now, this PR does not introduce any overhead.

stof · 2013-03-30T17:47:53Z

src/Symfony/Component/DependencyInjection/ContainerBuilder.php

@@ -861,8 +864,24 @@ public function findDefinition($id)
     * @throws RuntimeException When the service is a synthetic service
     * @throws InvalidArgumentException When configure callable is not callable
     */
-    private function createService(Definition $definition, $id)
+    public function createService(Definition $definition, $id, $tryProxy = true)


you need to update the phpdoc

And you should add @internal in the phpdoc to explain that it is only public because of the internal use in a closure, and should not be called by other code

stof · 2013-03-30T18:02:31Z

Your current implementation breaks on 1 point: recreating the proxy class when the original class changes. The class has to be added as a container resource for lazy services so that the container is dumped again when the class changes, so that the proxies are dumped again. Otherwise, the proxy might not match the class anymore.

What you would need is the logic of ContainerBuilder::addObjectResource but with a class name rather than an instance (which is easy as addObjectResource could then be rewritten as $this->addClassResource(get_class($object))

stof · 2013-03-30T18:10:21Z

For the ContainerBuilder case, using eval may be better than creating a temporary file on the fly and requiring it. You don't gain anything about caching the generated code (as you regenerate it each time) except potential race conditions (see Doctrine considering to change the generation of proxies when using auto_generate_proxies).
Btw, Twig is already using eval when you disable the template cache.

stof · 2013-03-30T18:19:49Z

Your code has a big issue: it creates a new proxy instance each time the service is retrieved from the container instead of reusing the same instance for container-scoped services. So $container->get('router') !== $container->get('router') when marking it as lazy.

stof · 2013-03-30T18:22:13Z

thus, getting the lazy service, then doing a method call (thus initializing the proxy) and then getting it again would give you the wrapped instance after that, being inconsistent.

Ocramius · 2013-03-31T01:39:28Z

@stof very good catch! Couldn't write a for that test because of the conflicting container names. I'll see if I can change the name of a generated container name and write something that covers that.

mvrhov · 2013-03-31T07:10:23Z

Also note, that the usage of eval may make the symfony2 projects that use lazy loading unusable on some shared hosts.

Ocramius · 2013-03-31T07:12:50Z

@mvrhov ouch! Do they turn it off? I can build a switch for that eventually if there's a way of recognizing it.

mvrhov · 2013-03-31T07:27:10Z

yeah. I worked for one a few years ago and we were disabling it. The problem was that that a large amount of code injections that were happening then abused eval to send a spam or worse. Trying to get unlisted from the sites that list spam sending IPs every few weeks also become troublesome.
There is disable_functions ini setting where all disabled functions a re listed.

Ocramius · 2013-03-31T08:00:08Z

@mvrhov I spawned Ocramius/ProxyManager#24 from that. It should not be handled in symfony itself.

Ocramius · 2013-03-31T08:54:21Z

@stof can you clarify when I should add a resource? I added addClassResource to the API, but now I'm wondering about what should trigger it. Should I do it in ContainerBuilder#register? Are there other locations where definitions are injected?

jalliot · 2013-03-31T13:03:18Z

The feature by itself would be a great addition but I agree with @Crell that the added dependencies are not so good.
Being able to reuse the CG library (if license compliant of course) would be a little bit better as it is already used by some Symfony2 bundles.

Besides, the generated class names of proxies should follow the naming convention used by both the CG library and Doctrine (with a __CG__ prefix and all, see ClassUtils) as it allows easily identifying proxies, wherever they come from, without having to test for all possible proxies interfaces out there.

Ocramius · 2013-03-31T13:22:24Z

To clarify, I modified the PR so that the dependencies are now optional.

@jalliot for CG Lib, I kicked that out and replaced it with Zend\Code, which is BSD-3-clause and therefore compatible. That's quite final, since I don't want to get back and rewrite this backwards without any real benefit.

That's anyway stuff that doesn't affect this PR's code directly. SF2 just benefits from the abstraction layer of ProxyManager and should not really care about how that is achieved except for BC breaks, performance and security issues (and license compatibility, as introduced by @Crell).

