Move remaining LoadBalancer classes to Rdbms

[mediawiki.git] / includes / services / ServiceContainer.php

<?php
namespace MediaWiki\Services;

use InvalidArgumentException;
use RuntimeException;
use Wikimedia\Assert\Assert;

/**
 * Generic service container.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 *
 * @since 1.27
 */

/**
 * ServiceContainer provides a generic service to manage named services using
 * lazy instantiation based on instantiator callback functions.
 *
 * Services managed by an instance of ServiceContainer may or may not implement
 * a common interface.
 *
 * @note When using ServiceContainer to manage a set of services, consider
 * creating a wrapper or a subclass that provides access to the services via
 * getter methods with more meaningful names and more specific return type
 * declarations.
 *
 * @see docs/injection.txt for an overview of using dependency injection in the
 *      MediaWiki code base.
 */
class ServiceContainer implements DestructibleService {

        /**
         * @var object[]
         */
        private $services = [];

        /**
         * @var callable[]
         */
        private $serviceInstantiators = [];

        /**
         * @var boolean[] disabled status, per service name
         */
        private $disabled = [];

        /**
         * @var array
         */
        private $extraInstantiationParams;

        /**
         * @var boolean
         */
        private $destroyed = false;

        /**
         * @param array $extraInstantiationParams Any additional parameters to be passed to the
         * instantiator function when creating a service. This is typically used to provide
         * access to additional ServiceContainers or Config objects.
         */
        public function __construct( array $extraInstantiationParams = [] ) {
                $this->extraInstantiationParams = $extraInstantiationParams;
        }

        /**
         * Destroys all contained service instances that implement the DestructibleService
         * interface. This will render all services obtained from this MediaWikiServices
         * instance unusable. In particular, this will disable access to the storage backend
         * via any of these services. Any future call to getService() will throw an exception.
         *
         * @see resetGlobalInstance()
         */
        public function destroy() {
                foreach ( $this->getServiceNames() as $name ) {
                        $service = $this->peekService( $name );
                        if ( $service !== null && $service instanceof DestructibleService ) {
                                $service->destroy();
                        }
                }

                $this->destroyed = true;
        }

        /**
         * @param array $wiringFiles A list of PHP files to load wiring information from.
         * Each file is loaded using PHP's include mechanism. Each file is expected to
         * return an associative array that maps service names to instantiator functions.
         */
        public function loadWiringFiles( array $wiringFiles ) {
                foreach ( $wiringFiles as $file ) {
                        // the wiring file is required to return an array of instantiators.
                        $wiring = require $file;

                        Assert::postcondition(
                                is_array( $wiring ),
                                "Wiring file $file is expected to return an array!"
                        );

                        $this->applyWiring( $wiring );
                }
        }

        /**
         * Registers multiple services (aka a "wiring").
         *
         * @param array $serviceInstantiators An associative array mapping service names to
         *        instantiator functions.
         */
        public function applyWiring( array $serviceInstantiators ) {
                Assert::parameterElementType( 'callable', $serviceInstantiators, '$serviceInstantiators' );

                foreach ( $serviceInstantiators as $name => $instantiator ) {
                        $this->defineService( $name, $instantiator );
                }
        }

        /**
         * Imports all wiring defined in $container. Wiring defined in $container
         * will override any wiring already defined locally. However, already
         * existing service instances will be preserved.
         *
         * @since 1.28
         *
         * @param ServiceContainer $container
         * @param string[] $skip A list of service names to skip during import
         */
        public function importWiring( ServiceContainer $container, $skip = [] ) {
                $newInstantiators = array_diff_key(
                        $container->serviceInstantiators,
                        array_flip( $skip )
                );

                $this->serviceInstantiators = array_merge(
                        $this->serviceInstantiators,
                        $newInstantiators
                );
        }

        /**
         * Returns true if a service is defined for $name, that is, if a call to getService( $name )
         * would return a service instance.
         *
         * @param string $name
         *
         * @return bool
         */
        public function hasService( $name ) {
                return isset( $this->serviceInstantiators[$name] );
        }

        /**
         * Returns the service instance for $name only if that service has already been instantiated.
         * This is intended for situations where services get destroyed/cleaned up, so we can
         * avoid creating a service just to destroy it again.
         *
         * @note This is intended for internal use and for test fixtures.
         * Application logic should use getService() instead.
         *
         * @see getService().
         *
         * @param string $name
         *
         * @return object|null The service instance, or null if the service has not yet been instantiated.
         * @throws RuntimeException if $name does not refer to a known service.
         */
        public function peekService( $name ) {
                if ( !$this->hasService( $name ) ) {
                        throw new NoSuchServiceException( $name );
                }

                return isset( $this->services[$name] ) ? $this->services[$name] : null;
        }

        /**
         * @return string[]
         */
        public function getServiceNames() {
                return array_keys( $this->serviceInstantiators );
        }

