Cache: Use lock guard for locking spinlocks

Now the locks will always be release, also in the presence of an
unantecipated exception.

server/modules/filter/cache/cachefilter.h

@@ -106,6 +106,31 @@ struct hash<CACHE_KEY>
 
 }
 
+/**
+ * LockGuard is a RAII class whose constructor acquires a spinlock and
+ * destructor releases the same spinlock. To be used for locking a spinlock
+ * in an exceptionsafe manner for the duration of a scope.
+ */
+class LockGuard
+{
+public:
+    LockGuard(SPINLOCK* plock)
+        : lock_(*plock)
+    {
+        spinlock_acquire(&lock_);
+    }
+    ~LockGuard()
+    {
+        spinlock_release(&lock_);
+    }
+
+private:
+    LockGuard(const LockGuard&);
+    LockGuard& operator = (const LockGuard&);
+
+    SPINLOCK& lock_;
+};
+
 #define CPP_GUARD(statement)\
     do { try { statement; }                                              \
     catch (const std::exception& x) { MXS_ERROR("Caught standard exception: %s", x.what()); }\

server/modules/filter/cache/cachemt.cc

@@ -69,18 +69,16 @@ CacheMT* CacheMT::Create(const std::string& name, StorageFactory* pFactory, cons
 
 bool CacheMT::must_refresh(const CACHE_KEY& key, const SessionCache* pSessionCache)
 {
-    spinlock_acquire(&m_lockPending);
-    bool rv = CacheSimple::do_must_refresh(key, pSessionCache);
-    spinlock_release(&m_lockPending);
+    LockGuard guard(&m_lockPending);
 
-    return rv;
+    return do_must_refresh(key, pSessionCache);
 }
 
 void CacheMT::refreshed(const CACHE_KEY& key,  const SessionCache* pSessionCache)
 {
-    spinlock_acquire(&m_lockPending);
-    CacheSimple::do_refreshed(key, pSessionCache);
-    spinlock_release(&m_lockPending);
+    LockGuard guard(&m_lockPending);
+
+    do_refreshed(key, pSessionCache);
 }
 
 // static

server/modules/filter/cache/lrustoragemt.cc

@@ -39,28 +39,22 @@ cache_result_t LRUStorageMT::get_value(const CACHE_KEY& key,
                                        uint32_t flags,
                                        GWBUF** ppvalue)
 {
-    spinlock_acquire(&lock_);
-    cache_result_t rv =  LRUStorage::do_get_value(key, flags, ppvalue);
-    spinlock_release(&lock_);
+    LockGuard guard(&lock_);
 
-    return rv;
+    return do_get_value(key, flags, ppvalue);
 }
 
 cache_result_t LRUStorageMT::put_value(const CACHE_KEY& key,
                                        const GWBUF* pvalue)
 {
-    spinlock_acquire(&lock_);
-    cache_result_t rv =  LRUStorage::do_put_value(key, pvalue);
-    spinlock_release(&lock_);
+    LockGuard guard(&lock_);
 
-    return rv;
+    return do_put_value(key, pvalue);
 }
 
 cache_result_t LRUStorageMT::del_value(const CACHE_KEY& key)
 {
-    spinlock_acquire(&lock_);
-    cache_result_t rv =  LRUStorage::do_del_value(key);
-    spinlock_release(&lock_);
+    LockGuard guard(&lock_);
 
-    return rv;
+    return do_del_value(key);
 }

server/modules/filter/cache/storage/storage_inmemory/inmemorystoragemt.cc

@@ -34,27 +34,21 @@ InMemoryStorageMT* InMemoryStorageMT::create(const std::string& name,
 
 cache_result_t InMemoryStorageMT::get_value(const CACHE_KEY& key, uint32_t flags, GWBUF** ppresult)
 {
-    spinlock_acquire(&lock_);
-    cache_result_t result = do_get_value(key, flags, ppresult);
-    spinlock_release(&lock_);
+    LockGuard guard(&lock_);
 
-    return result;
+    return do_get_value(key, flags, ppresult);
 }
 
 cache_result_t InMemoryStorageMT::put_value(const CACHE_KEY& key, const GWBUF* pvalue)
 {
-    spinlock_acquire(&lock_);
-    cache_result_t result = do_put_value(key, pvalue);
-    spinlock_release(&lock_);
+    LockGuard guard(&lock_);
 
-    return result;
+    return do_put_value(key, pvalue);
 }
 
 cache_result_t InMemoryStorageMT::del_value(const CACHE_KEY& key)
 {
-    spinlock_acquire(&lock_);
-    cache_result_t result = do_del_value(key);
-    spinlock_release(&lock_);
+    LockGuard guard(&lock_);
 
-    return result;
+    return do_del_value(key);
 }