For __CG__ I explicitly wanted to use __PM__ (or something different) because ProxyManager allows to hook in its own autoloader with its own rules depending on the naming strategy set in the proxy manager configuration. If that autoloader conflicts with the one in doctrine common, we have a problem. We don't want that, do we? :)

If you want to identify a ProxyManager proxy, you can use the utility within ProxyManager itself. An idea would be to drop the __PM__ constant from there so that you're forced to use the inflector instance and don't rely on a convention anymore.

stof · 2013-04-02T03:41:37Z

src/Symfony/Component/DependencyInjection/ContainerBuilder.php

+use ProxyManager\Factory\LazyLoadingValueHolderFactory;
+use ProxyManager\GeneratorStrategy\EvaluatingGeneratorStrategy;
+use ProxyManager\Proxy\LazyLoadingInterface;
+use ReflectionClass;


Symfony does not add use statements for classes in the global namespace

Will revert :)

lsmith77 · 2013-04-03T18:35:07Z

its an optional dependency but i agree that adding 2 more dependencies can be a concern. doctrine proxy and the cg lib are commonly used already in the Symfony2 ecosystem while proxy manager and zend code are less used.

i didnt check but ideally the code should maybe gracefully ignore the lazy setting in case the dependencies are missing so that no code would break if those optional deps are not installed.

Ocramius · 2013-04-03T18:37:36Z

@lsmith77 perfect, I will add the code required to let any lazy markers being ignored in the case where dependencies are not loaded.

stof · 2013-04-03T18:58:28Z

src/Symfony/Component/DependencyInjection/ContainerBuilder.php

+     *
+     * @api
+     */
+    public function addClassResource(\ReflectionClass $class)


why not passing a class name and building the ReflectionClass internally ? addObjectResource expects an object, not a ReflectionObject

Strict typing. This disallows unexisting classes upfront

Ocramius · 2013-04-12T09:46:26Z

Still need to fix the 5.3 failures

beberlei · 2013-04-30T12:38:33Z

src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php

@@ -11,6 +11,9 @@

 namespace Symfony\Component\DependencyInjection\Dumper;

+use ProxyManager\Generator\ClassGenerator;


Again here, can we abstract this against an interface to not violate the DIP? This dependency is optional, but the code makes it "required".

beberlei · 2013-04-30T12:42:35Z

To clarify my comments above, the proxy manager is an optional dependency and should therefore be hidden in an adapter, maybe even in its own Bridge, implementing a generic interface from DependencyInjection component

Ocramius · 2013-04-30T12:44:08Z

Agreed - fixing later today

…container

…hared services

…iled

…vices

…failures

…n `@throws`

Ocramius · 2013-04-30T21:29:36Z

I've opened #7890 with the suggestions of @beberlei

fabpot · 2013-05-01T03:58:33Z

closing in favor of #7890

@beberlei

This PR was squashed before being merged into the master branch (closes #7890). Discussion ---------- ProxyManager Bridge As of @beberlei's suggestion, I re-implemented #7527 as a new bridge to avoid possible hidden dependencies. Everything is like #7527 except that the new namespace (and possibly package/subtree split) `Symfony\Bridge\ProxyManager` is introduced | Q | A | ------------- | --- | Bug fix? | no | New feature? | yes | BC breaks? | no | Deprecations? | no | Tests pass? | yes | Fixed tickets | #6140 (supersedes) #5012 #6102 (maybe) #7527 (supersedes) | License | MIT (attached code) - BSD-3-Clause (transitive dependency) | Doc PR | Please pester me to death so I do it This PR introduces lazy services along the lines of zendframework/zendframework#4146 It introduces an **OPTIONAL** dependency to [ProxyManager](https://github.com/Ocramius/ProxyManager) and transitively to [`"zendframework/zend-code": "2.*"`](https://github.com/zendframework/zf2/tree/master/library/Zend/Code). ## Lazy services: why? A comprehensive example For those who don't know what this is about, here's an example. Assuming you have a service class like following: ```php class MySuperSlowClass { public function __construct() { // inject large object graph or do heavy computation sleep(10); } public function doFoo() { echo 'Foo!'; } } ``` The DIC will hang for 10 seconds when calling: ```php $container->get('my_super_slow_class'); ``` With this PR, this can be avoided, and the following call will return a proxy immediately. ```php $container->getDefinitions('my_super_slow_class')->setLazy(true); $service = $container->get('my_super_slow_class'); ``` The 10 seconds wait time will be delayed until the object is actually used: ```php $service->doFoo(); // wait 10 seconds, then 'Foo!' ``` A more extensive description of the functionality can be found [here](https://github.com/Ocramius/ProxyManager/blob/master/docs/lazy-loading-value-holder.md). ## When do we need it? Lazy services can be used to optimize the dependency graph in cases like: * Webservice endpoints * Db connections * Objects that cause I/O in general * Large dependency graphs that are not always used This could also help in reducing excessive service location usage as I've explained [here](http://ocramius.github.com/blog/zf2-and-symfony-service-proxies-with-doctrine-proxies/). ## Implementation quirks of this PR There's a couple of quirks in the implementation: * `Symfony\Component\DependencyInjection\CompilerBuilder#createService` is now public because of the limitations of PHP 5.3 * `Symfony\Component\DependencyInjection\Dumper\PhpDumper` now with extra mess! * The proxies are dumped at the end of compiled containers, therefore the container class is not PSR compliant anymore Commits ------- 78e3710 ProxyManager Bridge

