Unlock mutex when SpaceGroup cache object construction fails

clipper/core/clipper_instance.cpp

@@ -42,6 +42,18 @@
 
 #include "clipper_instance.h"
 
+template<class Lockable>
+class _MutexLocker {
+public:
+  explicit _MutexLocker()
+  {
+    Lockable::mutex.lock();
+  }
+  ~_MutexLocker()
+  {
+    Lockable::mutex.unlock();
+  }
+};
 
 namespace clipper {
 
@@ -90,7 +102,8 @@ namespace clipper {
 
   template<class T> typename ObjectCache<T>::Reference ObjectCache<T>::cache( const typename T::Key& key )
   {
-    T::mutex.lock();
+    _MutexLocker<T> lk;
+
     std::pair<int,T>* ptr = NULL;
     // find existing data
     for ( int i = 0; i < cache_.size(); i++ )
@@ -115,7 +128,6 @@ namespace clipper {
       }
     }
     Reference result( ptr );
-    T::mutex.unlock();
     return result;  // we have a ref to the new obj, so it is thread safe
   }