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Merge branch '3.4' into 4.0
* 3.4: Missing a dot in the last block of code adding note to config Add "url" key in dbal configuration Update console.rst Fixed the internal references of the serializer docs Minor code correction in guard authentication. Minor reword Update database.rst Review Typo fix: use correct parameter `options` [Serializer] Add docs for attributes context key Fix docs about making external requests with BrowserKit Add Lock component
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‎components/browser_kit.rst

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@@ -8,6 +8,12 @@ The BrowserKit Component
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The BrowserKit component simulates the behavior of a web browser, allowing
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you to make requests, click on links and submit forms programmatically.
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.. note::
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The BrowserKit component can only make internal requests to your application.
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If you need to make requests to external sites and applications, consider
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using `Goutte`_, a simple web scraper based on Symfony Components.
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Installation
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------------
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use Acme\Client;
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$client = new Client();
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$crawler = $client->request('GET', 'http://symfony.com');
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$crawler = $client->request('GET', '/');
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The value returned by the ``request()`` method is an instance of the
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:class:`Symfony\\Component\\DomCrawler\\Crawler` class, provided by the
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use Acme\Client;
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$client = new Client();
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$crawler = $client->request('GET', 'http://symfony.com');
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$crawler = $client->request('GET', '/product/123');
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$link = $crawler->selectLink('Go elsewhere...')->link();
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$client->click($link);
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// Make a request
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$client = new Client();
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$crawler = $client->request('GET', 'http://symfony.com');
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$crawler = $client->request('GET', '/');
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// Get the cookie Jar
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$cookieJar = $client->getCookieJar();
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// Make a request
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$client = new Client();
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$crawler = $client->request('GET', 'http://symfony.com');
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$crawler = $client->request('GET', '/');
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// Get the cookie Jar
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$cookieJar = $client->getCookieJar();
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use Acme\Client;
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// make a real request to an external site
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$client = new Client();
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$client->request('GET', 'http://symfony.com');
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$client->request('GET', '/');
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// select and click on a link
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$link = $crawler->selectLink('Documentation')->link();
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use Acme\Client;
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// make a real request to an external site
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$client = new Client();
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$client->request('GET', 'http://symfony.com');
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$client->request('GET', '/');
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// delete history
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$client->restart();