Ocramius mentioned this pull request Mar 30, 2013

Lazy services zendframework/zendframework#4146

Merged

Ocramius mentioned this pull request Mar 30, 2013

License compatibility Ocramius/ProxyManager#18

Merged

stof reviewed Mar 30, 2013
View reviewed changes

stof reviewed Apr 2, 2013
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stof reviewed Apr 3, 2013
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beberlei reviewed Apr 30, 2013
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Ocramius added 21 commits April 30, 2013 19:36

First implementation of lazy services via proxy manager

f503ad8

Adding basic logic to generate proxy instantiation into a php dumped …

67aef45

…container

Compiling proxies into the generated DIC file

f4a19c7

Upgrading dependency to ProxyManager 0.3.*

d2760f1

Suggesting ProxyManager in composer.json, removing useless calls

4a13f82

Adding failing test to demonstrate that proxy initialization breaks s…

a6a6572

…hared services

Fixing shared service instance

35fdded

Sharing services in the container should only happen when proxying fa…

bec7774

…iled

Adding tests for proxy sharing within dumped containers

468e92e

Fixing shared proxies into the container

4ecd5ad

Bumping required version of ProxyManager

11a1da9

Docblock for ContainerBuilder#shareService

5870fed

Adding ContainerBuilder#addClassResource

695e3c5

Adding test to check that class resources are registered for lazy ser…

c5a5af0

…vices

Fixing tests, registering class resources for lazy services

29899ec

Reverting import of global namespace classes

b5d0298

Lazier checks on the proxy structure (avoiding whitespace-based test …

cda390b

…failures

Getters for proxied services are public for 5.3.3 compatibility

1eb4cf7

Enforcing soft dependency to ProxyManager

b417969

Reverting documentation changes, adding exception types description i…

1e24767

…n `@throws`

Lazier checks on the proxy structure

450635a

Ocramius mentioned this pull request Apr 30, 2013

ProxyManager Bridge #7890

Closed

fabpot closed this May 1, 2013

Ocramius deleted the feature/lazy-services branch December 1, 2021 16:24

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Lazy services - service proxies #7527

Lazy services - service proxies #7527

Ocramius commented Mar 30, 2013

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jalliot commented Mar 31, 2013

Ocramius commented Mar 31, 2013

stof Apr 2, 2013

Ocramius Apr 2, 2013

lsmith77 commented Apr 3, 2013

Ocramius commented Apr 3, 2013

stof Apr 3, 2013

Ocramius Apr 3, 2013

Ocramius commented Apr 12, 2013

beberlei Apr 30, 2013

beberlei commented Apr 30, 2013

Ocramius commented Apr 30, 2013

Ocramius commented Apr 30, 2013

fabpot commented May 1, 2013

		@@ -11,6 +11,9 @@

		namespace Symfony\Component\DependencyInjection\Dumper;

		use ProxyManager\Generator\ClassGenerator;

Lazy services - service proxies #7527

Lazy services - service proxies #7527

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Ocramius commented Mar 30, 2013

Lazy services: why? A comprehensive example

When do we need it?

Implementation quirks of this PR

Todos

Crell commented Mar 30, 2013

Ocramius commented Mar 30, 2013

Ocramius commented Mar 30, 2013

lyrixx commented Mar 30, 2013

Ocramius commented Mar 30, 2013

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mvrhov commented Mar 31, 2013

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