Issue #1798222 by Berdir: Fixed Use lock around router rebuild to avoid race condition.

core/lib/Drupal/Core/CoreBundle.php

@@ -67,7 +67,8 @@ public function build(ContainerBuilder $container) {
     $container->register('router.dumper', 'Drupal\Core\Routing\MatcherDumper')
       ->addArgument(new Reference('database'));
     $container->register('router.builder', 'Drupal\Core\Routing\RouteBuilder')
-      ->addArgument(new Reference('router.dumper'));
+      ->addArgument(new Reference('router.dumper'))
+      ->addArgument(new Reference('lock'));
 
     $container->register('matcher', 'Drupal\Core\Routing\ChainMatcher');
     $container->register('legacy_url_matcher', 'Drupal\Core\LegacyUrlMatcher')

core/lib/Drupal/Core/Routing/RouteBuilder.php

@@ -7,8 +7,7 @@
 
 namespace Drupal\Core\Routing;
 
-use Symfony\Component\Routing\RouteCompilerInterface;
-use Symfony\Component\Routing\Route;
+use Drupal\Core\Lock\LockBackendInterface;
 use Symfony\Component\Routing\Matcher\Dumper\MatcherDumperInterface;
 
 /**
@@ -26,20 +25,38 @@ class RouteBuilder {
    */
   protected $dumper;
 
+  /**
+   * The used lock backend instance.
+   *
+   * @var \Drupal\Core\Lock\LockBackendInterface $lock
+   */
+  protected $lock;
+
   /**
    * Construcs the RouteBuilder using the passed MatcherDumperInterface.
    *
-   * @param Symfony\Component\Routing\Matcher\Dumper\MatcherDumperInterface $dumper
+   * @param \Symfony\Component\Routing\Matcher\Dumper\MatcherDumperInterface $dumper
    *   The matcher dumper used to store the route information.
+   * @param \Drupal\Core\Lock\LockBackendInterface $lock
+   *   The lock backend.
    */
-  public function __construct(MatcherDumperInterface $dumper) {
+  public function __construct(MatcherDumperInterface $dumper, LockBackendInterface $lock) {
     $this->dumper = $dumper;
+    $this->lock = $lock;
   }
 
   /**
    * Rebuilds the route info and dumps to dumper.
    */
   public function rebuild() {
+    if (!$this->lock->acquire('router_rebuild')) {
+      // Wait for another request that is already doing this work.
+      // We choose to block here since otherwise the routes might not be
+      // available, resulting in a 404.
+      $this->lock->wait('router_rebuild');
+      return;
+    }
+
     // We need to manually call each module so that we can know which module
     // a given item came from.
 
@@ -49,6 +66,7 @@ public function rebuild() {
       $this->dumper->addRoutes($routes);
       $this->dumper->dump(array('route_set' => $module));
     }
+    $this->lock->release('router_rebuild');
   }
 
 }

core/update.php

@@ -452,10 +452,12 @@ function update_check_requirements($skip_warnings = FALSE) {
   ->setFactoryClass('Drupal\Core\Database\Database')
   ->setFactoryMethod('getConnection')
   ->addArgument('default');
+$container->register('lock', 'Drupal\Core\Lock\DatabaseLockBackend');
 $container->register('router.dumper', '\Drupal\Core\Routing\MatcherDumper')
   ->addArgument(new Reference('database'));
 $container->register('router.builder', 'Drupal\Core\Routing\RouteBuilder')
-  ->addArgument(new Reference('router.dumper'));
+  ->addArgument(new Reference('router.dumper'))
+  ->addArgument(new Reference('lock'));
 
 // Turn error reporting back on. From now on, only fatal errors (which are
 // not passed through the error handler) will cause a message to be printed.