        /**
         * Define a new service. The service must not be known already.
         *
         * @see getService().
         * @see replaceService().
         *
         * @param string $name The name of the service to register, for use with getService().
         * @param callable $instantiator Callback that returns a service instance.
         *        Will be called with this MediaWikiServices instance as the only parameter.
         *        Any extra instantiation parameters provided to the constructor will be
         *        passed as subsequent parameters when invoking the instantiator.
         *
         * @throws RuntimeException if there is already a service registered as $name.
         */
        public function defineService( $name, callable $instantiator ) {
                Assert::parameterType( 'string', $name, '$name' );

                if ( $this->hasService( $name ) ) {
                        throw new ServiceAlreadyDefinedException( $name );
                }

                $this->serviceInstantiators[$name] = $instantiator;
        }

        /**
         * Replace an already defined service.
         *
         * @see defineService().
         *
         * @note This causes any previously instantiated instance of the service to be discarded.
         *
         * @param string $name The name of the service to register.
         * @param callable $instantiator Callback function that returns a service instance.
         *        Will be called with this MediaWikiServices instance as the only parameter.
         *        The instantiator must return a service compatible with the originally defined service.
         *        Any extra instantiation parameters provided to the constructor will be
         *        passed as subsequent parameters when invoking the instantiator.
         *
         * @throws RuntimeException if $name is not a known service.
         */
        public function redefineService( $name, callable $instantiator ) {
                Assert::parameterType( 'string', $name, '$name' );

                if ( !$this->hasService( $name ) ) {
                        throw new NoSuchServiceException( $name );
                }

                if ( isset( $this->services[$name] ) ) {
                        throw new CannotReplaceActiveServiceException( $name );
                }

                $this->serviceInstantiators[$name] = $instantiator;
                unset( $this->disabled[$name] );
        }

        /**
         * Disables a service.
         *
         * @note Attempts to call getService() for a disabled service will result
         * in a DisabledServiceException. Calling peekService for a disabled service will
         * return null. Disabled services are listed by getServiceNames(). A disabled service
         * can be enabled again using redefineService().
         *
         * @note If the service was already active (that is, instantiated) when getting disabled,
         * and the service instance implements DestructibleService, destroy() is called on the
         * service instance.
         *
         * @see redefineService()
         * @see resetService()
         *
         * @param string $name The name of the service to disable.
         *
         * @throws RuntimeException if $name is not a known service.
         */
        public function disableService( $name ) {
                $this->resetService( $name );

                $this->disabled[$name] = true;
        }

        /**
         * Resets a service by dropping the service instance.
         * If the service instances implements DestructibleService, destroy()
         * is called on the service instance.
         *
         * @warning This is generally unsafe! Other services may still retain references
         * to the stale service instance, leading to failures and inconsistencies. Subclasses
         * may use this method to reset specific services under specific instances, but
         * it should not be exposed to application logic.
         *
         * @note This is declared final so subclasses can not interfere with the expectations
         * disableService() has when calling resetService().
         *
         * @see redefineService()
         * @see disableService().
         *
         * @param string $name The name of the service to reset.
         * @param bool $destroy Whether the service instance should be destroyed if it exists.
         *        When set to false, any existing service instance will effectively be detached
         *        from the container.
         *
         * @throws RuntimeException if $name is not a known service.
         */
        final protected function resetService( $name, $destroy = true ) {
                Assert::parameterType( 'string', $name, '$name' );

                $instance = $this->peekService( $name );

                if ( $destroy && $instance instanceof DestructibleService )  {
                        $instance->destroy();
                }

                unset( $this->services[$name] );
                unset( $this->disabled[$name] );
        }

        /**
         * Returns a service object of the kind associated with $name.
         * Services instances are instantiated lazily, on demand.
         * This method may or may not return the same service instance
         * when called multiple times with the same $name.
         *
         * @note Rather than calling this method directly, it is recommended to provide
         * getters with more meaningful names and more specific return types, using
         * a subclass or wrapper.
         *
         * @see redefineService().
         *
         * @param string $name The service name
         *
         * @throws NoSuchServiceException if $name is not a known service.
         * @throws ContainerDisabledException if this container has already been destroyed.
         * @throws ServiceDisabledException if the requested service has been disabled.
         *
         * @return object The service instance
         */
        public function getService( $name ) {
                if ( $this->destroyed ) {
                        throw new ContainerDisabledException();
                }

                if ( isset( $this->disabled[$name] ) ) {
                        throw new ServiceDisabledException( $name );
                }

                if ( !isset( $this->services[$name] ) ) {
                        $this->services[$name] = $this->createService( $name );
                }

                return $this->services[$name];
        }

        /**
         * @param string $name
         *
         * @throws InvalidArgumentException if $name is not a known service.
         * @return object
         */
        private function createService( $name ) {
                if ( isset( $this->serviceInstantiators[$name] ) ) {
                        $service = call_user_func_array(
                                $this->serviceInstantiators[$name],
                                array_merge( [ $this ], $this->extraInstantiationParams )
                        );
                        // NOTE: when adding more wiring logic here, make sure copyWiring() is kept in sync!
                } else {
                        throw new NoSuchServiceException( $name );
                }

                return $service;
        }

        /**
         * @param string $name
         * @return bool Whether the service is disabled
         * @since 1.28
         */
        public function isServiceDisabled( $name ) {
                return isset( $this->disabled[$name] );
        }
}