‎components/lock.rst

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.. index::
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single: Lock
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single: Components; Lock
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The Lock Component
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==================
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The Lock Component creates and manages `locks`_, a mechanism to provide
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exclusive access to a shared resource.
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.. versionadded:: 3.4
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The Lock component was introduced in Symfony 3.4.
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Installation
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------------
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You can install the component in 2 different ways:
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* :doc:`Install it via Composer </components/using_components>` (``symfony/lock`` on `Packagist`_);
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* Use the official Git repository (https://github.com/symfony/lock).
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.. include:: /components/require_autoload.rst.inc
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Usage
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-----
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Locks are used to guarantee exclusive access to some shared resource. In
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Symfony applications, you can use locks for example to ensure that a command is
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not executed more than once at the same time (on the same or different servers).
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In order to manage the state of locks, a ``Store`` needs to be created first
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and then use the :class:`Symfony\\Component\\Lock\\Factory` class to actually
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create the lock for some resource::
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use Symfony\Component\Lock\Factory;
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use Symfony\Component\Lock\Store\SemaphoreStore;
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$store = new SemaphoreStore();
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$factory = new Factory($store);
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Then, a call to the :method:`Symfony\\Component\\Lock\\LockInterface::acquire`
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method will try to acquire the lock. Its first argument is an arbitrary string
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that represents the locked resource::
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// ...
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$lock = $factory->createLock('pdf-invoice-generation');
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if ($lock->acquire()) {
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// The resource "pdf-invoice-generation" is locked.
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// You can compute and generate invoice safely here.
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$lock->release();
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}
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If the lock can not be acquired, the method returns ``false``. The ``acquire()``
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method can be safely called repeatedly, even if the lock is already acquired.
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.. note::
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Unlike other implementations, the Lock Component distinguishes locks
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instances even when they are created for the same resource. If a lock has
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to be used by several services, they should share the same ``Lock`` instance
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returned by the ``Factory::createLock`` method.
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Blocking Locks
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--------------
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By default, when a lock cannot be acquired, the ``acquire`` method returns
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``false`` immediately. To wait (indefinitely) until the lock
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can be created, pass ``true`` as the argument of the ``acquire()`` method. This
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is called a **blocking lock** because the execution of your application stops
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until the lock is acquired.
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Some of the built-in ``Store`` classes support this feature. When they don't,
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they can be decorated with the ``RetryTillSaveStore`` class::
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use Symfony\Component\Lock\Factory;
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use Symfony\Component\Lock\Store\RedisStore;
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use Symfony\Component\Lock\Store\RetryTillSaveStore;
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$store = new RedisStore(new \Predis\Client('tcp://localhost:6379'));
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$store = new RetryTillSaveStore($store);
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$factory = new Factory($store);
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$lock = $factory->createLock('notification-flush');
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$lock->acquire(true);
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Expiring Locks
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--------------
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Locks created remotely are difficult to manage because there is no way for the
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remote ``Store`` to know if the locker process is still alive. Due to bugs,
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fatal errors or segmentation faults, it cannot be guaranteed that ``release()``
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method will be called, which would cause the resource to be locked infinitely.
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The best solution in those cases is to create **expiring locks**, which are
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released automatically after some amount of time has passed (called TTL for
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*Time To Live*). This time, in seconds, is configured as the second argument of
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the ``createLock()`` method. If needed, these locks can also be released early
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with the ``release()`` method.
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The trickiest part when working with expiring locks is choosing the right TTL.
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If it's too short, other processes could acquire the lock before finishing the
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job; it it's too long and the process crashes before calling the ``release()``
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method, the resource will stay locked until the timeout::
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// ...
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// create an expiring lock that lasts 30 seconds
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$lock = $factory->createLock('charts-generation', 30);
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$lock->acquire();
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try {
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// perform a job during less than 30 seconds
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} finally {
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$lock->release();
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}
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.. tip::
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To avoid letting the lock in a locking state, it's recommended to wrap the
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job in a try/catch/finally block to always try to release the expiring lock.
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In case of long-running tasks, it's better to start with a not too long TTL and
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then use the :method:`Symfony\\Component\\Lock\\LockInterface::refresh` method
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to reset the TTL to its original value::
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// ...
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$lock = $factory->createLock('charts-generation', 30);
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$lock->acquire();
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try {
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while (!$finished) {
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// perform a small part of the job.
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// renew the lock for 30 more seconds.
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$lock->refresh();
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}
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} finally {
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$lock->release();
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}
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Available Stores
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----------------
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Locks are created and managed in ``Stores``, which are classes that implement
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:class:`Symfony\\Component\\Lock\\StoreInterface`. The component includes the
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following built-in store types:
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============================================ ====== ======== ========
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Store Scope Blocking Expiring
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============================================ ====== ======== ========
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:ref:`FlockStore <lock-store-flock>` local yes no
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:ref:`MemcachedStore <lock-store-memcached>` remote no yes
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:ref:`RedisStore <lock-store-redis>` remote no yes
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:ref:`SemaphoreStore <lock-store-semaphore>` local yes no
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============================================ ====== ======== ========
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.. _lock-store-flock:
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FlockStore
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~~~~~~~~~~
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The FlockStore uses the file system on the local computer to create the locks.
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It does not support expiration, but the lock is automatically released when the
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PHP process is terminated::
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use Symfony\Component\Lock\Store\FlockStore;
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// the argument is the path of the directory where the locks are created
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$store = new FlockStore(sys_get_temp_dir());
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.. caution::
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Beware that some file systems (such as some types of NFS) do not support
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locking. In those cases, it's better to use a directory on a local disk
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drive or a remote store based on Redis or Memcached.
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.. _lock-store-memcached:
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MemcachedStore
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~~~~~~~~~~~~~~
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The MemcachedStore saves locks on a Memcached server, it requires a Memcached
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connection implementing the ``\Memcached`` class. This store does not
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support blocking, and expects a TTL to avoid stalled locks::
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use Symfony\Component\Lock\Store\MemcachedStore;
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$memcached = new \Memcached();
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$memcached->addServer('localhost', 11211);
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$store = new MemcachedStore($memcached);
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.. note::
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Memcached does not support TTL lower than 1 second.
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.. _lock-store-redis:
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RedisStore
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~~~~~~~~~~
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The RedisStore saves locks on a Redis server, it requires a Redis connection
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implementing the ``\Redis``, ``\RedisArray``, ``\RedisCluster`` or
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``\Predis`` classes. This store does not support blocking, and expects a TTL to
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avoid stalled locks::
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use Symfony\Component\Lock\Store\RedisStore;
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$redis = new \Redis();
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$redis->connect('localhost');
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$store = new RedisStore($redis);
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.. _lock-store-semaphore:
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SemaphoreStore
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~~~~~~~~~~~~~~
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The SemaphoreStore uses the `PHP semaphore functions`_ to create the locks::
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use Symfony\Component\Lock\Store\SemaphoreStore;
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$store = new SemaphoreStore();
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.. _lock-store-combined:
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CombinedStore
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~~~~~~~~~~~~~
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The CombinedStore is designed for High Availability applications because it
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manages several stores in sync (for example, several Redis servers). When a lock
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is being acquired, it forwards the call to all the managed stores, and it
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collects their responses. If a simple majority of stores have acquired the lock,
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then the lock is considered as acquired; otherwise as not acquired::
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use Symfony\Component\Lock\Strategy\ConsensusStrategy;
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use Symfony\Component\Lock\Store\CombinedStore;
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use Symfony\Component\Lock\Store\RedisStore;
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$stores = [];
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foreach (array('server1', 'server2', 'server3') as $server) {
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$redis= new \Redis();
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$redis->connect($server);
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$stores[] = new RedisStore($redis);
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}
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$store = new CombinedStore($stores, new ConsensusStrategy());
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Instead of the simple majority strategy (``ConsensusStrategy``) an
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``UnanimousStrategy`` can be used to require the lock to be acquired in all
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the stores.
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.. _`locks`: https://en.wikipedia.org/wiki/Lock_(computer_science)
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.. _Packagist: https://packagist.org/packages/symfony/lock
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.. _`PHP semaphore functions`: http://php.net/manual/en/book.sem.php

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