feature symfony#27456 [LOCK] Add a PdoStore (jderusse)

This PR was merged into the 4.2-dev branch.

Discussion
----------

[LOCK] Add a PdoStore

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#25400
| License       | MIT
| Doc PR        | symfony/symfony-docs#9875

This is an alternative to symfony#25578

Commits
-------

46fe1b0 Add a PdoStore in lock

Author: fabpot

src/Symfony/Component/Lock/CHANGELOG.md

@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+4.2.0
+-----
+
+ * added the PDO Store
+
 3.4.0
 -----
 

src/Symfony/Component/Lock/Store/MemcachedStore.php

@@ -57,7 +57,7 @@ public function __construct(\Memcached $memcached, int $initialTtl = 300)
      */
     public function save(Key $key)
     {
-        $token = $this->getToken($key);
+        $token = $this->getUniqueToken($key);
         $key->reduceLifetime($this->initialTtl);
         if (!$this->memcached->add((string) $key, $token, (int) ceil($this->initialTtl))) {
             // the lock is already acquired. It could be us. Let's try to put off.
@@ -80,13 +80,13 @@ public function waitAndSave(Key $key)
     public function putOffExpiration(Key $key, $ttl)
     {
         if ($ttl < 1) {
-            throw new InvalidArgumentException(sprintf('%s() expects a TTL greater or equals to 1. Got %s.', __METHOD__, $ttl));
+            throw new InvalidArgumentException(sprintf('%s() expects a TTL greater or equals to 1 second. Got %s.', __METHOD__, $ttl));
         }
 
         // Interface defines a float value but Store required an integer.
         $ttl = (int) ceil($ttl);
 
-        $token = $this->getToken($key);
+        $token = $this->getUniqueToken($key);
 
         list($value, $cas) = $this->getValueAndCas($key);
 
@@ -120,7 +120,7 @@ public function putOffExpiration(Key $key, $ttl)
      */
     public function delete(Key $key)
     {
-        $token = $this->getToken($key);
+        $token = $this->getUniqueToken($key);
 
         list($value, $cas) = $this->getValueAndCas($key);
 
@@ -144,13 +144,10 @@ public function delete(Key $key)
      */
     public function exists(Key $key)
     {
-        return $this->memcached->get((string) $key) === $this->getToken($key);
+        return $this->memcached->get((string) $key) === $this->getUniqueToken($key);
     }
 
-    /**
-     * Retrieve an unique token for the given key.
-     */
-    private function getToken(Key $key): string
+    private function getUniqueToken(Key $key): string
     {
         if (!$key->hasState(__CLASS__)) {
             $token = base64_encode(random_bytes(32));