fix a mutex use in ptr_cache

include/vapor/ptr_cache.hpp

@@ -35,24 +35,21 @@ namespace VAPoR {
 // Note : 1) Key must support == operator and = operator.
 //        2) BigObj must be able to be destructed by delete.
 //
-template<typename Key, typename BigObj, unsigned int Size, bool Query>
-class ptr_cache {
+template<typename Key, typename BigObj, unsigned int Size, bool Query> class ptr_cache {
 public:
-
     //
     // Constructors and Destructor
     //
     ptr_cache() = default;
-    ptr_cache(const ptr_cache&) = delete;
-    ptr_cache(const ptr_cache&&) = delete;
-    ptr_cache& operator=(const ptr_cache&) = delete;
-    ptr_cache& operator=(const ptr_cache&&) = delete;
+    ptr_cache(const ptr_cache &) = delete;
+    ptr_cache(const ptr_cache &&) = delete;
+    ptr_cache &operator=(const ptr_cache &) = delete;
+    ptr_cache &operator=(const ptr_cache &&) = delete;
     ~ptr_cache()
     {
-      for (auto& p : _element_vector) {
-        if (p.second)
-          delete p.second;
-      }
+        for (auto &p : _element_vector) {
+            if (p.second) delete p.second;
+        }
     }
 
     auto size() const -> size_t { return _element_vector.size(); }
@@ -64,19 +61,23 @@ class ptr_cache {
     //
     auto query(const Key &key) -> const BigObj *
     {
-        // Only need to apply the mutex if `Query` is true.
-        if (Query) const std::lock_guard<std::mutex> lock_gd(_element_vector_mutex);
-
-        auto it = std::find_if(_element_vector.begin(), _element_vector.end(), [&key](element_type &e) { return e.first == key; });
-        if (it == _element_vector.end()) {    // This key does not exist
-            return nullptr;
-        } else {    // This key does exist
-            if (!Query) {
-                return it->second;
-            } else {
+        if (Query) {
+            // Use a guard lock if queries can change ordering.
+            const std::lock_guard<std::mutex> lock_gd(_element_vector_mutex);
+            auto                              it = std::find_if(_element_vector.begin(), _element_vector.end(), [&key](element_type &e) { return e.first == key; });
+            if (it == _element_vector.end())    // This key does not exist
+                return nullptr;
+            else {    // This key does exist
                 std::rotate(_element_vector.begin(), it, it + 1);
                 return _element_vector.front().second;
             }
+        } else {
+            // Just query, no change whatsoever.
+            auto it = std::find_if(_element_vector.begin(), _element_vector.end(), [&key](element_type &e) { return e.first == key; });
+            if (it == _element_vector.end())    // This key does not exist
+                return nullptr;
+            else    // This key does exist
+                return it->second;
         }
     }
 
@@ -86,21 +87,21 @@ class ptr_cache {
 
         auto it = std::find_if(_element_vector.begin(), _element_vector.end(), [&key](element_type &e) { return e.first == key; });
 
-        if (it == _element_vector.end()) {  // This key does not exist
-            --it;                           // `it` points to the last element now.
+        if (it == _element_vector.end()) {    // This key does not exist
+            --it;                             // `it` points to the last element now.
             it->first = key;
         }
-        if (it->second)   // Destroy the old object held here.
-          delete it->second;
+        if (it->second)    // Destroy the old object held here.
+            delete it->second;
         it->second = ptr;
         std::rotate(_element_vector.begin(), it, it + 1);
     }
 
 private:
-    using element_type = std::pair<Key, const BigObj*>;
+    using element_type = std::pair<Key, const BigObj *>;
 
-    std::mutex                          _element_vector_mutex;
-    std::array<element_type, Size>      _element_vector;
+    std::mutex                     _element_vector_mutex;
+    std::array<element_type, Size> _element_vector;
 };
 }    // namespace VAPoR