OpenMPMutex "Copying" (#2794)

include/openmc/openmp_interface.h

@@ -29,11 +29,26 @@ class OpenMPMutex {
 #endif
   }
 
-  // Mutexes cannot be copied.  We need to explicitly delete the copy
-  // constructor and copy assignment operator to ensure the compiler doesn't
-  // "help" us by implicitly trying to copy the underlying mutexes.
-  OpenMPMutex(const OpenMPMutex&) = delete;
-  OpenMPMutex& operator=(const OpenMPMutex&) = delete;
+  // omp_lock_t objects cannot be deep copied, they can only be shallow
+  // copied. Thus, while shallow copying of an omp_lock_t object is
+  // completely valid (provided no race conditions exist), true copying
+  // of an OpenMPMutex object is not valid due to the action of the
+  // destructor. However, since locks are fungible, we can simply replace
+  // copying operations with default construction. This allows storage of
+  // OpenMPMutex objects within containers that may need to move/copy them
+  // (e.g., std::vector). It is left to the caller to understand that
+  // copying of OpenMPMutex does not produce two handles to the same mutex,
+  // rather, it produces two different mutexes.
+
+  // Copy constructor
+  OpenMPMutex(const OpenMPMutex& other) { OpenMPMutex(); }
+
+  // Copy assignment operator
+  OpenMPMutex& operator=(const OpenMPMutex& other)
+  {
+    OpenMPMutex();
+    return *this;
+  }
 
   //! Lock the mutex.
   //