MDL-36322 Errors when updating a Moodle instance with some misconfigured cache stores

cache/stores/memcache/lib.php

@@ -106,7 +106,15 @@ class cachestore_memcache extends cache_store implements cache_is_configurable {
             $this->servers[] = $server;
         }
 
-        $this->isready = true;
+        $this->connection = new Memcache;
+        foreach ($this->servers as $server) {
+            $this->connection->addServer($server[0], $server[1], true, $server[2]);
+            // Test the connection to this server.
+            if (@$this->connection->set("$server[0]:$server[1]:$server[2]", 'ping', MEMCACHE_COMPRESSED, 1)) {
+                // We can connect at least to this server.
+                $this->isready = true;
+            }
+        }
     }
 
     /**
@@ -121,10 +129,6 @@ class cachestore_memcache extends cache_store implements cache_is_configurable {
             throw new coding_exception('This memcache instance has already been initialised.');
         }
         $this->definition = $definition;
-        $this->connection = new Memcache;
-        foreach ($this->servers as $server) {
-            $this->connection->addServer($server[0], $server[1], true, $server[2]);
-        }
     }
 
     /**
@@ -276,7 +280,10 @@ class cachestore_memcache extends cache_store implements cache_is_configurable {
      * @return boolean True on success. False otherwise.
      */
     public function purge() {
-        $this->connection->flush();
+        if ($this->isready) {
+            $this->connection->flush();
+        }
+
         return true;
     }
 

cache/stores/memcached/lib.php

@@ -127,7 +127,21 @@ class cachestore_memcached extends cache_store implements cache_is_configurable
         $this->options[Memcached::OPT_HASH] = $hashmethod;
         $this->options[Memcached::OPT_BUFFER_WRITES] = $bufferwrites;
 
-        $this->isready = true;
+        $this->connection = new Memcached(crc32($this->name));
+        $servers = $this->connection->getServerList();
+        if (empty($servers)) {
+            foreach ($this->options as $key => $value) {
+                $this->connection->setOption($key, $value);
+            }
+            $this->connection->addServers($this->servers);
+            foreach ($this->servers as $server) {
+                // Test the connection to this server.
+                if (@$this->connection->set("$server[0]:$server[1]:$server[2]", 'ping', MEMCACHE_COMPRESSED, 1)) {
+                    // We can connect at least to this server.
+                    $this->isready = true;
+                }
+            }
+        }
     }
 
     /**
@@ -142,14 +156,6 @@ class cachestore_memcached extends cache_store implements cache_is_configurable
             throw new coding_exception('This memcached instance has already been initialised.');
         }
         $this->definition = $definition;
-        $this->connection = new Memcached(crc32($this->name));
-        $servers = $this->connection->getServerList();
-        if (empty($servers)) {
-            foreach ($this->options as $key => $value) {
-                $this->connection->setOption($key, $value);
-            }
-            $this->connection->addServers($this->servers);
-        }
     }
 
     /**
@@ -302,7 +308,10 @@ class cachestore_memcached extends cache_store implements cache_is_configurable
      * @return boolean True on success. False otherwise.
      */
     public function purge() {
-        $this->connection->flush();
+        if ($this->isready) {
+            $this->connection->flush();
+        }
+
         return true;
     }
 

cache/stores/mongodb/lib.php

@@ -130,7 +130,13 @@ class cachestore_mongodb extends cache_store implements cache_is_configurable {
             $this->extendedmode = $configuration['extendedmode'];
         }
 
-        $this->isready = self::are_requirements_met();
+        try {
+            $this->connection = new Mongo($this->server, $this->options);
+            $this->database = $this->connection->selectDB($this->databasename);
+            $this->isready = true;
+        } catch (Exception $e) {
+            // Tipically, a MongoConnectionException.
+        }
     }
 
     /**
@@ -176,8 +182,6 @@ class cachestore_mongodb extends cache_store implements cache_is_configurable {
             throw new coding_exception('This mongodb instance has already been initialised.');
         }
         $this->definitionhash = $definition->generate_definition_hash();
-        $this->connection = new Mongo($this->server, $this->options);
-        $this->database = $this->connection->selectDB($this->databasename);
         $this->collection = $this->database->selectCollection($this->definitionhash);
         $this->collection->ensureIndex(array('key' => 1), array(
             'safe' => $this->usesafe,
@@ -366,8 +370,12 @@ class cachestore_mongodb extends cache_store implements cache_is_configurable {
      * @return boolean True on success. False otherwise.
      */
     public function purge() {
-        $this->collection->drop();
-        $this->collection = $this->database->selectCollection($this->definitionhash);
+        if ($this->isready) {
+            $this->collection->drop();
+            $this->collection = $this->database->selectCollection($this->definitionhash);
+        }
+
+        return true;
     }
 
     /**

cache/stores/session/lib.php

@@ -361,6 +361,8 @@ class cachestore_session extends session_data_store implements cache_is_key_awar
      */
     public function purge() {
         $this->store = array();
+
+        return true;
     }
 
     /**

cache/stores/static/lib.php

@@ -358,6 +358,7 @@ class cachestore_static extends static_data_store implements cache_is_key_aware
     public function purge() {
         $this->flush_store_by_id($this->storeid);
         $this->store = &self::register_store_id($this->storeid);
+        return true;
     }
 
     /**